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EL34's can easily handle far more than the VJr PT's got to give. And without the el84 as a lowest common denominator, you're free to give it all that PT's got. A 100r/5w in R10 would do fine, but you MUST increase C6 to 47uF/450v to get that node's frequency rolloff point below 72Hz you get with 22uF. If you don't, the 60Hz AC hum will be an ugly problem. A 47uF cap will drop the rolloff point back down to around 33Hz, which is where it was with the original combination of 220R & 22uF.



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ah. I have 100uF in there now, but I've got 47uF if that's better.

I've been trying to make sense of the beast/octal/el34 threads at sewatt. but man.. you guys go off on a tangent for post after post..

plus my pc crashed and I had to reformat. so I don't have pdf readability yet... so it's been double nuts!




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Jumper r10. You don't need it.


turretboards.com has a Marshallized octal layout now' date=' under the "vjr stuff" page. I'll try to pull mine apart tomorrow and post up what I've got for values in it, because they're not what's published.






I have one nearly finished.. and another to build.

A 6V6 I made for a guy isn't pleasing him.. so he want's to try an EL34.

I sure wouldn't mind a few hints suggestions or outright ideas to make him happy.

Or me!


I know how hard it is to pul that chassis out and all.. so.. I do make nice pickguards.. and I just got a huge shipment of parts for amps and pedals you might like as a swap!



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Ok, from left to right across the board:


* I went w/the UFs for diodes, but I can't imagine it would possibly matter either way.

R11 = 220k

C6 and C9 = 47uf/450v

C7 and C8 = 22uf/450v

C11 = .1 (this looks like Mallory)

R10 = jumper

R12 = 1k/5 watt

R13 = 1k/2 watt (might as well use 5w here, too)

* Resistor from red wire on rail to pin #4 of el34 = 1k/5watt

C5 = 100uf/100v (experiment with uf rating here, but there's no reason for 1000uf, and 25v is pretty marginal on v rating)

R14 = 220R/5w

R5 = 470k (it looks like I used 1/2w here)

R15 = 1.5k/.5w

* resistors from ground to pins 2 and 7 = 100r/5w

C1 and C2 = .01 (sozo)

R3/R4/R7 = 100k/.5w

R2 = 10k/.5w

R1 = 1m/.5w

R8/R9 = 1.5k/.5w

C4 = 3.3uf/63v

C3 = 22uf/63v



The reason I ended up increasing the wattage ratings of the resistor to pins 2, 4, and 7 on the octal socket is because I had slightly smaller rated resistors in there before, and they went up in smoke with a KT77 tube. Bear in mind that the values that I have on this amp were only tested with an EL34 output tube. I'd caution about using a KT77, frankly, although I will admit that it sounded VERY nice for about a month, until it literally smoked those resistors.


Build it with these values for an EL34, match it with a single 12" Celestion g12h, and it'll breathe fire. VERY touch responsive, VERY gainy, bold, aggressive, and impressive. I continually get rave compliments on this amp, every Sunday night at the jam.

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coinky dink!

I was just on the amp and came in to post questions..

I've got a few things different, for sure.

but I've got everything you list so.. back I go.


This is great.. I think it gives me a much better chance of more effective tweaking than the place I was starting from.


C6 is 100uF now..

there's an R10 in there..

some others are a bit off.. some the same like the 22uF C3.

So.. now it's a matter of minutes before I can see what I like don't.. and even less chance of not liking it.



Thanks very much.


I'm using the MPS 010 OT here.. but I might swap to the Weber WSE15.. I think that's the right number for that.


Cool beans. out I go..

Let me know if you ever need a pickguard, I owe you one on that board anyway.

*ask me about that board sometime via email, heh.*


Thanks a million.


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100uf is fine for c6. I think I went w/2x47uf because I already had them on hand.


My OT is the WSE15. I can't speak to the MPS010.


The key thing that my tech buddy did when I brought it in for bench testing was to get the rail voltage and current up, because the stock PT is a bit anemic and leaves the EL34 a bit starved. That's why we jumpered R10 and fiddled with the other rail resistors. These rail changes increased the power output from around 4.5 watts to almost 7.5 watts. There were some voicing changes made too, to make it more bold.


Run at about 10:00 to noon, and with a good boost/overdrive in front of it for soloing, this is one very serious tone monster.


Let me know if you ever need a pickguard, I owe you one on that board anyway.

That may happen. I'm eyeballing teles lately...

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I have the Weber, too.. so mattndonna says this will handle an el34 ok, I'll try this one, then try the Weber.

Had to switch over to 5K as it was set up for the 6V6.


went pretty well.. I must have done this ok the first build. *L*


I rock tele guards!

So.. lemmee know.



The only thing different in mine right now is I didn't have Sozo is .01, only spragues, so out came the Sozo .022s.


And I was short a 220R for R14, so I found a 3W 240 that tested about 235R.


I tested no tubes and it's right at 393V R10 and down the line.


Working up the guts to put tubes in.

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it'll breathe fire. VERY touch responsive, VERY gainy, bold, aggressive, and impressive. I continually get rave compliments on this amp, every Sunday night at the jam.

Run at about 10:00 to noon, and with a good boost/overdrive in front of it for soloing, this is one very serious tone monster.


that's what you said.

And not a bit of exaggeration.

and I've got spragues instead of Sozos and a chinese power tube.

I could hardly believe my ears.


I can't find that mild hum so far. But I'll get it.

I have a couple of metal oxides in here.. but I thought they would produce hiss more than hum.

No hiss.


I'll put the Weber in and see what's up there.

and I've got 12AT7, 5751 and 12AU7 preamp tubes, I'll probably try them all.


I'm really really pleased with this.

And I appreciate you providing those values for me.. saved me a lot of messing about.


I can't sleep because I can't power it back up.

gonna be fun tomorrow..

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Sprague to Sozo will be noticeable, but probably not overwhelmingly so. I would suspect it'll be rather subtle. I noticed a difference in going from Mallory to Sozo, but again, subtle.


Get R14 to 220R when you can, and you'll squeeze a bit more horsepower out of it.


I've had really good luck with the JJ's, and in fact, had my original tested nearly new after a year in service, at 6-20 hours per week. I do intend to try out some other brands in there as well, but I really can't complain at all about the JJ EL34L.


I'd probably stick with a good, gainy 12ax7, rather than opting for lower gain preamp tubes. For one thing, those tubes have a different frequency response than a 12ax7, but mostly, I think you'll want a hot signal with this amp. YMMV, of course.


If you haven't mounted the chassis in the cabinet, the hum could be because of that.


Congrats on your latest! I think an EL34(L) in this amp is absolutely killer.

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I'll do that. I was surprised there were no 220s in the drawer.


I have to say this chinese tube sure sounds good.. if the JJ is better.. well I bought it for a test tube so.. yay!


I twisted some wires and it reduced the hum. I was being a bit sloppy/quick.. you know me..

I was just sitting right in front of it with the big tv on. and just had to turn a bit to quiet it down. .way loud, too.


And I just put the NFB in.. I was going to add a gain pot. but all I did was drill the hole.

NFB is pretty neat, really, if you want to soften it up. and the Tweed tone put the highs right back in place.



and thanks for the help and the congrats.

I'll go put the gain pot in. I think I'll start with 500K.. but I've got a 300K, too.. maybe that one.


I'm trying to remember.. you can put a resistor on the lead to the pot and that way the gain wont kill the volume when all the way down, if I recall.

I'll try a 10K.


Someone at sewatt said you can put a 5881 in here, with a switch. He said it was somehow better.. I forget.. but I really would have to hear better out of this amp. It's just gangbusters.


The dynamics! Sheesh I thought the EL84 did pretty well but you can get soooo soft with this and bring right back up to lookout!


I know I'm putting an EL34 in mine. Just gotta have it.


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Trouble in paradise..

I was a/b ing this with my modded marshall el84


I'd worked my way up both dials to about 1:00

and forgot to turn down the el34 when I plugged back in..

I was adjusting the tone right after I plugged in..


so I could see. through the little unfilled as yet gain pot hole..


a blue glow. pretty bright..

the power tube is in line that hole.. so you know what R and caps are in that area..


the tube didn't seem to glow at all.. I don't think i'd have missed that it being huge and right there.


so.. I gotta go in. I shut it off immediately.


could just be the chinese tube not being as sturdy as the JJs is reputed to be.



the difference was amazing.. I could not through any trickery or device get the bottom end out of the el84 the other had.

and it's bigger in the room.. steps farther outside the box, I guess you could say.

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through the hole the color was that purplish color like the EL156 on that page.

I reached for the switch too quick to see if the tube glowed too. it seemed at first to flicker as I looked at it.. so assumed I blew an R or the like.


I tried it again just now.. since all the components looked just fine and the wires were all fine solder joints fine.

and it worked perfectly.


could it have been something caused by plugging the guitar in at high volume!


I'll have to wait until tomorrow to run it a lot and see what happens.

guess I'll try it in the dark and keep my camera ready..



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I love to watch that violet cloud grow and fade as I play. Pretty cool actually. I think it was Aspen Pittman's Tube Amp Book had a mention of it. The more it glows, the leakier, or simply more contaminated the gas envelope is, and the sooner it'll die; compared to a tube with a near perfect vacuum where any remaining gas is inert (no violet clouds). But he also said that the ones that have at least a little bit of glow sound sweeter than tubes that don't! So enjoy it while it lasts. :)


Tweed tone oughta work about the same regardless of the power tube, so yeah, you know something's gotta be a little buggered up on that. Probably just the .0047uF cap to ground connection, though. No sweat.



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