Jana wrote:A new build--a JTM 15 (thanks Leo Gnardo for the name).
Wow, I'm honored & dee-lited! Thank you Jana!
Also bought a white marker just in case I need to re color any black insulated wire. Actually, I found this Pentel at a hobby shop & just tried it out - very fine line and works instantly - don't have to shake the thing 'til my arm hurts then smell xylene everytime I use it like the previous not so fine Marvy white marker. Also $2 cheaper. Excellent for hand lettering on black or dark surfaces.
A bit of background on the odd layout. I have had this combo enclosure with the speakers for about 15 or 20 years. I had a chassis in it at one time but it fell prey to experimenting and the chassis eventually was swiss cheese. So, I pulled it out and just used the enclosure as an extension cabinet. But, it seemed so lonely and dejected without a chassis to call its own. I scrounged through my junk pile and found another chassis from another experimenter project and decided to give it a try. I epoxied a lot of the unused holes shut. I was kind of stuck with the layout though--transformers on opposite ends, can caps up front, etc.
My concern was the long run of the OT primary and the proximity to the sensitive V1 and V2 tubes. I can't remember what I did with the other incarnation of the amp but I know I didn't have any problems with it. I think I must have flew the heaters high and tight and ran the OT Primary in the back corner on that one because on this one, I had some issues with oscillation from the OT primary coupling to the V1 wires and the input to V2 (which I changed to shielded wire). I have stabilized the amp now but the cathode wire on V1 has to be in that exact spot. I'm not happy with that.
I will tweak on this one and do some experimenting and then, when I can find a new chassis, I will tear it down and rebuilding it with a better layout.
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I do have the input lead shielded but I had that from the start.
The two places that I had interaction were from the cathode lead (common to both triodes in V1) and the lead to V2 from the mix resistors.
I changed the V2 lead to shielded
I moved the white wire for the V1 cathode. I had it on the scope with a signal and just by moving that wire a quarter of an inch or so, the oscillation went away.
Last edited by Jana on Mon Feb 10, 2014 1:36 am, edited 1 time in total.
Thank you Jana!
