problem 5E3, too sensitive amp, schratching guitar pots

[senadsa]

I need some help, this is my third 5E3 amp, and whit this one I have a problem... Amplifier is to much sensitive, and I have schretching pots on guitar when amp is on high power. It is too loud, and all voltages are correct.

[xtian]

Two different problems to deal with here. Scratchy pots can be an indication of coupling caps letting DC through, or, in the case of scratchy guitar volume, a bad tube in V1.

[senadsa]

well, it can be a problem... My tube is OK, but it is 12ax7, not 12ay7... In my previous 5e3 12ax7 works fine... I do not have 12ay7 now so I can't test it now...

[cbass]

Plug in a cable to the input and measure voltage from the tip to ground .

[senadsa]

On DC it says 0.362 V...

[xtian]

Yeah, that's pushing it. Anything over a few tens of millivolts will get your volume pot scratchin'. So throw in a 12AY when you get one, and that might also solve your "too sensitive" problem as well.

[cbass]

On DC it says 0.362 V...

There ya go either a bad tube a bad socket a conductive board .

[senadsa]

I took your advice, and do the following ... moved 68K resistors to the input connectors, coaxial cable signal led to the first tube. With the coaxial cable I brought signal to the tone control, and from the tone control coaxial cable to the second tube... (removed not used turets from the board...)

The guitar pot's are not scretching now!

Thanks a lot for support...

Still not satisfied with too sensitive amplifier, I believe that the problem will solve 12AY7, I should get one to test it... Thanks a lot for your advice and instructions, I must say that this is the first time that I write in this forum (mainly I'm reading about Dumble amp...), and I am very, very satisfied.

THANKS again,

Senad

[pdf64]

Good practice is to fit grid stoppers at the tube socket terminal, eg the 68k input resistors.

[senadsa]

Yes, I understand it... But for 5E3 in that case I'll need 4 wires from connector's to the tube. It's sounding OK now and I have only two wires...
It will be case in my next build - Dumble clone... (I'm just in love with that amp and I want it for myself...)

Here is some pictures of this elegant 5E3...

[cbass]

Good lookin amp. I still don't understand what you did to fix the voltage on the grid. Shielded wire should make no difference whatsoever in that respect.

[senadsa]

Well, you asked me to measure the voltage...

****************
xtian:
Yeah, that's pushing it. Anything over a few tens of millivolts will get your volume pot scratchin'. So throw in a 12AY when you get one, and that might also solve your "too sensitive" problem as well.
****************
xtian had explanation to me why it's scratchin... And I have start to explore...

THANKS xtian!

Those are short wires, but sometime it is enough to induct some small current. To be on safe side, I decide to test it with coaxial cable and without board connections, and this was OK. Next step was to remove unused turrets etc.

It is also possible that board was conductive?!?

Thanks to you and xtian, I had a clue...

[cbass]

Well glad you got it fixed .

[rp]

I don't see why shielded wire should fix the scratchy pots either but all's well that ends well. If you have a bad V1 tube try flipping it with the Pi see if the guitar pots clean up. I like a 12AX7 in a 5F6A (so did Marshall ) but it's just too much in a 5E3, pushes it into a bad place. Try a 12AY7, but then what did you put in your other 2 5E3s?

Too loud? Maybe you also have too efficient a speaker?

[Mark]

Aren't the Dumble guys here building 5E3 style amp using a 12AX7 for V1 and they are using 1K cathode resistors which would have a bit more output than a regular 5E3?

As far as scratchy pots, they seem to be more noticeable on guitars with a larger value volume control. I wouldn't always hear scratchiness when using my Strat, but it is more clearly heard on my Les Paul.