5e3 Debugging...

[fsuman]

All right guys, I've been a loyal lurker and finally decided to jump in and build a marsh 5e3. When I fired it up without tubes everything looked good. Put the tubes in and the issues started.
First off, the volume pots do nothing until you turn then up to 11-12, then they get louder. Also, no matter where the volume pots are the guitar comes thru nice and loud, I can control the volume of the amp with the volume knob of the guitar. Tone pot works just fine. The same thing happens on all four inputs.
The next issue is what sounds like 60hz hum that coincides with something inside of the 6v6 at v4 blinking or twinkling at a steady cycle.
Any ideas or help would be greatly appreciated

[pdf64]

I'd guess that you've left the grounds to/from the vol pots unterminated.
Re the hum, what's the voltage between each heater wire and ground?

[fsuman]

I ran a buss wire across the back of all the pots and terminated it at the input jack. Is that enough?

The heater wires to ground are 3.4VAC each

[JHow]

I think pdf 64 is asking you to check your volume pot connections. One lug of the pot should make a connection to ground. If that connection isn't happening, for reasons such as bad solder joint, no solder joint, etc. you can get symptoms like what you describe.

Regarding hum - in so many cases it will also turn out to be a grounding problem. My favorite places to acheive hum are filter cap grounds and input jack grounds followed by preamp grid wires.

[fsuman]

Success! all I had to do was actually ground the ground tab on the volume pots. I feel kinda stupid, but hey it's a lesson learned.

The only other thing going on now is the amp is pretty quiet with nothing plugged in, but when I plug into any of the inputs I get a terrible hum, but when I grab the barrel of the plug it drops dramatically, obviously a grounding issue but where should I be looking for the bad ground?

Thanks a bunch guys, it's nice to have a amp that works.

[JHow]

Try looking at the input jacks. Are they "switchcraft" type? How are they grounded? Are they tight on chassis? How does the lead to the first preamp grid run? Is it shielded? It's usually a simple ground issue. Jacks are so simple that they receive little attention - then they trip you up.

[fsuman]

They are switchcraft jacks. They are grounded by buss wire to all the pots and thru their own connection with the chassis. I'll try and tighten them. The input lead is pretty clean down. Not shielded however.

[JHow]

What happens if you lift the connection from jack to bus? What if you ground jack to another location? Does it get worse or better?

[fsuman]

When I lifted the ground off the jack and resoldered it most of the nasty hum disappeared, all that's left is what I would expect from a single coil p/u (I'm playing a tele). Thanks a bunch guys. Overall I'm pretty stoked about my new amp, now it's time to start breaking it in!

[JHow]

Glad it's working. You may still tweak a little bit more quiet out of the amp as you play with with it.

You are right about playing, while building amps is fun, the real goal is to play. At some point we have to put down the soldering irons and pick up the instrument.

[fsuman]

Haha, yeah at some point I'll get annoyed enough to start really searching out the last bit of hum, but right now it's just nice to play.

[Bruce / Mission Amps]

When I lifted the ground off the jack and resoldered it most of the nasty hum disappeared, all that's left is what I would expect from a single coil p/u (I'm playing a tele). Thanks a bunch guys. Overall I'm pretty stoked about my new amp, now it's time to start breaking it in!

I'm assuming you had no brass plate behind the pots and jacks... right?
So when you lifted the ground off the jack and resoldered it, does that mean it is soldered to the same place as before or did you move it or something?

[fsuman]

Sorry about the delay, real life getting in the way. No, no brass plate. It hummed the same whether the Jack was grounded to the pots or not so I soldered back in place and it seemed better. But in retrospect I thinks actually the same level of hum as before. Any other ideas?

[JHow]

I forget if you said earlier, but does hum get louder if you increase volume? This would indicate something before vol. control. Other quick fixes include chassis ground screw on three wire cord is tight?

[fsuman]

Definitely gets louder when you turn up the volume. I'll check the bolt.