Console tube amp help

[Eddie hy fi]

Have a vintage sylvania console stereo tube amp that works well but has had a back ground hum in it every since i got it -------ive tried many things and it sounds great but still has this back ground buzz or hum that does not change with volume and even with no input the amp has this same back ground buzz that you really only hear when idle or in quite times of music but id like to fix --------its not the power supply caps or the rca input wires , the amp was a 6L6 amp but some one has converted it to 6bg6ga --the resistors have all so been checked and some changed --the capacitors are nice and good and not that far off factory specs ----this amp has nice warm sound when it warms up and id really appreciate any help , as im not sure what to try next --some say to do something with heater wires , others say to add a ten ohm resistor to the over head high voltage wires , as they may be picking up a radio frequency buzz , what should i try next ? and can someone talk me threw it ? --id did some of the work but the buzz or hum remains no matter what i do , its in both channels , same level ,

 

[gadget73]

happen to have a model number and ideally a schematic ? Extra bonus points for a schematic marked up with any changes made.

 

[Eddie hy fi]

i do not have schematic and only numbers are on the power transformer they are Tr-205 798 6025 , amp looks similar to another i found here on AK, i can tell by old can cap numbers that the capacitor specs are close , where it called for a 40 , a 47 was used , where it called for a 5 , a 6.8 was used , -----all so i replaced that one diode , and added the CL-70 basic thermister ----

 

[egellings]

Oddly small OPTs for such large output tubes.

 

[cademan]

If the hum is in both channels it has to be a power supply problem and I can see that there is one original power supply filter capacitor still in use that probably needs to be replaced.

The can on the top left looks to still be connected to either one or more segment. Replace it completely wth a new one.

If not that capacitor, i'd probably do away with that neon front panel lamp.

 

[Eddie hy fi]

If the hum is in both channels it has to be a power supply problem and I can see that there is one original power supply filter capacitor still in use that probably needs to be replaced.

The can on the top left looks to still be connected to either one or more segment. Replace it completely wth a new one.

If not that capacitor, i'd probably do away with that neon front panel lamp.

The old can caps are not in use , only a ground remains near by them , ok im willing to try it with run light un hooked , man wouldn"t that be a easy fix !

 

[cademan]

I think I see a capacitor that could possibly be wired backwards. Don't know the specs but it says DL -8 on the side.

 

[cademan]

The old can caps are not in use , only a ground remains near by them

It looks like it might be a replacement but the one on the top left (bottom right) is still connected.

 

[Eddie hy fi]

Oddly small OPTs for such large output tubes.

The out put transformers are bigger than my two maggies and larger than another sylvania el84 amp that i have . the amp is probably around twenty watts a channel

 

[egellings]

They should be go for 15 watts or so. I find it funny how one of the 6BQ5/EL84/7189 output tubes on each side has its own little outrigger chassis to sit on.

 

[Eddie hy fi]

I think I see a capacitor that could possibly be wired backwards. Don't know the specs but it says DL -8 on the side.

Its a 47uf , 450 volt , thats the one with a diode that i replaced , i just copied the way it was and the cap is good and fairly new , are you sure the polarity is backwards on it ? and what is the purpose of this cap anyway , i did sort of suspect this cap too , but was and am not sure if its right or not ! the positive side just goes to ground on that one tube socket

 

[Eddie hy fi]

They should be go for 15 watts or so. I find it funny how one of the 6BQ5/EL84/7189 output tubes on each side has its own little outrigger chassis to sit on.

its a great little amp , i use it only to power my JBL 2404H compression tweeters , in a four way system and it works great for that !

 

[cademan]

Without a schematic, I would have thought it might be a bias scheme.

Does that amp use a 5Y3 or 5U4 rectifier tube also?

 

[Eddie hy fi]

Without a schematic, I would have thought it might be a bias scheme.

Does that amp use a 5Y3 or 5U4 rectifier tube also?

it uses 5u4

 

[Eddie hy fi]

it uses 5u4

yep i would agree about it being part of a bias thing , wish it had a bias adjustment

 

[cademan]

Where's the power transformers center tap? It should be chassis ground so I am not sure why the diode and capacitor?

Bias circuit would usually be connected to the output tubes.

 

[egellings]

Those little peanut pentodes do sound good. A sort of rich, creamy sound.

 

[gadget73]

They should be go for 15 watts or so. I find it funny how one of the 6BQ5/EL84/7189 output tubes on each side has its own little outrigger chassis to sit on.

they also made a single ended version of this amp. No "bump-outs". Guessing the whole deal was designed with economy in mind, one chassis and layout for both, just one gets an extra pair of holes and two things screwed to the side.

Stromberg-Carlson did something similar, but theirs looked more like a push-pull chassis that got a pair of chassis plugs popped into the empty holes where the other socket would have gone.

 

[Eddie hy fi]

Where's the power transformers center tap? It should be chassis ground so I am not sure why the diode and capacitor?

Bias circuit would usually be connected to the output tubes.

Sorry for delay , had to go help some one out . There is two other power transformer leads that must be the center tap , they go rite to ground , see photo , so what could that diode circuit be ?

 

[Tom Bavis]

I think I see a capacitor that could possibly be wired backwards. Don't know the specs but it says DL -8 on the side.

This looks like a negative bias supply - positive would be grounded.