trinityamps.com

OK, the "regular" channel of my Plexi works fine, but I just cranked the TMB channel for the first time, and there is a high-pitched whistling/squealing that kicks in when the volume and gain are past 2 o'clock. This happens with the guitar plugged in or not. Also, the channel hums without anything plugged in - the hum is noticeable at 8 or 9 o'clock and gets louder from there.

Does this sound familiar to anyone?

Another question: the clean boost switch does not add a lot of gain - is this the way it's supposed to function?

im familiar with thoses symptoms
check your input jack wiring and that the shielded cables are routed far from the board, it should calm thing down a bit.
for more boost, put a 1uf to 22uf in parallel with the first 2k7 resistor(the one switched) i think in mine i set it to 10uf....might try some more values soon as i find it a bit too bright and too much boost this way)

im still tweaking mine to get it where i want/need it to be. a little pita but at least im forced to learn how it really works, turrets boards are a godsend for those moments when i try everything i can get my hands on

Thanks. Would faulty input jack connections explain the squealing at higher volume settings?

For squeal, try reversing the OT leads (Blue / Brown) at the tubes

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

if squeal occurs at high volume id try to rerout/chopstick your area around the power tubes, theres signal and voltage wires passing close to each other there(by your pics) it might be coupling happening

So the blue lead should go to V4 and the Brown to V5?

Elegy, I braided the OT leads all the way to V5 - would untwisting them and separating them a bit decrease the chance of coupling? Or should I try to separate ALL wires leading to/from V5?

no, braidet is the right way to do it.
what im telling you is to try to cross high voltage wire with signal wires a 90degres angles and try to have a little distance between them, it can help.

reversing blue/brown can help too.

OK, I re-soldered all of the input jack connections for the TMB channel, switched the brown and blue OT leads at V4 and V5 and re-arranged the signal runs for more perpendicular and more distant relationships with the high voltage runs:



That took care of the squeal and the hum, and the jack connections are clean now. Thanks very much, Stephen and elegy.

I may look for a cap to add to the boost circuit, but first I want to be sure I wired the boost switch correctly, since I'm really not getting any additional gain from it. Are these the correct lugs to solder to?

Yes, assuming this is putting the extra 2K7 resistor in parallel with the existing 2K7 one and you should get a clean boost. Add 1- 25uf cap across the 2K7 boost resistor to taste if you want more boost.

BTW, all Good News!!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

So, just to be sure, I should place a 1 - 22uF cap across here? And also another 2K7 resistor?

No, just the cap, the resistor is already there! What you have drawn looks good.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks again.

Say, Stephen, I'm getting a reading of 1350 ohms across eacj of those 2k7 resistors, and also getting 235 ohms across the 470k resistor at the far right edge of that photo. Why would that be?

- Should get around 235K across that 470K resistor. I measured one here to confirm. Check your reading is in K, not ohms!

- Should get 2K7/2 when boost engaged across the pair. Two in parallel

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

OK, I put a 1.8 uF cap on the clean boost circuit and the boost is PERFECT now! Thanks to Elegy. I noticed the boost works only for the TMB channel and assume that's the way it's supposed to be.

I experimented with tubes - tried a pair of old Phillips JAN EL84s and a pair of Telefunkens as well. Both provide a nice, strident attack that is great for Beano tones on the simple channel. I liked the pre-JJ Teslas, though, for the silkier cleans and the lush overdrive. I have an old Sylvania long plate 12AX7 in V1, a Tungsram EC83 in V2, and an old GE JAN 12AX7 in V3. Now I'm officially DONE!! Great amp!!

Excellent. Glad it all worked out. Now that you've mastered that one, what's in your future

TRIWATT

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Tell me about the Triwatt - I don't see anything about it on the website.

LOL. Start here: viewtopic.php?t=1389

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

OK, you got my interest!

Meantime, there's one more issue with my Plexi that just started yesterday. I developed some fluctuant white noise in the TMB channel only. The noise is independent of whether anything is plugged into the input, and it gets louder/softer with volume control manipulation.

Does this sound typical of any particular problem?

How loud is it? There is some inherent noise with carbon comp resistors.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps