Well - OK, It is going to cost you about $10 to purchase the materials you need at WM. but you will have enough to fix 10 speakers.

SO, you have an AK Type N that somebody (you) put their finger through or Jr. poked it with a stick or whatever. Now it sounds like a nest of bees trying to put on a concert. You could save money by grabbing a role of TP and gluing it up in a nice ridged mess that looks like a 2nd grade art project or you could fix it right with about $1 worth of materials available at Walmart.

This project requires no special tools, just a little patience. I've dome this before (a lot) so I can do it in about an hour. I would expect a first-timer would need 2 - 3 hours

If your cone is ripped or even partially missing, this job is much easier than doing the math required to calculate the shape of a flat piece of material which becomes a cone,  SO, take care to preserve as much of the original cone as possible. I will mention here that the diameter of the circular cut-out is about 11" becoming about 8" when the ends are glued forming a cone.

If the spider (metal thing in the center of the cone) or the voice coil (see pic. below) is damage or missing it must be repaired or replaced. This article does not cover VC rewinding or fabricating a new spider. 

Begin by unsoldering the magnet wire leads going to the voice coil. Then remove the screw holding the spider and the screws holding the metal ring (3 pieces) around the outside edge of the suspension (pictured 2 and 3 below).

Use a scraper to separate the suspension from the basket (speaker frame). Don't worry about keeping the old material intact, but do keep a piece for reference later when you cut out the new suspension.

The cone should now be lifted out of the basket with the spider and VC still attached.

Sometimes the VC attachment to the cone is so loose that they fall apart - sometimes not. Again, the object here is to separate the VC and the spider from the old paper cone while keeping the old cone as intact as possible since you are going to use it as a pattern for the new cone.

I have found that brushing on a little lacquer thinner around the edge of the spider can loosen the glue. Basically this is a metal ring pressed into the VC that captures the inner edge of the paper cone between the spider and the VC. Caution: too much solvent (thinner) leaking onto the VC will break down the adhesive holding the coil to the former (round tube). So be careful. In the end you will probably have to scrape some of the old cone material off of the edge of the spider since these areas need to be clean before reattachment.

Next, cut the old cone along the original seam allowing the paper to lay flat. Observe the original overlap and allow for the same overlap on the new cone so that the cone can be formed by gluing the edges together.

Above, left to right: Spider, Voice coil and the new cone assembly

Now - or sometime - run down to WalMart and get a folder of black greeting card material from the craft department (about $6). It will have many 12" X 12" sheets of card material that is nearly perfect for early speaker cones. In the same department find a yard of black canvas material (about $4). Make sure that the canvas is cloth, not plastic that looks like canvas. If you can't find black, you can dye or paint other colors (if paint is used, go lightly with black lacquer NOT enamel, which can become ridged). The material should be about the thickness/flexible as your jeans (real jeans not "stretchy" jeans). You might even be able to make the surround out of old jeans.

Lay the old paper cone on top of the new card-paper and draw around the edge. If pieces are missing from the original cone you are going to have to extrapolate the missing circumference from what you have. This can be done simply by rotating the piece that you have around a FIXED center. For this it may be easier to tape the old cone to the new paper and locate the center of the circle and MARK it. This might take some 8th grade geometry and a compass, but you can do it with out the compass. Hint: use the radius - 1/2 the diameter - and make arcs in the center with one leg of the compass - stick - ruler fixed on the outer edge. Three or more arcs will intersect at the center of the circle..

You can lay the metal spider on the marked center and draw around the circumference. Then make a mark about 3/16" inside of the spider circumference since this material must be captured between the spider and the voice coil. Make another circle and cut it out.

The pie-shaped chunk that must be removed so a cone can be formed should be guesstimated from the original. Keep in mind the edges of the cut need to overlap about 1/4 inch so they can be glued.



Now cut the new suspension from the canvas. You can cut out 3 pieces like the original had or just use one. If you use 3 pieces they must overlap about 1/4 of an inch and be glued together to form a ring. These attachment areas can become stiff especially if too much glue is used, so one piece is a lot easier.

You can use a piece of the old surround or the outer lip of the basket to draw a circle on the canvas. If the basket is used, when you make your cut remember that the material will fit inside of the lip so the cut should be made about  1/8" inside of the mark. You will now have a circle of canvas about 11" in diameter.

Use your compass - ruler - stick - whatever, to mark the inside edge of the material. Finding the center as described above might be useful. Use a piece of the old surround material to check the width of this material. There must be enough to reach the outer lip of the basket and have enough to overlap the new cone about 1/4 of an inch. When you are done you should have a ring. The outer edge will not be visible but attention to the inner edge will pay off since it is visible and uneven cuts will look bad.

Glue the edges of the pie-shaped cut-out together forming a cone with the center missing (cut-out for spider/VC)

Lay your new cone on top of the new surround material. Check that there is about 1/4 inch of material overlapping the paper ALL THE WAY AROUND the outer edge of the cone. Use a small paint-brush to spread yellow wood glue on the outer edge of the paper cone and the inner edge of the cloth surround. You can use a contact cement but I have found cones attached using it will fall apart later. Let the assembly dry for about 1/2 hr. If the overlap of the material is uneven it will be difficult to center the cone assembly, so take care.

Now the cone is set on top of the voice coil former (tube) and the spider is pressed into the former capturing the inner edge of the cone between them. Like with the surround, care must be taken to center the components or the cone will be impossible to align and the VC will rub on the pole piece (center of the magnet structure). Make sure that you are attaching the cone to the proper end of the VC former since the voice coil is closer to one end and an error will move it out of the magnetic gap. This is usually a tight fit - be careful not to damage the cone. A little bit of glue will both lubricate the spider/cone/VC connection for assembly and secure the finished product.

Allow the glue to dry for a few minutes.

Put the cone assembly back inside of the speaker basket sliding the voice coil into the magnetic gap around the pole piece. The 2 wires leading to the voice coil should end up at the correct place in the basket which is CLOSEST to the original atachemet points. Not observing this precaution will make hooking up th VC wires correctly - impossible.

At this point the surround should be sitting near the correct position around the circumference of the basket.

The next step is critical - The object is to align the cone/VC so that it does not rub on the pole piece or magnet structure.

This is sort of a three-handed maneuver so before you start, grow another hand or, possibly, ask for help (only required on the first attempt).

What I do is to put the screw back into the center of the spider, screwing it to the pole BUT leave it loose enough to move the spider around. By this point you will be able to estimate the quality of the rebuild by observing the fit of the VC inside of the magnetic gap. It should be loose and free to move BUT it may still rub.

Now, if everything is symmetrical the surround should be laying evenly inside of the outer lip of the basket. Using your soldering iron, Holes for the screws can be punched/burned through the canvas surround. Or you can use a blade or punch but I have found the hot iron easier. The three metal clamps are lined up over the surround capturing it between them and the basket. With the screw holes burnt/cut attach the 3 pieces but leave the screws loose so that the surround can be adjusted slightly.

Placing slight pressure on the inner cone area/spider will allow you to observe the fit of the VC inside of the gap. IT MUST NOT RUB on the pole or the magnet structure. Assuming that the VC former has not been damaged/bent and that the VC wire is still bound to it, slide the spider around on the center screw until the coil is centered in the gap - no longer rubs. Tighten the screw.

If you are having trouble centering the VC slight adjustment of the surround can be made but not enough adjustment can be made to compensate for a cone that is not symmetrical. Glue can be applied around the edge of the basket to secure the surround but this will make further adjustment impossible. Tightening the screws holding the  3 metal clamps is usually enough to secure the cone.

Reconnect (solder) the VC leads to the attachment points.  Use your ohm meter to check the continuity of the VC.

The speaker is ready to test.

If you have any interest in the battery-powered supers of the 1921 - 1928 era, be sure to check out:
https://www.russoldradios.com/1920s-superheterodyne.html
Caution, the page is large, probably too large for dial-up connections.

The Apex Microdyne Superheterodyne from 1925 is an 8-tube battery powered super that was sold as a kit. It has a stenciled panel. All of the transformers are labeled Apex and are comprised of 2 IFs, 1 IF filter, and 2 audio interstage transformers.

There have been a few of these for sale lately and a few more in collections on the net. After examination of the pictures there is one thing that is notable in that every radio is very similar. This is a departure from the typical kit-build that usually incorporates parts and wiring added by the builder. This leads me to believe that either a complete kit that was mostly pre-assembled was being sold or that the radios were completely assembled prior to delivery to the customer.

The ad above is from Radio Digest of Aug 26, 1925. Note the price of $97.50.

As found above. Or rather, fresh out of the box.

The second audio interstage was open. It had leaked quite a bit of the potting material - bee's wax - all over the place. The other transformers had leaked a bit of wax as well. Since the parts of the transformer housing are held together with 2 pins  the seal is poor enough to allow leakage especially if the radio is stored in a warm environment. Cleaning off all of the hardened, sticky wax was the biggest task in restoring the chassis - well - and fixing the open 2nd audio - below.

The buss wiring on all of these kits is very similar. One reason to believe this was built by a radio shop is the remains of a shop claim tag, torn into chunks and used as an insulator/spacer to prevent shorts - Above.

This really wasn't necessary unless the chassis was going to be handled roughly. Possibly in shipping? Which would also lead one to believe that this was a pre-delivery addition by the builder.

Soldering joints, though corroded, are good and no buss wire broke free in transit.

2nd audio interstage taken apart showing potting material - wax.

With the wax removed the transformer is loose. Since it is so similar and not visible I just inserted a standard (156) replacement and wired it up.

The power is wired through a 7 conductor plug (center rear). The 2 black wires connect to a ~4.5V C battery which was located on the chassis.

Even though the cabinet looked pretty good, it was made of mostly solid walnut and the finish was mostly gone leading to warping (the issue with "solid" wood). Sine the panels were several boards that had been joined the warping had split the joints apart as well as twisting them somewhat.

The only way to make it right was to not only bust the cabinet apart but to also break apart the panels and rejoin the individual pieces after making minor cuts to remove the stress that broke the glue joints. Note the lighter new piece grafted to the rt. side panel. This piece was missing. (center right)

Never enough clamps - or hands.

Ta-Da. Sue holds reassembled cabinet less lid.

The finish is med. walnut DYE (not toner) topped with several coats of clear shellac.

This radio does not have an antenna coil like the Victoreen (previous post) so it needs a loop antenna. My test loop is shown above.

Above is a video with the radio in use.

A couple of notes:
Hand capacitance is an issue in tuning. The tuning caps could use some more shielding. The big, brass dial of the Apex vernier is electrically connected to the rotor so it probably makes this worse than when a plastic dial (knob) is used.
The little switch (knob) on the lower left enables the user to select either one or both stages of audio amplification - using 6 tubes or 7 tubes total.  Using the 2nd audio while tuning has some advantages and tone is better (this may be somewhat related to the new audio trans installed in the interstage), But the audio level is adequate using only the first audio stage.
When the radio is "tuned" for the most conservative use of the batteries = lowest A voltage, the oscillator can stop. Turning up the A voltage will prevent this but run the tube filaments hotter.

THIS is, a Superheterodyne kit from Victory Products/ Victoreen.

As with most of the other 1920's superhet radio in the collection, this was a 'kit". Sold as a kit to try to avoid legal complications with RCA.

I am almost certain that this was constructed by the end user rather than a radio shop or other professional and the proof of that resides in the wiring error resulting in a missing meter. More on that below.

This is a rather typical early 20's 8-tube super which uses UX201As. It does have an antenna coil giving it some flexibility as compared to those designs that require a loop antenna, There is even a switch/jack that allows switching between a loop for improved directionality over a long-wire.

This was a stress-inducing purchase from Pay-Bay. The seller is a nice person. She tried to pack it well and maintain a reasonable shipping cost. But even on this short trip, the nature of these 20's cabinets allows a lot of movement of the chassis. The result was a broken cabinet.

All of the cabinet was constructed from solid walnut, which sounds good, but a veneered plywood cabinet would probably broken at the seams rather than splitting the wood. There were split/broken pieces on both sides. Also, plywood is far less likely to warp.

Well, this did make one decision easier. The cabinet was going to have to be refinished caus' no amount of Go-Joe is going to rub out that split.

The decorative trim on the right was broken long ago. Having the trim intact on the other side made it easy to construct a mold and new trim was made (above)

The rough ride broke loose several pieces of the square buss wire used in the original construction. The second audio interstage transformer had open windings, possibly because someone had tried to take it apart. Otherwise, all of the parts were here, less the already mentioned volt meter.

For the most part, the builder used high quality parts. Some probably came with the kit, others might have been purchased separately.

Above is the failed interstage trans. They were produced by a company I have never seen before and in a fashion that is very unusual for an audio transformer. The core was solid iron rather than the usual laminated stack. This solid core was shaped like a spool on which the primary and secondary were scramble/bulk wound. Then the spool was inserted into a iron pipe, held in place with the machine screw (above). Both windings were open so I just wound on enough #38 to fill the spool with a 3 to 1 ratio.

This transformer design is probably not the best for audio quality since the unlamented core is going to generate a lot of eddy currents. This might be the cause of some of the raspyness when using both audio stages in the video (below).

All of the Victory Products transformers were in good shape. This label would seem to indicate an early production date, possibly late 1924.

The original builder did a good job. The positioning of the transformer is slightly different than the later drawings and he used 5 of the 1A glass regulator/resistors rather than a 3rd and possibly , 4th rheostat for filament control. But in my testing the loss of these controls simply made tuning easier with no apparent downside.

Unfortunately it appears that the builder was following a diagram similar to the one below, which is found on several locations on the net. I have made a mark near the volt meter (in red) to note the connection of B+ to the meter. (Above) is one of the buss wires that fell out when the radio was unpacked. As with the diagram it appears to run from B+ to the meter location resulting in 3 conductors/connections for the meter. Now, most meters only have 2 connections, + and -. And I can not recall a meter of this vintage that needed 100V DC for anything. I suspect that at some point high voltage damaged the original meter which is why it is missing.  I used a meter from a Radiola to fill the holes for pictures but it is wrong.

Cleaned up, rewired, resoldered, polished and repaired (below).

After checking the A circuit, I brought up the B+ and there was a station playing LOUD and clear (Faux Sports). I cant recall this ever happening before, at least SOME tuning had been required.

This radio has such good gain that the 2nd audio really isn't necessary AND it appears that the builder also knew this since he incorporated a slight mod to the last audio jack that turns the filament off when the 2nd audio (201A) is not used, saving some A battery life. To commemorate the builder, I left this mod in place.

Below is a video I shot just after powering the super up for the first time (for me). The meter would be reverse polarized with the original wiring so it is for looks - now. The fateful B+ conductor was omitted in the reconstruction.

The drawings for this radio in Rider's vol. 1 do not show the meter to have a B+ connection and are very useful to a person needing to do some reconstruction on one of these radios.

Duane had said that the meter might have been a switchable unit allowing the user to check/set both A+ and B+ voltages. I knew that such a meter would have to have had an integrated switch since there was no facility for an outboard switch on the front panel.

Harry was digging through a listing for a group of old meters and located the one pictured above. Not only does it work, but, this Jewel meter matches exactly the buss wire connection/position of the original construction. That makes it likely that this was the type of meter original used.

Thanks Harry!

Harry said "Hay, before you put away the plating equipment why don't you try to make a Radiola 18 hood?" Well - - because I don't need one. But, the challenge was there, so I did.

These parts were made using the electro-forming process described in the post below. The Radiola lamp hood was somewhat easier to make than the Neutrowound tube-shield, but still required an hour or so to cut off the flashing and attach the clips.

Above  I think that the new one is on the left.

Tabs installed on the back.

Some of these were, or have become, darker so the one above was painted to match.

While removing the nodules created on the outer surface of the form, I noticed how attractive they could be. So I salted this one (below) while the surface was still active, that is, fresh from the copper sulfate bath.

The colors on the copper nodules are easier to see in the off-focus shot below.

There was no need to do this step, but I thought it was cool.

OK, the chemistry experiment is done - at least for the moment.

If you are new to my blog - HI. If you have read a few of my posts you already know that I have a tendency to go to extreme lengths to recreate original-looking parts for my radio restorations. and, this one has been on my mind for a while now.


Below is a picture of "Number 2" the 1926 Neutrowound receiver that almost became a "parts set".

https://www.russoldradios.com/blog/number-two

Without restating the story linked above, it was a wet, nasty, rusted mess, missing all but two of the tube shields.

These radios are expensive. Parts, particularly the shields/caps are seldom for sale and when they are tend to demand a high price. Searches for after-market replacements resulted in finding a lot of interest in finding replacements with only the slightest hint that someone might have made a few - at one time.

SO, what to do?

Yep, there were 2 remaining shields/caps when I received the radio. I borrowed one for the other example, which is on display in our museum leaving this radio short 5 caps.

The restoration turned out just fine but one of the measures of value/sales price is whether the caps are missing. A radio in similar condition might be worth twice as much as one missing the caps. The only source for replacements is scavenging them from poor examples, that, while cheaper, might still cost $200 or $300. Add to that cost the long wait for such a "parts set" to become available for sale.

So, I had to find a way to make replacements. Above is an original and the first of the ones I have made.

The originals seem to be brass, formed by stamping on a dye. There are parallel marks on the sides of the originals left by this process. Then the parts are nickel plated.  A small hole is present where the part was hung on a wire in the plating solution.

It is possible that one could convince a machine shop to construct new dyes. Then stamp out original=looking parts that would to be sent to a plating shop. It would probably be cheaper to purchase one of those expensive parts-sets from E-Pay.

There has been some discussion about making parts through a process of electroforming. This can work well, with good results on small, flat parts or parts with shallow depth. Larger parts can be a problem.

I really did not expect this to work - I'll tell you why - and tell you why it did.

First, a friend, Harry, needed some 2 watt dog-bone resistors. I had never made a form/mold for these. Construction of the form is not too complicated. Making the mold - one that works, or works more than once can be a challenge. The sturdy, fairly ridged, high-temp silicon is not cheap. But since Harry was going to buy some for his project I thought that this would be a good time to try.

The red, 2-part silicone is rated at 60 on the Shore-A hardness scale, a measurement for flexible plastics. The parts must be weighed and mixed. Then, air bubbles must be removed ( a process I wish I had invested more time, but again, I really thought this would not work). Fortunately, I had a good scale and the other necessary tools. OH(!), also, I had an example from which to make the mold. Without having one of the original caps, this would have been much more difficult.

At this point I should point out the need for a plating set-up like the ones I have used in previous projects but in this case, I wasn't plating a part but, rather making one.

The inside of the silicon mold is brush-painted with graphite powder. This stuff is worse than the silicone for getting on everything. So care must be taken or your tools and the operator will be covered with the stuff. It really does a good job of making a conductive surface which, with the buss-wire conducts the negative charge to the mold.

Throw, or the ability to plate, especially into a hole, is the challenge here. For tube-people this should not be hard to visualize. The charged particles from the solution are attracted to the negative electrode. New, replacement metal moves into solution from the anode which is a copper plate. Like in a vacuum tube, the charges move most easily between the closest points of the anode and cathode. This makes throwing into the hole difficult. As you can see, copper collects on the face of the mold and the wires. Getting it into the bottom of the hole is nearly impossible without redesigning the anode.

Below, the part removed from the mold. The small specks on the surface are caused by imperfections in the mold (bubbles) but these are easily removed in the polishing process.

Removing the flashing and polishing the part prior to the last step is probably the most time consuming.

Unlike with woodworking or painting, the part must be polished PRIOR to the last finishing step. This will result in a flat, shiny surface after the nickel is applied. Some polishing can be done to the nickel but it is way to late to remove scratches or other imperfections after the nickel is applied.

Following the removal of the flashing, the part is polished in preparation for nickel plating.

I like the looks of the polished copper. It would be cool to have a radio with polished copper shields but not very original (looking).

.

Five new caps. Can you pick out the original? It is near the middle of the radio.




So - Is it likely that I will make enough of these to sell a few - NO. It just takes too long and I have radios to work on.

Do I recommend trying this yourself? Probably not. The initial investment alone for tools and materials is way too much to build JUST these - but if you already have the equipment - possibly.

Why "possibly"? Again, time and difficulty. It is hard to make this work and failures are almost certain.

BUT, now you know that it can be done.

Additional picture of inside added by request:

Plating at or above 1A per Sq. in. will plate faster but more nodules/ferns will appear on the inside and flashing.

McMurdo Silver Masterpieces were among the best radios of the time and of those the Masterpiece V and VI were particularly outstanding. They would be the center piece of most collections even if they weren't covered with chrome. Their tone, audio quality/power, BFO, audio expander and selectable IF bandwidth elevated them to the same quality and performance as units made by Scott or even the venerable Zenith 1000Z.

Masterpiece VI from 1937

BUT they are difficult to work on, even if you had the tools and schematic. Each one was somewhat custom made- in real terms. So the claim that each radio was built specifically for each buyer might actually be true AND an impediment to restoration today. (Much more on this coming in the next post)

Sadly, not many were made. I'm sure that the price had a lot to do with that. Similarly, their price today has kept them out of most collections. Worse yet, they became well known for the hi-fidelity of their components. Unlike most radios of the time, a cabinet was optional so a complete radio consists of the tuner/pre-amp (above), a power supply/audio amp (below) and a massive, dual field coil, 18 inch Jensen pedestal speaker (2nd below).  Today a complete radio might sell for around $6000.00 with or without a cabinet. Each of the components can be sold separately today (a boon for pickers on Pay-Bay). Where a nice unrestored receiver might go for around $1000, an amplifier can sell for nearly that much alone. The real problem has been that overseas demand has driven the price of the Jensen Super-Giant to ridiculous levels as high as $7000 in the recent past - around $3000 to $4000 today.

.Amplifier/ power supply

For that kind of  money, it is hard for even a dedicated radio collector to resist selling the speaker and, unfortunately that is what has happened to many of these . So, today, it has become common to find a Masterpiece receiver alone in its cabinet with the speaker and amp long gone to Asia.

The receiver chassis is still worth having, but, all of the cool functions and wonderful tone can only be imagined. Though not absolutely unique,  finding a substitute for the missing speaker is always a compromise in both quality and reduces the value of the radio as a collectors item.

Fortunately, I have just completed the restoration of a collection of McMurdo Masterpieces and there were a few parts left over. No there weren't any 18" speakers (though I have purchased one from the collection) but there was one, sad, rusty MCMV amp chassis and a single filter choke,  It seems that someone had replaced the power transformer with a smaller, unsuitable unit and, subsequently gave up on the project after it overheated evidenced by visible melted insulation on the primary wires.

I have long thought about building a power supply/amp suitable for running the many orphaned Masterpieces. I considered using a Scott 800B PS/amp. It could work. Or I could start with a brand new chassis. This would be a lot of work. It seemed easier to use the MSMV amp chassis that I already had.

After a few days of grinding and polishing my arthritis was protesting loudly. Maybe a new chassis would have been easier. But now that the rust and pitting was gone, I needed to make sure that it did not rust again. I considered gloss black paint. It would look nice but not very original for a radio known for CHROME (!). Well, I won't mess with chrome - too toxic. But nickel plate seemed like a good idea. It could be chromed later - if it just had to be done. So that is what I did.

A nickel plated chassis can be polished to nearly the look of chrome. There is a slight color difference. Chrome is more blue-ish. I wasn't going to that extreme. The way it came out, a lay-person might think it was chrome anyway unless it was sitting beside a chromed piece. I was happy- enough. And I did not have to cut out all of those holes.

SO NOW WHAT?  Having only the single filter choke and the tube sockets ment that this was going to be a custom assembly any way you looked at it. Then I had an idea - What about a universal PS/amp capable of driving any natural magnet speaker. The thought of not being constrained by the normal factory-look restoration intrigued me. "Let's take it one step further - how about a PS/amp that could run either a MSMV OR a MSMVI? So it was to be!

Now all that I needed was a pile of hard-to-find parts. I went through my transformer pile focusing on several REALLY BIG ones removed from 1960's electronic (tube) organs. I never thought that I would use one of these. They were over-kill for even the largest 30's radios or even stereo amp projects. I'm glad that I kept them.

The PS uses 2, 5Z3 rectifiers, so the trans must provide at least 6A at 5V and the DC requirement was for at least 300ma at about 450V. There was also the requirement to heat 18, 300ma tubes.  I needed both hands to lift this one!

Besides all of the little parts, I needed another choke, a interstage trans for the MSMVI input and an output trans capable of handling the push-pull 6L6s. And I needed to hit the target voltage for the receiver, around 340V under load, without having the 2 original field coils in the circuit. PLUS avoid the hum caused by removing said field coils which were also used for filtering. Skill - or luck, either would be fine with me.

Here is a list of the objectives:

1. Start with a MSMV design
     The MSMVI has the 2nd audio on the receiver chassis but the MSMV needs the 2 6C5s to drive   the push-pull 6L6s .

2. Find the missing 2nd choke at about 10h 200ma
     B+ for the output 6L6s is taken after the first choke. So the 2nd choke must be good for about 200ma.

3. Find an interstage transformer for the MSMVI input to the final audio stage.
     The 2nd audio stage is on the receiver chassis so routing the signal through the V's 6C5s will produce too much gain/noise. Also the VI uses the interstage as part of the bass control, omitting it would also eliminate this control function. A 1:1 or a slight step-down will be best since additional voltage gain is unnecessary.

4. Add a suitable output trans 
     Since the original one is on the speaker on both the V and VI. 8 ohms would be best. Ours provides both 4 and 8 ohm  secondary taps.

5. Increase the values of the filter caps to help compensate for the loss of the field coils.
     I used a 10uf 630V film cap in the first position that originally was two .5uf at 400V in series resulting in a value of .2 (point 2) at 800V. They were probably trying to take it easy on the 2 rectifiers by using a small or no cap prior to the first choke. Then a 47uf 450V 105c electrolytic in both the 2nd and 3rd filter position. I wasn't sure whether I was going to need a resistor to drop B+ to the receiver to 340V at this point so if I had to add a resistor I thought I would add a 4th filter cap as well. Turns out that neither were needed.

6. Wire the original 6 pin speaker port/socket to accommodate the VI receiver
     Since the FC speaker is not used the 6 pin plug is available to power a MSMVI  the V uses the original socket.

7. Determine the best point to insert the audio from the interstage to the final amp.
     The V application is as it originally was but I needed to inject the signal from the interstage at the grids of the 6L6s without affecting the output from the 6C5s too much. The interstage trans provides the inverted signal for the VI that was accomplished by the 6C5s on the V. The 6C5s are cap coupled to the grids  by .1 (point 1) caps. I chose this point to inject the signal using .045 caps to try to prevent some of the loss that would occur by placing the transformer windings across the output of the 6C5s.
     This worked great. I balanced the inputs by driving the amp with a stereo signal, R through the V port and L through the VI port to compare the levels. I reduced the value of R11(K) from 500K to 50K to compensate for a slight loss. This resistor is one of the "custom" parts to be covered in a later post.
     This all could be made easier with a switch for V and VI but I did not want to have to remember to make the switch - or to look at it.

8. Use 1/2 of the transformer's 12V filament winding for the receiver and 1/2 for the amp (as was done on the organ (donor organ ;)
     The receiver draws 16 or 18 X .300A or about 5A at 6.3V

9. Check for proper voltages and make adjustments.
     The new power transformer delivered about 750V for the B+ where as the original delivered about 1000V. This is OK - actually required since the resistance across the field coils will be missing. Some compensation can be made in the filter chokes. On the V they are both the same, about 10h and 50 ohms each but on the VI the 2nd one is about 10h but 125 ohms. Which explains some of the differences in the V and VI speaker field coils (again more later). The only adjustment that was needed was on the cathode resistor for the 6L6s. At the stated value of 250ohms 20W (these are almost always 10W and often show signs of overheating) we had 39V on the cathodes. So it was a good time to upgrade to a 25W 180 ohm unit which gave us about 26V on the cathodes and improved bass response too.

10. Find a place to put all of the "extra" components.
     I extended the mounting bolts for the chokes so that the output trans and interstage trans could be mounted, though I did plat the bell for the output trans and mounted it on top with the 2nd choke being relocated below. There are good reasons for doing this, also to be covered later.

11. Upgrade wire. Use 600V neoprene for a "original" look but much better service. Upgrade fuse holder since I didn't have an original. Clean up the original layout for best wire routs. Add a convenient terminal strip for the various B+ voltages. A good place to terminate the chokes and caps and take measurements.

Underside with everything mounted. The three wires coming out the top are the speaker out, 4 ohms and 8 ohms. I have not provided an on off sw yet.

Top side. Note the output trans in place of the original 2nd choke.

Above is a demo using a VI  receiver chassis. The VOM is monitoring the B+/screen voltage to the receiver chassis. The B+ to the 6L6s is about 420V.

I still need a bigger bench - - -

Russ

I was going to part it out. The two Radiola interstage transformers were good.

The "restorer" could not get the knobs off, so he could not get the chassis out of the cabinet. "No sweat"' he thought. I'll just slather poly on everything - the dials, knobs and bezels included. But first, since I can't get the cabinet stripped of the old finish properly, I'll just scrape it with a knife(?).

Well, when he got done, it looked pretty good from around 10 feet away. Sue said that she liked it. So it was diverted towards 2 or 3 days of restoration which was mostly figuring out how to get the poly off of everything.

The former owner managed to remove most of the character of the wood by scraping the front panel. So much so that the bezels were raised by a little lip where the scraper could not reach. So I added a little bit of grain and a knot or two prior to refinishing.

Completed 5-tube TRF - 4 each 199 and one UX 120 for audio output. I still need to find the paper instruction label for the underside of the lid.

Craig's List item. Before and after.
Yeah, the radio chassis had a few issues, but, so did the cabinet.

Fortunately, in the process of replacing the front veneer with a single sheet of Mahogany, the seller did not get the damaged front panel firmly glued to the arch. Unfortunately, the original trim was lost.

Since the back side of the panel was also damaged, I found it was easier to just make a new panel. The picture above shows the original front after it was reglued and cleaned up. At one point I was going to re-veneer but other damage caused me to reconsider. Much of the grill area had been "patched" with a filler similar to Bondo or some sort of wood filler.

The geometry of the arch trim is a somewhat more  difficult than most people would think. Not impossible, but, just try to calculate the inner curve (at a tangent to the outer curve).

The rest was router work and adding the Zebrawood veneer.

IF the most important consideration regarding the restoration of a chassis is the amount of rust, then this one was not so bad. Unfortunately the power transformer had been replaced and was missing it's cover. Another interesting deficiency was discovered in the tuning cap. There was just enough oxidized metal deposited on the insulators to cause the volume control circuit not to work.

This volume control is much better than a simple rheostat placed on the antenna input but also more complicated. If you get a chance, it can be seen here:

http://www.nostalgiaair.org/Resources/480/M0001480.htm

Aah, Spring, fresh flowers and old radios!

P.S. No, I didn't pay $100 for it.

Russ

Or Masterpieces - which seems a bit contradictory.

In the 1920s and 1930's there were several radios that went by the name "Masterpiece". The term would seem to indicate the best of the best at least as much a one individual or manufacture was concerned. There was the exceedingly common Freshman "Masterpiece" which was rather average as far as 1920s TRF radios go. It was a good radio, but that was about it. A better name would have been, Freshman Average Radio. Then there was the Parker McCrory Masterpiece 733 From 1937  (See: https://www.russoldradios.com/unique-radios.html  3rd entry) which was a really nice 30's battery radio. It was way above average, but a "masterpiece"? Well maybe. And then there was McMurdo Silver, a guy that intended every one of his radios to be a masterpiece. By the time he got to his 5th version, the Masterpiece V, I would say the name fit very well.

I was doing the chassis restoration on a Zenith Stratosphere for a friend and fellow radio accumulator when he mentioned having several (about 7) McMurdo Silver Masterpieces. For the most part, they had been awaiting restoration since 2015. The project had been started, a lot of the parts had been rechromed, but the chassis restoration was unfinished. One thing led to another and before I knew it I was up to my elbows in Master-pieces.

Most radio collectors do not own a Masterpiece. I would guess that  significant percentage have never seen one,   face-to-dialface.. Even more elusive are the 18-inch "Super Giant" pedestal speakers since many of them were removed along with the separate amplifier and sent off to be use for other purposes.

Having entered into this project at the end, I never got to see the original cabinets. For that matter and as you can see, UPS just started delivering parts and pieces. And, at that, many of the speakers/chassis had been partially disassembled. It was a GRAND jigsaw puzzle.

In the photo above note the chromed pedestal on the V and VI Super Giants. They were not built that way and had been chromed along with a lot of the other parts as a matter of taste. Two were to be kept and two more were to be sold along with the matching radios. The V is on top with two VIs below.

Underside of the main (radio) chassis of a MSMVI.
There seems to have been a lot of changes around the addition of a "MIC" circuit along with the "Phono" input for the VI. (left side of chassis)

Above is the power supply/amp for a MSMV. Note the 6 tubes - 2 each 5Z3, 6J5 and 6L6s. That combination gets really HOT. Keep the power cables away from the tubes. As a note for future restorers, the MSMV amp/speaker incorporates 2 field coils in addition to the 2 chokes seen above. FC 1 has a DC resistance around 400 ohms and FC2 around 4K ohms. FC 1 is inline with the B+ to the radio and FC2 is shunted to ground. You get about 350V  to power the main chassis.

The MSMVI PS/amp above has a 25hz power transformer which is much larger than a standard 60hz unit.

The MSMVI power supply/amp only has 4 tubes 2 each 5U4s and 6L6s. The supply is very similar to the V less the 2 6J5s, but the DC resistance of the field coils is considerably higher than the V with FC1 at around 700 ohms and FC2 around 8K ohms. So the speakers are not interchangeable.

Another interesting thing to note at this point is that the tubes on a MSMV are all metal by Raytheon with the exception of the two 5Z3s. On the MSMVI all of the tubes are glass except the two 6L6s which may have also been glass on some units (ST bulb). At the time of manufacture the only difference between the 5Z3 and 5U4G was the base.

MSMVI topside with coil covers (shields) removed.

There are 3 more tubes on the MSMVI receiver chassis but 2 less on the PS/amp chassis for a gain of 1 over the MSMV.