50 Watt lead board kit ?

Gonzo · Post by **Gonzo** » Sun Jan 23, 2005 2:34 pm

I've been assembling the 50 Watt lead board kit I bought from George and was wondering a few things. Which schematic to go by and why the peramp tubes on the wiring guide show 8 pin sockets?

Also V4 & V5 on the amp I'm putting this board in have 5.6K resistors between pin 5 and 6. Should they be removed?

Flames1950 · Post by **Flames1950** » Sun Jan 23, 2005 9:37 pm

How many different schematics do you have? They all are pretty much the same for a 50 watt Lead, only minor differences that come to mind depending on the age of the amp are the bright cap on the Volume I pot (not on the board), the Presence control (not on the board anyway) and different value feedback resistors. Or different bias & bias feed resistors if you're running 6550's vs. EL34's. But the board layout will be the same anyway, just subbing values in.
Didn't you get a schematic with the kit, or is all that info on the CD that everyone is having problems with?
The 5.6K's sound like input grid resistors to the power tubes. Typically 50 watters don't have them, but it won't hurt to leave them either. They are there to help stabilize the amp's output section and may darken the tone a little (you may be hard pressed to hear the diff with or without anyway.) They usually go straight into pin 5, but there's no connection for pin 6 anyway. (Usually the screen grid resistors use pin 6 as a mounting point though; Do you not have the 1K 5watt screen grid resistors? If not, move the 5.6K's and get the 1K's installed instead!! Worry about whether you need the 5.6K's later in that case.)
You can try the amp without them and see if it's OK or just leave them, your choice.
Don't know what to tell you about 8 pin preamp sockets. Are you sure it only shows 8 pins, or just 8 connections (pins 4&5 are connected together in a 12AX7, leaving eight wires to hook up)?

Gonzo · Post by **Gonzo** » Mon Jan 24, 2005 6:36 am

In the 50 watt folder there are two schematics. 1987 and 1959.
The 8 pins shown on the wiring guide preamp sockets must be to show the connections.

This is not a marshall amp I've been working on. It's a layout I got from Huffmans site he calls his Plexi 50 watt.

I was able to figure out quite a bit yesterday.
I had to put 1K 5watt resistors on V4 and V5 pins 4&6 and a 100k on V2 pin1&6 and connect 1 to 7.

The only questions I have now are on V3 .
Pins 3&8 are connected on my amp. Do I leave that?
I had a wire on pin 2 but the wiring guide shows nothing on pin 2.

I don't understand the schematics well enough to figure this out.

Thanks for the help.

Billy Batz · Post by **Billy Batz** » Mon Jan 24, 2005 8:15 am

1987 is a 50W amp.

Your right. Looking at the graphic in my Metro CD the preamp tubes show 8 pins. No big deal. It just leaves out pin 9 which is a heater. You hook up the heater supply to 4+5 and 9 and then you dont worry about it after that when your doing the board.

Yes pins 3 and 8 are jumped.

What wire are you talking about on pin 2? If your referign to V3 again then something definitely should be there. The 2 grids of V3 (2&7) are wired to either of the 1M resistors on the PI. The plates (1&6) come from the 82k and 100k plate resistors on the PI.

Gonzo · Post by **Gonzo** » Mon Jan 24, 2005 4:44 pm

Billy Batz wrote:
What wire are you talking about on pin 2? If your referign to V3 again then something definitely should be there. The 2 grids of V3 (2&7) are wired to either of the 1M resistors on the PI. The plates (1&6) come from the 82k and 100k plate resistors on the PI.

Yes V3.
In the MetroAmp CD go to the 50 Watt(1987) folder and open the Adobe file "board schematics" . Scroll down to the picture "WIRING GUIDE 50 WATT".
Check out V3 .
It shows a green wire from a 1M to pin7 and a green wire from a 1M to pin 3.

In the "iMAGES" folder there is a picture called "50w install picw notes" that has colored print for each connection. On V3,from the 1M resistors it says "green wire to V3, pin 7 and "green wire to V3, pin 2.

That would be the correct wiring ?

That's what's been throwing me for a loop.
I'm not very good at following schematics but it just doesn't seem right. Could that be a mistake?

Sorry to be a pain ...
Gonzo

Billy Batz · Post by **Billy Batz** » Mon Jan 24, 2005 5:42 pm

Yeah its a mistake. Both 1Ms go to their respective grids. The one on the right to pin 2 and the one on the left to pin 7. The 470 goes to pin 8 with a jumper to pin 3.

George your getting an infamous reputation for some of the mistakes on the CDs.

Flames1950 · Post by **Flames1950** » Mon Jan 24, 2005 5:49 pm

Not to kick him when he's down, but I think Gnugear did a lot of the graphics for the CD's.....definitely time for some proofreading and editing.

Gonzo · Post by **Gonzo** » Mon Jan 24, 2005 6:12 pm

I kept comparing that layout to the 1987 schematic (not easy for me) and the way the old board was wired. Never figured it could be a typo.

The BASS and MID controlls are mixed up on that same drawing too.
But I won't mention that. LOL

I'm very impressed with the board kit. That red board looks cool with Sozo's on it.

AS soon as I get my new pots from George I'll be firing this baby up.

Thanks for the help.

Billy Batz · Post by **Billy Batz** » Tue Jan 25, 2005 1:51 pm

There are a few mistakes on the CD but this is another reason you should familiarize yourself with reading schematics. If you have a schematic to go from you dont have to rely on other peoples graphics to know how to wire up pots.

Post by **VelvetGeorge** » Tue Jan 25, 2005 4:27 pm

Duely noted. I'll get on fixing the mistakes.

George