New 36W build, guidance needed

Double-Bubble! Place for discussing the 36W version...

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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

TriodeLuvr wrote:
Tue 12/15/20 8:36 pm
I just want to mention that the design represented in the schematic regarding the grid stoppers is incorrect. I suspect a misprint in the schematic, but regardless, there's no valid reason for the existence of stoppers on only two tubes. Also, to be effective at eliminating oscillation, stoppers need to be soldered directly to the grid pins with the shortest possible leads.
If there's a mistake in the mesa schematic, I wouldn't know. What I can tell you, though, is that the peavey does indeed sport 100R 5W resistors on the screens of two out of 4 output tubes. I can trace that out on the circuit board I have on the bench. It might have something to do with the fact that the peavey allows you to pull two tubes to reduce power. I'm not sure, but I will wire all 4 tubes equal.
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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

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crgfrench
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Re: New 36W build, guidance needed

Post by crgfrench »

Henrik76 wrote:
Tue 11/10/20 3:28 am
...in the Peavey schematic, only one out of two paralleled EL84s has a screen resistor on it! This seems very dubious to me and I cannot see why that would be, unless it's a misprint.
Are you referring to R46 and R55? I agree, it looks like R46 should be shifted down and R55 should be rotated 90 degrees counterclockwise, pivoting at its upper end. Is the circuit actually wired that way? maybe the diagram has errors.
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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

Yup, and it is indeed wired like that. Makes no sense to me, but I guess they must have had their reasons.

Cheers,
Henrik
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crgfrench
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Re: New 36W build, guidance needed

Post by crgfrench »

Huh... well, it's not like 100R does a lot anyway.
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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

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Channel one, input and first stage complete. DC30-ish. Grid load switchable between 68k and 1M.

Cheers!
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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

Progress!
CH1 stage 2, CF and tone stack plus LTP phase inverter.
CH2 5879 first stage also completed.
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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

It's filling up in here. Hope to hear some noise later this week, if the lady of the house let's me work... :wink:
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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

She's alive! hurray
Both channels functional right out of the can. Word of advice: I went in my den to work after nailing a beautiful bottle of red. Had to redo most of that work :? ..... Glad I caught it before I powered her up. Had the pinout on the 5879 all messed up.
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I had to make some significant adjustments in the PS to get the screen voltage down below 300, but now we're at 280, with 395 plate volts. Biased to dissipate 15W per side. Sounds sweet now, but I have yet to add a master volume so I'm very limited as to how far I can go on the volume.
To be continued....
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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

I've tweaked the PS to where the voltages are sensible throughout and I'm happy to report that it sounds excellent, and LOUD!
However, I have more hiss and static than I'm willing to accept, so now starts the tedious process of trying to iron this out without sacrificing tone. It'll be a tough one.
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TriodeLuvr
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Re: New 36W build, guidance needed

Post by TriodeLuvr »

Glad to see it's working! I'm building into a Peavey VK112 combo case, but the original chassis is gone. It's been a challenge to build a chassis this size and to fabricate a front panel almost 500mm (19.5") long. I finished the engraving on front and rear panels a couple days ago, but then my computer crashed. I'm dead in the water until I fix it.

Anyway, I was just wondering where you found the long terminal strips you're using. I have a good stock of terminal strips, but nothing as long as those. That would be handy. Also, did you add the pop rivets holding the parts of the chassis together? If so, are they aluminum or stainless?

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Jack
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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

The pop rivets are aluminium.
The terminal strips are 9-lug items that I found on ebay. Check item no 193375184021.

Cheers!
Henrik
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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

Matchless-inspired master volume and treble cut wired up and working well. Sweet-sounding tremolo added to the 5789 channel. :P
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Henrik76
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Re: New 36W build, guidance needed

Post by Henrik76 »

I was going to attach a **** sound demo, but for some reason, the file format was invalid
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JMPGuitars
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Re: New 36W build, guidance needed

Post by JMPGuitars »

Henrik76 wrote:
Fri 01/15/21 5:14 am
I was going to attach a **** sound demo, but for some reason, the file format was invalid
Post it on youtube or another media sharing service, and share the link here.

Thanks,
Josh
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