Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Reduction => Topic started by: Dr. Exotica on January 14, 2014, 06:54:05 AM

Title: Integration problem
Post by: Dr. Exotica on January 14, 2014, 06:54:05 AM

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:

• 0A   102
• 1A   104
• 0B   85
• 1B   104
• MJE350-E     103
• MJE350-C     103
• MJE350-B     102

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

Title: Re: Integration problem
Post by: Paul Birkeland on January 14, 2014, 10:19:49 AM

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?

Title: Re: Integration problem
Post by: Dr. Exotica on January 14, 2014, 11:38:13 AM

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.

Title: Re: Integration problem
Post by: Paul Birkeland on January 14, 2014, 11:39:31 AM

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

Title: Re: Integration problem
Post by: Dr. Exotica on January 14, 2014, 03:26:28 PM

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