Valve Junior

Valve Junior Circuit board and Wiring, with Additions

 

I’m building up to having another session with the Epi Valve Junior, planning to replace the output transformer, which might not be absolutely necessary, but I fancied a change. Was going to buy a Hammond 125CSE but in the end plumped for a Danbury electronics DB1087 from Ampmaker.com. It is not that much different from the stock transformer (epi v3) a little larger and rated for 5-7 watts. It will leave me with the stock tx spare which I might use in another build or possibly for a tube driven spring reverb for my other amp (VHT special6 Ultra). I haven’t decided yet.

I’m going to remove the Pentode-Triode switch, I don’t mind the tone in Triode mode but hardly ever use it. I’m going to experiment with either reducing the EL84 cathode bypass cap to either 10u or maybe even 4u7 and would like to hear what the effect would be of leaving it out completely, maybe have that option on a switch. Using the VHT sp6U I have found I like the depth switch at around 1 or 2 O’clock, 4u7 or 3u3 bypass cap, and even at 220n it sounds pretty good.

The Epi is still too bass heavy, even with V1 K-bypass caps at 4u7 and 2u2 with the 2u2 on a partial pot in series with 100n in parallel over the whole lot. The interstage attenuator r6-r7 has reduced resistance 470K for each, in place of 1M, R6 is a variable resistor, so the lower 3db point should have increased, even more so when r6 = 0, which is good with the increased gain that gives. But still too muddy for me. Plan to drop the coupling caps to 10n, and then see if there’s a need to reduce el84 K-bypass cap which is currently at 47u. Think I’ll go for 10u anyway, then assess it from there.

Compared with the VHT it has a higher sig:noise ratio, (not measured, just by ear) which is a prompt to get inside that VHT sometime to figure out why it is so noisy. I have a few plans for the VHT too, but that’ll have to wait, because these VJ mods will take a long time to finish with the rate that I work, which is very slow due to various problems with dizzy head, varying numbness in hands, arms and legs, and back ache from hell, but it will be worth it in the end.