Console tube amp help

[Eddie hy fi]

Up date - its running now and still has a bit of hum but it does not seem quite as bad , when i un plug the driver tubes hum goes away , so maybe its not even in the out put stage ? --------still has that great warm sound , it was not the transformer orientation , because ive tried that and when i put them back to original position hum stay the same threw it all - this amp has such warm sound , we have to fix this issues , going to focus on drive tube grounds and area next , why are the 6an8s creating hum , looking for my xtra 6an8s tubes now , but think i tried switching them out all ready before

 

[Eddie hy fi]

Up date - its running now and still has a bit of hum but it does not seem quite as bad , when i un plug the driver tubes hum goes away , so maybe its not even in the out put stage ? --------still has that great warm sound , it was not the transformer orientation , because ive tried that and when i put them back to original position hum stay the same threw it all - this amp has such warm sound , we have to fix this issues , going to focus on drive tube grounds and area next , why are the 6an8s creating hum , looking for my xtra 6an8s tubes now , but think i tried switching them out all ready before

Tried my spare set of 6n8a driver tubes , same hum issue , no difference , got to stop for now , girl friend coming over , but will pick this up when i can , not giving up , it must be in driver tube circuit , or a ground issue

 

[cademan]

Driver tubes could certainly be the whole problem. They are most likely microphonic which manafests itself as hum. Maybe try some metal tube shields and ground them to the chassis. If it were a power supply problem, it would still hum even when the 6AN8's are removed.

I hate hum. Tube amps are supposed to be hum free even by design. None of my tube amps hum only slight hiss with your ears up to the speakers.

 

[Eddie hy fi]

Driver tubes could certainly be the whole problem. They are most likely microphonic which manafests itself as hum. Maybe try some metal tube shields and ground them to the chassis. If it were a power supply problem, it would still hum even when the 6AN8's are removed.

I hate hum. Tube amps are supposed to be hum free even by design. None of my tube amps hum only slight hiss with your ears up to the speakers.

Thanks , i do have a pair of tube shields on hand to try out on my next test , those dam 6an8s tubes , maybe i should get some adapters and try a different tube !

 

[nerdorama]

I really don't think any of this is going to help much until the wiring situation is sorted. With the filament currents flowing in the chassis you have a direct injection of 60Hz noise into the signals. I know you would like to find an easy solution, like swapping tubes, but with a console amp like this it was designed to be as cheap as possible. Sound quality wasn't the driving motivation. If you want it quiet you should attack it from good wiring layout and grounding practices.

 

[gadget73]

many of the triode-pentode tubes are prone to heater-cathode leakage on the triode side. Comes from their generally rough operating conditions, not so much because of the tubes themselves. I had an ST-70 here that didn't hum, but the leakage was so bad it caused the inverter output to be extremely distorted. It was showing around 150k, a new one has resistance greater than 10meg.

 

[Eddie hy fi]

I really don't think any of this is going to help much until the wiring situation is sorted. With the filament currents flowing in the chassis you have a direct injection of 60Hz noise into the signals. I know you would like to find an easy solution, like swapping tubes, but with a console amp like this it was designed to be as cheap as possible. Sound quality wasn't the driving motivation. If you want it quiet you should attack it from good wiring layout and grounding practices.

If its the filament current that i hear then it must be coming from the driver tube area , im staying focused on that area , so far ive added a ground wire between the two driver sockets and catching a few other things in that area , ans ive gone over some solder points and im going to try the tube shields and ive found that each driver tube socket has a silver mica type capacitor going to ground and im thinking this cap should be and was a ceramic type, so ive switch both those out , -No-swapping tubes is not going to do it ----i may do even moor but im not willing to rewire the whole amp

 

[Eddie hy fi]

Well ,i failed again , it still has that same background hum , no worse but still there , grounding amp to pre amp is no help ,metal tube shields are no help , when i unplug a rca input there is a loud high pitched scream , so it does not like those unloaded , should i add a film type capacitor to the line input wires and what about that resistor on the line input wires to each driver tube ? --------what to do next , should i twist the heater wires going to driver tubes in circles ?

 

[Eddie hy fi]

Well ,i failed again , it still has that same background hum , no worse but still there , grounding amp to pre amp is no help ,metal tube shields are no help , when i unplug a rca input there is a loud high pitched scream , so it does not like those unloaded , should i add a film type capacitor to the line input wires and what about that resistor on the line input wires to each driver tube ? --------what to do next , should i twist ,the heater wires going to driver tubes in circles ?

all so thinking about getting around the 6an8 tube , buy getting some tube adapter converters , i know i should just give up on this whole amp

 

[gadget73]

They don't cost goofy money. Honestly for the price of an adapter and some other tube you can easily get 6AN8's.

 

[cademan]

Rabbit hole!

Tubes you can experiment with but have different pinouts and would need adapters or socket rewiring: 6GH8, 6U8, 6EA8, 7199(hard to find and expensive).

Man, I am so sorry about your hum. I hate chasing hum.

 

[Eddie hy fi]

Ordered the tube adapters and will be going with 6gh8a ---but i all so now feel it is a tube bias issue in the driver circuit , that some resistors and pots may solve , but ill need help wit that one

 

[Kyri]

I know it might be a longshot, but on a smaller Sylvania amp I got in UK, I first got a step down transformer and the amp always hummed slightly, but enough to be annoying. Only after checking voltage did I find it too high (above 6.3V for the heaters and 128V coming in!)
Once I changed to a transformer on which I could measure and lower the voltage to 117V it made a big difference, I never even think about hum anymore.
Have you measured your input voltage - and if it is on the high side can you find a way to lower it to see if it helps? It might be totally unrelated but easy to check.

 

[Eddie hy fi]

I know it might be a longshot, but on a smaller Sylvania amp I got in UK, I first got a step down transformer and the amp always hummed slightly, but enough to be annoying. Only after checking voltage did I find it too high (above 6.3V for the heaters and 128V coming in!)
Once I changed to a transformer on which I could measure and lower the voltage to 117V it made a big difference, I never even think about hum anymore.
Have you measured your input voltage - and if it is on the high side can you find a way to lower it to see if it helps? It might be totally unrelated but easy to check.

I do know that the line or input voltage varies a bit between 117 and 121 volts , mostly its at 120 , i know that whats i see on my monster serge protector thing on my other stereo system

 

[Kyri]

I do know that the line or input voltage varies a bit between 117 and 121 volts , mostly its at 120 , i know that whats i see on my monster serge protector thing on my other stereo system

Doesn't sound much higher. Mine was at nearly 128V. I forgot to mention that the step down transformer hummed, so some of the hum was coming from that, so I can't be sure how much benefit to the hum, lowering the input voltage had. On mine it did drop the heater voltages from 6.8 to 6.3V (the right level). It was by measuring this that I realised the input voltage was likely high in the first place. So the life of the tubes would be lower if I left it high. I put a voltmeter on my variable transformer so now I can see what is going on. The input voltage does vary a bit but at least I can compensate for it now.

 

[trainbuftony]

Maybe try getting your filament wiring in order.
If your filament winding running current through the chassis then you are going to have hum. Wire them up so that all the filaments are on a twisted filament bus.
Put a 100 ohm pot on the bus with filament 6v across the full pot. Ground the wiper to the first can cap, and adjust the hum until its gone.

 

[Eddie hy fi]

Doesn't sound much higher. Mine was at nearly 128V. I forgot to mention that the step down transformer hummed, so some of the hum was coming from that, so I can't be sure how much benefit to the hum, lowering the input voltage had. On mine it did drop the heater voltages from 6.8 to 6.3V (the right level). It was by measuring this that I realised the input voltage was likely high in the first place. So the life of the tubes would be lower if I left it high. I put a voltmeter on my variable transformer so now I can see what is going on. The input voltage does vary a bit but at least I can compensate for it now.

Amp still on the bench , just taking a brake now , ill measure the plate volt with my meter to see if its way over 6.3 ----if it is i know there is a way to dial it back , just on the driver tubes , with a pot , one meg pot i think

 

[Eddie hy fi]

Maybe try getting your filament wiring in order.
If your filament winding running current through the chassis then you are going to have hum. Wire them up so that all the filaments are on a twisted filament bus.
Put a 100 ohm pot on the bus with filament 6v across the full pot. Ground the wiper to the first can cap, and adjust the hum until its gone.

not sure i understand , you mean the plate 6.3 going to all tubes ?

 

[trainbuftony]

6.3v winding goes to the filament not the plate.
If one phase is run using the chassis as a conductor, that needs to be changed so the current is delivered via wires. The pot simply references the filament to ground and nulls the hum.
Leave the plates alone, they'll bite you.
Start as has been suggested by getting the filament current complout of the chassis.
That may not completely eliminate the hum, bit it's the first step in the "order if operation"

 

[Eddie hy fi]

6.3v winding goes to the filament not the plate.
If one phase is run using the chassis as a conductor, that needs to be changed so the current is delivered via wires. The pot simply references the filament to ground and nulls the hum.
Leave the plates alone, they'll bite you.
Start as has been suggested by getting the filament current complout of the chassis.
That may not completely eliminate the hum, bit it's the first step in the "order if operation"

i dont know how or where , all the tube sockets are grounded to the chassis , how could i get around that , look at the photos which wire is the 6.3 ? the brown wire ? or the yellow , either way it is a one wire deliver and gets it ground threw chassis , your asking me to rewire the whole amp on a maybe , ive done so many other things on a maybe and they have all failed , now what ?