To variac... or NOT to variac.. THAT! is the question....

[HilltopExplosion]

I'm sure it's been beat to death, but is it "safe" to run your amp with a variac between 88 to 100 volts... CRANKED. I looked through the history, and got tired of reading, couldn't find what I was looking for. Sometimes I run my 6505+ around 100 volts, for extended lengths of time, same with my EVH 5150III 100 watt head , volume around noon, and my BE100 down to 88 volts, full throttle. Questions are

1) Am I doing damage to the amp,

2) Am I "stripping" the tubes like I've seen a bunch of arguments over.. but never a definite answer, causing premature failure.

Thanks!

 

[paulyc]

Re-bias the amp for the lower voltage and it won't matter. This is what EVH did effectively by just cranking the bias in the amp with the voltage down...

 

[HilltopExplosion]

Re-bias the amp for the lower voltage and it won't matter. This is what EVH did effectively by just cranking the bias in the amp with the voltage down...

Thanks! Appreciate it.. For instance on my BE, running eh6ca7, at 88 volts and bias cranked, It's only reading 18 ma at idle. Is this a problem?

 

[zoom club]

The heaters don't care what the bias is, they are designed to run at spec. Why do you think amp builders isolate heater voltage from the b+ when they design amps with a variac as part of the circuit? It doesn't hurt the amp but will shorten tube life.

 

[HilltopExplosion]

The heaters don't care what the bias is, they are designed to run at spec. Why do you think amp builders isolate heater voltage from the b+ when they design amps with a variac as part of the circuit? It doesn't hurt the amp but will shorten tube life.

Um... I dunno, but I'll believe you. When I was young my dad said "Son, you are a REAL hard worker.. and do you know what you are BEST at? I said " No dad.. what's that" he said " Fuck'n my stuff up" I just didn't want to apply that principle to MY stuff now. Thanks!

 

[PatF]

18ma sounds a little low, the bias supply resistor might need to be swapped.

I would keep the variac at 100v if you want to be safe. And get the bias up in the 30+ma range. (Double check that #)

Lots of guys go lower than 90v without stripping problems. That's the risk you take if you want to run it like that. At least they are easily replaceable tubes.

 

[HilltopExplosion]

18ma sounds a little low, the bias supply resistor might need to be swapped.

I would keep the variac at 100v if you want to be safe. And get the bias up in the 30+ma range. (Double check that #)

Lots of guys go lower than 90v without stripping problems. That's the risk you take if you want to run it like that. At least they are easily replaceable tubes.

Appreciate the help! I keep a bias an matching meter hooked up while dropping the voltage, at 100 volts i'ts at 28-30 ma, so instead of swapping parts just yet, I will work within safe ranges. I appreciate everyone's comments.

 

[lll]

The answer to the question (to variac or NOT to variac...) is an emphatic "yes".

I've been running my modded JTM45RI @100v for about 3 years now with volume on 8-9... with zero issues.

I did have to change the bias supply resistor to get in the correct range... this sounds
like your issue with only 18ma.

The other trick is to bias after you've variac'd down (~40ma for EL34/6CA7 types).

I'm never going back to standard.

 

[HilltopExplosion]

The answer to the question (to variac or NOT to variac...) is an emphatic "yes".

I've been running my modded JTM45RI @100v for about 3 years now with volume on 8-9... with zero issues.

I did have to change the bias supply resistor to get in the correct range... this sounds
like your issue with only 18ma.

The other trick is to bias after you've variac'd down (~40ma for EL34/6CA7 types).

I'm never going back to standard.

Appreciate the info, what I did was turned bias all the way up @ 120 volts, it was 50ma at idle. Then watched as I turned voltage down and played, adjusting volume and gain, amp sounds good at 88-90 volts, but only 18ma.. right now it looks like a 47k resistor, if I decide to change it, what would you recommend?

 

[Iskra68]

Is this putting the cart before the horse with high gain and master volume amps? Do you hear a significant tonal change to make it worth while? Anyway, what is your bias resistor before the diode? If you increase that value you will get the same effect as decreasing the 47k bias resistor connected to the pot to bring up your ma.

 

[HilltopExplosion]

Is this putting the cart before the horse with high gain and master volume amps? Do you hear a significant tonal change to make it worth while? Anyway, what is your bias resistor before the diode? If you increase that value you will get the same effect as decreasing the 47k bias resistor connected to the pot to bring up your ma.

I appreciate the info, but I'm not gonna touch it. I am not qualified. I was looking for opinions and experience, and am in way over my understanding of an amplifier. If what I'm doing won't hurt it, I'll run 'er like she is.. This is what it sounds like

https://soundcloud.com/user-437728583/b ... mark-aliff

BE100 BE channel
Pres-5
Bass-2
Mid-10
Treb-4

No settings were touched except vol, gain, and voltage (90 volts AC)
sm57 Chinese v30, duplicate clip with 23ms between, panned hard L and R

Riff
1 Gain-10 vol 3
2 Gain-10 vol 5 90 volts
3 Gain-7 vol 10 90 volts
4 Gain 10 vol 10 90 volts
5 Gain 8 vol 5 SAT switch
6 Gain 8 vol 8 SAT switch 90 volts

 

[blackba]

I use a variac for a few of my vintage amps, but I only go down to 115v. Not sure if you found my old thread, but I remember being told to stay above 100vac due to the tube heaters.

I will say I am very happy with the amps at 115vac. Gone are the very sporadic cracks and pops I used to get on my ac50 at full line voltage. Only thing I don't like is I have to take my variac with me if I travel with the amp is less I want to rebias. I find the tone much more consistent since I am controlling the voltage.

 

[HilltopExplosion]

I use a variac for a few of my vintage amps, but I only go down to 115v. Not sure if you found my old thread, but I remember being told to stay above 100vac due to the tube heaters.

I will say I am very happy with the amps at 115vac. Gone are the very sporadic cracks and pops I used to get on my ac50 at full line voltage. Only thing I don't like is I have to take my variac with me if I travel with the amp is less I want to rebias. I find the tone much more consistent since I am controlling the voltage.

Thanks Blackba, no I did not see your post, but just read it.. I appreciate the help. I have a rock crusher attenuator also, and it's hard to get a good balance between using the two, at 90, my amp seems more touch sensitive and has more sustain without sacraficing low end, but is LOUD. if you use the attenator it seems to kill the sustain. At 120, you have to put 'er to 'er to get that ahhhh mid sustaining sound.. but you know the deal, even louder.

I appreciate everyone's comments.

 

[Stradazone]

I use a variac for a few of my vintage amps, but I only go down to 115v. Not sure if you found my old thread, but I remember being told to stay above 100vac due to the tube heaters.

I will say I am very happy with the amps at 115vac. Gone are the very sporadic cracks and pops I used to get on my ac50 at full line voltage. Only thing I don't like is I have to take my variac with me if I travel with the amp is less I want to rebias. I find the tone much more consistent since I am controlling the voltage.

Thanks Blackba, no I did not see your post, but just read it.. I appreciate the help. I have a rock crusher attenuator also, and it's hard to get a good balance between using the two, at 90, my amp seems more touch sensitive and has more sustain without sacraficing low end, but is LOUD. if you use the attenator it seems to kill the sustain. At 120, you have to put 'er to 'er to get that ahhhh mid sustaining sound.. but you know the deal, even louder.

I appreciate everyone's comments.

If it's still too loud maybe try slaving and using the variac? I do this with my Superlead and get pretty good results, the tone you want at any volume, sounds better than the attenuator by itself

 

[HilltopExplosion]

I use a variac for a few of my vintage amps, but I only go down to 115v. Not sure if you found my old thread, but I remember being told to stay above 100vac due to the tube heaters.

I will say I am very happy with the amps at 115vac. Gone are the very sporadic cracks and pops I used to get on my ac50 at full line voltage. Only thing I don't like is I have to take my variac with me if I travel with the amp is less I want to rebias. I find the tone much more consistent since I am controlling the voltage.

Thanks Blackba, no I did not see your post, but just read it.. I appreciate the help. I have a rock crusher attenuator also, and it's hard to get a good balance between using the two, at 90, my amp seems more touch sensitive and has more sustain without sacraficing low end, but is LOUD. if you use the attenator it seems to kill the sustain. At 120, you have to put 'er to 'er to get that ahhhh mid sustaining sound.. but you know the deal, even louder.

I appreciate everyone's comments.

If it's still too loud maybe try slaving and using the variac? I do this with my Superlead and get pretty good results, the tone you want at any volume, sounds better than the attenuator by itself

You are exactly right, I knew if I messed with it long enough, and talked to you guys, I'd get it. I found what I was looking for, BE variac'd into rockcrusher, then cab, line out to fx, then EVH return to cab. so if I want FX, I hit FX switch, if not, let it ride. Problem is luggin' 'round all this gear! Thanks! Now if I can capture this sound..

 

[southpark tube lab]

what is the point of lower voltage.the plates and screens need the rite voltages to work

 

[HilltopExplosion]

what is the point of lower voltage.the plates and screens need the rite voltages to work

I thought it was so I could crank my amp up without blowing something up. If you listen to the clips, there is a big difference in tone at different volumes/gain with the same tone settings, at different voltage, AND that's why I asked the question. I found my amp runs best at 110 VAC.. Don't know why, but it sounds better to me than at 120. Appreciate the comment though...