Integration problem

[Dr. Exotica]

I am having a problem with the Integration C4S board in one of the four subcircuits - perhaps someone has some insight.

The tale of woe:

• Assembled the Seduction, all checked out, sounded quite nice
• When building the Integration boards, I found out that only two (rather than four) of the 356 ohm resistors were included in the kit. I decided that rather than hassling Eileen for two resistors, I would pick up some at Radio Shack
• A few days later when headed out to work, I briefly checked the manual and thought I needed to pick up some 120K ohm resistors. Stupid mistake on my part.
• I built the boards, connected it all up, and of course the voltage readings were way off. ~25-30Vdc rather than 60-90Vdc (this is from memory).
• After a whopping 5 minutes reviewing what I had done, I realized the resistor mistake.
• I picked up some resistors (had to run two in series to get close to 356) and soldered everything up.
• Three of the four sets of LEDs lit up. Three of the four subcircuits read correct voltages (76-77Vdc).

On the problem channel, I read the following:
[list type=decimal]
[*]0A  102
[*]1A  104
[*]0B  85
[*]1B  104
[*]MJE350-E    103
[*]MJE350-C    103
[*]MJE350-B    102
[/list]
My understanding is that item 2, 4, and 6 should be around 77Vdc in order to match the other three subcircuits on the C4S's.

Any ideas? All looks fine with visual inspection. I hope I haven't fried one of the transistors or LEDs.

Many thanks,
Erik

 

[Paul Birkeland]

The resistor value is 237 Ohms for the C4S R1. 

Your IA/OA are about the same voltage (the IB/OB are in the ballpark).  Can you swap tubes to see if this follows a particular tube?

 

[Dr. Exotica]

You are correct wrt 237 Ohms for C4S R1. I checked my board (brought it to work today) and I have a 220 Ohm resistor in series with a 15 Ohm resistor for R1. Figured 235 Ohms was close enough.

I'll try swapping tubes tonight.

 

[Paul Birkeland]

The other common issue is that the center leg of the MJE350 dissipates a lot of heat, and is a little difficult to solder properly sometimes.

-PB

 

[Dr. Exotica]

PB yells bingo!

Exactly right. I tried rotating the problematic C4S (two symmetric circuits) and swapped the tubes. Looks like one of the 6922's is bad - the wonky voltages followed the tube.

Thought I was losing it with assembly - glad (kind of) it was the tube. First bad tube I've ever had.

Thanks for the help.

Erik