Magnavox 8802 Very Low Volume

[Markmayne]

Rescued and 8802 amp from a Magnavox console and converting it for stereo listening. I read the forums about adding the resistors due to the lack of a balance pot and did that. Lastly I have a toggle switch. I can’t seem to get any volume looking for some advice. Attached are a couple of pics.

 

[gadget73]

by not getting any volume do you mean you get nothing at all, or the volume is low?

 

[Markmayne]

The volume is very low

 

[gadget73]

about equal in both channels? Likely power supply then

Have you checked the voltages at the 4 terminals on the can cap? Three will be high voltage DC, near 300 volts on one of them. Measure to chassis ground and be very careful. Let me know what you get on each symbol. Its visible inboard of the terminal, should be blank, square, half circle, and triangle.

this really is going to want a full overhaul for reliability reasons but one thing at a time here.

 

[Dswankey]

What are you using a Pre-amp source? I'm wondering if that could be an issue.

 

[dfoulk]

Rescued and 8802 amp from a Magnavox console and converting it for stereo listening. I read the forums about adding the resistors due to the lack of a balance pot and did that. Lastly I have a toggle switch. I can’t seem to get any volume looking for some advice. Attached are a couple of pics.

Do you know the condition of the tubes?

 

[gadget73]

^ kind of where I'm going with power supply voltage checks. Should be a clue, but I have my doubts that the tubes in both channels are equally whipped. I could absolutely believe a whipped 6CA4 though, and that would affect both channels.

 

[Markmayne]

about equal in both channels? Likely power supply then

Have you checked the voltages at the 4 terminals on the can cap? Three will be high voltage DC, near 300 volts on one of them. Measure to chassis ground and be very careful. Let me know what you get on each symbol. Its visible inboard of the terminal, should be blank, square, half circle, and triangle.

this really is going to want a full overhaul for reliability reasons but one thing at a time here.

Blank-17
Half Circle-281
Square-278
Triangle-249

 

[Markmayne]

about equal in both channels? Likely power supply then

Have you checked the voltages at the 4 terminals on the can cap? Three will be high voltage DC, near 300 volts on one of them. Measure to chassis ground and be very careful. Let me know what you get on each symbol. Its visible inboard of the terminal, should be blank, square, half circle, and triangle.

this really is going to want a full overhaul for reliability reasons but one thing at a time here.

The volume is very low in both channels

 

[Markmayne]

What are you using a Pre-amp source? I'm wondering if that could be an issue.

I used a Heathkit AA-11 preamp, HK730 output & headphone, and IPhone

 

[gadget73]

Blank-17
Half Circle-281
Square-278
Triangle-249

sounds good, slightly high but to be expected with higher line voltages. Not a dead rectifier like I was thinking though.

https://audiokarma.org/forums/index.php?attachments/aa1zkuc-jpg.2854904/

has the schematic. Stock it lists 255, 250, and 240 and 15 volts on the output tube cathode. You're at 17 so the output tubes are working normally.

ok back to those feedback resistors up front. They are in fact 390 ohm right? If thats open or high in value it will have poor gain. I can't quite make out the colors but it doesn't look right for a 390 to me.

I usually ground those to the terminal in the middle of that terminal strip, but it shouldn't matter a ton so long as its a good connection. Soldering to the chassis can be difficult though, so maybe worth confirming its actually making good electrical connection.

 

[Markmayne]

They in fact are 470

 

[Markmayne]

They in fact are 470

Do you have a recommendation or a favorite with a link. I will start with replacing them with the recommended installation on the terminal strip. As a side note I was told that the current resistors I installed would suffice. I am a bit of a novice with tube amps. I truly appreciate the advice and support.

 

[Mr Boochie]

I enlarged the schematic, a little. May help.

 

[Mr Boochie]

Try this. Pull all tubes one-by-one and use electronic contact cleaner on the tube's pins and the sockets. Work the tubes in-&-out a few times to really clean the things.

I'm hoping both 6EU7 have corroded pins and just need cleaning. Clean your input jacks, too.

You don't have access to a tube tester?

Tell us the results! Good luck!

PS: I like Deoxit D-100 or CRC contact cleaner. Do you have any electronic cleaner in the garage, for your auto fixes? That will work.

 

[Markmayne]

I enlarged the schematic, a little. May help.

Thank you I am currently printing it out!

 

[Mr Boochie]

The volume is very low in both channels

One other thing. How are you connecting the input? Are you using the proper plugs or using jumper lines?

The reason I ask, is the input are grounding types. So, the signal will be grounded if the input plugs are not the proper types.

 

[Markmayne]

Try this. Pull all tubes one-by-one and use electronic contact cleaner on the tube's pins and the sockets. Work the tubes in-&-out a few times to really clean the things.

I'm hoping both 6EU7 have corroded pins and just need cleaning. Clean your input jacks, too.

You don't have access to a tube tester?

Tell us the results! Good luck!

PS: I like Deoxit D-100 or CRC contact cleaner. Do you have any electronic cleaner in the garage, for your auto fixes? That will work.

Will do. I do not have a tube tester.

One other thing. How are you connecting the input? Are you using the proper plugs or using jumper lines?

The reason I ask, is the input are grounding types. So, the signal will be grounded if the input plugs are not the proper types.

 

[Markmayne]

I am using quality cords, no jumpers. I thank you for the advice. I will clean the tube terminals.

 

[Markmayne]

Contact cleaner & brush good recommendation