Right Channel Issue, Continued...

[Jameson]

After grounding issues I saw in this thread, I ran a new pair of orange twisted wire parallel to the CAT5 already in place from the right input jack to the potentiometer which seemed to resolve the issue. Then I went away for two weeks for work, came back, and had an even worse sound problem on the right hand side.

I ran all the resistance checks. Everything was fine except the middle pin of the RCA jack. I reflowed that joint, which didn't solve the problem. I replaced the other orange pair from the tube to the pot and that didn't solve it either. At this point I'm wondering whether it's the pot or RCA jack itself, or if I've had a run of broken CAT5, or if I am truly garbage at soldering or what.

 

[Jameson]

Here's a SoundCloud link to the sound that was coming out of the right channel. This was a cheap set of headphones with nothing plugged into the amp's input recorded by my iPhone. The noise started right after the LEDs on the C4S lit.

 

[Paul Birkeland]

What is the resistance reading that you are getting that's concerning? 

Some of your joints could indeed use a little extra solder/heat.

 

[Jameson]

At the center pin on the right RCA the reading was over limit.

 

[Paul Birkeland]

What reading do you get between the outer pair of lugs on the volume pot where the orange wires land?

 

[Jameson]

On the A side: 1 ohm. On the B side: over limit

 

[Paul Birkeland]

1 ohm is not really a possibility for what I'm asking for.  Maybe this will help.

 

[Jameson]

Ah, ok. Sorry.

96.7K on the top lugs, over limit on the bottom (orange) lugs.

 

[Paul Birkeland]

That indicates that your pot is damaged and needs to be replaced.  It is very difficult to damage a potentiometer, but occasionally crud can get inside and destroy the wiper or excessive tugging on the lugs can disconnect them from the carbon track.

 

[Jameson]

Thanks, PB.

I’ve had weird balance issues from day one - including a tube that was damaged. What are the chances all of those things are due to the pot being damaged?

 

[Paul Birkeland]

That's very difficult to say.  Tubes are incredibly resilient and will often tolerate issues like this without any complaining.

 

[Jameson]

Got it. Ordered a replacement.

In the meantime, does the Stereomour stock kit use the same pot? Could I scavenge that while waiting on the replacement to ship?

 

[Paul Birkeland]

Yes, just be sure to use the pot that says "A100K", not "B100K".

-PB

 

[Jameson]

Thanks, PB.

If I make it out to Seattle I owe you a nice bottle of something.

 

[Jameson]

Alright, well... I'm still seeing issues. The left channel is fine, but the right channel sounds like it's under water. Very muffled. If I poke around, the only thing that is making noise is the pins toward the front of the chassis.

Here's what I've done so far.

• I scavenged the A100K pot from my Stereomour kit and installed it.
• Replaced the orange striped pair from the pot to the tube and the terminal strip.
• Reheated the joints on any pin that made noise when I poked it, specifically A8, A9 and A10.

I'm kind of at a loss at this point. Am I missing any potential causes? Should I just rip out the right side around the tube and start over?

Also - I emailed the replacements address a couple of times and haven't gotten a response. Not really in a hurry, but I want to make sure my emails aren't getting sent to spam.

 

[Paul Birkeland]

Recheck your voltages and resistances.

 

[Natural Sound]

Jameson, sorry if this is obvious but did you try swapping the tubes from left to right? Also, I've had a few 6FJ7's with steel pins that were kind of cruddy. Sometimes removing and replacing the tube solves this. Other times I've used Doc B's' "Cotton Swab chucked into an electric drill with a little metal polish trick" to clean up the nastier oxide examples.

I wouldn't go "ripping anything out" at this point if I were you. A more systematic troubleshooting approach like PB has been helping you with makes more sense.

 

[Jameson]

Resistances were all good. Right input pin was 93.2K, left was 94.8K.

Voltages were also good:

Terminal	Manual	Observed
2	65-95	80.2
3	15-18	18.8
4/5	0	0
6	385	378
7	400	406
10	380	383
16	65-95	79.5
17	15-18	16.8
18/19	0	0
20	385	384
21	400	410
24	380	390
H2, H5	+/-2.8-3.2	3.3, 3.31
H4, H7	+/-2.8-3.2	-3.13, -3.14

 

[Jameson]

Jameson, sorry if this is obvious but did you try swapping the tubes from left to right? Also, I've had a few 6FJ7's with steel pins that were kind of cruddy. Sometimes removing and replacing the tube solves this. Other times I've used Doc B's' "Cotton Swab chucked into an electric drill with a little metal polish trick" to clean up the nastier oxide examples.

I wouldn't go "ripping anything out" at this point if I were you. A more systematic troubleshooting approach like PB has been helping you with makes more sense.

I was a slight bit dramatic. I’m a little frustrated after having been at this a few hours.

It hadn’t followed the tube when I checked yesterday, but I didn’t try again yet. I’m give it another go tomorrow

 

[Paul Birkeland]

If that doesn't resolve it, let us know and I can write up a set of instructions for installing jumpers through the amp.  This should at least narrow down the problem area.  I can also give instructions for tracing a 60Hz AC signal through your amp with your multimeter.

-PB