Amp Check and Bias

metalhead3ecr · Post by **metalhead3ecr** » Thu Nov 22, 2012 10:00 am

Is this looking any better?

I ran out of solder for the moment...but the connections will be a lot more solid and shiny when I get some more. Also, is it normal to use the two Mallory 150's there? Should I swap them out?

julkke · Post by **julkke** » Thu Nov 22, 2012 10:14 am

The joints could be better. When soldering, you gotta heat up the component's leg and the turret, and feed the solder to those, not to the soldering irons tip.

I suggest to watch this video, it's really kewl http://www.youtube.com/watch?v=cIDydYIVTqU" onclick="window.open(this.href);return false;

The mallories will be fine.

metalhead3ecr · Post by **metalhead3ecr** » Fri Nov 23, 2012 11:16 pm

I am getting 0 on pins 1 and 8 of the power tubes. Everything else is up to snuff (o.k. readings, fuses are good, DMM is good)...where should I troubleshoot?

I know Curt's amp has some different resistors in this area. Should I change the 47k , 150k, and 15k to what Curt has?

julkke · Post by **julkke** » Sat Nov 24, 2012 4:19 am

Pics? Check those grounds with a multimeter. Are you using 1 ohm biasing resistors?

neikeel · Post by **neikeel** » Sat Nov 24, 2012 5:44 am

metalhead3ecr wrote:I am getting 0 on pins 1 and 8 of the power tubes. Everything else is up to snuff (o.k. readings, fuses are good, DMM is good)...where should I troubleshoot?

I know Curt's amp has some different resistors in this area. Should I change the 47k , 150k, and 15k to what Curt has?

But 1 and 8 of the power tubes are tied and grounded - you are not expecting any volage there (unless as already suggested you arre using the 1 ohm resistors). Remember you are measuring mV across a 1 ohm 1% resistor.

Have you checked pin 5 of your output tubes - you should have approx -40vdc there?

metalhead3ecr · Post by **metalhead3ecr** » Sat Nov 24, 2012 8:01 am

Yes I have the resistor to ground on V4 and V5 but I still get 0. I do have a negative bias on pin 5 after the 5.6k resistors of around -40. The power tubes look rather cold when the standby is flipped...

demonufo · Post by **demonufo** » Sat Nov 24, 2012 8:07 am

What meter do you have and what scale are you using?

metalhead3ecr · Post by **metalhead3ecr** » Sat Nov 24, 2012 8:17 am

The meter is a Cen-Tech P37772 haha it's not a Fluke. And I'm on mVDC.

metalhead3ecr · Post by **metalhead3ecr** » Sat Nov 24, 2012 8:24 am

Here is a pic of the dmm

julkke · Post by **julkke** » Sat Nov 24, 2012 9:08 am

Post a pic of your power tube socket wiring.

metalhead3ecr · Post by **metalhead3ecr** » Sat Nov 24, 2012 12:03 pm

Hope these help. I plan on cleaning all the sockets up today. Kinda tough to see with the Xicon's in the way...

julkke · Post by **julkke** » Sat Nov 24, 2012 12:22 pm

Yeah a bit hard to see. Have you checked with your meter that pins 1 and 8 are getting ground connection?

metalhead3ecr · Post by **metalhead3ecr** » Sat Nov 24, 2012 12:28 pm

Yup. I got the beep of continuity. I did notice I was missing two grounding wires on the 1st stage. I just added them. Maybe this will fix it?

julkke · Post by **julkke** » Sat Nov 24, 2012 12:31 pm

Try it and see. Check everything against a layout again.

metalhead3ecr · Post by **metalhead3ecr** » Sat Nov 24, 2012 1:30 pm

I think that is the ticket! Thanks for all your help. However I need some new preamp tube sockets.Mine are so mangled it's dangerous... Are there ones that can handle my sloppy soldering

Any recommendations?

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