trinityamps.com

Been gone from here for a long time, but wanted to get back in to post some follow-up comments as I tried to resolve the voltages listed in this thread in addition to a new issue I wanted to ask about.

First, the voltages: I have checked all of the the things suggested in this thread, in addition to checking continuity, resistor values all through the amp (but particularly those in the path of the pins with low-ish voltages), and swapping tubes. The only thing I can find wrong is that pretty much all of the resistors are off from their value by varying amounts -- I think they are probably all within their error tolerance, but I am wondering if it is possible that if they are all off by varying amounts if that could all add up to the low-ish voltages?? In the end, the amp works (all inputs) and I am playing it quite regularly -- I just have no idea how close to the "real thing" mine sounds since I have never played the "real thing".

Now for my new question: when I am playing the amp pretty much dimed (on either channel), the cruchy chords/rhythm are all there and sound pretty fantastic, but when I play some lead licks there is this funny overtone to the sound that, and here comes my best description, sounds like I am playing through a phase pedal or something. It is particularly noticeable when I play a single note and hold it, then add some vibrato to it -- definite phase sound. Has anyone experienced something similar to this? Could this be caused by my voltage problems (I am thinking not since folks have said that my voltages are low on certain pins but not terribly low) or would it be something else?? Any help would be GREATLY appreciated!

By the way, I built two 1x12 cabs and a head cab to complete the setup -- someday I will post pics (they came out quite nicely).

Thanks,
Bigfoot

With regards to your new issue, you're not the only one who's noticed it, if it's what I'm thinking.

My sIII does something similar, or did when I first built it. It was driving me & Stephen nuts trying to figure it out. It only happens when pushing the amp pretty hard. Later on I did a partial rebuild when I converted it to a V6. I tidied up the lead dress quite a lot. That artifact is still there, but nowhere near as noticeable - hardly at all in fact. If I wasn't looking for it I'd probably never even notice.

If it makes you feel any better, my JMP 2204 build has a touch of it also, as do my stock Laney & Traynor. My V6 does not do it in 6V6 mode. I have KT-77's in the 2204 now and it has vanished. The Traynor has 6L6's now and it's fine too.

So, I'd recommend some chopsticking. I suspect it's some sort of interference caused by the wrong wires being a tad too close, exacerbated when EL84's (or EL34's) are running hard. I had originally thought it might be in the PI but I have no empirical evidence. I can tell you when I cooled down the signal to the PI it did fix it, but it may have just been because the gain in the output stage was lower.

Good luck with it!

Kirb

P.S. I built another V6 - the "Plexi" version - for a fellow forumite & it had no issues at all. Guess I was getting better with the lead dress. I also think his amp sounds WAY better than mine! It just freakin ROCKS.

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SG + Brit tube head = Nirvana

Yes, it could be some high frequency oscillation creeping in when the amp is being cranked, in which case chop-sticking, judicious use of shielded wire and twisting OT connections may help. It could also be caused by a bad filter cap. And you could try installing a Zobel filter on the OT secondary to reduce the speaker impedance peak in the high frequency range which causes an impedance mismatch at high frequencies, particularly affecting the performance of EL84s and to some extent EL34s (both are pentodes). A 10ohm 5W resistor in series with a 2uF non-polarised cap across the OT secondary has been reported to give good results. Alternatively, just think of it as a cool built-in effect.

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Great tones come in small glass jars!

I hear ya on the cool built-in effect, but i would prefer a pedal to provide the effect than the amp.

Sorry to be a pest, but could you "dumb it down" a bit for me:

Chopsticking -- I know generally what this is, but could you clarify for me exactly what it is? Do I just take a stick and touch all wires, components, tube pins, etc. until I hear a change in sound? Also, for my problem, I assume I would do the chopsticking with the amp dimed?

Zobel filter -- if possible, could you draw the mod on a schematic for me? Or at least clarify what the "OT secondary" is?

I am an accountant by trade so I definitely struggle a bit when I need to troubleshoot one of my projects. I am ecstatic that my amp works and sounds really pretty good -- I would like to figure out this "phase" issue though.

Stephen/Coco -- do you have any thoughts on my two issues that you could contribute?

Thanks everyone!!

Bigfoot

Just use a chopstick to move wires around and see if the position of certain wires affects the sound. Run the amp at whatever settings cause the problem most.


The output transformer has a primary winding that goes to the power tubes, and a secondary winding that goes to the speaker(s). In this case you join the resistor and the cap in series, and then connect that contraption between the 8 ohm output connection on the OT and the output ground connection of the OT.

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Great tones come in small glass jars!