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Post subject: Problems after retubing my Twin Reverb
Posted: Sun Jun 21, 2009 3:53 pm
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I just replaced all the tubes in my Twin Reverb (~1980 - the 130 watt beast) and now there's virtually no power - there'sound but very low volume. Some of my buddies said I may need to have it "biased". Is this something I can do myself and does anyone have instructions? How do you know when it's right?

Thanks!


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Posted: Sun Jun 21, 2009 4:11 pm
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Take it to someone that does it for a living. You can kill yourself with the voltages in any amp if you don't have a clue what your doing.By the way, welcome to the forum.

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Posted: Mon Jun 22, 2009 10:38 am
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Last edited by tinker tech on Wed Jul 29, 2009 10:50 am, edited 1 time in total.

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Posted: Mon Jun 22, 2009 6:22 pm
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Biasing can be done without proper instruments, but it's guesswork at best. Also you're dealing with very high voltages and you need to be inside the amp to do the biasing.

You could have a dead tube (happens even with new ones) or a horribly mismatched power tube pair. It's also possible that replacing a dead tube with a functioning one took out some other component.

As a broad comment, little volume or tone tends to suggest a bad tube in an output pair. But you'd need a way to test that or risk doing even more damage by trying substitutions.

All in all, I'd take it to a qualified tech and have them handle it. They can usually test for all the above possibilities and more, often in under an hour once they get to it.


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Posted: Thu Jun 25, 2009 8:07 am
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Last edited by tinker tech on Wed Jul 29, 2009 10:50 am, edited 1 time in total.

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Posted: Mon Jun 29, 2009 8:53 pm
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tinker tech wrote:
Just a tip- The PI has just as much to do with output as the pwr tubes.
...At mojo .com I have found a ...Bias-Blaster, ya jest plug it in to the amp. with the tubes in it, an turn a control by the tubes with the instructions they gve ya ..An it is rebiased...does any body know any thing about this,.??I am thinking about ordering one...Would like to hear any comment about it ..Be fore I order one...Thanks...


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Posted: Tue Jun 30, 2009 12:31 pm
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Last edited by tinker tech on Wed Jul 29, 2009 10:51 am, edited 1 time in total.

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Posted: Mon Jul 06, 2009 6:27 am
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Why don't you just put all the original tubes back in and then just change one at a time? If you have a bad tube, that should single it out. Is the problem in both channels or just one?


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Posted: Mon Jul 06, 2009 11:34 am
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Does anyone have a link to that bias blaster? I'd like to look into this.


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Posted: Mon Jul 06, 2009 11:47 am
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atolleter wrote:
Does anyone have a link to that bias blaster? I'd like to look into this.
..Yes I have the address for the "Bias master", It is mojotone.com, when ya get there scroll down, looking on the left side, an cleck on "test equipment", you will see it. Hoever it is Pricie...Like $230.00 Hope this ans. your quiston...Allso wile you are there watch there Vidio on useing it....


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Posted: Mon Jul 06, 2009 11:52 am
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Great, thnx. Very cool. I like the tutorial.

They have it here too:

http://www.thevintagesound.com/store/tu ... p-386.html

Could be a could investment over time. Re bias an amp is like what? $50 maybe.


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Posted: Mon Jul 06, 2009 11:58 am
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atolleter wrote:
Great, thnx. Very cool. I like the tutorial.

They have it here too:

http://www.thevintagesound.com/store/tu ... p-386.html

Could be a could investment over time. Re bias an amp is like what? $50 maybe.
..Not hardly, they told me $50.00, but it would take a mounth to get it back,now if ya want it in two weeks, it would be $125.00, now if ya want it back in one or two days...Well that would beeeee......$200.00...WOW... What a rackit...


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Posted: Mon Jul 06, 2009 12:07 pm
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Damn, that is a racket. They charge you for quick service. Whatever happened to first come first served.

My local shop uses an amp tech on a contract, he's only there 3 days a week to work at that shop. Last time I used him to replace the power supply it took over a week if I recall, which is fair sine he had to get the part shipped. But they gave me a small amp to use in the meantime. At least that's good service. If they had told me they would charge me for quick service I would have told them to stick it.


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Post subject: Twin retube
Posted: Wed Jul 08, 2009 8:48 pm
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Hi All ! I'm new to this forum. Been playing guitar in bands for 50yrs. and repairing and restoring amps for 20yrs. My name is Art. Just stopped by to research specs on a newer amp for a guy and noticed the forum. If I can chime in on the Twin retube, the suggestions posted above are very good. Especially the individual tube swap for the pre amp and importance of the phase inverter tube. I would also echo the necessity of quality tested and guaranteed tubes. Yeah, you'll need a tech. Unless this amp has been modified, it has a hum-balance circuit(which is good to have)and fixed bias that is an internal component adjusted circuit rather than a variable adjusted type. Just my take on the meter- It measures cathode current only. This would not provide the plate voltage. I would recommend Weber's Bias Rite meter. Good Luck! Art


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