Amp making popping sounds and noise?

[67Mopar]

I have popping and noises coming from my amp. Here's what I've done so-far...

- I bypassed the presence pot = no change.
- Bypassed the preamp by plugging into the effects loop return = popping and noises disappear!
- Sprayed all pots and inputs = no change.
- Touched every solder point to address possible cold joint = no change.
- Removed V1 = no change.
- Remove V2 = popping and noise stops.
- Remove V3 = popping and noise stops.
- I did not remove the PI valve.
- Removed the leads to the preamp volume pot = no change.
- I moved the wires with a chopstick with the amp on = no reaction.
- Cycled through 3 sets of power and preamp tubes = no change.

The amp makes these noises with and without a cable/guitar plugged-in. The standby switch also pops a bit now when I put the amp into standby mode/DC off. Looking at the schematics, there is a JFET that works with the preamp gain attenuation... Could this be the source? Remember, the noises cannot be heard when I plug into the effects loop return.

I can usually track-down most issues, but this one has me baffled!

[pops]

Does it make the noise even with the volume turned down and nothing plugged in? If so the 100k plate resistors.

[Leo_Gnardo]

I have popping and noises coming from my Cornford

That would make it a pop-Cornford. Pie fight starts at 11.

[Gibsonman63]

Does it make the noise even with the volume turned down and nothing plugged in? If so the 100k plate resistors.

Plus the plate resistors for the power tubes. BF Fenders exibit the same behavior when the 470R on the tube sockets get too cooked.

[surfsup]

cold solder prior to the return input?

[Jana]

It seems to be something related to V2. Which parts of the circuit are V2? There are 5 triodes on this schematic--which ones are for V2?

[67Mopar]

Does it make the noise even with the volume turned down and nothing plugged in? If so the 100k plate resistors.

No noise when the MV is turned down. It increases as I increase the MV pot. Doesn't matter if anything is plugged in or not.

[67Mopar]

cold solder prior to the return input?

I've touched every solder point with 60/40 = no change.

[67Mopar]

It seems to be something related to V2. Which parts of the circuit are V2? There are 5 triodes on this schematic--which ones are for V2?

Triodes #3 and #4 are V2. The only change I made was to the 100pf 'fizz' cap. I replaced the ceramic cap with a silver mica cap. I checked the amp with, and without the cap = no change.

THANKS for the replies! I ordered a full set of Takman CF resistors, so I figured I would just rework the entire circuit. That doesn't tell me where the problem is though...

[guitardude57]

You may also have a shot supply cap for that tube as well. Try bypassing, with another cap, and see if it stops.

[67Mopar]

You may also have a shot supply cap for that tube as well. Try bypassing, with another cap, and see if it stops.

Would those be one of these 47uf/450V caps?

I completely rebuilt the boards on this amp, and it's been running flawlessly since the rebuild. Until now that is...

[guitardude57]

Trace the pin 1 and pin 6 wire to the related caps. Yes, it will be one of the 47 uF jobbies. It does happen time to time, to have a failure in a new lytic cap... or any part, for that matter.

Looks like each preamp tube has a board for parts mounting.
I imagine, the 2nd tube board supply cap (if on the board) is possibly faulty, or bad solder. Follow the wires to the correct cap, and inspect solder joinery / try bypass with other cap if solder is good. Just parallel is fine, won't hurt anything. If the pops go away... that cap is bad/leaky.

[67Mopar]

Thanks!

Dammit! Those are new Panasonic supply caps!

[guitardude57]

I would also use F&T caps rather than Panasonic or IC's.

[Jana]

I'm looking at the second photo. The tube socket in the middle sort of to the left (a 9 pin socket). There is a wire going across the socket to bridge two pins. Is that wire touching the center shield pin thing? If so, and if it's not soldered to that pin, I would highly suspect that as a source of noise and pops.