Amp retube: rebias?

[mirko]

Hi everyone,

 

I want to change the power tubes of my amp, an ENGL Thunder 50 combo.

Currently the tubes are Sovtek 5881/6L6GC (I think stock tubes, but not sure since I bought it used) and I want to replace them with Ruby 6L6GC M STR.

Do I need to rebias the amp? If yes can I do it by myself and how?

 

thanx in advance

[guitarman_nebr]

usually when you change the power amp tubes, a rebias is needed. especially when you are changing brands of tubes. unless your amp has a fixed bias. check into it.

 

to answer if you can do it yourself, in a word, NO!!

 

okay, that was over dramatic. you really need to know what you are doing when cracking open an amp chassis. lots of power in there that can easily stop the heart.

 

you can be taught. read up on it, maybe have your tech let you watch. do the research and see if you want to chance it. once you are shown how, it is not so bad.

 

a rebias is worth it for optimal tube life and tone.

[thesplawnster]

 

usually when you change the power amp tubes, a rebias is needed. especially when you are changing brands of tubes. unless your amp has a fixed bias. check into it. to answer if you can do it yourself, in a word, NO!! okay, that was over dramatic. you really need to know what you are doing when cracking open an amp chassis. lots of power in there that can easily stop the heart. you can be taught. read up on it, maybe have your tech let you watch. do the research and see if you want to chance it. once you are shown how, it is not so bad. a rebias is worth it for optimal tube life and tone.

 

 

Words to live by and I mean live by. without you amp even being plugged in the caps can hold enough power in there to zap you. Do a search on amp bias and then to make it safer get a biasrite from Ted Weber. https://taweber.powweb.com/biasrite/br_page.htm

You will want to live to hear your mp when your done so be careful. Here are a couple of sites to help but there are many more.

http://www.aikenamps.com/Biasing.html

 

http://www.diyguitaramp.com/bias.html

[mirko]

thank you for replying..

I understood that don't have the knowledge and the experience to do it by myself.

Too dangerous and complicate!!

I'll ask a technician to do it.

 

Anyway, is possible to do the tube change (from Sovtek 5881 / 6L6WGC to Ruby 6L6GCMSTR) without biasing?

 

Aren't the tube types compatible?

[Twebbz]

You need to check the bias even if you're replacing the old ones with the exact same tubes.

[Sex Panther]

Yes. Either read up on how to do it safely/properly, or take it to a tech.

[rockon1000]

 

usually when you change the power amp tubes, a rebias is needed. especially when you are changing brands of tubes. unless your amp has a fixed bias. check into it.

 

 

 

Fixed bias needs checking/adjusting when swapping tubes. Some fixed bias do not have pots that allow for adjustment ,some do. Whether or not they have an adjustment pot they are still "fixed" bias. Confusing isnt it! -they are both fixed bias. In the case of those without adjustment the factory usually sets the adjustment on the cold side allowing for variance in tubes

 

Cathode bias on the other hand doesnt have an adjustment and are somewhat "selfadjusting". They may be running to hot after a tube change and should at least be checked. My V32 (cathode biased )is running at 13.5 watts dissapation which is a bit too hot for a 12 watt tube. However changing the resistor is the only solution. I left it like that. shorter tube life is all that will happen.

 

If you read up on it you can learn to bias your own amps. I have in the last year just to broaden my knowledge. Yes, I learned how to drain the caps first! ;)Bob