Completed sex kit: No sound from right channel

[Paul Birkeland]

Woah, pull the C4S boards and put the plate load resistors in.  It's really important to have a working kit before installing the upgrade.

When you say "it blew", what blew? How did it blow?

 

[mpent]

The 220 ohm resistor at B1 and 19. When I went to measure the voltage at b1 as soon as I touched te terminal with the red probe the terminal popped with electricity and the resistor blew.

 

[mpent]

I'm kind of discouraged and really confused. The unit was working before i installed the upgrade and after. Voltages were withing range overall including those for the upgrade but clearly that right hannel issue remained an eventually got worse. But i have no clue why it now seems to be falling apart. I will pull the C4s board and replace the resistors that were removed to install the upgrade then repost.

 

[Doc B]

It sounds to me like a good evening to take off from working on the amp. Coming at it fresh will often give you a new perspective.

 

[Paul Birkeland]

Put a piece of wire in place of that 220 Ohm carbon composition resistor, then let us know about your voltages.

If the amp was working pre-C4S, then go ahead and leave that in.

-PB

 

[mpent]

The wire is already in there as you previously suggested. Just to be clear I soldered in a piece of black hook up wire from B1 to 19 in place of the 220 resistor. The voltages I got in both terminals fluctuated in the 60s.

 

[Paul Birkeland]

Just for the sake of curiosity, remove the 0.1uf cap on that channel, then recheck the voltage at 19.

-PB

 

[mpent]

After removing the .1uf cap from the circuit I checked the voltage at 19 and it rose steadily, slowing down a but at 200 but continued to rise until 251 at which time I pulled the lead of the meter off the terminal. Presumably it would have continued to rise.

 

[Paul Birkeland]

There are really two options here:

1.  The 249K resistor is not connected or not working - measure it and really be sure it is properly soldered in place.
2.  You have a badly defective tube and this problem will move to the other channel if you swap the tubes.

I'm pretty sure you've tried both of these, but I would triple check this.  There should just be the wire leaving 19 and going to your tube socket, and the 249K resistor going to ground on that T-strip.

-PB

 

[mpent]

Checked the resistance on the 249k and it reads well. Switched the placement of tubes and the issue went to the left channel. Voltage on pin 9 was steadily rising into the 300s. Voltage on pin 19 was fluctuating in the 26 range. So what next???

 

[adamct]

Based on Paul's last post, it sounds like you've got a bad tube. Get a new one and you could be all set.

Best,
Adam

 

[adamct]

You can contact Eileen to request a replacement.

 

[Paul Birkeland]

So when you swap tubes, you still get DC voltage at 19?  Do you also get DC voltage at the same position on the other side of the amp?

-PB

 

[mpent]

Yes. The voltage reading at 19 was fluctuating in the 26 range. With the red lead clipped onto terminal 19 it was reading 26 with the fluctuations in the tenth of a point...26.3, 26.8, 26.5 etc.  Terminal 9 was  giving me a steadily rising reading into the 300s.

 

[mpent]

So, PB, what do you think?

 

[Paul Birkeland]

Set the tube that you believe to be the culprit to the side, try listening to each channel, shutting the amp off and moving the good tube between channels just to be sure this is the issue.

-PB

 

[mpent]

So yes it was definitely a tube issue. I got a replacement tube, put it in and there was a firework show inside the replacement when I switched the amp on.  My guess is that tube was bad as well. Luckily, I ordered a couple more replacements off eBay. I removed the C4S board and replaced the 150k resistors. Previously, one of the LEDs went out so I wanted to just kind of start fresh and deal with the C4S after I get the amp working properly. So now, 2 new tubes in there. Voltages have improved.  Voltages that are off:

A1-36
9- rapidly fluctuates bet 45-52
B1-18
19-rapidly fluctuates bet 18-21

No sound from right channel. If I turn the gain all the way to the max, sound then kicks in at right channel

 

[Paul Birkeland]

Now is probably a very good time to post a photo of the socket wiring on the side having issues.

-Paul

(don't throw any new tubes in there until you post this photo, fireworks indicate a pretty serious problem)

 

[mpent]

Both a and b sockets. Not sure if these pics will be good enough.

 

[Paul Birkeland]

It is very, very, very important that two bare leads which do not connect to the same terminal do not touch each other inside the amplifier.

In your first picture, I see several places where this is occurring.

I also see things like the STP going to tube socket pins 7/8 on the right side going up and over the 8.2K resistor.  If that piece of STP pushes that resistor into the chassis plate, it will vaporize the resistor with a loud bang, and possibly damage the other components.

I would suggest going back to the manual and attempting to mimic what is shown in the manual as much as possible. 

One short that I see in particular would cause fireworks inside the tube.

-PB