Completed Stereomour—left channel crackles/pops/hisses/distorts [solved]

[Paul Birkeland]

I would triple check the 220 Ohm stoppers, you may have a broken one.

To be safe, you can replace them with easily sources carbon film resistors between 10 and 1000 ohms of whatever wattage you happen to find.

PB

[funandfunny20]

Hello!

I tested the resistors and both measured 220 and 230 respectively.  This leads me to believe that they are no burnt out.


Any other suggestions?

Thanks….sorry for all the bother. 

[funandfunny20]

Just tried another resistance check—terminal 14 reads 0. 



Any ideas as to what I should check next?

[Paul Birkeland]

If terminal 14 reads 0 Ohms,  then you'll get no left channel.

If terminal 14 reads 0 Ohms, then OA will be 0V.

I would suspect a wiring error at the 9 pin socket, or contact between pin 6 on the 9 pin socket and pin 5, or potentially contact between pins 6 and 7 (less likely).

-PB

[funandfunny20]

Okay,

Just got home a measured the amps…there are a couple of odd measurements.  The amp's right channel currently crackles/distorts like a bad tube.  So, I switched the tubes and the problem still persists on the same side.

Resistance:
T1 *; T2 *; T3 0; T4 248.4; T5 1.406; T6 0; T7 107k; T8 0; T9 97k; T10 0; T11 1.64; T12 248; T13 0; T14 *; T15 *; T16 1.18; T17 *; T18 0; T19 *; T20 1.18; A1 1.19; A2 *; A3 248; A4 1.19; C1 1.4; C2 *; C3 248; C4 1.4

The one's out of spec are C1 AND C4.

Voltage:
HV+ 398;
T1 370;   T2 195;   T3 0;   T4 fluctuates around 0;   T5 61;   T6 0;   T7 0;   T8 0;   T9 0;   T10 0;   T11 60;   T12 fluctuates around 24.0;   T13 0;   T14 220;   T15 369;   T16 60;   T17 398;   T18 0;   T19 398;   T20 60;   A1 61;   A2 368;   A3 fluctuates around 30.0;   A4 62;   C1 61;   C2 370;   C3 fluctuates around 40.0;   C4 61;   IA 399;   IB 399;   OA 199;   OB 220;  KREGS 2.48;   -regs 0. 



T1 *; T2 *; T3 0; T4 248.4; T5 1.406; T6 0; T7 107k; T8 0; T9 97k; T10 0; T11 1.64; T12 248; T13 0; T14 *; T15 *; T16 1.18; T17 *; T18 0; T19 *; T20 1.18; A1 1.19; A2 *; A3 248; A4 1.19; C1 1.4; C2 *; C3 248; C4 1.4



What do you guys think?

[Doc B.]

I think you may have a bad solder joint somewhere in the right channel side. Try reheating the connection associated with the right channel 2A3 and wires from the 12AT7 that go to that 2A3.

[funandfunny20]

Thanks Doc…it appears the issue is solved—the amp is working!

However, I'm slightly skeptical of my work, so I'll post back later if the amp stays working tonight and tomorrow.  Crossing my fingers.

[funandfunny20]

So, I'm still having issues.

About every couple of minutes the amp pops and cracks loudly on the right channel.  When you tap the amp, it pops/cracks.

This is definitely a sign of a loose solder joint somewhere, correct?

I've resoldered everything associated with the right's socket.  Meaning, A1-4, Terminals 1-5 have all been resoldered.  I know it's a definite shot in the dark, but should I resolder any other areas of the amp?  I feel like I've thoroughly gone through the C4S board.

Any help would be greatly appreciated. 

[Paul Birkeland]

About every couple of minutes the amp pops and cracks loudly on the right channel.  When you tap the amp, it pops/cracks.

This is definitely a sign of a loose solder joint somewhere, correct?

Yeah, you're spot on!

Run it with a cheap speaker hooked up to it, then start gently poking and prodding with a wooden chopstick to determine where the funky joint is.  (It will force a pop when you it it)

Do not hesitate to poke the transistors on the C4S board, one of them may be the culprit as well.

[Doc B.]

I see Peebs was typing at the same time -

Yeah if you have eliminated a tube as the cause it's most likely that there is a connection that is getting flaky as the amp warms up. That would have me looking for two wires that might be a little too close together and making contact when they expand as they get warm, or a wire soldered thru a terminal that might not have a really smooth fillet of solder between the wire and the terminal. Sometimes a joint that looks like that actually has a layer of flux inside the joint that is breaking the continuity.

Just as a general example a very nice customer came by this week with a very nicely built Crack. All voltages were good and LEDs lit, but he was only getting sound from one channel. It turned out that tucked under one of the Speedball boards there was a wire with the insulation pulled back a little more than average, and it was just barely brushing the terminal next to the one it was soldered to. It took me a couple of tries to find it by poking around with an unsharpened pencil. When I touch the wire or the things connected to it it made some gnarly crackles (which is why we troubleshoot with $20 headphones!). I reshaped it a bit to make sure it wouldn't touch anymore and we had two channels playing.