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Old 02-06-2017, 08:16 AM
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Kamakiri Kamakiri is offline
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Expert electronics opinions needed: Radiola 60

I'm working on an RCA Radiola 60. This is gonna get good, so follow along and put on your thinking caps

The Radiola 60 was the first AC powered radio made, and has a split chassis....one side of the chassis is the radio itself, and the second is referred to as the SPU (Socket Power Unit). Diagram of the unit is below.....RCA wasn't very forthcoming in any of the service literature as to part values, as they didn't want any small companies stealing their patents. I was able to verify the values of everything so far, though.

Here's the issue

After fiddling with the radio forever, changing tubes and doing the center tapped 1 uF and dual .5 uF caps in the radio unit, I was able to get just one station on the radio, 550 AM. If I power up the radio after it sits for a few minutes, it comes in with a decent audio level, but quickly sags to barely audible. Obviously I have alignment issues, as I used my signal generator up the AM band and by the time it hits 1000 KC you can barely hear it at all.....but one thing at a time.

The diagnosis and repairs

Tested the resistors in the SPU, everything looked good. As you can see in one of the attached diagrams, the SPU is connected to the radio with a terminal strip.

The book shows voltages as follows:

Terminals 1 to 7 - 200 VDC (I have about 135)
Terminals 2 to 7 - 210 VDC (I have about 160)
Terminals 3 to 7 - 160 VDC (I honestly don't remember)
Terminals 4 to 7 - 110 VDC (same....)
Terminals 8 to 9 - 5 VAC (spot on)
Terminals 10 to 11 - 2.25 VAC (spot on)

To begin with, I dug out all of the beeswax and replaced the capacitor network inside the one can (they tested good, but given the issue I wanted to make sure to start fresh there). No change.

Then, I went through the tests shown and the only one that failed was an open across the G to P (small pins) contacts of the 80 socket....showing an open high voltage winding of the power transformer. Apparently this is a common issue on these, and from what I can find this is the end result.

Question #1: Am I barking up the correct tree?

If I am, then I have an unorthodox idea for a replacement that I think will work......

I've also attached a diagram of the power supply in an average radio powered by a 5Y3. If I were to use the 5Y3 in place of the 80 along with that transformer, choke, and cap network.....would I be able to use that out of a junk radio if I had a resistor network to get the voltages correct? Shows 280 VDC on pins 2 and 8 of the 5Y3 in this diagram, and I could drop that down with wirewounds. Basically, build my own custom SPU......or, is there a known better replacement instead?

Your ideas and thoughts are appreciated!!
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Old 02-06-2017, 09:45 AM
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I think you are right about the B+ secondary being the issue...You can confirm it by connecting a DMM in 500 VAC mode to the center tap of the B+ winding and metering both plates with the power on...One probably is getting zilch voltage.

Really all you need to do is replace the B+ winding. If you've been able to measure the voltage to one of the plates from the original then you can try somethings....Get a variac and see how close to line voltage you can get your donor trans before it matches the output of the original and then see what B+ is with both 80 plates getting AC adjust for proper DC and see what the variac is set at. If you have the variac only up at %40 of line voltage then you could try disconnecting the line winding of the new trans and connect the heater winding of the new trans to the 2.5V heater winding of the original transformer.

Basically if you keep the original trans and want to use a new one you can juggle where you connect the new one and what windings you use to get the correct voltage step up ratio with respect to the line voltage....I've done stuff like this with newer sets. When you find something that works I'd recommend taking the temp of both transformers every 10min on the first power up then every half hour for 1-3 hours of run time to make sure the new config does not cause overheating. If nothing overheats your golden.
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Old 02-06-2017, 10:32 AM
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Since a 5Y3 and an 80 are electrically the same, all I need to do is find an appropriate transformer. I do have an Admiral 19A11 parts chassis here, and the voltages on the Sams on pins 2 and 8 on the 5Y3 are 240 VDC....which brings me in the neighborhood. Plus it's not so ungainly huge that I can't sneak it somewhere.

Now, realizing that coming to this point has stretched my knowledge of power supplies about as far as it's ever been....would I just basically wire it in, disconnecting and using the wires from pins 2 and 8 from the 5Y3 to plate on the 80....then plug that in separately from the main AC in from the radio, hooked up to the variac, and increase the AC from the variac while watching the DC voltage until it levels off where it should be?
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Old 02-06-2017, 12:28 PM
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How much of the new PS are you planning to use? Are you planning to replace the 80 with a 5Y3 or run both some how?

What I would do is use only the transformer from the parts set. Mark all leads (ie. line, 6.3V heater, 5V rect heater, rect plate winding and it's center tap) before harvesting the parts trans.

To start, disconnect the original rect plate winding (including center tap) on the radiola (tape over the ends so they don't short). Connect the rect plate winding from the new parts trans to the plates of the 80, and the center tap of the new trans to chassis output pin 7 (ie. where the old center tap used to connect), then connect the line input of the new trans to a variac. Meter the High dc output of the PS chassis, and if feasible the AC plate voltage on the rect tube. Report back the variac setting that gives designed DC rail voltages.
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Old 02-06-2017, 01:51 PM
EdKozk2 EdKozk2 is offline
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Hi Tim,
Before you get carried away. The tested voltages you show would seem to be correct. Tubes like the 71's normally never were operated above 180 volts and voltage drop through plate reactor seems correct at 135 volts. The second picture you posted shows/ states that tube #7, a 227 has a plate voltage of 160. That's what you found. I think your troubles are elsewhere in the radio. You could have shorts in the trimmer caps, opens in the coils, etc.
Have you tried signal injection starting from the 71 output back to the 1st RF amp.
Ed
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Old 02-06-2017, 02:45 PM
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I'm a newbie when it comes to doing so....so no. I can tell you that I was able to follow up the dial with my signal generator going from 550 on up to about 800 before I noticed a dropoff in volume, if that tells you anything.

For the rest, I'm going off countless internet searches where people attempted to repair their Radiola 60s and they seemed to succeed....to a point. For the readings I'm taking I'm just going off the specific instructions in the RCA manual and following that guidance.
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Old 02-06-2017, 03:06 PM
EdKozk2 EdKozk2 is offline
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Tim,
Sometimes bent or corroded plates of the tuner will short. Also make sure the voltages on the oscillator are correct.The oscillator can stop working in the middle of its' tuning range due to faulty or dirty parts and contacts. You can use an oscilloscope to do a lot of the signal tracing, even checking for RF as long as your scope has a wide bandwidth, at least 2mc or greater. You can watch if the oscillator is cutting out as you tune the radio.
Ed
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Old 02-11-2017, 08:25 AM
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Let's assume that even though I own a nice scope, that I have no idea what I'm doing with it

The tuner has no bent plates....the chassis is very clean as well.

Since I'm left with nothing in my wheelhouse other than to give this plan a shot, here's where I'm at. I have the transformer out of the Admiral 19A11 chassis and everything properly labeled. Based on the Admiral schematic, are there any wires that need to be tied together on this transformer before I begin going to work?
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Old 02-11-2017, 11:54 AM
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For now don't connect any wires leaving that trans to each other (especially ones from the same winding).

Assuming the Radiola has good filament voltage to the 80. All you need to do is swap rect plate windings, power the admiral trans line winding off a variac, and meter it as you increase the voltage. Once B+ is at factory levels measure the variac output. depending on what it is there are ways of using multiple windings and or the two transformers in tandem to get AC inputs that do not match line voltage.
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Last edited by Electronic M; 02-11-2017 at 11:57 AM.
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Old 02-11-2017, 01:01 PM
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Quote:
Originally Posted by Electronic M View Post
For now don't connect any wires leaving that trans to each other (especially ones from the same winding).

Assuming the Radiola has good filament voltage to the 80. All you need to do is swap rect plate windings, power the admiral trans line winding off a variac, and meter it as you increase the voltage. Once B+ is at factory levels measure the variac output. depending on what it is there are ways of using multiple windings and or the two transformers in tandem to get AC inputs that do not match line voltage.
The 80 is likely wired as a full wave rectifier, so you will also need to connect the center tap of the plate winding to ground.

Edit add: Just looked at the schematic, apparently B- is not grounded in this set, so the center tap is just connected to the common point of the two filter caps, as shown.

jr

Last edited by jr_tech; 02-11-2017 at 01:34 PM. Reason: add info
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Old 03-08-2017, 01:33 AM
EdKozk2 EdKozk2 is offline
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Hi Kamakiri,
Just curious, did you ever get the Radiola 60 power supply conversion working? If you did, did it solve the volume issues ?
Ed
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Old 03-08-2017, 06:05 AM
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It's in the queue. Right now I'm making one CTC-5 out of two, finishing a total recap on a CTC-15, and diagnosing a hot plating horizontal output on a '68 Silvertone Silver Sentry color. Hoping to have all of those knocked out within a week.....then the Radiola goes back on the bench
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Old 04-06-2017, 06:36 AM
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It's working!

Would've been an interesting experiment to jump the secondaries, but no matter how I looked at it I couldn't figure out where I'd mount the second transformer. I let discretion be the better part of valor and picked up a used SPU (Socket Power Unit, or power chassis) on ebay for about $35 that claimed to have proper tested voltages.

Installed it in the radio, and bingo! Seems my diagnosis was right on the money.....I'm listening to the news on it right now

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Last edited by Celt; 04-07-2017 at 06:21 PM.
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Old 04-06-2017, 10:49 AM
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Old 04-06-2017, 01:01 PM
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I remember watching all the Muhammad Ali fights when I was a little boy....back in a day when broadcasters had unmistakable personalities....
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