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Troubleshooting a 1958 Magnavox Cabinet

xXTomcatXx

xXTomcatXx

New Member
Been lurking here on AK for a while, first time posting though.

My Situation
I'm new to this hobbie. I've recently purchased a 1958 Magnavox Turntable cabinet in great shape. I replaced all the electrolytic and paper caps in the amp (a 185-23).

My Problem
The sound seems great, but I'm only getting it from one of the six speakers (SP1, a 15 inch). Inspecting the other speakers and the schematic, I discovered a pair of 100v 2uf paper caps and one nonpolarized 25V 16uf electrolytic cap "downstream" from SP1. I removed and tested the caps and all three are 50% above their rated capacitance. I've ordered replacements for the two paper caps, but I'm having trouble locating a replacement for the electrolytic. Any recommendations?

Questions
1. Would a failed cap cause no sound whatsoever to come out from the speakers, or should I be looking elsewhere in the circuit?
2. Could the balance pot be causing any of these issues? Turning the pot in one direction makes the working speaker louder. Turning it in the opposite direction silences it.
3. The speaker only plays when the selector is turned to "Internal" it's otherwise silent when set to "Internal/External". I'm not sure if this is an unrelated issue or not.

Thanks in advance for any help you can offer this newbie.
 
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Hello xXTomcatXx. Welcome to AK. Sounds like one my dad had, Yes a bad cap can cause problems in the sound of the drivers. As for the electrolytic cap a good place to check would be Parts Express for replacement Non Polarized E caps. The small value caps can be replaced with film caps (as everybody here does). The selector has nothing on the input for external so no sound. Pictures would help seeing the system. Hope this helps.
 
Also places like Mouser or Digikey would be a good place to find the NP lytic. You might have to have a couple caps to make the 16uf value

Have you checked the other speakers with a multimeter to make sure they are good?

Yes the balance pot could be causing the problem. You could try bypassing it and see if you get sound
 
NAD80 said:
Hello xXTomcatXx. Welcome to AK. Sounds like one my dad had, Yes a bad cap can cause problems in the sound of the drivers. As for the electrolytic cap a good place to check would be Parts Express for replacement Non Polarized E caps. The small value caps can be replaced with film caps (as everybody here does). The selector has nothing on the input for external so no sound. Pictures would help seeing the system. Hope this helps.
Click to expand...

Thanks for getting back to me. I appreciate the help. Unfortunately I struck out at Parts Express as well. Below is a link to the schematic if that helps. The SP1 speaker seems to be the only one working.

https://1drv.ms/b/s!ArBfwkiz1grikOtFlb8r-enjDNzvTg
 
elitopus said:
Also places like Mouser or Digikey would be a good place to find the NP lytic. You might have to have a couple caps to make the 16uf value

Have you checked the other speakers with a multimeter to make sure they are good?

Yes the balance pot could be causing the problem. You could try bypassing it and see if you get sound
Click to expand...

Thanks for the help, elitopus. I'm looking through Mouser now, but not having a ton of luck. Would it be possible to replace the 25V 16uf lytic with a 25V 15uf?

Regarding checking the other speakers with a multimeter. What's the process exactly? Am I looking for continuity?

Similarly, is there a simple way to bypass the balance pot?

Thanks again.
 
The 16mfd cap can be made up by adding 2 cap values in parallel, 12 +4, 15 + 1 for example. The voltage of the cap only matters if it is that you don't go below the original voltage rating.
 
NAD80 said:
The 16mfd cap can be made up by adding 2 cap values in parallel, 12 +4, 15 + 1 for example. The voltage of the cap only matters if it is that you don't go below the original voltage rating.
Click to expand...

Thanks, I found some on digikey and put the order in. Hopefully this solves the problem. Otherwise I'm completely stumped.
 
I know I'm in the recap pile. Have seen caps from the 70's dried up. Have stuff that needs recapped.
 
NAD80 said:
Hello xXTomcatXx. Welcome to AK. Sounds like one my dad had, Yes a bad cap can cause problems in the sound of the drivers. As for the electrolytic cap a good place to check would be Parts Express for replacement Non Polarized E caps. The small value caps can be replaced with film caps (as everybody here does). The selector has nothing on the input for external so no sound. Pictures would help seeing the system. Hope this helps.
Click to expand...

UPDATE: I've recapped the speakers, and it resulted in no change whatsoever. Additionally, I was able to test each of the speakers individually with an external source, and they all work. I'm officially stumped. Any ideas? Working my way back on the circuit, the next thing "upstream" from speakers themselves is the "Int/Int-Ext" selector switch and the output transformers (two). From what I've read, it's highly unlikely that either of those would go bad (especially two transformers simultaneously). Is there a way to test the transformer to make sure it's "seeing" and "outputting" what's expected by the speakers?

Also, one small correction. Previously I stated that it was SP1 that was functioning. I misidentified the speaker. It is in fact SP5, the other 15" speaker that is functioning.

Lastly, should I move my question over to the tube amp forum at this point?
 
NAD80 said:
Possibly the switch itself needs cleaned with DeOxit? Leave the switch to internal?
Click to expand...

Funnily enough, my issues arose after hitting all of the pots and switches with Deoxit (Treble, Bass, Loudness, Int/Ext, Balance, and Hum). I've never heard of Deoxit causing a problem, but do you think it could have knocked something loose, and started causing the issues?
 
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