5150 problem

[g1]

Then I guess the schematic we are both looking at is not the right version. You will need the proper one with the layout.
But in the meantime, try to find out why you were not getting bias on the other side of the 220K back in post #34.
Something on the output board must be shorting that line to ground.
And make sure the solder is good at all the power tube sockets.

[Enzo]

C201/202 are going to be tiny things that look like resistors, but are usually pale green instead of resistor color.

[Enzo]

Ah, that answers it all. Those small "100 ohm resistors" are really 100pf caps. That is why you can't find the caps, and they measuer open becuase they are caps. If one of them is shorted, it will kill the bias to those two tubes.

[Valvehead]

ahh!

they certainly look like 100r and have the same color bands

can those be clipped out ?
the reason i ask is i had a mod written down from years back...that said somethiong about removing the 100p caps on the tube pcb ?

[g1]

Thanks for clearing up that mystery Enzo!
So these are what you had previously replaced with 100R 1/4W ? Now one has opened but one is still intact thus killing the bias?
You can clip them for testing, I would guess they are there to prevent oscillation so probably best to replace with proper parts.

[Enzo]

Yes, of you installed 100 ohm resistors in place of them, they would ground off your bias. I don't think the bias supply capable of burning one out, after all there would be a 220k resistor in series with each.

[Valvehead]

ok--ill get her fixed and fired up ! ill post results

[Valvehead]

wow.

still not right..

i clipped out the 100p caps ... i dont have any here..but it should at least idle normal---yes ?

Now , i have a nice steady 44mv bias at each pin 5 .

BUT-- measuring across the OT , shunt , i have 25ma on 1 side and 90 ma on the other...and sure enough...1 tube is starting to red plate....

this is with 4 totally different 6l6 tubes than before .

im going to swap tubes around...but if thats not it....?????????????

[Valvehead]

ok-----

i got real lucky... it was just a power tube.

as far as the shunt readings.......i forgot that some amps like the 5150 wont read even across the ot. My fault .

I just played the amp for 20 minutes and all is well !!!

THANKS to all you for the help---on a serious note---im getting old and alzheimers runs in the family. I find myself forgetting the little things....a lot . Sorry to be a pain in the arse guys !

[tedmich]

did the diode vaporize on the PA board? carbon film can cause shorts and arcing even if cleaned real well

[Valvehead]

forgot to post----- amp is working great now --cheers guys !