I just installed a board in a newer RI w/ FX loop...HELP!!!!

77custom · Post by **77custom** » Thu Mar 30, 2006 10:17 am

This is not a repeat!!!! But I did install a 2203 board in my 2003 1959 reissue. The amp is working but, I have a loud buzz coming out of the speakers. It sounds like a ground problem, but I found that my heaters are running way high. 53 vac way high!!! Here's waht I have on V4

Pin 1+8- 0
Pin 2 + 7- 53 VAC
Pin 3- 438
Pin 4- 431
Pin 5- -38
Pin 6- 435

The reissue has a hum balance on the heater. I DID NOT install it on the PTP board. Do I need to ? Is this the reason I'm getting the buzzing and hi voltage? GEORGE!!!! Did you install the hum balance on the 1959 reissue you converted?
Help Please!!!

I'm at work at the moment and will not be with the amp until 9:00 p.m. est.

Thanks,

Ed

Billy Batz · Post by **Billy Batz** » Thu Mar 30, 2006 10:22 am

You dont need a hum balance but if Im not mistaken if it had that then the heater winding probably isnt center tap'd. So you have to use 2 100ohm 2W resistors to ground form each side of the 6.3v winding. You can do it on the V1 socket even. Just add the resistors to pins 4 and 9 and puot them to ground via a grounding lug on one of the socket mounts or board mounting standoffs. Without some ground reference the AC will not cancel out the noise and you will get hum and oscillation.

The closer in exact value the 2 100ohm resistors the better. In fact thats what the hum balance is. It replaces one of the resistors with a pot so you can dial it in exact to the other resistance. BUT with a pot it can slip or work itself out or any number of mechanical problems. 2 1% metal film resistors are more then enough.

77custom · Post by **77custom** » Thu Mar 30, 2006 11:26 am

Thanks Dan!!

That makes sense. Well if all goes well, I will be using the amp this weekend. One more for you. There is a center tap coming off of the transformer. Is it possible to use it? (Right now it's just soldered to a turret going nowhere. That's how it was set on the reissue board too). What is involved in this situation?

Thanks again,

Ed

Billy Batz · Post by **Billy Batz** » Thu Mar 30, 2006 1:22 pm

Center tap to what? How do you know its a center tap is it in a group of 3 wires? I dont really know enough about the newer RIs to say for sure. I believe both bias leads go to the board in them. Where was it at on PCB before you replaced the board? What was it attached to through the traces?

77custom · Post by **77custom** » Thu Mar 30, 2006 2:46 pm

Billy Batz wrote:Center tap to what? How do you know its a center tap is it in a group of 3 wires? I dont really know enough about the newer RIs to say for sure. I believe both bias leads go to the board in them. Where was it at on PCB before you replaced the board? What was it attached to through the traces?

Well, assuming Im correct. The schematic shows the wire with a no connection abbreviation (N.C.) Then on the physical board a green wire is coming out of the transformer and was soldered to a turret that has no traces to it. So I believe it is a dummy turret and I also believe it to be the center tap for the filiment. Try this link to Dr.Tube. The No connection filiment tap is located in the bottom right of the schematic. E5 location.
http://www.drtube.com/schematics/marsha ... -60-02.pdf

Billy Batz · Post by **Billy Batz** » Thu Mar 30, 2006 4:01 pm

It looks like grounding it should be it then

77custom · Post by **77custom** » Thu Mar 30, 2006 4:30 pm

Here's a picture of the board lower right corner of the board GN11

77custom · Post by **77custom** » Thu Mar 30, 2006 10:21 pm

Well, it's 10:20 est. I'm happy to announce the amp is now working properly. No unwanted noises, the effect loop works fine. I haven't had the opportunity to open it up yet. But, tomorrow will be gig #1 with the new and improved conversion.

Dan, I especially want to thank you for taking the time to explain a couple things to me. It really helped. If I was computer recording able I would record some stuff but at the moment I am only able to learn one thing at a time and that is working on/trying to build/mod amps. It's a great feeling when you take something apart and put new stuff in it and have it working in the end. I know it's not always going to be a smooth road, but working on amps and guitars is something I really enjoy. I hope to be able to learn more from all of you here at the Metro Amp Forum

Thanks again,

Ed

Bainzy · Post by **Bainzy** » Fri Mar 31, 2006 7:19 am

What's the extra .1uf Sozo cap for? Every Marshall I've seen has either 1 or 3 on the circuit board, yours has 2.

Billy Batz · Post by **Billy Batz** » Fri Mar 31, 2006 7:46 am

The presence cap is on the board

Bainzy · Post by **Bainzy** » Fri Mar 31, 2006 8:29 am

Thought it might be something like that. I guess that explains why my presence pot had no caps on it when I took out my PCB and fitted the PTP board