I made a tweed delux clone.
When I play it very lightly its ok but if I dig in, just a little, it makes loud
farting out sound and that continues if I stop playing. (almost like a 60Hz hum)
It will "reset" itself if I power down then back up.
Any ideas what this might be?.....bad cap? bad tx?
Dan
The Blues is my Business....
and Business is good.....
Something is either oscillating or you have a misbiased/unreferenced stage, it sounds like.
Make sure your wiring is neat and follows whatever layout you used. There's not a lot of gain in a 5E3 so there's not a lot of places for error. Make sure your output transformer primaries aren't reversed.
Make sure your 12AX7 grids in stage 1 and 2 are referenced to ground correctly.
Can you narrow your problem down to one channel or the other? If you plug into the bright channel and turn the normal volume off and vice versa, do you still have the problem? Do you have the standard interactive volumes?
I had a couple minor issues with my 5e3. I went back and re-flowed all the solder joints. That fixed 99% of my issues. That is where I would start, but since you've fired the amp up, make sure your caps are discharged before you do it.
Is this intermittent sound a farting sound, or is it an electrical kind of faint background buzzing/sizzling sound. (If it is the latter, it could be bad output tubes, in which case subbing in a different set of output tubes should help. You got to have a spare set handy anyway, so why not get some today?)
Well I was working on it and it made the noise and this time it didn't go away......I pulled ALL the tubes....Power and Preamp..and it still make the noise......to make it go away I removed the output transformers center tap....is my OT smoked?
The Blues is my Business....
and Business is good.....
I think its not. Anyway, you can always make sure of it. If you now are concerned about your OT, solder it out and try surging your heater voltage (AC of course) into the secondary coil. Be very careful and measure the voltages on the primary taps:
CT to Left
CT to Right
You should find there relatively high voltages and they should be approximately equal. If done properly, this method gives you the full picture of any shortages/disconnections inside the OT.
And the main issue might be just a bad cap in the signal route. You can try to unsolder all the blocking capacitors and measure them with your multimeter on the highest resistance range.
Remember - when you firs touch the cap leads with your meter - it will show a low resistance value until the cap is fully charged. So you must connect the leads to the meter and wait. If the cap is good (no DC leak) the resistance shown on the display with time will go into the infinity, and the meter will show the same picture it shows when its taps are just in the air.
The other reason may be an oscillating that is being started after you go over some signal volume. The oscillation may well be out of audible range, but the tubes will still try to amplify it. Thus in conjunction with the blocking caps, such oscillation biases the following gain stage so it start to "fart".
The best way to find out is to get an oscilloscope and then see what happens after each stage.
Cheers. Ace.
If you want something to be done well - do yourself.
Dan