Please forgive me... A blasphemous question

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ricks57custom
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Please forgive me... A blasphemous question

Post by ricks57custom »

Hi all,
I have been playing my TW schematic A4 clone for a few months now and I realize that it's just not me. :cry: I never thought That I'd be upset about so much gain. I play it and then my Marshall plexi and I realize I like the warmth that doesn't seem apparent in the Wreck.

Anyway, my question is this:
I was thinking about converting it to a JTM45 (preamp and filtering) but keeping the Heyboer trannies. Do you guys feel this is easily done, minus a few changes (components, rebiasing, etc) or is the trnasformer set not appropriate for this kind of change. Also, would KT66 tubes be out of the question.

Thanks for the help guys,
Rick
gnugear
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Re: Please forgive me... A blasphemous question

Post by gnugear »

I'm a little worried about this too. I haven't built my wreck yet but I've heard that they're super bright. Maybe you could make it more like a Komet instead? They don't seem to be quite so bright.
Moose
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Re: Please forgive me... A blasphemous question

Post by Moose »

Before you completely rewire the thing:

Look at your speaker compliment. I prefer G12H for 1 or 2 drivers in an open back. Greenbacks are great in a 4x12 closed back, but too bright for my taste alone. I've heard others have good luch with things like Weber's version of the Fanes. Whatever it is, consider how the cabinet responds as this IS a bright amp, but I suspect the circuit was tuned for old style Marshall 4x12 cabinets.

Try changing the slope resistor on the tonestack. This helps sometimes.

Try changing the bypass cap on the first stage cathode to something lower. around 1uF. I know it sounds counterintuitive, but sometimes less is more.

Obviously, monkey with values of the coupling caps. Especially the .1s at the PI and the .02s at the power tubes. More means more bass -- but too much will actually make it seem LESS bassy and more mushy on the top end.

Try 6L6 or KT66 in the poweramp with the rest of the amp as is. You'll need to rebias and you might find a different value grid resistor and/or screen resistor will help control them, but each of these tubes gives a warmer and more punchy bottom end tone, and they both have a lot less sizzle on them when compared to EL34s. I'm personally fond of KT66s.

You could even try a switch to go from fixed to cathode bias. This amp is bright, but not super bright so it'll hurt you. It's voiced as a lead amp and has a voice that will cut through the mix. It is also VERY pumchy with that super stiff power supply. If you want more rhythm tone, a cathode bias scheme will provide a darker and slightly softer and more compressed tesponse. This might help a lot.

Any one of these mods is easier than switching the preamp all around to get it JTM45ish, which is why I thought I'd throw them out there. The trannies WILL handle KT66s, but just barely. They're about 45watts worth, so keep the voltages below 430 and keep the screens controlled and you'll be OK. Don't try for maximum power or anything.

For Gnugear -- consider a liverpool. I experimentally discovered that poweramp circuit. I hated my 18watter and started swapping components and when I was mostly happy it was almost identical to the values in the liverpool. The amp I did this on does NOT sound like an express, but damn is it responsive. Came out similar in wattage to an express, but really sounds like a super fun to play marshall with some extra harmonic content. Ever since, I'm jonesing to make a full liverpool and compare it directly to an express -- alas it is on the long list of amps I want to build and I haven't done it, but I am sure it's a great option for those who are averse to the lead voicing and no-compromise philosophy of the Express.
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LeftyStrat
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Re: Please forgive me... A blasphemous question

Post by LeftyStrat »

Those transformers should be fine for a JTM45. Your B+ will be lower than a traditional JTM45 (my JTM45 has about 460 on the plates), so you may loose some volume (which probably isn't a bad thing).

6.6k taps on the OT would be perfect for KT66's, though the 5k might sound good if you want to experiment with the transitional JTM45 that used EL34's.

Take a look at the Germino Club 40:

http://www.germinoamps.com/products.htm

Your B+ would be similar, there are some tasty clips of this amp here:

http://www.germinoamps.com/soundbytes.htm
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Funkalicousgroove
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Re: Please forgive me... A blasphemous question

Post by Funkalicousgroove »

I've built a couple of KT66 powered Express inspired amps and like them very much, you could also add a switch to bypass that 3rd gain stage so that you can get clean as well as grit-
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ricks57custom
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Re: Please forgive me... A blasphemous question

Post by ricks57custom »

Thanks for the help everyone.

Moose I aprreciate you alternate solutions. My problem isn't so much a bright issue as it is a gain and feel issue. It doesn't clean up much (which I knew about but didn't realize was so important to me) and I find the sound fatiguing to my ears. I have really been falling in love with the sound of a JTM 45 lately and since this is my testing amp I thought I'd give it a shot. Good news about the KT66s. I'm also thinking of of putting in a DPDT switch for tube/diode rectifier.

Dumb question: I've only got one input for the guitar. That means I only need to use one half of V1 for the input, right?
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LeftyStrat
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Re: Please forgive me... A blasphemous question

Post by LeftyStrat »

ricks57custom wrote:
Dumb question: I've only got one input for the guitar. That means I only need to use one half of V1 for the input, right?
That's correct, but you may consider wiring both halves up and sending the single input to both jacks. Most every that plays a JTM45 jumpers the two inputs. Especially when playing a strat. If you have room you may consider a switch.

If you decide to only use one half, use the second triode, the second half tends to be quieter (or so I have been told).

There is also a jtm45 group on yahoo groups you may consider joining. They have a lot of good schematics, layouts, wiring diagrams, etc. in the files section.
ricks57custom
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Re: Please forgive me... A blasphemous question

Post by ricks57custom »

DENIED! :oops:
Lefty, the JTM45 Group denied my acceptance. Don't know what I did wrong.

I planned out my course of action and it doesn't seem too difficult. I guess my only question is regarding the tube rectifier: My bias is controlled from a bias tap on the transformer, as opposed to the standard way. Does the rectifier tube need to be regulated by the bias tap (like on the standard bias circuit) or is it fine with just heater and PT connection?

Thanks,
Rick
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LeftyStrat
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Re: Please forgive me... A blasphemous question

Post by LeftyStrat »

The PT HV leads connect to pins 4 and 6. The 5v leads connect to pins 8 and 9. You take the B+ off of pin 8. No need for bias. I've attached the main schematic. I'll ask on the list what is going on.

Oh, and another piece of advice. Try the new ECC803 (long plate 12ax7) in v1. Really nice tube and sounds as good as some of the NOS Telefunkens I have.
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ricks57custom
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Re: Please forgive me... A blasphemous question

Post by ricks57custom »

Lefty,
That makes total sense. Thanks for all the help, I really appreciate it. It's great to have so many knowledgeable people at this board.

Rick
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LeftyStrat
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Re: Please forgive me... A blasphemous question

Post by LeftyStrat »

The moderator on the jtm45 list wants to know what email you used to join, he says they haven't denied anyone joining.
ricks57custom
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Re: Please forgive me... A blasphemous question

Post by ricks57custom »

Lefty,
It might have been under my wife's address. I'll try joining again under my address.

One quick question: I'm using the Heyboer trannies that Toneslut sells. According to this link the the primaries (yellow) would be attached to pins 2 and 8 and the secondaries (gray) would be attached to 4 and 6 or the recitifier, correct?

http://www.toneslut.com/transformers/tr ... agrams.gif
PeteRH
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Re: Please forgive me... A blasphemous question

Post by PeteRH »

I never thought That I'd be upset about so much gain.
I thought the same when I built an expresso...but in my case it really turned out not to be the gain but the associated graininess and harshness that came with it. I think a true Express doesnt have that harshness and has that much gain that it almost becomes unstable and it becomes an oscillator...endless sustain and feedback. The bottom line is you cant get the sustain without the gain IMO.

Alessandro uses a 12Au7 in the third stage and others have tried 12AT7's at various stages.....others as someone stated just before switch it out completely. If you just want a gain reduction it is the easiest approach. It will get rid of some of the hash as well. It will be a nice amp but no wreck.

Cheers
Pete
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LeftyStrat
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Re: Please forgive me... A blasphemous question

Post by LeftyStrat »

No, other way around. Yellow leads connect to 4 and 6, yelllow/red to ground, gray to 6 and 8. B+ comes off of 8.

The guys on the list said try joining again.
ricks57custom
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Re: Please forgive me... A blasphemous question

Post by ricks57custom »

LeftyStrat,
I just re-applied to the JTM forum. My name there is ricks66jazzmaster.

I'm now slightly confused. You mentioned attaching the 5v to pins 6 and 8 but I've looked at the schematic and it suggests pins 2 and 8. Is there a reason to use pin 6 instead of 2?

Thanks.
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