Issue with Crack Voltage [solved]

[lwhitit]

Hi All,

I need some help here as I have hit a wall.

The resistance checks are within spec but here are my Voltage checks:

Terminal Voltage
1 75-90 (89)
2 170 (164)
3 0 (0)
4 170 (164)
5 75-90 (147)
6 0
7 100 (108)
8 0
9 100 (148)
10 0
11 0
12 0
13 170 (165)
14 0
15 185 (187)
20 0
21 206 (211)
A1 90 (147)
A2 0
A4 0
A5 0
A6 90 (89)
A7 0
A9 0
B1 90 (89)
B2 170 (163)
B3 100 (108)
B4 90 (149)
B5 170 (165)
B6 100 (147)
B7 0
B8 0

The LED on 9 is lit but the LED on 3 is not.

I attached a picture of my crack as well

Any help would be appreciated as I have re-soldered and rewired a few of the troubled spots to see if i could fix it but no luck.

[Paul Birkeland]

Are both halves of your 12AU7 glowing?  Most often we see these voltages manifest when the A4/5 connection isn't solidly made.

-PB

[lwhitit]

Are both halves of your 12AU7 glowing?  Most often we see these voltages manifest when the A4/5 connection isn't solidly made.

-PB

Hi and thanks for the reply. It looks like only the back of the tube is lit. I attached photos of both the tube lit and the A4/5 connection so you can see what I see.

[Paul Birkeland]

The long, exposed finger of wire leaving A5 is not such a good thing to have.  If that wire moves down and touches the chassis or the 9 pin socket retainer, you will have a dead amp.

I would recommend cleaning up those connections a bit, and I'd imagine in the process you'll end up with both halves of your 12AU7 glowing.

-PB

[lwhitit]

The long, exposed finger of wire leaving A5 is not such a good thing to have.  If that wire moves down and touches the chassis or the 9 pin socket retainer, you will have a dead amp.

I would recommend cleaning up those connections a bit, and I'd imagine in the process you'll end up with both halves of your 12AU7 glowing.

-PB

I cleaned up all the connections but no change in voltage or the A3 led. Next step?

[Paul Birkeland]

Do you have both halves of the 12AU7 glowing?  (Also, wrap the metal lead of that LED around A3 so it doesn't also short to ground.

-PB

[lwhitit]

Do you have both halves of the 12AU7 glowing?  (Also, wrap the metal lead of that LED around A3 so it doesn't also short to ground.

-PB

If you look at the attachment 283 you can see the tube when I power on the amp (no change since the cleanup). It looks like only one side is lit (barely).

I will clean up the A3 LED since it would not light up I didnt want to play with the LED any more till I checked in here.

[lwhitit]

If you look at the attachment 283 you can see the tube when I power on the amp (no change since the cleanup). It looks like only one side is lit (barely).

I will clean up the A3 LED since it would not light up I didnt want to play with the LED any more till I checked in here.

To give a better view of my 12AU7. Could there be an issue with the tube?

[Paul Birkeland]

Yes, this is quite possible.  We do test all of our tubes before they leave here, but there are occasions where damage occurs.  In this case, I'd imagine that the internal connection the heater on that half of the 12AU7 may have broken off during shipping.

You can e-mail replacementparts(at)bottlehead(dot)com regarding this matter, and we can replace that tube for you. 

-PB

[lwhitit]

Yes, this is quite possible.  We do test all of our tubes before they leave here, but there are occasions where damage occurs.  In this case, I'd imagine that the internal connection the heater on that half of the 12AU7 may have broken off during shipping.

You can e-mail replacementparts(at)bottlehead(dot)com regarding this matter, and we can replace that tube for you. 

-PB

Thanks PB,

I emailed RP to request a new tube. I really hope that is the issue because I have double checked everything and cant figure out what is wrong. I will triple check tonight just to be sure.

[lwhitit]

Hi PB,

Update: I received the new tube today and just tried it out. After plugging it in and turning it on I get the A3 led lit and both sides of the tube lit.

Running through the voltage check everything out of spec looks good now. Sound out of both channels.

Looking at both tubes physically this tube looks much newer. I went through a few LEDs thinking that was the issue but I am happy that I showed you the original pictures to give me advice on cleanup.Going to try this out for a bit and then on to the SB.

Thanks,

[Paul Birkeland]

I'm glad to hear that a different tube fixed the issue.

I still use a fair number of tubes from the 30's, generally age isn't such a big deal

[lwhitit]

Back again PB

Installed the SB and I am getting weird voltage readings. I went back and confirmed all connections and re-soldiered before asking.

3/4 LEDS on big board lit other 4 leds are lit but very low.
Terminal Voltage
1 75-90 (89)
2 170 (164)
3 0 (0)
4 170 (164)
5 75-90 (147)
6 0
7 100 (108)
8 0
9 100 (148)
10 0
11 0
12 0
13 170 (165)
14 0
15 185 (187)
20 0
21 206 (211)

Can you point me in the right direction?

[Paul Birkeland]

Your voltage at T5 is causing all the other problems.  Reheat the middle leg of the MJE-350 on the small board feeding T5. 

-PB

[lwhitit]

Your voltage at T5 is causing all the other problems.  Reheat the middle leg of the MJE-350 on the small board feeding T5. 

-PB

I tried it tonight but no change. I checked the voltage of the three legs on the 350 the middle lag comes in at a lower rate. When checking the voltage touching the middle and either end leg causes the leds to light up bright. What should I try next?