Author Topic: One channel out on my '59 RCA TPR-8  (Read 5673 times)

spiritofradio

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One channel out on my '59 RCA TPR-8
« on: June 02, 2015, 02:44:31 PM »
I'm getting ready to start tracing this issue, but I hoped this is something that might be a common problem that has been faced before. I'm certainly not the sharpest pencil in the box on these things. The TPR has a separate Amp from the tuner chassis.  The speaker wires out the back of the amp are black yellow and red, and they in turn supply the console speakers.  Yellow sounds perfect on phone, am, and fm.  Red I get squat on anything.   Red and yellow together and I get one channel out all speakers. Each channel has it's own output transformer.

If I bump the preamp tube for the problem channel, the speaker will chirp but I'm pretty certain it's just the spark/surge from the tube and not audio trying to get through.  I've swapped the power tubes, the preamp tubes and tried a different rectifier, but the result is always the same. Darn right channel.  Cleaned and recleaned the pots, switches, and the ext. int. switch in the back where the speaker leads exit the amp from.     I'm guessing the next step is to check the output transformers?
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

Larry H

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Re: One channel out on my '59 RCA TPR-8
« Reply #1 on: June 02, 2015, 03:14:56 PM »
It's highly probable that there's an open resistor in the audio circuitry of the channel that's out.  Remove the tuner and amplifier both from the cabinet.  Check every single resistor in both the amp and tuner for an ohm reading with a multimeter.  Don't worry about ohm values, you are just looking for an open resistor.  If you find a resistor that won't give any reading, you've found the problem.
--Larry

spiritofradio

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Re: One channel out on my '59 RCA TPR-8
« Reply #2 on: June 02, 2015, 03:24:14 PM »
great!  that should be easy enough.   I'm amazed at how simple the amp circuitry is, compared to other sets I've seen.  I love how RCA uses a master ground wire that crosses over the length of the chassis.  Keeps things very neat and easy to get at rather than using studs on the tube sockets or posts on the chassis.   I'll check them tonight and follow up.   Thanks!
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

Hull Rust

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Re: One channel out on my '59 RCA TPR-8
« Reply #3 on: June 02, 2015, 03:24:44 PM »
RS-177 schematic

spiritofradio

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Re: One channel out on my '59 RCA TPR-8
« Reply #4 on: June 02, 2015, 03:29:02 PM »
thats' my amp!    dude you're the best.
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

Larry H

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Re: One channel out on my '59 RCA TPR-8
« Reply #5 on: June 02, 2015, 04:18:52 PM »
great!  that should be easy enough.   I'm amazed at how simple the amp circuitry is, compared to other sets I've seen.  I love how RCA uses a master ground wire that crosses over the length of the chassis.  Keeps things very neat and easy to get at rather than using studs on the tube sockets or posts on the chassis.   I'll check them tonight and follow up.   Thanks!
The larger RCA amps had this grounding bus.  Makes it so easy to ground your replacement electrolytic capacitors to.
--Larry

spiritofradio

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Re: One channel out on my '59 RCA TPR-8
« Reply #6 on: June 02, 2015, 05:00:44 PM »
ha, that's exactly what I did.    If I could pick your brain one last time about methods.  I have heard both thoughts on this and would like a console specialist take.   I currently replace E's by cutting the old terminal off the bottom of the cans, leaving the original solder intact, then soldering the positive end of the new cap to the terminal.  Not the prettiest, but it seems to be very secure, short of installing a terminal strip.

The other way I have heard done, which I haven't tried, is soldering the new caps directly to the existing terminals, without clipping them from the cans.  Sounds really clean, but doesn't the paralleling rule of caps come into play? ( doubles the MF).   

I may have answered my own question here........  is a terminal strip the preferred method?
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

624Magnificent

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Re: One channel out on my '59 RCA TPR-8
« Reply #7 on: June 02, 2015, 05:39:30 PM »
I may have misunderstood the two examples you gave but you should be completely separating your new caps from the old can terminals. Those old caps are still in the can and they should be completely disconnected and the three or four terminals that come out the bottom of the can should be left as stubs with nothing connected to them. You can leave the ground wires that are attached to the twist tabs that connect to the outer shell of the can. These are grounds and are directly soldered to the chassis so don't pose a problem to anything. Your new caps should have their positive terminals connected to the wires / resistors that used to go to the can terminals and they can "float" in the chassis or if you need to you can add a terminal strip somewhere in the chassis.
Tom

spiritofradio

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Re: One channel out on my '59 RCA TPR-8
« Reply #8 on: June 02, 2015, 05:50:16 PM »
yep, that's what I thought.  I don't like floating them, it seems so disorganized especially in the smaller devices.  I think i'll pick up some terminal strips and start using them as a solder point.  Who sells them?  I don't recall seeing them on any of the private cap sellers like Sal or Radio Daze or Just Radios
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

624Magnificent

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Re: One channel out on my '59 RCA TPR-8
« Reply #9 on: June 02, 2015, 06:23:06 PM »
I guess I'm lazy, I use shrink tubing or hook-up wire and float my caps. I try to be neat but there are times when terminal strips would be handy. The ones that I see most often in this type of work are "5 position terminal strips". There's lots of vendors, Amazon, Mouser, Digi-key, Radio Shack, etc. There's dozens of different types.
Tom

Larry H

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Re: One channel out on my '59 RCA TPR-8
« Reply #10 on: June 02, 2015, 06:55:44 PM »
ha, that's exactly what I did.    If I could pick your brain one last time about methods.  I have heard both thoughts on this and would like a console specialist take.   I currently replace E's by cutting the old terminal off the bottom of the cans, leaving the original solder intact, then soldering the positive end of the new cap to the terminal.  Not the prettiest, but it seems to be very secure, short of installing a terminal strip.

The other way I have heard done, which I haven't tried, is soldering the new caps directly to the existing terminals, without clipping them from the cans.  Sounds really clean, but doesn't the paralleling rule of caps come into play? ( doubles the MF).   

I may have answered my own question here........  is a terminal strip the preferred method?

Replace one electrolytic at a time in a large amp like this by my method.  Cut the wire to an electrolytic lug, and see where that wire originates from (the other end).  Solder the positive of the electrolytic to the origination point, then solder the negative to the grounding buss.  It's that easy. 

I used to use the terminal strip method, but hardly ever use a terminal strip anymore.  I like installing them from their source directly to ground.

Normally, the positive of an electrolytic originates at a tube socket somewhere.
--Larry

spiritofradio

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Re: One channel out on my '59 RCA TPR-8
« Reply #11 on: June 02, 2015, 10:28:02 PM »
It's highly probable that there's an open resistor in the audio circuitry of the channel that's out.  Remove the tuner and amplifier both from the cabinet.  Check every single resistor in both the amp and tuner for an ohm reading with a multimeter.  Don't worry about ohm values, you are just looking for an open resistor.  If you find a resistor that won't give any reading, you've found the problem.
Man there's alot of resistors.  Gotta clip one end of every one of them too huh?  Gotta get ready for that project.  I did take voltages on all 6 wires coming and going from the output transformers.  The only variance was the green wire that comes from the right channel output transformer to the terminal where it meets the speaker wire.  Where the same wire on the left channel reads 2 ma, the right channel wire reads 0.  when connected to the speaker directly the left is loud and clear, and the right has the very faintest of sound but it is definately the right channel as it responds to the balance knob approriately.  So the right channel output transformer is putting out less voltage however all the line in voltages match the left channel line in voltages.  I'm wondering if I should try subbing out the output transformer before clipping all the resistors...
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

Larry H

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Re: One channel out on my '59 RCA TPR-8
« Reply #12 on: June 02, 2015, 10:31:59 PM »
NOPE, don't clip out any end of any resistor.  You take ohm readings with the set unplugged from electricity.....  do not try to do this with it plugged in.....

Just put a probe on one lead of the resistor, other probe on the other lead, and see if you get an ohm reading. No reading... bad resistor!!!!!!!!!

All you will be doing here is checking for open resistors.  This is the quickest way to find out if there's an open one somewhere.  I could do it in 15 minutes.
--Larry

spiritofradio

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Re: One channel out on my '59 RCA TPR-8
« Reply #13 on: June 03, 2015, 05:07:08 AM »
NOPE, don't clip out any end of any resistor.  You take ohm readings with the set unplugged from electricity.....  do not try to do this with it plugged in.....

Just put a probe on one lead of the resistor, other probe on the other lead, and see if you get an ohm reading. No reading... bad resistor!!!!!!!!!

All you will be doing here is checking for open resistors.  This is the quickest way to find out if there's an open one somewhere.  I could do it in 15 minutes.

When you read how to do these things, the pics and the narrative always refer to a disconnected resistor.  So if I'm just checking for an Open resistor, it can remain connected, but if you were verifying the actual resistance you would need to clip, is that the rule?  That saves a bunch of time. I checked about 20 last night, focusing on the right channel, and all had some reading.  That's why I starting to think if they are still connected I might be getting a reading off the set itself.

Thanks so much for following up with me on this.  Troubleshooting is something I need to get better at....patience and getting organized is probably the first thing I need to learn.
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

Pat L

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Re: One channel out on my '59 RCA TPR-8
« Reply #14 on: June 03, 2015, 09:20:56 AM »
No need to clip the resistor from the circuit. Our concern here is resistors that are drifted high. A lower reading in circuit is possible, but it should never be higher. If it reads higher in the circuit the resistor is at fault.