Warm up my Twin Reverb

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Warm up my Twin Reverb

Postby 1965Strat on Tue Jul 02, 2002 5:13 pm

Hey guys, I've got a Twin Reverb that's been modded to blackface specs, but it's still very bright and somewhat harsh sounding.<P>Is there anything I can so to mellow this amp a bit? Thanks guys.
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Re: Warm up my Twin Reverb

Postby jcs on Tue Jul 02, 2002 5:28 pm

what are you running for power tubes? are they biased fairly hot? that is the 1st thing i would check...jcs
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Re: Warm up my Twin Reverb

Postby 1965Strat on Tue Jul 02, 2002 5:37 pm

I'm running EHX 6L6's<BR>I'm not sure how the bias is set.<BR>What is a mA setting for these tubes?
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Re: Warm up my Twin Reverb

Postby DreamTone7 on Tue Jul 02, 2002 5:43 pm

...if it's harsh, it's a good bet the tubes are biased cold. BTW, what kind of speakers?
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Re: Warm up my Twin Reverb

Postby 1965Strat on Tue Jul 02, 2002 5:47 pm

Well right now it has JBL K120's in it I think. They have black frames.<P>I have also used it with a Bogner 4x12 with Greenbacks in it and it still sounds weak.<P>I was wondering if I used EL34's in it, if that might help it.<P>What is a good bias setting for a 6L6?
Interviewer: So Jimi, what's it like being the greatest guitarist in the world?

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Re: Warm up my Twin Reverb

Postby DreamTone7 on Tue Jul 02, 2002 7:25 pm

...here's another shot at the bias thing:<BR> <A HREF="http://www.tone-lizard.com/lesson8.htm" TARGET=_blank>http://www.tone-lizard.com/lesson8.htm</A> <P> :D
He that hath an ear, let him hear.
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Re: Warm up my Twin Reverb

Postby dean on Tue Jul 02, 2002 10:05 pm

FWIW and IMHO, replace the JBL's with something like the C12N. JBL's have always sounded harsh to my ears, and I am not alone in that opinion. IMO, the best speaker for a TR is an EV. (Hendrix used EV's in his Marshall cabinets, too.)<BR>Replace the phase inverter coupling cap with a cap in the .01-.02 range. Change the negative feedback resistance by replacing the 820 ohm resistor with something like 22-27K. Separate the preamp cathodes. This also lets you manipulate channel gain independently.<BR>Bias to the hot side of things. You can do this adjustment with your ears if you are cautious and confident. While playing, adjust the bias in the direction that warms the signal...counter-clockwise if you are looking at the bottom of the chassis. When the plates of the power tubes start to turn red, you have gone outside the safe range of operation. When they run red, they only have a few minutes of life left; so turn the adjustment in the other direction until the redness goes away. That is as hot as those particular tubes will run in that amp. You can go in the other direction until the harshness reappears. That is the other end of the range of usable settings. Find what you like within that range. This is one of the beautiful things about these amps. With only your ears and a screwdriver, you can judiciously set bias with the amp in running condition. Numbers are useful, but it is the sound that you are after. Within the range of 'correct' current draw, you can personalize your sound. This method also lets you replace tubes while out of touch with your tech and/or electronic equipment.
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Re: Warm up my Twin Reverb

Postby 1965Strat on Wed Jul 03, 2002 3:09 am

I found a simple way to increase the warmth from a Twin Reverb tonight.<P>Increase the bias from 22mA to 40mA!!! (B+ 450)<P>The guy who biased the amp for me (before I became an amp lady of the evening) set it like this and I though it sounded okay until I developed ears. :)<P>It sounds great now, and that is with JBL K120's! I can't wait to hear it through my Dr. Z 2x12 cab that's coming!<P>Thanks guys!
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Re: Warm up my Twin Reverb

Postby jcs on Wed Jul 03, 2002 3:26 am

i thought that would do the trick!!! just make sure the plates arent red!!!!! jcs ;) :cool:
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Re: Warm up my Twin Reverb

Postby 1965Strat on Wed Jul 03, 2002 3:34 am

The only thing that is red are the filaments and the solid metal rod that goes the lenght of the tube. I assume that the plates are the big grey things in there (I'm an idiot I know) and they are not red. there is also a really cool blue glow in the tube. I've heard this is normal.
Interviewer: So Jimi, what's it like being the greatest guitarist in the world?

Jimi: I don't know, ask 1965Strat.

I couldn't believe it either!

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Re: Warm up my Twin Reverb

Postby DreamTone7 on Wed Jul 03, 2002 12:00 pm

...to borrow a phrase from EVH, "....if it sounds good, it is good." Yes, a little blue glow is normal.<P>Amperex: BTW, there is a simple mod you can do to lower the B+ without using a variac on SS rectifier amps: <A HREF="http://vintageamps.com/PlexiPalaceUBBcgi/ultimatebb.cgi?ubb=get_topic&f=1&t=003192" TARGET=_blank>http://vintageamps.com/PlexiPalaceUBBcgi/ultimatebb.cgi?ubb=get_topic&f=1&t=003192</A> <BR>It may also work on indirectly-heated cathode type tube rectifiers, but I haven't tried it there (yet!)
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