All Filter Caps swapped! Still some hum on Clean and Overdrive Channel of Red Knob!!!

[jalexquijano]

I finished replacing all the filter caps on my Fender the Twin aka Red Knob. Its weird i still have some hum on the clean channel which is accentuated when i increase the treble pot and on the overdrive channel which increases when i dial the gain over 6. Is this normal? or could V7 preamp tube be microphonic and thus causing the hum?

[Enzo]

There are MANY causes of hum in a tube amp - or any amp for that matter. Filter caps ONLY affect power supply ripple hum.

[nosaj]

I finished replacing all the filter caps on my Fender the Twin aka Red Knob. Its weird i still have some hum on the clean channel which is accentuated when i increase the treble pot and on the overdrive channel which increases when i dial the gain over 6. Is this normal? or could V7 preamp tube be microphonic and thus causing the hum?

Well here's one way of ruling out your tubes. You have 2 channels I believe on that amp. Choose a channel you want to check out be it 1 or 2. If you choose channel2 Pull a tube from Channel 1's preamp and swap it with V7. With a little musical chairs you should be able to rule out a tube or find the problem tube.

nosaj

[jalexquijano]

V7 preamp was microphonic!

[1ampman]

I believe that amp has a hum balance control on the back. They can be touchie. With nothing plugged in the amp, amp on, stand by off, turn it up to 10 on the master and channel vol. Turn adjustment till quiet. A small adjustment can make a big difference...

[DrGonz78]

I believe that amp has a hum balance control on the back. They can be touchie. With nothing plugged in the amp, amp on, stand by off, turn it up to 10 on the master and channel vol. Turn adjustment till quiet. A small adjustment can make a big difference...

If you look at the schematic, "The Twin", you will see two resistors in place of a hum balance pot. So, if this is the correct schematic, there is no hum balance pot to adjust. Perhaps you are thinking of the Fender 75 or earlier 80's twins that might of had balance hum pots?

[jalexquijano]

Th Red Knob Twin "THE TWIN" does have a hum balance pot. The first preamp tube was microphonic. Just sourced a Brand new Groove Tube 12AX7-C made in China and hum was greatly reduced.

[g1]

The 'balance' pot on the back of the red knob "The Twin" is the bias balance for the output tubes. It should be adjusted for 0VDC between TP201 and TP202.
It's not a typical 'hum balance' like you usually see in the filament circuits.
Like Dr.Gonz mentioned, R302 and R303 take the place of the traditional 'hum balance' pot.

[Enzo]

They are both hum balance pots. The heater virtual center tap adjusts away the heater related hum. The power tube balance control adjusts the idle current to be the same on both sides, but the net result of that is to put hum at its minimum. In fact some schematics tell you to adjust it by ear for least hum.