Well, I built up a couple of Bogen 7868 amps with original tubes and iron and I'm having an issue with a single ended amp that makes we wonder.
When I was running it into 100% mismatch read, 8ohm tap to 16ohm load. I saw little sparks from where the red lead enters the paper bobbin of the OT. This was dimed after 10-15 minutes.
When I run it at the matched impedance I have no sparks. Am I right in thinking the a 100% mismatch should be no problem or is it different with SE designs ?
All my voltages are on and the tube tests fine. I don't want to go digging into the windings as I'm sure it will just make things worse.
Should I treat this as a potential weak area and try to correct it or just run only at the correct taps.
Thanks for any input gents.
Marc
Tiny little sparks... in my OT
Moderators: pompeiisneaks, Colossal
Tiny little sparks... in my OT
Heavens, an unused PI input !
Re: Tiny little sparks... in my OT
Well, I'm going to step up and say that if it sparks with a mismatch, then it is sparking when matched, too. At any rate, that tranny is not long for this world.
Most people stall out when fixing a mistake that they've made. Why?
Re: Tiny little sparks... in my OT
I'm going with Rooster on this one--that OT is headed for the graveyard. Probably what happened is the mismatch gave you a high impedance which resulted in some flyback arcing. Once the arcing happens the damage is done--the path for future arcing has been created and it will happen again until it eventually shorts out. It is probably also arcing internally where you can't see it.
Re: Tiny little sparks... in my OT
Thanks for the reply. I was kind of prepared for that.
I guess I will sort out what to replace it with.
Probably will sound better too.
I guess I will sort out what to replace it with.
Probably will sound better too.
Heavens, an unused PI input !
Re: Tiny little sparks... in my OT
If it were me, I'd run it only at the correct impedance. The higher load running mismatched increases the voltage swing when running a big signal (overdrive and full up volume). It's just like a spark plug in a car engine. If you decrease the voltage (running matched), you likely won't generate enough voltage to jump the gap and arc. The amp might run just fine for along time running matched impedance.
Re: Tiny little sparks... in my OT
Is the amp in question the CHB10?
Are you using the Bogen SE output transformer?
Are you using the Bogen SE output transformer?
Tom
Don't let that smoke out!
Don't let that smoke out!