5150 fuse problem

[srv69]

I checked he board to and tried replacing one of the screen grid resistors. When I got the amp hooked back up the main power fuse blew and the only thing that I can think of is that maybe I hooked up one of the jumper wires wrong... can anyone let me know how the brown/blue/red jumpers and black/green/white/orange jumpers are supposed to be connected. Other than that that I tried flipping the red/blue/brown fuse around and it blew the 2amp fuse on the board. I can't think of what else the problem might be though...

Any help would be appreciated,
thanks,
Sam

[Jerry P]

The brown, blue red has the brown going towards the back of the amp. The orange on the other connector goes towards that brown, blue, red connector. I doubt that caused the fuse to blow. If you had those hooked up wrong the amp would have howled real loud.
Jerry

[srv69]

I checked and replaced certain screen grid resistors and I'm still having problems on the 3rd tube socket not drawing any current... are there any other possible problems besides screen grid resistor and tube socket that I could check for maybe on the main board?

[Jerry P]

The tube. The heater circuit not working on that tube socket. A bad connection of some type an open trace on the circuit board. A tube, resistor, or heater problem are the most common.
Jerry

[Jerry P]

If you can take voltage measurements for each of the pins on the tube sockets I can tell you more. If you're not familiar with electronics you might consider taking to to a tech.
Jerry

[srv69]

With no tub in the socket it the voltage read:
1=-1.5mv
2=23v
3=cycled to 130mv then dropped possibly reader error
4=-44.5v
5=447v
6=452v
7=22.95v
8=0v

This was without a tube in the socket, hope this helps... Thanks for the help so far!

Sam

[Jerry P]

It looks like your readings are about right. You have your pins numbered backwards. 8=1 and 1=8. Measure the A/C voltage between the pins you called 2 and 7. The the tube get hot? Can you see the filament glowing on that tube?
You've tried swapping tubes around and it was always that tube socket that had no current draw?
Jerry

[srv69]

the problem follows the socket as far as I have been able to find by switching tubes... the filaments on that socket do glow and appear to be working fine. The ac voltage on pins 2 and 7 appears to be 0vac but I am still getting 23vdc.

[Jerry P]

Hmmmm, well if you read zero volts A/C then your heater for that tube isn't working and that's why you have zero current draw, but, you say it gets hot and you see it glowing so the heater must be working.
I'm totally lost now! At this point there's really nothing more I can offer without having the amp in front of me. I would do this, if your handy with electronics you should look at everything related to that socket. If the others all work fine, that tube works fine in other sockets, then there's no other thing it could be. It has to be something related to just that socket. Maybe the socket itself? Does gently wiggling the tube in the socket with the amp on cause any noise?
Jerry

[srv69]

I ended up going back in and doing a touch up solder job on all the tube pins and somehow that fixed the problem... I guess I just got lucky the second time around.

thanks for all of your help and I hope to have this amp modded by you in the future,
Sam

[Jerry P]

Awesome! I don't remember if I asked this before, are they JJ 6L6's? I've have a lot of problems with the JJ's in the last 8 months or so. They changed to using smaller pins on their tube bases and they don't make a good connection in the 5150 power tube sockets. I've seen a lot of problems with tubes not working and noises. I use Svetlana or TAD 6L6WGC-STR in the 5150's now.
Jerry