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On they go!

Thanks Joe, I have added a couple 120v muffin fans and wired them in series to slow them down, my question is, would it be beneficial in any way to put the metal strips back on the amp that cover the output transistors? I have the covers off for now and the fans blowing right on the transistors

Thanks for the link, I'll see what he says. Id like to have that for my 2000 preamp

I've been considering that. I have a couple I snagged from my local vintage stereo shop earlier this year and I'm glad I did now. I could use those as a go-by. They seem incredibly simple to make, but I know nothing about cabinetry. If I go that route I would also like to make some for my early...

I'm looking for a couple original wood cabs for my PL400s Thanks ! Keith

I got both amps hooked up to my Infinitys and they are rockin'. I gave it the gusto last night and they REALLY sound nice :laughing6: The LED boards are very cool. I love watching the meters dance while on the most sensitive setting. The dimmer comes in handy to get the brightness in both amps...

Well that's embarrassing lol. Joe you nailed it. We're back on track. Bias is now in range. Thanks!!!

Thanks George. I'm thoroughly perplexed now. I've been double checking the quasi BOM, and went back and looked over the baggies that had the optional full comp/ quasi parts to make sure I actually put in the quasi parts. It appears I did. I Reflowed all the solder joints on that side, and...

Everything is the same on both sides except connection 10 and 9 10L is .375 10R is .032 9L is .960 9R is .499

Visually , I'm not seeing an inconsistency, but it doesn't hurt to have another set of eyes looking, do guys see anything?

The bias transistor checks out. I also made sure the leads weren't switched at the control board. I'll start going over the board with a fine toothed comb look looking for an inconsistency between the right and left side of the board. This amp was actually working, so it must have been...

Damn! I whiffed it again. It bought up fine with the variac and DBT. My DC offset # were pretty much a zero on both channels. Bias on the left channel I dialed in about .375v but the right side is much too low, Its about .037v when the pot is in the same position as the left. I must have...

About to shake down my second amp (the '74). This WOPL-ization went by pretty smoothly. Wish me luck. After the 3rd or 4th one I imagine it goes pretty quick. Btw Joe, thanks for pre-bending all of the leads. That is much appreciated.

Sure nuff is! just been too busy headbanging and watching the meters dance. It's a sweet piece. So far so good. The dual voice coil Watkins woofers sound so alive with these amps. Awesome punch and impact.

I think we're there guys! Bias set at .375 both channels I'm digging the LED board!

Joe could do a better job of explaining it but from what I understand the oscillations are more prone to the negative column (2nd and 4th) than the positive column.

Thank you! Yes this is a quasi comp configuration. I have RCA 410s in the bottom row of the 2nd and 4th column (from the transformer).

Damn Joe, you're good! Nope, I didn't. I remember now that I accidentally populated d3 and d4 for full comp, I fixed d4, but missed d3.

I was following the bias setting instructions. Nothing plugged into the amp. Just my DMM hooked to the test points. I turned the bias pots fully CCW, let the amp warm up, 10-15 mins for good measure. Bias is at .415-ish volts on the left channel, and also .415-ish on the right channel. Pots are...

I think the heatsink was just a little bit misaligned, which caused the transistors to go into their sockets and the screws to go in pretty normally. The heatsink was pushed just a little too far to one side and the screw threads would just barely touch it. That's my theory anyway. After I got...