New Build - JM/AN Wonderland

[sonicmojo]

Aloha,

Just finished my new JM style amp (in the wonderful AN Wonderland chassis)! It is sounding pretty great and I am entirely pleased with the results so far with my '74 Bassman 100 iron. I will be fine tuning this over the next few days.

I am chasing down a small bug that is driving me nuts. It an intermittent tick sound about every 3-4 seconds. Sound gets louder if I turn up the amp volume. It does not matter if a guitar is plugged in or not.

I've traced the source area (I think) to V1. If I pull the tube or ground the signal after V1, the tick goes away. The tick also goes away if I remove the 500pF cap parallel to the 220K grid stopper on V1-pin 7. I've replaced that cap but it happens with another. Any ideas on what could be happening? I attached a link to the original layout below.

Thanks for your help.

Layout:
https://ampgarage.com/forum/download/fi ... &mode=view

[xtian]

I would suspect noise from cell phone, wifi router, computer, etc. V1 is the most sensitive to stray RF.

[sonicmojo]

I would suspect noise from cell phone, wifi router, computer, etc. V1 is the most sensitive to stray RF.

I think I ruled that out by unplugging anything around it and moving my phone far away. If I ground the input at V1-pin 2, the sound still happens. It is in my garage so not much in there. I feel as though something is loading up in the circuit and then popping. I tried paralleling the new filter caps and it did not change anything but I might try to replace the one for B+5. Attached a sound file. Ignore the car driving by in the background...

[sonicmojo]

So I tried several things, disconnecting local negative feedback, replacing plate resistor for V1-6. Substitute a different filter cap for B5. Even replaced the wire to pin 6. Nothing helped. The sound starts occurring at V1-6 for sure with my probe tests. Still occurs even if I disconnect the downstream coupling cap. Does not seem to be there at the V1-7 grid but could be getting amplified and I just can't hear it - perhaps something in the tone stack is doing it.

One new symptom. It only starts to happen (at least this last time) when the amp gets fully warmed up.

I am starting to think socket? I'd hate to have to swap that out until I exhaust all other ideas......


EDIT: Think I'm barking up the wrong tree. I can still hear an almost inaudible click if I pull V1,V2,V3. Maybe this is happening downstream and just amplified by V1.

[sonicmojo]

So my issue appears to be the standby switch. It is not grounded to the powder coated chassis.

If I just touch a grounded test lead to the switch, "pop", then it takes a bit of time to build back up to the ticking.

I saw other posts about this being a "common thing" and the solution being to ground the switch to the chassis. This is automatic of course if you don't have powder coat. I assume this is a static buildup issue with all that juice flowing through the switch. Is it good practice to make sure the standby (and power switches) are grounded? Or do I have a faulty switch? It is a standard Carling SPST amp switch.

Now on to tuning the Reverb. I have to dime the controls to get it to where I like it.....

[sluckey]

I would remove the wires from the STBY switch and solder them together. Then run the amp like that long enough to verify that the tick is indeed gone.

[sonicmojo]

I would remove the wires from the STBY switch and solder them together. Then run the amp like that long enough to verify that the tick is indeed gone.

Good idea. I ran it for a long while with just a ground lead alligator clipped on the switch and it did not come back so I went ahead and dremeled out some of the powder coating on both the standby and power switches and reinstalled them with good internal tooth lock washers and verified that the switches were for sure grounded. The tick seems to be fully gone. I’ll report back if not....

[ChopSauce]

Yes powder coating is famous for providing electrical insulation. Wasn't a star washer providing enough contact to the bare metal?

[martin manning]

So the thought is that a static charge builds up on the switch housing until it arcs over at the bushing?

[sonicmojo]

Yes powder coating is famous for providing electrical insulation. Wasn't a star washer providing enough contact to the bare metal?

The switch did not have a star washer. At the time I first installed, I couldn't find one big enough. I measured it before I fixed and there was no continuity. I had to steal one from a stomp switch. Lesson learned the hard way!