A Few Questions

[hippiebob01]

Hey guys, I have a few questions and was wondering if you could help me out.

1. On my 5E3, every tube that I put in V1 seems to be microphonic. I know for a fact that most of them are good (except for a few bad EH tubes). Could I have gotten a bad tube socket?

2. When I turn the volume on my 5E3 up past 10, it gives off a high frequency whine (not feedback). I want to say its a microphonic tube, but I don't think that's the case. What else could it be?

3. On my strat, I have it wired stock, except that the second tone pot is wired to the bridge pickup. When I turn the volume down from 10 to say...8, it introduces a lot of noise. What could be wrong with the wiring?

4. When I touch my speaker, a good bit of hum goes away. This makes me think that I haven't grounded my speaker correctly. What should I look for?
Thanks for reading.

[jerryjg]

From my experience, yep, youve got microphonic preamp tubes. Change them out. Seems awefull farfetched, to think 3 tubes would all be microphonic, but Thats about excatly what happened with my Bassman. V1 is very sensitive, and gave me problems like you.
Go to tube depot, i think, and order an Electroharmonix tube screened for microphonics, and get a high gain one also while your at it. A 2 dollar upchage on each tube,for the screening. Youll be good to go.

[chuckocaster]

i am no expert on amps, here is my interpretation:

1: something in the V1 circuit may be off, i really doubt you had 3 bad tubes in a row. do you have the shield on it?

2. check your wire layout. amps will get noisy when dimed, but there shouldn't be any whine, that to me would indicate "crosstalk" between wires. when i used to do sounds for a living, i always made sure to run the mic or speaker wires 90 deg to the power wires if i had to cross them.

3. double check your grounds/

4. try running a wire with a tab on it from the negative tab of your speaker to under the nut of one of the speaker mounting screws. i've had to do this a couple times to get the speaker grounded correctly.

[hippiebob01]

Yeah Chuck, I tried a few known good tubes and they were still "microphonic". thats what led me to believe it was the socket. no i did not have the shield on, but i'll try that next.

on the speaker, the negative tab is the red one, correct? its a weber 12s.

[steve25]

Your whine to me is oscillation, not microphonics, wiring and component layout need to be checked.

[chuckocaster]

nope, red is hot.

[yankeerob]

Heh - all good advice - 5E3's are 'hot' little b*stards - I've had this sort of thing with a number of circuits inc our little ME-1... seems that even though we rigorously earth the bodies of the Alpha pots we use (yer I know we could spend more dough on 'better' pots) you sometimes get noise or oscillation - just goes to show how far out of your way you need to go to be vigilant in routing your wiring... I don't think it's the toob m'self