Help: Right Channel Not Working [resolved]

[lindseyj12]

Thanks in advance for any help with this!

I've had a Crack Speedball for about 4 years now, lightly used. I recently moved, and upon setting her up I discovered the right channel is not working (tried multi headphones and messed with the inputs). I wasn't really sure where to start diagnosing this, so I went through the old instructions and tested the voltages as follows.

Crack Speedball

Small PCB:

Terminal   Spec Voltage (DC)   My Readings:   
OA       60-90V         71
IA       170-270V              174
B-A/B    0V                 0
IB       170-270V              174
OB       60-90V         74

Big PCB:

Terminal   Spec Voltage (DC)      My Readings:
OA       75-100V              103
OB       75-100V              174
G       0V                 0
B+       170-195V              174

Anything else I should check?

Thanks!

[Thermioniclife]

Ok it looks like the small board is good. Do both sides of the 6080 glow? if one side is not that will not let that side of the tube conduct causing the higher than expected voltage you see. make sure all solder joints are sound on the 6080 and do a voltage check on the heater pins on the 8 pin socket.

[Thermioniclife]

It may be best to reflow the solder joints in the amp as it's possible that in the move the amp could have received a bad trip that exposed an iffy connection. Also if you have a spare 6080 you could try that.

[Paul Birkeland]

The wire leaving OB on the big board may be broken, or the wire between that wire and the tube socket may be broken.

[lindseyj12]

Thanks for the responses guys.

I checked the wires from OB -> Terminal 7, and Terminal 7 -> B3, and they are show no issues.

Just reflowed the 6080 terminals, no change. I suspect it may just be the tube. Both sides are glowing, but at the top of the tube one side is glowing bright, and the other not at all. I'm going to order a new one and see if that fixes it.

As for checking the voltage on the heater pins, are there any directions you can point me to? I know the heaters are pins 7 & 8, but I don't know where to measure between, and what voltages I'm looking for.

Thanks!

[Thermioniclife]

Set your meter to ac volts and put one probe on pin 7 and the other on pin 8

[Paul Birkeland]

I would set your meter to beep for continuity, then put one end on OB and the other end on B3 and be sure that it beeps. 

Beyond that you could reflow the transistor solder joints on the PC board. 

It is very unlikely that this is a tube issue.

[lindseyj12]

AC Volts on the heater pins comes up at 5.6.

Continuity between OB -> B3 checks out.

Reflowed transistors, and any other suspect joints on the larger board.

Ordered a tube anyway... itching to experiment...

[lindseyj12]

OK, so the new RCA 6AS7G came in the mail, and it turns out the old 6080 tube was the reason the right channel wasn't working.

That, however, doesn't fix the weird voltage issue I'm having.

My observation, and that of my DAW, is that the volume in the left channel is several db louder and noisier than the right channel. Any thoughts on what might be causing this, and/or where to start looking?

New voltages:

Small PCB: Terminal:    Spec Voltage (DC):    My Readings:    OA 60-90V 70.7 IA 170-270V 176 B-A/B 0V 0 IB 170-270V 175.8 OB 60-90V 73.7 Big PCB: Terminal:    Spec Voltage (DC):    My Readings:    OA 75-100V 101.7 OB 75-100V 99.6 G 0V 0 B+ 170-195V 175.9 Thanks, Lindsey

[Paul Birkeland]

Can you measure AC output voltages with the pot half way up and all the way up? (this is best done without headphones connected, but using a 1/4" to 1/8" adapter in the headphone socket and either a 1/8" TRS to RCA cable to get the measurements or just measuring directly on the jack)

[lindseyj12]

My findings are a little odd... Right has slightly higher voltage at 50% volume, left has higher voltage at 100% volume.

50% Max Vol:
Left: 11 VAC
Right: 11.1 VAC

100% Max Vol
Left: 45.8 VAC
Right: 45.5 VAC

Thanks,
Lindsey

[Paul Birkeland]

11V vs. 11.1V is .07dB.  You can't hear that.

45.8V vs. 45.5V is .06dB.

How are you getting 45V at the pot?  Maybe 45mV?

[lindseyj12]

I've only got two AC settings on my DMM - 200 & 500. I think I was using 200. I used a TRS to Dual TS and tested both tip/sleeves.

I dropped a spectrum analyzer on the return in my computer, and it appears to be a 60hz hum. It may be caused by my other electronic - something I'll try to mess with tomorrow. It's a very audible volume difference and a really obvious difference in my DAW, but I'm not sure if it's as simple as a nearby transformer getting picked up.

Thanks,
Lindsey

[Paul Birkeland]

A meter with 200V and 500V AC ranges won't usually resolve these voltages properly.

[lindseyj12]

I figured it out! The problem was somewhere between the chair and the DMM. . . User error. The left/right balance seems to be *nearly perfect, although I may be experiencing placebo from prior bias.

Thanks for all the help and incite guys!