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Tube Amp Do's and Don'ts

#21
Surly said:
+1

Buy function generator and a working 'scope that's cheap; just good enough to look at a sine wave. If you need, make a voltage divider to make the sine wave (smaller) readable; 2 resistors like a 64K and a 6.4K for example. Get four large ceramic 1 ohm/100 watt resistors to make a 400 watt load. Finally, some cables and a multimeter that does AC RMS (some do average) voltage, also good for ohming out stuff...

I understand that not everyone can actually do this, but with a little effort you can have a test bench for under $50. I do.
Click to expand...

woah,

actually, while all this stuff might be the "proper" way, there are easier ways to do the biasing as well. i.e. biasing meters:

http://thetubestore.com/testers.html

but honestly, reading from the OP's original comments, I WOULD NOT DO THIS YET. since, this is your first tube *anything*, you might greatly hurt yourself. but those w/ a little EE under their belts, or have working knowledge of circuits, its still a good idea to learn how to bias your amp.
 
#22
i would also add DO tell your bandmates that may be less experienced with tube amplification to simply refrain from using/touching/breathing on the amp. i have the mispleasure of working with a "guitarist" who doesnt even know what the tone knobs on his instrument do.
 
#23
BassmanPaul said:
I have never turned any of my tube amps to standby before turning them off. I always kill the power and the residual charges left in the amp are drained as the tubes cool off.

Paul
Click to expand...

This is what I do. It drains the caps if I remember correctly. Don't put it in standby then turn it off. Standby on a tube amp is a heater.
 
#25
I have noticed standby seems to be only on guitar amps. Never seen one on an organ amp, PA amp, mono-block, stereo or any other gear. I have tube gear that has no stand by and I do not see any reason to put a hole in the chassis to add one. All tube gear from the 50's to 70's. I aint talking no 6v6 amp either.
 
#26
Surly said:
+1

Buy function generator and a working 'scope that's cheap; just good enough to look at a sine wave. If you need, make a voltage divider to make the sine wave (smaller) readable; 2 resistors like a 64K and a 6.4K for example. Get four large ceramic 1 ohm/100 watt resistors to make a 400 watt load. Finally, some cables and a multimeter that does AC RMS (some do average) voltage, also good for ohming out stuff...

I understand that not everyone can actually do this, but with a little effort you can have a test bench for under $50. I do.
Click to expand...


jokerjkny said:
woah,

actually, while all this stuff might be the "proper" way, there are easier ways to do the biasing as well. i.e. biasing meters:

http://thetubestore.com/testers.html

but honestly, reading from the OP's original comments, I WOULD NOT DO THIS YET. since, this is your first tube *anything*, you might greatly hurt yourself. but those w/ a little EE under their belts, or have working knowledge of circuits, its still a good idea to learn how to bias your amp.
Click to expand...

I can do very basic car stereo wiring, but I would not want to mess around with that kind of "big bug" zapping voltage:hiding: Besides, it IS still new and might this tinkering void any warranty if I had an accidental oops? Even though I read on the other VB2 threads that some Ruby El34 tubes can crank this amp up to 280 watts, I'd rather not take any chances...yet.
 
#27
Surly said:
+1

Buy function generator and a working 'scope that's cheap; just good enough to look at a sine wave. If you need, make a voltage divider to make the sine wave (smaller) readable; 2 resistors like a 64K and a 6.4K for example. Get four large ceramic 1 ohm/100 watt resistors to make a 400 watt load. Finally, some cables and a multimeter that does AC RMS (some do average) voltage, also good for ohming out stuff...
Click to expand...

So that's basically making a load on the output end of the amp if I understand what you just said?
 
#28
Turning the amp to standby or off doesn't matter to drain the high voltage at shut down, that is done by power supply components (like bleeder resistors if equipped otherwise that charge will last a long time no matter what you do). I recommended to turn to standby ONLY so you don't have to remember to turn to standby before next power on.
Many older amps didn't have standby switches, tubes were more plentiful and cheap. It is undeniable that high voltage applied to a tube when cold by solid state diodes (tube rectifiers are different and don't pass high voltage till THEY warm up) will strip emmission material from the cathodes in the tube and shorten tube life or cause premature failure.
You can move a tube amp hot, but gently, the grids in tubes are softened when hot (they are metal and metal softens with heat). Next band needs to come up, shut off as soon as your done, pack everything then move your amp head with care. That is proper care if you choose not to fallow that advice, it's your wallet not mine.
For anyone making their own load for biasing, BUY a NON-INDUCTIVE load resistor, chain several if you like but a typical wire wound resistor is inductive and will not allow the amp to bias properly with a scope. I've had to rebias to many amps from using an inductive load.
Enjoy the glow :bassist:
 
#30
STANDBY: The Standby mode
allows the tubes to warm or remain
warm without high voltage being
applied to them. This extends tube
life. This switch should be OFF
when first turning the amplifier on.
Allow the unit to warm up for 20
seconds before switching to the
ON position. During short periods
of non-use, the amp should be put
into Standby mode.
 
#31
bassmodder said:
I have noticed standby seems to be only on guitar amps. Never seen one on an organ amp, PA amp, mono-block, stereo or any other gear. I have tube gear that has no stand by and I do not see any reason to put a hole in the chassis to add one. All tube gear from the 50's to 70's. I aint talking no 6v6 amp either.
Click to expand...

Most of the older tube designs used a tube rectifier. This will not supply high voltage until it warms up. By this time the other tubes too have heated and can use the B+. Standby was a convenience feature for live music amps. Nowadays there ARE HiFi tube amps with standby switches or delayed B+ to avoid cathode stripping.

Paul
 
#34
Try all the different brands and models that you can afford. Afford, meaning don't get a NOS Telefunken 12AX7 ribbed plate "just because." Try some stuff out like Sovtek (super cheap, durable, and damn loud), JJ (cheap, a little more harmonically rich), Tung-Sol and all that stuff. Mesa/Boogie tubes are (IIRC) re-branded Sovtek tubes that pass M/B's rigorous testing, and JJ's have been recommended for Ampegs to retain more of that Ampeg sound. I like tubedepot.com. Their prices are consistently lower than most other websites, and they beat most ebay prices.
 
#36
I realize that the Amps forum already has several stickied threads. But this one would seem to be a good candidate for stickying too.

To those of us who have played solid-state amps almost exclusively (i.e. moi), the world of tubes is kind of a dark and mysterious alternate universe. This discussion is shedding some light on it... :hmm:

MM
 
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#37
Don't bring the amp in the shower with you unless you have unplugged it first.
;)
Actually, my recommendation is that you get a multimeter and have someone show you how to test the bias on individual tubes. And keep one hand in your pocket while checking the bias.
 

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