Having Issues with Resistance Check

[skyej]

I am putting together a SEX kit for a friend, and have run into some issues. I know it isn't a whole lot of information to go on, but I have included my resistance values below. Hopefully you guys can provide some intuition about my problem! When the volume is at zero, I have resistance issues with 15,25, and A3. However, when I go to full volume, everything checks out except for the input pins. Let me know what you guys think, or if you need any more info. Thanks!

Pin	From Manual	Pot Full CCW	Pot Full CW
right center pin	100k	90k	0.9k
left center pin	100k	90k	0.9k
1	*	4.8m	40m
2	0	2.7	2.7
3	0	2.7	2.7
4	*	6.36m	4.9m
5	*	30m	6.2m
6	*	12m	3.9m
7	0	2.7	2.7
8	0	2.7	2.7
9	249k	249k	249k
10	*	5.5m	40m
11	*	4.7m	28m
12	0	2.7	2.7
13	0	2.7	2.7
14	??	4.1	900
15	890	384	900
16	*	33m	8.9m
17	0	2.7	2.7
18	0	2.5	2.6
19	249k	249k	249k
20	*	12m	5.7m
21	*	10m	4.9m
22	0	2.7	2.8
23	0	2.7	2.7
24	??	4.2	904
25	890	386	900
A1	249k	249k	249k
A2	*	5m	7.7m
A3	680	172	690
A4	??	172	690
A5	*	450k	5m
A6	1.27k	1.2k	1.2k
A7	*	753	752
A8	*	750	756
B1	249k	249k	249k
B2	*	36m	36m
B3	680	690	684
B4	??	228	685
B5	*	450k	7.3m
B6	1.27k	1.2k	1.2k
B7	*	753	752
B8	*	754	754
C1	*	753	754
C2	*	753	752
C4	*	753	753
C5	*	753	753

 

[Paul Birkeland]

The 900 ohm reading from the center pin to ground when the pot is turned all the way clockwise isn't too concerning, seeing that it's 90K when all the way open, there's probably just a bit of error with the meter.

The other variations are terminals that have capacitors "in the way" of getting the most accurate readings, so seeing readings that aren't zero is reassuring.

I'd move onto voltages.

 

[Paul Joppa]

You should have the rev 1.1 manual, June 15, 2012 - right?

The first two lines suggest that the RCA jack center pin is not wired to the "hot" end of the pot, but rather to the center lug. In that case, make sure the other lugs are properly wired as well.

I suspect that A3 and A4 have the same reading because they are accidentally connected to each other. B3 and B4 appear to have the same problem, intermittently. Because of the way the lugs are twisted, it is sometimes easy to mis-read which lug goes with which tube pin. (Not like I ever made that mistake ...  :^)

A4 and B4 are the driver grid, and should be 220 ohms with the volume all the way down, 100K with it all the way up.

 

[skyej]

Awesome. Thanks for the responses! I am going to take a look tonight, and see if I can figure if I crossed A3 and A4. I will also check that my lugs on the pot are correct. I will let you know the outcome.

 

[skyej]

Turns out ALL of the resistance issues were resolved when I fixed the crossed connection between A3 and A4. There was an ugly solder tower that was contacting the side of the resistor between A3,B3 and pin 12,22. I put in the rc circuit tight, and in both the A and B sides, the jacket of the resistor was just barely contacting the the tube pin of A4, or B4. I bent the top of the pin over to the side, and voila, correct resistances across the board. This resolved the input center pin issue, pin 15 issue, pin 25 issue, and obviously A3,B3 and A4,B4 issue. Picture below.

I know how ugly it looks, but I have resoldered about every pin connected to A3,4 at least 3 times trying to figure out what was going on.

Thanks for your help!!! I am going to check my voltages now.

 

[skyej]

It works!!!!! Thanks all for you help. I am going to enjoy this amp now. It's been a long build.

 

[saildoctor]

I like the matte/glossy black look!