Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hatchhh on April 03, 2010, 03:29:07 pm
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Hi:
I have a 61 super 6G4A - I have been going through trying to right some of the poor choice of capacitors and wiring that the previous owner had done to the amp. I have been following the layout religiously, but when I got done, and put it all back together I get no volume in either the normal or vibrato channels. Are there any likely suspects that I should check first? Like I said I tried to follow layout, but I am relatively new to this, so I probably missed something.
Thanks for the help.
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Nothing coming from the speaker? No noise, a hiss or anything?
Check the obvious:
- right tubes in the right places
- speaker plugged in
- input working correctly (e.g. guitar and cable)
- check all your heater voltages
- check your B+ voltages
If still nothing, post all your tube voltages, preferably with the schematic so we know which tube is which.
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check the speaker out jack , are the 4 speakers all connected properly ?
C.
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Also, although hacked, it presumably worked before you corrected things. So check 3 times for a wire running to the wrong eyelet (especially underboard wires) and for cold solder joints.
A fast method to test for where the amp stops/starts working:
Get a small screwdriver with an insulated handle, or use a meter probe. Carefully touch the grid of the output tubes with the tip of the probe with the amp on. Be very careful about working around live voltage and be sure not to short anything with the probe tip. If the amp is functioning from the output tube grid to the speaker, you should hear a small click or pop when you touch the grid with the probe. Did I say that an insulated handle is mandatory?
Next, go to the plate pin of the phase inverter, and repeat. You should hear the same click/pop at the speaker. There's high voltage here, and an insulated handle is mandatory. Are you getting the impression this is important? :grin:
Repeat this touch test at the grid of the phase inverter, and you should hear a louder click/pop. That's because of the amplification of the stage. Continue working backward through the circuit to each previous plate and grid, and the clicks will continue to get louder. When you find the point where you go from getting a click at one test point to no click at the next earlier point, you've found a place where the signal chain is broken. Look for bad solder joints, wires to wrong places, shorts, opens, etc. In a restoration where the amp previously worked, the fault will almost exclusively be builder error. That's normal and we all learn to be more careful the next go round.
This method assumes good voltages throughout the amp. You could do this test in place of measuring voltage, if you're reasonably certain everything is as it should be. Or, you could even combine this test with measuring plate and grid voltages by keeping your ground lead clipped to the chassis while you probe (with 1 hand!) the plates and grids. The click will occur regardless of whether you use a screwdriver or a meter probe.
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Thanks for the input. I'll get after it and see what I can figure out.
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check the speaker out jack , are the 4 speakers all connected properly ?
C.
'61 super is a 2 x 10 combo..... :wink: