Tube Amp Archive

Presence...

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I see. Would twisting the 2 wires help? Should they be as close to the chassis as possible?

Working on a presence wiring pic...

...I should admit that I don't nearly, *completely* understand this stuff. I am reconfiging the bright switch per Martin's diagram, but I need to think about why it will work wired that way, other than the obvious elimination of excess lead length. Question: This amp get to full volume by 9:00 to 10...

I'm going to work these suggestions. They all make sense to me...now. Wouldn't have a week ago! Like you wrote Bob - "Oscillatious the enemy lives up there where the infant signal wanders" - so true! It's all happening up there in "V1-BrightSwitch-VolPot-ville". Again, thanks again for taking me fro...

Will do Bob. Shortening the bright switch --> Vol pot wires makes sense. I don't understand what you mean by gluing the bright caps to the bright switch - shortening them? I'll spend time looking at TMB wiring, too. I really want to get this playable. I've never played anything like this. Such beaut...

There is no grid stopper resistor (~1k) soldered at pin 2 of V1. I've swapped many tubes. Tried several guitars. When the guitar is NOT plugged in, the buzz comes from the wire between the bright switch and the volume pot - even getting my hand close makes it get loud. With the guitar plugged in the...

I'm adjusting lead dress with minimal success, but I'll keep trying. I will try different tubes in V1, as well. I found the the wire connecting the middle lug of the bright switch to the middle lug of the volume pot is by *far* the most sensitive in the amp. The slightest touch with the wooden stick...

V1 12AX7 is very noisy - it rattles like crazy when touched. Swapped it - still rattles, so not the tube. The voltages on all 12ax7s are still a little high: 174 on V1, Pin1 (spec 160) 1.7 V1 Pin3 (spec 1.4) 157 V1 Pin 6 (spec 143) 1.2 V1, Pin 8 (spec 1.0) When I contact multimeter with pin 1 on all...

Martin, Richie, Littlewyan - swapped the OT primaries. That did it. Apparently, the guide I had either had it reversed, or the transformer was wired that way. In any case, it is up and running. Now I need to run down a pretty loud "hum/buzz" issue. Gets bad as the amp is turned up with guitar full v...

I do realize that what I described in the diagram as the cathode resistors are in fact the screen supply (pin 9). Those are fine.

The cathodes (pin 3) are now wired to to 62/10 resistor...with a noise that immediately gets my dogs howling.

Reconnected pins 3 of EL84 to 62/10 resistor.

Progress, however, now...

When standby is switched on there is a loud squeal with volume at 0. With volume up a bit there is squeal + "feedback" howl (for lack of better term).

Martin - I was posting while you were. I'm on it.

I found the problem, and I think Martin was onto it.

The wire from pin(s) 3 on EL84 to the 62/10 resistor is disconnected. It runs under the board and I couldn't see it. Reconnecting now...

Martin:

with amp off and caps drained (does this make a difference?)...

Resistance measured for:

EL84-pin3 to "left side" of 62/10 resistor: no reading (open?)

"right side" of 62/10 resistor to ground: 0.11

across 62/10 resistor: 61.1

Thanks guys. Richie - Do you mean the 220K resistor that connects the 47/450 cap with ground? That's in the right place. Sorry for poor resolution on pic. I'll put up a better one. Littlewyan and Kwijabo - The cathode resistors are *not* connected where the Ceriatone layout illustrates it should be....