Tube Amp Archive

Sorry, this is the correct C1998 OT dagnall winding schematics

http://forum.gtlab.net/cgi-bin/yabb2/Ya ... 1166911150

cirillic but grreat link

Thanks again epis

Hi epis, I'm posting in 5 different forums and you are the only one that helped me. Thanks for this picture. Your exact link does not work and I can't do any search in this cirillic forum. I tried also with babel fish translator but with no success Your picture is the winding schema for Marshall 100...

epis wrote: two 60 windings in parallel is for 4Ohm,in series for 8Ohm

Hi epis, this is not correct, we are not speaking about resistance, we are speaking about coil windings, so if 60 windings are 4ohm impedence, then two 60 windings in series (120) is 16ohm impedence

I know Brian because I bought some of his trannies and they are amazing. I don't ask him because what I'm looking for is "his secret", he has unwound original Drake and Dagnal OTs and obviously he knows everything but this is his business. My problem is that if I buy Marstran or metropoulos or mercu...

I would like to build a replica of 784-139 OT for Marshall 50W plexi. I've looked all over the net to find all details but I've collected just few info. I know that these are considered precious secrets and people are doing their business with it ... anyway I try Here the result of my search, as you...

after lot of tries and tests I eventually limited the issue to reasonable levels, even if the problem didn't disappear completely. Here the main changes that helped me: - shorten ground presence directly to pots ground wire - shielded cable for some lead signal wires - shorten wires that were too lo...

someone on Metro forum seems to have a similar problem and fixed it removing 1ohm bias resistor (!!!???) of output tubes. http://forum.metroamp.com/viewtopic.php?f=4&t=28090&p=275076&hilit=jtm+squealing#p275076 It really makes no sense to me but I will try this too. After that I think I'll have to r...

wires from PI to output tubes are twisted. I also tried another thing: I swapped OT wires in the output tubes and obviously also wires coming from the PI inverter. I moved ground connections of 16+16 can near preamp chassis zone, I tried to move every wire inside the chassis but notjing changes: the...

I've tried a lot things, some with sense and others (I admit) with no sense, but really this issue is driving me crazy: - I changed presence cap - I changed 0.1u PI caps - removed feedback - I removed 47pF cap between anodes of V3 (PI) - Moreover I did some other tests on output tubes section: I rem...

I have a problem with a JTM45 clone I've just finished to build, I've already built 5 of them, but I never faced this problem before. When I set presence control to 10 (max) I have a very bad sound with a very strange kind of sustain feedback. In attachment I put a short mp3: in the first part you c...

sorry, forgot to say that I tried also to change all tubes in the circuit, one at a time

Really I did reflow all solders but I still had the problem.
As I said in previous topic I also tried a couple of 6L6GC but nothing changed.
The only thing that fixed the problem immediately was grid stopper resistors. I mind that I tried it at last, but at least now all solders are almost perfect!

I put 5.6K resistor grid stoppers and the problem is completely solved!!!
Anyway I really dont understand why I've been using this amp for one year without grid-stoppers and suddenly I need them: it's a mystery....
Thanks everybody for your precious help

I re-soldered almost all the circuit: output tubes pins, all bias circuit, all pots and all solderings that may appear not so good, but nothing changes. So next try I will put a grid stopper on pins 5 (I will go for 5k resistors). I will also try to disconnect feedback (never tried yet). Another str...