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81

Tube Amp Building - Tweaks - Repairs / Re: Mixing Resistors

« Last post by sluckey on March 07, 2026, 03:16:43 pm »

So, next question: if I input each of my channels separately into the two grids of an LTP phase inverter, do I need mixing resistors?

No mixing resistors are needed because the mixing takes place inside the LTP PI tube.

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Tube Amp Building - Tweaks - Repairs / Re: Mixing Resistors

« Last post by dickjonesify on March 07, 2026, 02:49:25 pm »

So here’s a different angle on mixing two channels. I decided to convert this amp to a LTP phase inverter. When reading up on how they work, I learned the grid of the ‘bottom’ triode can be a 2nd input, often for another channel. I had to look around but found a few examples of that. Here’s one from Sluckey’s 18 watt Marshall…



In every case I’ve seen, there are no mixing resistors in this setup. Except that there’s always a post tone stack volume control on both channels right before the phase inverter, which counts as a resistor, unless they’re cranked all the way up I guess haha.

So, next question: if I input each of my channels separately into the two grids of an LTP phase inverter, do I need mixing resistors?

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Tube Amp Building - Tweaks - Repairs / Re: 6V6 JCM800 channel switch

« Last post by JGk on March 07, 2026, 01:16:39 pm »

Thanks so much sorry I over looked the first reply. 

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Tube Amp Building - Tweaks - Repairs / Re: Peavey Classic 30 - Update

« Last post by BrianS on March 07, 2026, 12:07:57 pm »

Not that it helps at all, but I learned a long time ago that these folded circuit board Peaveys are a time sink and not worth repairing. They aren't made to be serviced at all.  I won't work on them in my shop.
Good luck!

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Tube Amp Building - Tweaks - Repairs / Re: Ever seen a shorted Orange Drop?

« Last post by BrianS on March 07, 2026, 12:04:10 pm »

I'm sure you are correct as to why it failed, and that was my assumption as well.  When I took the back off the amp, I noted that the size 22 solid core speaker wires were not connected the speaker at all, and when they were, it looked like they were just hooked around the speaker connections with no solder.
I plan on replacing the cap with a .0022uf, 1200V rated ceramic cap.  I am going to assume the folks at Gibson added the cap to help remedy some issue with the frequency response or tone shaping of the amp. The customer claims this is their favorite amp, and I want to minimize the changes to the circuit to just what they asked for.
To minimize the chance of the speaker coming disconnected, I have attached longer, more robust speaker wires & properly fitted Quick Connect terminals.

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Tube Amp Building - Tweaks - Repairs / Re: Peavey Classic 30

« Last post by sluckey on March 07, 2026, 10:57:40 am »

I don’t understand the diodes CR6 and CR4.

Those high voltage diodes (typically 3KV) are protection diodes. They will prevent high voltage flyback pulses from damaging OT, tubes, and sockets in the event that the speaker is not connected.

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Tube Amp Building - Tweaks - Repairs / Re: Peavey Classic 30

« Last post by bbmade on March 07, 2026, 10:34:39 am »

I know the amp should get new filter caps but it seems like it’s in the V7 circuit somehow.  I’m already to the point in time where it doesn’t make economic sense to service this amp.  I’m wondering what the diode on the plate of V7 and V5 are there for.  I see the plates are coupled to the OT but, I don’t understand the diodes CR6 and CR4.  I’ll be pondering this until next week when I have time in my shop again.

I did a service on one of these a couple of years ago.
The crackling sounds familiar..
What I did then was to change all the electrolytic caps in the PS. Those were originally some shitty chinese ones. I replaced them with mostly Rubycon caps. This amps sounds amazing!!

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Tube Amp Building - Tweaks - Repairs / Re: 6V6 JCM800 channel switch

« Last post by sluckey on March 07, 2026, 10:25:18 am »

Hi doing a JCM800 6V6 on an old chassis I have that has a single input and I would like to use a switch to go between the high and low outputs instead of re-drilling the chassis. I was wondering if anyone had build one and had a schematic or a layout available.

I answered this three days ago in the "6V6 JCM 800 build: re-tasking old build" topic.

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Tube Amp Building - Tweaks - Repairs / Re: 6V6 JCM800 channel switch

« Last post by dickjonesify on March 07, 2026, 10:22:06 am »

There’s a page in Sluckey’s Amp Scrapbook for that. You’ll still need a hole for a switch, though.

https://sluckeyamps.com/misc/Amp_Scrapbook.pdf

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Tube Amp Building - Tweaks - Repairs / Re: Princeton-ish Reverb design - 12AT7's and Sand!

« Last post by sluckey on March 07, 2026, 10:10:51 am »

Do you have the schematic in a more visual format?

Here you go...