New Build Stereomour II [resolved]

[amritdesai]

Paul,

At D2 I am getting a negative value -2.27VDC. This value is also slowly changing. After a few seconds it has worked its way to -2.05VDC
At A2 I am getting constant 391 VDC.

Amrit

 

[Paul Birkeland]

What voltage do you have at T20?  How about T19? And T34?

 

[amritdesai]

T19: -2.13 VDC
T20: -2.14 VDC
T34: -2.17 VDC

 

[Paul Birkeland]

How about 31?  31 and 44 tie together through one of the little 130 Ohm resistors, then 31 feeds 34 through another one.  You have no B+ at 34, and I suspect maybe no B+ at 31 either, but we know you have high voltage at 44. 

Therefore, it is most likely that there is a loose resistor or a blown resistor that is preventing your Stereomour from working.

 

[amritdesai]

T31: 122 VDC
T44: 434 VDC

Amrit

 

[Paul Birkeland]

Carefully poke at the resistor between 31 and 44 with something that doesn't conduct (chopstick).  I would be willing to bet that it's loose.  Also be aware that you have some voltage on the capacitor at T31 that may not have a convenient way to bleed off.

If the resistor is not loose, try measuring it with your meter to confirm its value (again, be careful of high voltage persisting after the amp is shut down).

 

[amritdesai]

The resistor is not loose.

Going to T31 I am not getting a reading from the 130 ohm resistor. Going to T30 I am getting ~128 ohms.

You are correct the 130ohm 2W metal film resistor going to T31 seems to be blown.

Any other worthwhile measurements to I should take?

I am so grateful for your help! Thank you so much.

Amrit

 

[Paul Birkeland]

I would just replace the resistor, then recheck your voltages.

-PB

 

[amritdesai]

Paul,

I had to replace two of the 130 ohm resistors near the offending area. I rechecked everything and am happy to report the amp is powering up and tubes are glowing. Thank you so much for your help!

After a couple of hours last night listening there was some noise coming from the left channel - the offending channel. It was mostly static with some popping and would grow then disappear entirely, then would come back. I figured maybe a capacitor has been affected based on the irregularity and behavior of the noise.

I listened briefly for an hour this morning - no noise or popping whatsoever. So I'm going to wait a few days before making any conclusions.

Thanks again Paul, your diagnosis was spot on.

Amrit

 

[Paul Birkeland]

I've never had a capacitor present the problem you are describing.  When you have a capacitor issue, it is generally very obvious.

Crackling is most often bad solder joints or a tube that needs to run in for a while.

-PB

 

[amritdesai]

Ha, good to hear! If the noise comes back I'll again re-inspect the solder joints.

Thanks again Paul!