New Stereomour: Left channel not working

[wilberforce]

Hi. I just got my Stereomour completed, and kudos to Doc, Paul, Eileen, and the gang--it was fun to do, and the instructions are great.

Here's the deal. It seems that the DMM that Parts Express sells for $5.00 is worthless for voltage testing. At least *I* couldn't get any readings from it, although the resistance checks were fine. Yes, the amp was plugged in, with fuse, tubes got warm (as noted here, it's hard to see a glow in daylight).

I decided to skip the voltage tests since I couldn't get a reading, and hooked it up to a couple of speakers and ran an iPod into it. When turned on, you can hear an intermittent buzzy sound that comes and goes in short bursts from the left speaker. Music only seemed to be coming from the right speaker. I switched the 2A3 tubes to see if one was bad, but still, it was the left speaker with the buzzy bee sounds, and no tunes.

Help! Where should I start looking? Bad solder joint, maybe?

Obviously, I need a better meter--there's a Radio Shack close by, suggestions for a meter are welcome as well.

Edit: just trying swapping the left and right RCA jacks of the iPod cable to eliminate the possibility of a bad interconnect. Still the buzzy bee on the left, and it continues with the volume down, or up.

[Grainger49]

Wilber...

Then the next thing anyone wants is voltages.  Get a meter that works, maybe borrow a good one.  Then post your voltages and the expected voltage.  Giving both voltages allows one to look at the construction of a given terminal or tube pin and see what is there without flipping back and forth to see what voltage should be there.

[wilberforce]

Thanks, Grainger.

I'm now thinking that the problem with the meter was pilot error. This is most technical I've ever gotten, and the little sheet that came with the meter hardly describes how to use it. But I got 1.5 V out of an AA battery, so I think the meter's fine (not the greatest, but I think it will work.

SO. I measured voltages. First number is expected voltage, second one is what I got this morning. Some of it is WAY off, indicated with an asterisk.

Terminal Strips
1   350   373
2   230   200
3   0   0
4   0   0
5   60   63
6   0   0
7   0   0
8   0   0
9   0   0
10   0   0
11   60   0 *
12   0   0
13   0   0
14   230   211
15   350   420
16   60   63
17   380   405
18   0   0
19   380   419
20   60   0 *

Four pin socket
A1   60   63
A2   350   372
A3   0   0
A4   60   63
C1   60   180 *
C2   350   419
C3   0   0
C4   60   180 *

Active load PC board
IA   380   420
IB   380   405
OA   230   209
OB   230   212
Kreg (both sides)   2.5   2.4
-reg (both sides)   0   0

I'm going to look real close at the connections of the output transformer and choke from the C side, but what do I know?

[wilberforce]

I re-flowed the solder on the connections between the OT-2 and terminal 11. Still reads 0.

Anyone? Arggh. This had to happen on the weekend...

[Paul Joppa]

Looks like the "C" tube is not conducting.

First check, does the filament glow? It's not very bright and can be hard to see. If not, make sure the socket is oriented correctly, and the tube is correctly inserted - the filament pins are a bit larger than the plate and grid pins, and should be closest to the hum pot.

Assuming the pins are correct and the heater is getting power, is to trace the connections. C1 and C4 should go to the hum pot through the two 22 ohm resistors, and the hum pot center tap (the adjustable wiper) goes to T20, then through the resistors to T10 which is grounded.

[wilberforce]

Looks like the "C" tube is not conducting.

First check, does the filament glow? It's not very bright and can be hard to see. If not, make sure the socket is oriented correctly, and the tube is correctly inserted - the filament pins are a bit larger than the plate and grid pins, and should be closest to the hum pot.

Assuming the pins are correct and the heater is getting power, is to trace the connections. C1 and C4 should go to the hum pot through the two 22 ohm resistors, and the hum pot center tap (the adjustable wiper) goes to T20, then through the resistors to T10 which is grounded.

Hi, Paul, thanks for chiming in on a Saturday!

OK. Yes, the filament glows (with the lights out and the curtains drawn), and the pins are correct. I had seen posts regarding the polarity issues before I started the build.

I traced all the connections you listed, and they are as they should be. I re-soldered each of them, including terminal 8, but no dice--I'm still getting the same voltage readings. ?

[wilberforce]

I don't know if this will help, but here's some pics:

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi951.photobucket.com%2Falbums%2Fad353%2Fbillwolfer%2Faudio%2FP1010505Medium.jpg&hash=c2989b972577fa7584d7551c51720b099ad33f56)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi951.photobucket.com%2Falbums%2Fad353%2Fbillwolfer%2Faudio%2FP1010506Medium.jpg&hash=bc5daf651aac1d7a7f0c2668f96e09fab9d3931f)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi951.photobucket.com%2Falbums%2Fad353%2Fbillwolfer%2Faudio%2FP1010507Medium.jpg&hash=dbd5fbf8bd8a87c3643a7e354822d088a5eb8bde)

Higher resolution pics are here:

http://i951.photobucket.com/albums/ad353/billwolfer/audio/P1010505.jpg

http://i951.photobucket.com/albums/ad353/billwolfer/audio/P1010506.jpg

http://i951.photobucket.com/albums/ad353/billwolfer/audio/P1010507.jpg

[Doc B.]

I would suggest rewetting A1, A4 and both ends of the cathode resistor.

[wilberforce]

I would suggest rewetting A1, A4 and both ends of the cathode resistor.

Hi, Doc, thanks for the reply. I just now did that, including both ends of both cathode resistors (those are the 1.6k ohm, yes?). No dice. I still get zip from terminal 11, C1 and C4 are reading 201 volts, and A1 and A4 read 61.

[wilberforce]

I must say, it's extremely gratifying, and unusual, to have the designer of the product AND the President of the company helping me on a SATURDAY! Wow, you guys are good!

[Doc B.]

I goofed. I meant rewet C1 and C4. Also make sure that the 4K7 resistor in parallel with the 1.6K resistor is rewetted on both ends.

I must say, it's extremely gratifying, and unusual, to have the designer of the product AND the President of the company helping me on a SATURDAY! Wow, you guys are good!

I have to admit that I'm partly avoiding going out and mowing that 2nd half acre of lawn. Oh, and thanks for that Capital P. ;^)>

[wilberforce]

I goofed. I meant rewet C1 and C4. Also make sure that the 4K7 resistor in parallel with the 1.6K resistor is rewetted on both ends.

I must say, it's extremely gratifying, and unusual, to have the designer of the product AND the President of the company helping me on a SATURDAY! Wow, you guys are good!

I have to admit that I'm partly avoiding going out and mowing that 2nd half acre of lawn. Oh, and thanks for that Capital P. ;^)>

You don't need to mow no steenking lawn, you're the President For Life!

BUT... I resoldered C1, C4, and both ends of the 47k resistor, and still get the same over the top voltages from C1 and C4.

[wilberforce]

I hope at least you have a riding mower for that much lawn. My brother made just one modification to his John Deere: a cup holder for the beer.

[Paul Joppa]

Resistance from C1 and C4 to ground?Voltage at T20 and T10? Including voltage at the resistor wire? And voltage at the middle terminal of the hum pot? And on the 22 ohm resistors? I still think we're looking for a failed solder joint somewhere along that chain, which is why I'm suggesting checking voltages on the wires that go to the terminals as well as the terminals themselves.

Hmmm.... I don't see anything about swapping tubes. Swap the 2A3s, if you haven't already.

[wilberforce]

Resistance from C1 and C4 to ground?Voltage at T20 and T10? Including voltage at the resistor wire? And voltage at the middle terminal of the hum pot? And on the 22 ohm resistors? I still think we're looking for a failed solder joint somewhere along that chain, which is why I'm suggesting checking voltages on the wires that go to the terminals as well as the terminals themselves.

Hmmm.... I don't see anything about swapping tubes. Swap the 2A3s, if you haven't already.

I did swap the tubes, first thing, I thought I posted that.

Voltage at T20 and T10 is 0, look at the asterisks on my voltage post.

Didn't look at voltage on the hum pot middle terminal.

I agree that there must be a failed solder joint somewhere--I was very careful to follow the instructions, and I've been looking at it all day trying to catch something that was mis-wired.

I think that some of these voltages you're asking about are not listed in the manual's checklist, but I'll check them in the morning.

Thanks again for the help--we keep going, and one of these solder joints re-done will be the culprit.