ultraman31
100+ Head-Fier
I checked the tube by swapping, but still the same left channel.
I checked the tube by swapping, but still the same left channel.
Glad you got it working!I know I'm way late to this project but I built Pete M's more simple "low-voltage hybrid headphone amp" to use as a tube preamp in my system first and became interested in this higher level project (hybrid mosfet-maxed) because of his mentioning it on his project page. I intended to adapt it to use as a preamp as well since I don't listen through headphones these days. I've built more complex things like Nelson's BA-3 and Wayne's BA2018 preamps so thought this project should present no hurdles...everyone else go it to work just fine so I should have no issue, right?
Here was the problem(s) that plagued me after the build was complete. Once powered up to 27V the regulator would shut down, I could never get both tubes biased when in circuit (maybe one but not both), and the tubes would glow brightly. All signs of an high current flow, right? Painstakingly rechecked all the components previously mentioned in this forum. Removed the mosfets and retested them them put them back in. Checked the K170s & J74s I bought from the diyAudio store (they were fine). Checked the whole PCB for anything touching or causing a short. Could find nothing suspect for high current flow. Finally I was left looking at the OnSemi LM317 regulator. I happened to have some TI LM338s around and dropped one of those in place. Low and behold everything stabilized and I'm now currently letting the unit warm up for 30min or so to finally set all the biases. I can't blame the use of LM317 in the circuit since all of you used it successfully so must have been that the batch mine came from was not as hardy as the ones you folks used many years ago. Now to keep checking everything for a few more days before making SE input/output connections and see what it sounds like.
Cheers,
Pete