RCA radio and 45 rpm record player. - UK Vintage Radio Repair and Restoration Discussion Forum

sparkymike · 28th Jul 2025, 6:53 am

I bought an RCA radio (FM & AM) from the USA many years ago when postage was not so expensive. It is complete with a 45RPM RCA player which sits on the top of the cabinet. These units were used in a large TV set which also had a 33rpm seperate player. It has all the original RCA valves and with its 6V6 GC output valves, it sounds (or did !!) very good. The other day I connected it up to a speaker and 110 volt supply but am getting quite a mains hum. I have checked all three sections 30uf/30uf/40uf of the reservoir/smoothing cap and all fine, if anything slightly higher than stated on the circuit. I have gone through the other caps and all seem to be ok, according to my cap tester.
With my scope there is a perfectly flat trace after the smoothing electrolytics and all through the set until the output from the output transformer where I get a typical mains voltage trace. Any thoughts how I can proceed ? When switched to radio , I can just pick up one station on AM and it is very faint and distorted.
Mike.

Nuvistor · 28th Jul 2025, 7:14 am

You say a typical mains voltage trace on the output transformer, the output valve/socket could have a heater/cathode leak, if I understand your description correctly.

sparkymike · 28th Jul 2025, 7:59 am

Just checked the output transformer and primary reads approx 510 ohms. Drawing states 530 ohms, so probably ok. Will have a check on the output valve bases. Circuit below, lucky I have the original factory service pamphlet, Model 7T143, RCA Victor (Television,radio,phonograph combinations.)
I was thinking of replacing C42 and C44 as a matter of course.

sparkymike · 28th Jul 2025, 8:04 am

Top view of chassis.

sparkymike · 28th Jul 2025, 9:01 am

Panel lights are not working but valve heaters were on. Now wondering if there is a short somewhere between heater supply and chassis.

Edward Huggins · 28th Jul 2025, 11:53 am

This looks to have a nice specification. I noticed that you have previously been using this. Bear in mind your 45prpm turntable will run slow if the pulley has not been changed.

sparkymike · 28th Jul 2025, 1:25 pm

Hi Edward,
I think the usual dodge is to slide a small piece of plastic tube over the motor spindle. These players don't have belts, the motor spindle just drives direct to the rubber idler wheel if my memory serves me correctly. I have as yet to restore the player, but at the moment, am concerned that possibly there are shorted turns on the main transformer heater winding. Hopefully not, but a quick check this morning looks like the heater terminals on the valve bases go direct to chassis. ( meter reading around 3 ohms but maybe bad connection.
I did find a "dry joint " on one of the output valve bases where a wire had been carried through the terminal hole and on to another point,but I could not see a trace of solder, so "no joint" would be more accurate than dry joint.!!
Mike.

Chiltern · 28th Jul 2025, 4:42 pm

Quote:

Originally Posted by sparkymike

Hi Edward,
I think the usual dodge is to slide a small piece of plastic tube over the motor spindle. These players don't have belts, the motor spindle just drives direct to the rubber idler wheel if my memory serves me correctly. I have as yet to restore the player, but at the moment, am concerned that possibly there are shorted turns on the main transformer heater winding. Hopefully not, but a quick check this morning looks like the heater terminals on the valve bases go direct to chassis. ( meter reading around 3 ohms but maybe bad connection.
I did find a "dry joint " on one of the output valve bases where a wire had been carried through the terminal hole and on to another point,but I could not see a trace of solder, so "no joint" would be more accurate than dry joint.!!
Mike.

Correct, with jukeboxes the usual answer was a spring pushed over the motor spindle. measure your motor spindle and PM me the size. for jukeboxes I used to have springs wound with various wire specs and certainly will still have a selection some where.

Is the 45 deck something like this?

Alan

sparkymike · 28th Jul 2025, 5:14 pm

Hi Alan, yes exactly the same. I have around six of these varying in years. Some now working. Some I have changed the motor to 250 volt.
Mike.

sparkymike · 29th Jul 2025, 9:47 am

The hum sage continues. I believe that somewhere from the panel lights to the mains transformer there is a leak to earth, so that is my next move. Valve heaters light up but panel lights don't, although i think they are on same winding.
Mike.

sparkymike · 29th Jul 2025, 4:38 pm

Got the scope out and thumbnail below shows trace from the point after smoothing/reservoir caps. Could a fault in the rectifier valve cause this ?
Mike.

sparkymike · 30th Jul 2025, 10:31 am

Now got the panel lights working. A 3ohm wire wound resistor in line with the supply wire was causing them not to light. It was reading 3 ohms, but for some weird reason was not passing current.
Mike.

Techman · 30th Jul 2025, 12:32 pm

I don't think you've said (unless I've missed it) whether the hum is independent of the volume control setting or not. If it's regardless of the volume control then it's in and around the output stage and there could be internal leakage in the valve or surrounding circuit somewhere, but the more likely culprit would be the reservoir/smoothing capacitor/s, although you say you've already tested them. Personally, I think cap testers are usually a waste of time and proper diagnostic fault finding is the best way to 'test' for any faulty capacitors. Failing anything else showing up I would be temporarily tacking another electrolytic of the appropriate value and voltage rating across the main smoothing reservoir capacitor and noting whether this made any difference to the hum level or not.

Edward Huggins · 30th Jul 2025, 12:57 pm

Definately agree with the above. I mean your unit must be mid-to-late 1950s to use Octal valves - thus making those caps 60+ years old.

sparkymike · 30th Jul 2025, 4:43 pm

I am goung to change the output valve capacitors, the .001 1000volt ones on each valve anode. When I was checking them with my cap tester, I got the same type of hum through the speaker, powered I guess by the cap tester battery. They look pretty tired anyway, so when I can find some, I will change them as a matter of course. Most on Ebay are 630 volt. Maybe ok ?

Mike.

Nuvistor · 30th Jul 2025, 9:30 pm

Farnel have a selection, unfortunately they are radial not axial but will do the job, not sure if there is a min order, if so try CPC-Farnel.

PJL · 31st Jul 2025, 7:12 pm

You need to replace the audio coupling capacitors C32 and C35. You also need to work out a way of measuring the output valve anode currents, I suggest you measure the voltage across each half of the output transformer primary and when switched off (and discharged ) measure the resistance of each half so we can calculate the anode currents.

The bias is created across R42 in the earth path, also measure this voltage.

sparkymike · 12th Aug 2025, 2:02 pm

Re. C42 and C44,(see circuit in early post.) is the rating of these caps critical or could they be .01 for example ? How are they calculated in the design. In the Hammond organ amplifiers, they are not present yet same output valves are used.
Mike.

Nuvistor · 12th Aug 2025, 4:14 pm

C42/44 won’t be critical, but 10 times the value is rather a lot, I would stick to something with 10% of the stated value.
A 0.01 will likely reduce the upper audio frequencies.
See what others say but that’s my take on the question.

Uncle Bulgaria · 13th Aug 2025, 12:41 pm

When you say you tested the filter/reservoir capacitors, did you take them out of circuit and apply the rated voltage and check for leakage? Or as Techman says in post #13, tack another electrolytic across the main smoothing capacitor and note any change in hum. The metal cased main capacitor blocks of this era are much more reliable than other electrolytics in general, so can often be OK even if other components in the same unit are decrepit and beyond help.

If the coupling capacitors are wax types and ancient, they ought to be replaced as a matter of course to save expensive damage to valves and the output transformer. 0.01µF 1000V polypropylenes are available from Cricklewood here. As a reputable supplier they're likely to be more reliable than from a random eBay seller.

28th Jul 2025, 7:14 am	#2
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,567	Re: RCA radio and 45 rpm record player You say a typical mains voltage trace on the output transformer, the output valve/socket could have a heater/cathode leak, if I understand your description correctly. __________________ Frank

28th Jul 2025, 7:59 am	#3
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	Re: RCA radio and 45 rpm record player. Just checked the output transformer and primary reads approx 510 ohms. Drawing states 530 ohms, so probably ok. Will have a check on the output valve bases. Circuit below, lucky I have the original factory service pamphlet, Model 7T143, RCA Victor (Television,radio,phonograph combinations.) I was thinking of replacing C42 and C44 as a matter of course. Attached Thumbnails

28th Jul 2025, 8:04 am	#4
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	Re: RCA radio and 45 rpm record player. Top view of chassis. Attached Thumbnails

28th Jul 2025, 9:01 am	#5
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	Re: RCA radio and 45 rpm record player. Panel lights are not working but valve heaters were on. Now wondering if there is a short somewhere between heater supply and chassis.

28th Jul 2025, 11:53 am	#6
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 9,137	Re: RCA radio and 45 rpm record player. This looks to have a nice specification. I noticed that you have previously been using this. Bear in mind your 45prpm turntable will run slow if the pulley has not been changed. __________________ Edward.

28th Jul 2025, 6:53 am	#1
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	RCA radio and 45 rpm record player. I bought an RCA radio (FM & AM) from the USA many years ago when postage was not so expensive. It is complete with a 45RPM RCA player which sits on the top of the cabinet. These units were used in a large TV set which also had a 33rpm seperate player. It has all the original RCA valves and with its 6V6 GC output valves, it sounds (or did !!) very good. The other day I connected it up to a speaker and 110 volt supply but am getting quite a mains hum. I have checked all three sections 30uf/30uf/40uf of the reservoir/smoothing cap and all fine, if anything slightly higher than stated on the circuit. I have gone through the other caps and all seem to be ok, according to my cap tester. With my scope there is a perfectly flat trace after the smoothing electrolytics and all through the set until the output from the output transformer where I get a typical mains voltage trace. Any thoughts how I can proceed ? When switched to radio , I can just pick up one station on AM and it is very faint and distorted. Mike.

28th Jul 2025, 1:25 pm	#7
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	Re: RCA radio and 45 rpm record player. Hi Edward, I think the usual dodge is to slide a small piece of plastic tube over the motor spindle. These players don't have belts, the motor spindle just drives direct to the rubber idler wheel if my memory serves me correctly. I have as yet to restore the player, but at the moment, am concerned that possibly there are shorted turns on the main transformer heater winding. Hopefully not, but a quick check this morning looks like the heater terminals on the valve bases go direct to chassis. ( meter reading around 3 ohms but maybe bad connection. I did find a "dry joint " on one of the output valve bases where a wire had been carried through the terminal hole and on to another point,but I could not see a trace of solder, so "no joint" would be more accurate than dry joint.!! Mike.

28th Jul 2025, 5:14 pm	#9
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	Re: RCA radio and 45 rpm record player. Hi Alan, yes exactly the same. I have around six of these varying in years. Some now working. Some I have changed the motor to 250 volt. Mike.

29th Jul 2025, 9:47 am	#10
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	Re: RCA radio and 45 rpm record player. The hum sage continues. I believe that somewhere from the panel lights to the mains transformer there is a leak to earth, so that is my next move. Valve heaters light up but panel lights don't, although i think they are on same winding. Mike.

29th Jul 2025, 4:38 pm	#11
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	Re: RCA radio and 45 rpm record player. Got the scope out and thumbnail below shows trace from the point after smoothing/reservoir caps. Could a fault in the rectifier valve cause this ? Mike. Attached Thumbnails

30th Jul 2025, 10:31 am	#12
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	Re: RCA radio and 45 rpm record player. Now got the panel lights working. A 3ohm wire wound resistor in line with the supply wire was causing them not to light. It was reading 3 ohms, but for some weird reason was not passing current. Mike.

30th Jul 2025, 12:32 pm	#13
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,589	Re: RCA radio and 45 rpm record player. I don't think you've said (unless I've missed it) whether the hum is independent of the volume control setting or not. If it's regardless of the volume control then it's in and around the output stage and there could be internal leakage in the valve or surrounding circuit somewhere, but the more likely culprit would be the reservoir/smoothing capacitor/s, although you say you've already tested them. Personally, I think cap testers are usually a waste of time and proper diagnostic fault finding is the best way to 'test' for any faulty capacitors. Failing anything else showing up I would be temporarily tacking another electrolytic of the appropriate value and voltage rating across the main smoothing reservoir capacitor and noting whether this made any difference to the hum level or not.

30th Jul 2025, 12:57 pm	#14
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 9,137	Re: RCA radio and 45 rpm record player. Definately agree with the above. I mean your unit must be mid-to-late 1950s to use Octal valves - thus making those caps 60+ years old. __________________ Edward.

30th Jul 2025, 4:43 pm	#15
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	Re: RCA radio and 45 rpm record player. I am goung to change the output valve capacitors, the .001 1000volt ones on each valve anode. When I was checking them with my cap tester, I got the same type of hum through the speaker, powered I guess by the cap tester battery. They look pretty tired anyway, so when I can find some, I will change them as a matter of course. Most on Ebay are 630 volt. Maybe ok ? Mike.

30th Jul 2025, 9:30 pm	#16
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,567	Re: RCA radio and 45 rpm record player. Farnel have a selection, unfortunately they are radial not axial but will do the job, not sure if there is a min order, if so try CPC-Farnel. __________________ Frank

31st Jul 2025, 7:12 pm	#17
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 6,170	Re: RCA radio and 45 rpm record player. You need to replace the audio coupling capacitors C32 and C35. You also need to work out a way of measuring the output valve anode currents, I suggest you measure the voltage across each half of the output transformer primary and when switched off (and discharged ) measure the resistance of each half so we can calculate the anode currents. The bias is created across R42 in the earth path, also measure this voltage.

12th Aug 2025, 2:02 pm	#18
sparkymike Octode Join Date: Dec 2006 Location: Colchester, Essex, UK. Posts: 1,175	Re: RCA radio and 45 rpm record player. Re. C42 and C44,(see circuit in early post.) is the rating of these caps critical or could they be .01 for example ? How are they calculated in the design. In the Hammond organ amplifiers, they are not present yet same output valves are used. Mike.

12th Aug 2025, 4:14 pm	#19
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,567	Re: RCA radio and 45 rpm record player. C42/44 won’t be critical, but 10 times the value is rather a lot, I would stick to something with 10% of the stated value. A 0.01 will likely reduce the upper audio frequencies. See what others say but that’s my take on the question. __________________ Frank

13th Aug 2025, 12:41 pm	#20
Uncle Bulgaria Dekatron Join Date: May 2016 Location: Cornwall, UK. Posts: 3,004	Re: RCA radio and 45 rpm record player. When you say you tested the filter/reservoir capacitors, did you take them out of circuit and apply the rated voltage and check for leakage? Or as Techman says in post #13, tack another electrolytic across the main smoothing capacitor and note any change in hum. The metal cased main capacitor blocks of this era are much more reliable than other electrolytics in general, so can often be OK even if other components in the same unit are decrepit and beyond help. If the coupling capacitors are wax types and ancient, they ought to be replaced as a matter of course to save expensive damage to valves and the output transformer. 0.01µF 1000V polypropylenes are available from Cricklewood here. As a reputable supplier they're likely to be more reliable than from a random eBay seller.