Home OTL Asylum

OTL, Output Transformerless Amplifier User Group.

RE: Somehow it involved a fuse

I reinserted tubes to start measuring bias and thought again about the fuses. Visually they all looked intact but when I used the continuity tester one of the two 5A slow blow fuses on the front of the amp was not making the short and the ohmeter showed infinite resistance. Strangely when I measured grid voltage on all the tubes at pin 4 they all showed 184-5 on the left and 181-2 on the right, even without the left fuse in circuit. With the fuse out I depressed the voltage offset switch and even without that fuse it was pinned at zero. I put a new fuse in to its place and listened and it sounds good. I think that pulling and reinserting the fuses or the tubes must have cleaned some crud off of something to make the difference. Otherwise the tubes that I thought had to be balanced one row of six to the other row I now know have reinserted to be balanced left to right. Now offset is at zero and sound is balanced between the two amps. No explanation readily available but sound is back.

As an aside to Ralph, are there any different roles played by the five 6sn7 tubes that would let me know which needs to be least microphonic, which needs the best plate to plate match or if any of the tubes need to match one another. On my amp, looking from the front, the rightmost tube is next to the xlr jack and the leftmost tube is next to the offset meter.

Thanks again for the advice.


This post is made possible by the generous support of people like you and our sponsors:
  Kimber Kable  

Follow Ups Full Thread
Follow Ups


Post a Message!

Forgot Password?
Moniker (Username):
Password (Optional):
  Remember my Moniker & Password  (What's this?)    Eat Me
E-Mail (Optional):
Message:   (Posts are subject to Content Rules)
Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:  Automagically notify you when someone responds.