In the previous post the substitute UV 199 tubes are demonstrated in an early 1920s TRF radio. Now I wanted to test the UX 199/UX 120 versions along with another application for the UX 201A version.

I realized that there aren't many - any, small radios using the later UX tube versions in the museum display. There are a couple in storage, not easy to get to. There is the Thompson Minuet, I really did not want to pull it off of the shelf and risk damaging the speaker cone that Buford Chidester made for it. And then there is this really big  Remler super. Well at least the top cover was already removed for display.

The Remler is a cool radio!

I had purchased it about 5 years ago along with about a dozen other radios at an auction near Portland. It always seems that radios come in bunches and I am always in a hurry to clean them up. I do test them, but, generally move on to the next one after as quickly as possible.

Now I had a little time to explore and the first thing I needed to do was verify that the unit was functioning normally. It Wasn't. The second RF section in the TRF wasn't contributing at all.

It did not take long to find the problem which was a relief since there are a lot of moving parts and the potential for broken wires, but that was not it,

The second section of the tuning cap was shorted. This was not from broken parts but because of a wiring issue. The 3 sections of the ganged cap are isolated from each other until that little wire, seen near the bottom of the picture above is installed. On most tuning cap assemblies the moving plates (rotor) are all grounded to the shaft that moves them leaving the stationary plates (stator) to be connected in the grid circuit. On this assembly Remler had wanted to stagger the grounded plates - in other words the moving plates (rotors) in the center section were grounded. This must have confused somebody WHO grounded the stator as well as the rotor. I could tell from the obviously factory connections on the trimmer what the design configuration was.

The fix resulted in better gain from the TRF section.

I suppose that at This point I should explain that unlike any other early super that I have seen, This radio will operate as a superheterodyne OR as a TRF. And that is one of the reasons that I think it is so cool. With a "normal" super from this time you would tune and tune listening for a squeal and then tweak the IF and oscillator until you had a station. OR you would just have some noise - start over. On this radio you can turn up the TRF filament rheostat and get the same functionality as a 5 tube TRF, which is what it is in that setting. When a station is found turn down the TRF (you don't need that much input to the IF section) and adjust the super for the best audio. It really is much easier.

If you want to understand the other cool functions, like the IF that uses the sum of the freq. and local osc. there are a few good sites. Start at this one:

http://www.duanesradios.info/html/infradyne_superheterodyne.html

Now on to the tube substitution.

Below is a demonstration of the Infradyne:

Below, the 01A (201A) substitute is used in the 1st audio socket.

In the video below the 01A sub is used in the 2nd detector position with the superheterodyne section running.

During the testing process I decided to inspect the IF assembly. Below is the IF, removed and flipped over. IMO these non-potted IF transformers are so much easier to deal with than other manufactures units.

I decided to just go-for-it and replace all 3 of the UX 199s in the IF section. I believed that this was probably not going to work - but it did.  The higher gain of the substitute tubes along with other differences required retuning the IF.

Using the tree tubes there is a savings of 1/3A in the filament supply.

As one last note, I never did show or sub the UX 199 used as the oscillator since it is stuffed in behind the meter so close that it is almost impossible to get out.

I used a 3S4 just to see if it would work, it does, but the 3V4 is probably better. In the case of the 3S4 the jumper between the plate and screen could be replaced by a resistor to reduce the screen voltage which is not required in the 3V4.

Well, this concludes this project, at least for now. I have another chrome plated monster to work on.

Russ

P.S. Don't miss Part I below.

OR is there - -

I just looked up 201/01A postings on E-Pay. It looks like prices are up since the low around 4 years ago. Then it was not uncommon to be able to buy these for $10 - $15. Looks like it is $20 - $25 now. One thing you can be sure of - they aren't making new ones.

There is plenty of history on the 201 online so some research should be done, if you are interested.

I have more than enough UX201s to last a long time, especially considering that the plastic base, long pin tube was really only original equipment for about a year with the previous versions running back to about 1920. And since I try to put the original brand/type of tube in my restorations - well, that is why I have plenty.

But, many people only care about the radio working - and being cheap (me too).

I have thought about this for a while and it is a sure thing that I am not the first. Here is how it goes - build a replacement for the UX201/01A for less than $2.50.

You are gonna' need a 4 pin base like off of an 80. Depending on your radio, this base may or may not need to have the side pin for the Bayonet/UV base - depends on how old your radio is. Then, a standard 7-pin miniature socket. These should both be available from your junk drawer.

Then look in your tube stash for a 6C4. I picked this tube for it's characteristics - basically it is 1/2 of a 12AU7.  It is called a power triode by RCA. If you don't have one, E-Pay has some for about $1, some NOS. I just bought 15, about half of them NOS for an average of $1.10 - Sorry, there will be more.

Then 4 wires and a jumper will connect the 2 sockets/plugs. Connect the 7 pin socket, pins 3 and 4 to the big pins, pin 6 goes to the small pin on the right (Pins up, big pins closest to you) and the plate to the remaining small pin. Then place a jumper between pin 3 (fil) and pin 7 on the 7 pin socket. This is the cathode connection.

To test as a 201 use the same settings as an 01A but you will need to lower the bias from about 48 to near 0.

In testing this tube works great as an audio amp including a 112 . I tested it in my AK 20 in all positions with setting as they were for the 201s and it worked great as a detector and audio amp improving tone and level some and about the same as the 201 in the RF amp sockets.

BUT, BUT it is a 6V tube. Yeah, it doesn't matter. It takes about 10 seconds to warm up. BUT, BUT, BUT the cathode will be damaged - well if it goes to "sleep", just run it at 6V in your tube tester for a while. In reality these tubes were often run at low filament voltages to keep noise down in audio circuits and as a way to get bias for finals - look up some of the Fisher amps using the 12AU7 and 12AX7. It will be fine.

Also it only draws .15A of filament current. This will make your power supply/battery happy.

So a UX 201/01A sub is cool but what makes me nervous is testing with UV-199s and other more expensive/temperamental tubes.

I say temperamental since it seams that a UV or UX-199 can go to sleep just setting in it's box. Sure they can be rejuvenated, at the risk of destroying them. During the restoration process it sure would be nice to have a sub that doesn't cost $50 and up (metal base UV), then put in the correct tubes for display.

Again, looking in the inventory under cheap and plentiful I find the 3V4 miniature 7 pin tube. I have 12 of them. This tube is a pentode but don't let that bother you. The filament is a center tapped common cathode with the tap already jumpered to the suppressor grid. So one more jumper between the plate and screen and you have a triode.

https://www.radiomuseum.org/tubes/tube_3v4.html

The filament is 2.8V but running it at 3V should be no problem. The current draw is .05A. This is just perfect to replace both the UV and UX 199. COST?? - About $5 on Pay-Bay.

Go back to your parts box - assuming it is not still dumped out on the floor - and find another 7-pin mini base. Now, the UX-199 base is a little harder to find than the one for a UX-201. It has the same pin spacing and sizes but is over-all smaller in diameter. Good/bad news is that there are a lot of bad ones around. The UV-199 is harder to come by, even bad ones. Your are going to have to search for "display tubes" which should be priced at $1 or $2.

OK! this is as good a place as any to post:
THE PIN OUT ON A UV199 IS NOT THE SAME AS A UX199!!!!
Anybody trying to test one without knowing this will be fine until they hook up a UV199 and push the "TEST" button - and - BOOM goes the filament, since you just put plate voltage on it.

Examine the pin-out, courtesy of RM:

https://www.radiomuseum.org/tubes/tube_3v4.html

On your tube tester, use an ADAPTOR for the UV based tube. Both should give you about 1500 GM on the settings for a 199 (or a 99 on most Hickok tube testers).

OK, OK, just one more - for now.

How about the UX-120. This is the "power" triode output on many radios that use the 199s. The adaptor above is going to work in that socket but the B+ needs to be kept to 90V. How about using a 3S4 instead? It has about the same configuration s the 3V4 but a different pin-out.

I need to do more testing on the UX199 and UX120 subs. I will post further as results become available

If you find these posts useful, don't forget to check the "like" below. Thanks

Russ

I stated somewhere, probably more than once, that my interests include early radios up to 1942 and later Hi-Fi from around 1955 to 1979.

Why, you may ask, do I exclude the decade between 1945 and 1955? Cabinets, those rectangular, featureless cubes with doors that degraded further with the "blond", yellow and whitewashed finishes that continued into the 60s.

The problem, for me, is two fold.  First, these designs tend to hog floor space. Second, unless you design a room around them, these consoles don't fit well with most décor. Or even more simply put, they are just not to my taste. I know that my feelings are not universal, but demand and prices over the years do indicate considerable sympathy. I will have to concede that after considerable resistance, a 3 channel Motorola has been added to the display - and I kind of' like it.

 Unfortunately there were some great radios hidden inside of those cabinets. Scott and Meissner were just two of the high end manufacturers that followed this trend. They had to. It was the style of the time.

Fisher consoles are often stripped of their tuners to be installed in cabinets like those that became popular in the 60s and 70s. I suppose that this is preferable to losing the whole console to the land fill, but, one day (maybe today) the original cabinet will be missed.

So when recently I was given a number of these late 40s, upper-end radios, I simply stashed them in the parts room and moved on to the good stuff.  I suppose that fate and my desire to preserve history collided when it became necessary to clear out the parts room - or put a warning sign on the door - Enter at Your Own Risk!

Among these radios was the Scott 510 discussed below and a Scott 800 that I have not addressed yet. But the ones that interested me most were the Meissners. There was quite a collection - none were complete and none had a cabinet.

First there was the 2961 amp - REAL radio candy from 1947! I just could not ignore this PS/amp with push-pull parallel 6L6GA output tubes. Turns out the 6L6s are wired for triode operation which reduces the power output considerably (as compared to pentode operation). This amp/dual power supply was the heart of a 2961 tube radio - I wish that I had the rest of it.

Since I had neither the original 2961 receiver nor the amps for the 9-1093-7 and 9-1093, I built an adaptor to use them in combination as well as with a 9-1091C receiver (later).

At this point I will confess that the original configuration of the 9-1093 had only (ONLY!) 24 tubes, but what the heck. Here is a video. The original coaxial speaker and OP transformer are also missing so I had to adapt -

Meissner 9-1093-7 and 2961   (26 tubes)

The 1093-7 chassis was in the best shape of all of them with the black finish and red lettered labels remarkably intact. Yet it also needed the most work.

Along with the standard restuffing of paper and electrolytic capacitors, this unit also had about half of the carbon resistors way out of tolerance. I was able to replace all of the resistors with NOS carbon comp resistor from my parts inventory. This kept the bottom side of the chassis looking original as well as the top side.

During the parts replacement all eyelets are cleaned and the original mechanical contact is restored prior to soldering. This keep the eyelets and contact strips from "bulking up" with old solder and the old component wire ends also maintaining the original look and reducing the chance of intermittent contacts.

You might note the -7 on this model number. This one is the only reference to that suffix that I have found. The other version is just 9-1093. I have one of each and there are at least 3 very significant differences.

The -7 version has an on-board preamp tube for phono mounted at the end of the FM circuit and inside of the area that shields the last IF, 2 limiters and the discriminator. The other version has a hole/cover in the chassis but uses a separate pre-amp module with 6V and B+ coming from the main chassis. Interesting that the pre-amp must be plugged in in both cases to an RCA input connector.

The -7 version also has the nice black paint and the controls are mounted directly to the front of the chassis rather than being spaced back several inches in the other version.

Meissner 9-1091C

This is another AM FM (mono) chassis from about the same period. It has somewhat more versatility as compared to the 9-1093 since it has it's own power supply and push-pull 6J5s capable of driving almost any amplifier. But, it still does require a separate amplifier chassis. This radio has 17 tubes including a 6U5 eye tube to display signal strength. Like the 9-1093, AM and FM reception and audio quality are very good.

This 2961 amp uses push-pull-parallel 6L6GA wired as Triodes. It has 2 rectifiers. The 5Y3G supplies B+ for the tuner chassis and a 5V4G provides B+ for this chassis.  There is a separate filament transformer.

One of the features of this amp that is notable is the socketed filter capacitors, one for each of the B+ supplies. These caps use a 4 pin socket like the one used for an 80 or 2A3 tube. They are secured by a clamp. This sure would have made servicing the filters easier. They could have been changed out every couple of years to avoid failures.

This collection of Meissner radios also includes a Signal-Shifter EX ( low power CW transmitter ) and a much smaller kit radio. I will post any updates on those as I get to them.

It seems that many radios were sold as kits or replacement chassis for a cabinet that a customer already owned. This is consistent with the company's other offerings of  quality OEM and replacement parts. Some were sold under the name Maguire. You might want to do more research under the name Thordarson-Meissner / Mt. Carmel, Illinois. Thordarson is still in business. (Thanks Ron)

To conclude, this series of radios, especially the large chassis with FM, were very high quality only lacking the chrome to be compared with the very high end radios of the time. If you happen upon one of these radios and have never heard of, or seen one, you are not alone. If the price is right, you might want to add it to your collection.

Nipper-

Time to clean out the parts room. And, what to do with the Victor Micro-synchronous receiver chassis? It was very rough and over the 5 or 6 years it had been there, not very useful. I guess that I had just kept it for the top cover. I had always thought that it would have been nice if the heavy, stamped covers were more visible inside of the RE-XX cabinets,

Well, the chassis is gone but Nipper has been polished and mounted  (that sounds wrong ). I'll set him on top of the "Talking Machine" display.

Probably the best way to add quality programing to your old radio collection is with a low-powered, local transmitter broadcasting personally selected content.

Such devices have become inexpensive and, to some extent, reliable. Issues with these transmitters are usually associated with noise, interference and modulation levels/quality. There are at least two instances where using a Part 95 transmitter is not the best solution.  First, those people with only one or two radios might not want the additional expense and the associated hardware for their small collection/display. More significant for us "serious" collectors is the inherent mediocre audio quality and it's reproduction on a very high end radio like a Scott, McMurdo Silver or any of the high tube count radios of the 1930's to the 1970's. It is difficult to get the performance that these radios are capable of without quality input.

Many of these high-end radios came with phonographs or at least a phonograph input that can be used with modern source equipment. The most significant drawback associated with using your MP3 device as an input is the relatively small signal voltage that they generate for audio output.

The other significant compatibility issue is that even the mightiest, 25 tube (or more) hi-fi system built prior to 1955 was only single channel (mono) reproduction. So even with a quality phono input, the question is  - "So where do I plug-in this other cable". Using a "Y" adaptor that ties your right and left stereo channels together (with no isolation) is usually a bad idea and might even damage some devices.

The simplest solution in many cases is to build a matching transformer/cable using 2 small output transformers. This will provide isolation for the R and L channels of the MP3 device along with a voltage boost - and less than great frequency response. This is still a good choice if you have a phono input or can manufacture one.


What we have here is completely different.

First a little background: Mentioned below - and still lacking the story it deserves - is a collection of radios/chassis/parts donated to the cause in early summer of this year. Among these was a Scott 510. All of the components were there including the cabinet which was the typical, rectangular, late 40's box with a couple of doors - not my favorite design. This cabinet was originally finished in the white-washed color that was popular in the 1950's. Along with the yellow-ish finishes of the same period, also, not a favorite. The overall delaminated, banged up, falling apart condition contributed to the decision to not restore.

The receiver chassis used in the 510 is good, maybe even very good, but certainly not consistent with the quality and leading edge design of earlier Scott models. So, I scrapped that chassis too.

The remaining chassis is the chrome-plated power supply/audio amp seen in the first picture, above.

This is a nice unit using a 6SN7GT driver and push-pull 6L6s for output. And look at the size of that audio-output transformer (8 ohms only). The published frequency response is 30 to 20k hz at +/- 1 db.

http://www.nostalgiaair.org/Resources/592/M0016592.htm

It was built with a dual power supply using both a 5y3GT and a 25Z6GT as rectifiers. The 25Z6 was no longer necessary since it only supplied the receiver chassis. There was also a nice large choke (underside of chassis) that was now no longer needed. Having recapped the unit, I decided that it would be nice to incorporate this choke into the amp's power supply. So I reduced the value of R48 from 375 ohms to about 275 ohms and installed the choke between the first and second filter caps.

Testing the amp using input from my Samsung phone, I found the output to be way too low to be satisfying. There was just not enough voltage out of the phone to drive the 6SN7 grids (in parallel). The extra, now unused rectifier socket was also screaming - "stick a tube here". So I did.

The objective was the same as stated above, to provide isolation, voltage gain and combine (mix) right and left channels. Since I had plenty of power supply overhead - lacking the need to power the receiver chassis, the obvious solution was the addition of a 6SL7gt stage prior to the 6SN7 driver.

So how is this done? Easy. Just look in the index of your RCA tube manual under the chapter on Resistance Coupled amplifiers. WHAT? You don't have a tube manual - don't tell anybody and get one here:

http://bama.edebris.com/manuals/tubesandvalves/

The directions are pretty simple. Pick your B+ voltage and desired characteristics from table 5 (I was using RCA 25 from 1966) and dig out the few additional parts that are needed. The drawing and specs are for a single triode. Your are just going to need to double this up for the 2 triodes in the 6SL7. The plates of both triodes will be tied together and feed the grid of the 6SN7 through a coupling cap also speced in the chart. Note that you could probably use a single cathode resistor/bypass cap, but I used 2, one for each cathode.

Most applications are going to need an additional tube socket and a person could use a 12AX7 but I already had a socket - given that it would probably be better further from the rectifier but that would require another hole and the 6SL7 that I chose had the aquadag coating which resulted in ALLMOST no hum. Rolling a few other tubes into this position resulted in some hum. I might add a shield - or not.

The test results were plenty of gain, good frequency response and little or no noise.

I also upgraded the 6L6s to 6L6GCs so that I could play with higher B+. As it is, B+ is running at about 380V. I added 2 shielded cables with RCA jacks to the back of the chassis. You might want to add a coupling cap of around .01uf to each input to the grids of the 6SL7 to provide some safety for your device should one of the grids fail and crash into the plate resulting in B+ going to your phone/device. Otherwise, isolation is good as is the mixing of right and left channels.

- - - Or the second 1926 Neutrowound.

From the post below, here is how the second Neutrowound receiver looked when it arrived - soaking wet.

Other than the rust, this one also had wasp nests inside, crunchy - dried out rubber tube mounts, open interstage transformers, missing on/off switch, missing knobs and no finish left on the wooden base.

I started off by sand-blasting all of the metal cabinet pieces and replating the corner trim and tube shields/caps.

This is one of those radios that needed to be taken entirely apart, each part cleaned, serviced/rebuilt and then reassembled.

I repainted the cabinet with wrinkle paint, which was easy since it was over 100 deg. outside. Having coated it twice, I just set it out in the sun and it wrinkled up just fine. It was then top-coated with black lacquer to bring up the gloss. CAUTION: lacquer will severely  mess up this wrinkle-paint. It must be applied really dry.

The base/board was stripped, filled and sanded then sprayed with shellac.

The rest just needed a lot of cleaning and the same re-stuffing of components that was performed on the earlier unit.

Fortunately, the missing knobs are similar to those used on a lot of 1920s radios. Unfortunately, I still need 5 of the tube shields/caps.

A couple of other notes:

Both of these radios were missing the 6 bolts that hold the top cover on and I'll bet this is quite common since reinstallation of these bolts takes a bit of  fishing. So they were probably left out having once been removed for service. If you need some, they are 4 inch long #10 X 24 machine screws with a slotted head.

If you need to replace interstage transformers, use 3:1 (three to one) rather than 5:1. If you use 5:1 transformers, you will probably end up overdriving the last audio stages. This will result in really noisy poor audio.  If you have a 5:1 with a tapped secondary, just use 1/2 of the secondary. That is what I did here.

If anybody find a few extra shields/caps, I could use a few. BTW they and the end trim are plated brass.

Russ

Sorry it has been so long since I posted. Honestly, if the smoke from the forest fires was not so thick outside, right now, I would probably be on my way to the shop.

About two months ago we were given a large collection of radios, chassis and parts. This was such a nice thing to do. The collector had just retired. He had a lot of projects and travel planned and did not want to liquidate the collection by selling individual radios.

So after two truck/trailer loads, there were radios stacked in the shop and at both the front and back doors.

Well, I may be a radio collector (hoarder), but I am also unable to allow stuff to pile up for very long. So for the past two months I have been cleaning, restoring, donating, selling and disposing of this collection. But, that is not what this post is about. The rest of that story will be posted later.


THIS story is about the two 1926 Neutrowound receivers that I acquired in the meantime.

Of the two, the one pictured above, was by far in the worst condition. Even though it was well packed, it arrived soaking wet. That probably did not account for the rust and bug nests, but it didn't help either. BTW, none of those tubes were good either. All of them had open filaments.

I am in the process of saving the specimen above. The greatest challenge will be finding the missing tube shields/covers.

For the moment, we'll concentrate on the other unit, below.

I won't take the time to illustrate the history of Neutrowound Radio Manuf. except to say that this division of Advanced Automotive Accessories only made radios for 4 or 5 years. This "Shielded Breadboard" design carried through those years with a few modifications.

Though this is a good radio, by 1926 the design was a bit dated. Then by 1928, the battery powered TRF was really behind the times. I can't really see why this design was popular in any of the years it was produced.

Pictures really don't express the size of this radio, measuring almost 3 feet long. It had 3 stages of tuning and the 3 dials rather than a single dial, as was becoming the standard of the time. I suppose that in a home that was yet to be "electrified" the need for batteries in 1927/28 was not a problem but elsewhere, the new AC powered radios were more desirable

.

Radio construction on a "breadboard" was quickly becoming a thing of the past.

There are two significant and nearly universal challenges to restoring any of these radios. The first is RUST. A crinkle coat paint was applied to the outer metal surfaces. In the 1927 models this could be a striking blue or red. In all of the models, adhesion - at least in the long term, was not so good. This lead to a lot of rusted cabinets  (see top pictures). Coupled to that, it seems that in the finishing process, shellac was applied (smeared) to the inner surfaces of the metal. This hit or miss finish led to rust on the inner surfaces as well.

The second and probably most encompassing issue is caused by the degradation of the gum-rubber mounting of the Kellogg tube sockets.

The first two tubes have somewhat of a "hard" mounting since the screws pass through the socket flanges, through the 1/4 inch gum-rubber and into the breadboard. The last 4 tube socket are fully floating on the rubber strip shown above having been replaced.

I have not seen an example of this radio where the rubber has not become powdered or at least the consistency of a sugar cookie. Needles to say, the rubber should be replaced. Gum-rubber sheet is not a common hardware item anymore and the cost of a piece may be significant. Mounting the sockets on new rubber is not an easy task either.

Above, I am holding an original piece of the rubber mount.

As you can see, mounting the sockets requires careful placement and compression of the rubber. This mount must compress the rubber without making a big hole in it, which would require starting over. I had to make a jig to hold the nuts/washers while compressing the assembly from the top. Otherwise, at least 3 (frustrated) hands would be required. By the time I made a few of these, the task was not so impossible, but at first it certainly seemed so.

Now consider what would happen if the sockets/tubes were not in the correct position.  You probably would not notice until you tried to replace the top cover and even more so as you tried to install the shields. In other words, incorrect placement results in the tubes hitting the top cover and/or the shields. The best you could hope for in this situation would be for the rubber base to give enough to allow the tube to fit through the hole at a slant - not acceptable.

Other common issues include failure of the 3 interstage transformers pictured in back, above. And, the replacement of the two .5 uf paper capacitors. I restuffed/rebuilt all three of the interstage transformers and the metal-box capacitors for an original look.

I was able to save the original crinkle finish with just a little touch-up as well as the finish on the board. Not so lucky on the other radio, but, more on that one later -

The Masterpiece V receiver chassis. Note the chrome grid-cap shields on metal tubes. This radio has 5 bands with a range up to around 65mhz. It has 20 tubes counting the eye tube. There is a BFO designed for CW. The audio output is two 6L6s into what was the 18" Jensen, gone now but I am using two Jensen A12s like in the Masterpiece VI, and added a separate tweeter.

What is under all of those chromed shields? Better take a look if you are going to do a restoration - a lot of paper caps.

The underside of the chassis resembles a communications receiver such as a Hallicrafters.

Almost all of the original resistors were well within spec. This was a big contrast with the Strat chassis that I was working on simultaneously in which almost all of the carbon comp resistors were way out of spec.

The power/amp chassis is also chromed. Not quite as nice as the main chassis but still presentable.

Back side

The 2 Jensen A 12 speakers were not original equipment (according to my friend Norman B.) but were included in the exchange as was the Oxford cabinet. This cabinet is most often seen with the later 15-17 model but since all cabinets were optional, any cabinet that fits is appropriate. A note, that it has been reported that the Masterpiece V will not fit in cabinets made for the 15-17 without removing the chromed cover is puzzling since the chassis fits very well in this example.

The shelf was drilled for a pedestal mount speaker, probably also an A12. The front baffle is new and all 3 speakers are mounted to it.

The two Jensen A 12s have different FC DCR. One being about 250 ohms and the other being 5K ohms. This is good and similar to the FC values on the original Jensen Super Giant. An additional 50W 1K ohm resistor is placed inline with the two field coils which drops the B+ to just the right value and keeps the FCs from passing too much current and getting hot. A pair of Jensens with 800 ohm and 7 or 8K ohm field coils would be better but very hard to find. A pair like these is still a challenge to locate and not cheap.

I  think that the Masterpiece V is one of the best radios sold prior to WWII. Especially among those that were available to the general public (omitting some of the high tube count Scotts).

It will receive up to 65mhz, a real advantage over the Strat. This is probably a credit to the tube choices and the fact that the metal tubes were superior for RF circuits to the G type glass tubes in the Strat.

I set the 0-beat on the BFO while adjusting the IFs. It is very useful for CW signals. While the level of the BFO is not adjustable, a little careful tuning will allow SSB signals to be demodulated. This is also an option the Strat does not have.

The audio is good, really good for 1935, yet in a comparison with the 25 tube Zenith it is not quite as impressive. It does have separate bass and treble controls (tone only on the Strat) but the treble is not quite as crisp and max bass is not quite as strong as the Strat.. In this respect the 8 45 triodes with separate bass and treble interstage transformers works well for the Zenith. Keep in mind that the 18 inch Jensen would probably have helped the bass somewhat, but I am comparing apples to apples since the Zenith was stock with two A12s and a tweeter - the same configuration I am using in the MSM-V.

Tuning is always on the fast ratio until you reach the desired spot and then you can slow tune back, using the same knob. Fast and slow tuning are  separate controls or manually switched on most other radios.

There is an audio expander circuit. I'm sure it ads dome dynamic range to some music, but speech is a little weird with the volume going up and down. The expander can be switched off.

The same control will give you narrow and wide IF control. The wide IF setting would probably be used on strong broadcast stations whereas the additional 2 stages of IF selectivity are a real gain for shortwave listening.

The dial is easy to read and fairly accurate if aligned properly.

I would rather have the on of switch on either the tone or volume control but McMurdo used a separate switch mounted on the side of the cabinet.

If there is any interest, I could do a more complete comparison between the MSM V and the Zenith Strat and maybe the Scott 16 and/or the Philco 37/116 (though it is 2 year newer) and the GE M-125 (also from 1935) just for fun.

Well I couldn't wait for the tubes to get here, so I substituted some used ones in both chassis and began testing. It WORKED on the first try. Yeah, even I would not have bet on that but I'll take it.

My bench is not all that large so it take a few additional carts and such to hold all of the parts.

I did not get off with no issues though. Actually there were two.

Below you see the control/signal cable that runs between the chassis. There are three conductors that carry line voltage. Depending on the plug polarity (it is not polarized) and whether the set is on or off 120V can be on any - or 2 of the three wires. These 3 wires are twisted within the armored cable. Over years of rubbing and becoming brittle, there were many abrasions on these wires. The result could have been a short but what I saw was 120V AC on the chassis intermittently.

I knew that this cable was a problem. I had hoped that some repair to the end was going to suffice since an exact reproduction was going to be hard to produce. But now I have given into that reality.

The other issue was less significant. In the comments on the earlier Strat post below John mentioned a problem with the "Q" relay not working. Well this one - the one I rewound - didn't work either. So -

I resisted the urge to take it apart and rather measured the source voltage. It was around 300V with a short warm-up. I measured the connection to the plates of the 85 tube. It was at around 280V. So I had continuity across the relay coil and an expected voltage drop meaning that the 85 was conducting.

I then checked the grid voltage generated by the AVC tube. Something close to 0 volts allows the 85 to conduct. A signal as high as 10V will switch the 85 off, deenergising the relay. I was seeing from -.4V to about -7V. So my AVC signal was good. (when the relay is energized the closure shorts the secondary of the high frequency interstage transformer which mutes the audio until another strong signal is tuned).

So what was the issue? Checking the less than deluxe relay (see pictures in the earlier post) I found that a little nudge closed the relay. The simple solutions would be to lessen the spring tension or move the stop so that the magnetic coil was closer to the throw. I chose the latter approach and all was well.


Below is a short video after alignment. The radio is only on a short antenna so short wave reception is limited. However, when I switched on the upper band I did receive several stations, WWV and even CB transmissions. This is notable since the oscillator section of this receiver is a bit challenged above 22mhz. So I was pleased.

So this concludes the chassis restoration. Once the NIB tubes arrive (42, 5Z3 and 45s) the chassis will be reinstalled into the cabinet.

Since this project was a trade, labor less parts for a unrestored McMurdo Silver Masterpiece V, I had declined the cabinet work, instead preferring to do the fun part. The cabinet was refinished by a friend, Gary, who lives a bit north of here. The cabinet is finished, but I have only seen pictures, so far. Probably within the next two weeks you can expect to see pictures of the reassembled 1000Z.

While this project was running I was also restoring  the MPV. It is also finished - a very impressive 20 tube radio in itself. When I get some time I will post some pictures of it in the next blog.

Russ

While waiting for the arrival of the NIB replacement tubes for the Stratosphere project I have had time to work on the Atwater Kent 768Q first mentioned two posts below.

I had been lucky enough to have completed the AK 559N project a short time ago. This radio is also of that vintage with similar cabinet design as well as chassis design along with the associated common issues.

The  768Q is a 8 tube "farm" radio meaning that it was battery powered. In most circumstances, this was an effort to provide radio receivers to a large portion of the country that had yet to acquire commercial electric service in the mid 1930s.

This radio shares a cabinet with other AK models such as the AK 447. Other than the power source, significant differences between these models include  - tube count, the lack of a shadow meter and the use of a pin-type speaker using a natural magnet rather than a field coil. Most of these differences reflect the considerations that must be made to improve battery use economy. The addition of an additional tube also reflects this consideration. The 8th tube is in the audio output, the 768Q having push-pull 30s driving the speaker directly through a center tapped "magnetic" coil. This coil energizes the speaker accomplishing cone movement as compared to the voice coil in a dynamic speaker such as in the 447.

I had to use 3 separate power supplies to generate the necessary voltages. 2V for the tube filaments, 180V for the plate voltages and -22V for a C voltage (bias). I did experiment with lower plate voltages. Except for a slight decrease in volume the radio performed well down to about 135V. (decreasing the C voltage accordingly).

Above, the before and after view, noting that the cabinet had been stripped by one of the previous owners and had incurred damage including the loss of veneer as well as some structural damage.

Besides restuffing all of the capacitors and building 3 replacement resistors (note the metallic end caps of a slightly different grey/silver color) most of the rubber insulated wire was also replaced. See pile at bottom of picture above.

This chassis had survived storage very well, maybe better than any other AK of the period that I have worked on. Most of the original resistors were OK and the rubber wire was remarkably well preserved - estimating that only around 1/3 was cracked or had hardened insulation. None the less, I replaced all of the wire on the IF and RF transformers and the interstage transformer even if it appeared ok. Having the radio apart for service made replacement of the wire more practical now rather than waiting for it to fail and I did not want to take the transformers off again later. So all in all , I replace about 90% of the original rubber insulated wire with new neoprene rubber insulated wire of the same colors - or at least close.

As is often the case, the rubber insulation on the black wire was always bad and failure of other colors also tended to be similar in all examples. It seems that the pigment has something to do with the failure rate. Also degradation by mold/fungus seems to be a factor so wire that is isolated in a can or elsewhere  usually is in better shape than the mass under the chassis.

The original speaker had been removed - unplugged. It probably went to some hi-fi project, for which it would not work (well) or maybe another radio since the original owner had some interest in restoring this radio and probably had other projects as well.

Other than the cabinet being stripped/sanded, it looked like somebody had done a bit of poking around under the chassis, cutting a few wires, but nothing else.

Above: The radio in operation on the bench. Note the dial lamp. Dial lamps were often omitted from farm radios to reduce A battery consumption. It is nice that AK decided to include this option probably because it was a high end set, even for a farm radio. If the user wanted to conserve power he could have just removed the bulb.

The pin type speaker is of the same size as the original (there were two different models of speaker used in this radio). It is similar in appearance to one of the original speakers. It is not a dynamic speaker rather one that uses the lever action attached to a pin that exerts force on the cone. The "permanent" magnets are not permanent and often need repolarization. It can reproduce midrange frequencies pretty good but is very poor at reproducing low frequencies.

To make this speaker work  ,I had to remove the winding (coil) and rewind it with a center tap which goes to B+ with both ends going to the plate of one of the push-pull number 30 tubes. A number 30 is a triode similar to a 01A but with a 2 volt common cathode filament. They are efficient but don't produce a lot of audio, so using 2 in PP was a good option.

I had never noticed before that 2 of the 5 knobs have serrated edges, probably for better grip.

Above is a demonstration of the cool band selector. The 2-speed tuning is on the upper right. The knob on the lower left is a multiple position tone control and the one in the lower center is a local/distance switch.

The local distance switch is useful since it is easy to overdrive the front end increasing distortion. Testing using my AM transmitter required the switch to be in the local setting for best reproduction.

The radio has 3 SW bands with the upper band going to about 22.5 mhz. Reception on the shortwave bands is good.