67 Superlead/Superbass Board into my JCM800 1959 MKII

Megachunk · Post by **Megachunk** » Thu Nov 10, 2005 10:28 am

That'd be a big 10-4, good buddy.

Megachunk · Post by **Megachunk** » Thu Nov 10, 2005 1:28 pm

Billy Batz wrote: Theres only 2 wires on a 100W or 50W PT go to ground and they both ground at a chassis grounding lug (say one near the filter can in the corner).

On the old PCB, the White goes to the 27K resistor hooked to the solo diode, and the yellow goes to a turret labeled "lamp" that doesn't seem to be hooked to, or have a trace, to anywhere. Just confused as to where the yellow would go...

On the red lead cap that connects closest to the jacks, does one lead run to one side and one to another? Do you cross-connect the terminals? I'll stop now, promise!

Flames1950 · Post by **Flames1950** » Thu Nov 10, 2005 4:17 pm

Part of the reason that some of the 10K's are gone in the JCM800 is that the voltages are lower to begin with. You may find that if you're using a different power tranny than stock that you want those resistors back in place.

White wire is typically the bias supply, yellow grounds as a center tap on Heyboer trannies -- is that what you were using?

Megachunk · Post by **Megachunk** » Thu Nov 10, 2005 6:23 pm

Not using those Heyboers, just stock. I referenced the Heyboer diagram on George's CD. Since the yellow goes to "lamp" which goes to nowhere, I think it's clearing up for me now. I assume on the cap with the red leads by the preamp tubes, one (red lug)goes to one side of the 10K resistor left over and the other (yellow lug) goes to the other end.

Thing I'm wrestling with now is the 1/2 power mod someone did. Took out a speaker jack, put in a switch. Looks like it shuts down 2 tubes. Hate to bother you guys, I know you have amps to build. Thanks so very much, all.

BTW, that your hot rod? Got a 65 Lincoln Continental myself, bone stock, sans paint.

Billy Batz · Post by **Billy Batz** » Thu Nov 10, 2005 7:39 pm

That half power switch doen nothing more then pulling 2 tubes does. Same thing.

Flames1950 · Post by **Flames1950** » Thu Nov 10, 2005 11:27 pm

BTW, that your hot rod? Got a 65 Lincoln Continental myself, bone stock, sans paint.

Yeah, I bought that as a blue rustbucket back in '86. My dad and I had it up on rollers all that winter getting it ready to paint the next spring. So I got a couple of years of high school out of it. It desperately needs a repaint now, it looks good from fifty paces but it's had so many dings and scratches patched up that it's pretty wavy close up anymore, and the lacquer is checking in many places.

Anyway with a stock PT you won't want any extra resistors. I suspect the whole reason for less resistors and less caps was that overall the voltages were low enough by that point that Marshall deemed it safe to use one cap -- where previously they used two tied together and dividing the voltage between them.

Megachunk · Post by **Megachunk** » Fri Nov 11, 2005 10:34 am

Cool man, got it done. Wondering about polarity. Are my atoms backwards? Here's a link to a pick of it so far. See anything amiss?

http://www.surfcitymultimedia.com/metro67.html

Flames1950 · Post by **Flames1950** » Fri Nov 11, 2005 6:50 pm

Yeah, the two 10uF Atoms in the bias section need to face the other way.