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Author Topic: tube amp attenuator  (Read 9959 times)

crane

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tube amp attenuator
« on: October 24, 2010, 03:09:06 AM »
Hi!
I'm looking for an adjustable tube amp power attenuator build. The problem is - I can't find any adjustable attenuator schematic.
May be some of you guys have seen them somewhere...
Thanx.

J M Fahey

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Re: tube amp attenuator
« Reply #1 on: October 24, 2010, 08:42:21 AM »
What power are we talking about?

crane

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Re: tube amp attenuator
« Reply #2 on: October 24, 2010, 12:33:29 PM »
100W tube head.
I guess actual power is bigger than that because of the signal clipping

J M Fahey

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Re: tube amp attenuator
« Reply #3 on: October 25, 2010, 05:41:29 AM »
Yes, of course.
The attenuator will need to dissipate safely almoust double the nominal amp  power output.
To begin with , start by pulling symmetrically two power tubes and *not* switching transformer taps, contrary to what most say.
Isn't that enough?.
Or you want to go down to bedroom levels?

phatt

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Re: tube amp attenuator
« Reply #4 on: October 25, 2010, 07:32:52 AM »

Hi,
    You will find weber mass Attenuator schematics here:
http://www.freestompboxes.org/viewtopic.php?f=2&t=2287

*First posting on the page ,,3 schemos :tu:

AFAIK, you don't need to log in to view the links or whatever you call um?

100 Watts :o     oh you poor soul,  ::)
It will make your job so much easier by doing this with small amps.
Hint.

As long as you understand the down side to these things and are prepaired to work with less than ideal sonic reproduction then yep it might work for you.
It depends greatly on what exactly you want to achieve with Attenuation.
i.e. Bedroom practice/ Recording/ Live use.
Have fun, Phil.

crane

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Re: tube amp attenuator
« Reply #5 on: October 25, 2010, 02:14:02 PM »
Thanx for your replies!
Sometimes pulling out tubes is not an option (in case of a stubborn guitar player :D - not me)
My main need is to get a nice tone for playing gigs.

bry melvin

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Re: tube amp attenuator
« Reply #6 on: October 25, 2010, 04:48:47 PM »
instead of an attenuator....take a look at Yellow Jacket adapters... (or tone bones) They take 6l6 and replace with el84

They work...with no internal mods necessary.

phatt

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Re: tube amp attenuator
« Reply #7 on: October 25, 2010, 10:48:15 PM »
Thanx for your replies!
Sometimes pulling out tubes is not an option (in case of a stubborn guitar player :D - not me)
My main need is to get a nice tone for playing gigs.

OK,, Rock or Metal?

If Rock/Blues ,,,, then you are missing out on something great. 8|
Pull the 2 tubes as JMF mentioned,,, or better still install a switch allowing you to switch them on and off at will. (just find and old Mesa circuit to see how simple it is to do)

This mismatches the OT and really helps to thicken the tone.
(Should be standard on ALL 100 Watt Heads)
IME the Amp looses little SPL by doing this but does enhance the tone.
You will get a much fatter sound.
You can also install a Dana Voltage Reg Kit along with the above.
This will give you SPL control so the amp stays in the magic zone without deafening the crowds. (You do have thousands of Fans I hope? Winky)

you can hunt down King TUT's Power scaling circuit (very similar to Dana idea)
Google *LondonPower Kevin O'Conner* you will soon catch on.

As to Metal,, never really was interested in playing power chords or blinding fast riffs that make no music melody,, (shrugg) but hey it's a free world.
If that your bag then Others here will have plenty of ideas for you I'm sure.
Phil.

crane

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Re: tube amp attenuator
« Reply #8 on: October 26, 2010, 09:31:50 AM »
instead of an attenuator....take a look at Yellow Jacket adapters... (or tone bones) They take 6l6 and replace with el84

They work...with no internal mods necessary.
This is a nice idea, but the price is silly for just a piece of ceramic (there is no circuitry inside right?)
I might try to build it my self. I can get 6P14P (russian el84) dirt cheap here (for about 2$ a piece)

to phatt:
I will try to persuade my friend to pull the tubes out. Who knows, maybe he will listen to me.
100W for rock/blues is 4 times overkill I think. That dude plays metal (still 100W is overkill. but you know - sometimes look and feel is more important).
I use 100W diy tube amp for playing something like post metal and I never found the head to be too powerfull. But than again - tastes differ. We are not here to judge but to try to help :)

bry melvin

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Re: tube amp attenuator
« Reply #9 on: October 26, 2010, 03:16:41 PM »
never had one apart, but however they contain the biasing components(resistors at least) needed for the switch (cathode bias) and voltage drop. Other wise you could just rewire a socket saver!
not really that  expensive considering you leave your original bias setting alone. You then install them with the included tubes for ~120 per pair... OR buy them without tubes for 80 a pair. You end up with essentially two amps for that price. 100 watt/20 watt or a fifty/ten. You mark your bigger tubes so the bias is perfect when you put them back in ...you DON:T rebias for the el84s. The biggest fault with them is they WON'T fit in some heads

FWIW I actually started using those when 7591s were impossible to obtain for my 64 Guild amp(only a 20% drop in power for those) However I have also found them useful for my JCM 800s. Don;t have to rebias as You do when pulling tubes. So you can decide to use EL84 or 34 At SOUND CHECK time. Pulling tubes on the JCM 100 watts always messed up the bias on mine anyway.
and of course you CAN't pull tubes on a fifty watt JCM and it is STILL too loud for small venues as those HAVE to be either cranked or modded to keep from being too trebly.

Considering a current reissue JCM800 (or equivalent) is around 2000 and an 18watt Marshall type close to that they are actually a cost saver.

Lastly they don;t add wear...Attenuators are bad for tube life You essentially are diming it all the time.
Variacing the amp is even worse.

J M Fahey

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Re: tube amp attenuator
« Reply #10 on: October 26, 2010, 03:39:19 PM »
Quote
I can get 6P14P (russian el84) dirt cheap here (for about 2$ a piece)
*Very* interesting, can you provide any links?
Thanks.

phatt

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Re: tube amp attenuator
« Reply #11 on: October 27, 2010, 07:43:07 AM »
Hi bry melvin,
                  You say you have to *Rebias* when pulling 2 tubes?
You must have a strange amp? headscratch.
AFAIK, The Mesa 60/100 watt switch has no bias altering settings, only an on/off switch for 2 of the 4 cathodes.
In a well setup fixed bias Quad this should not need attention.
Phil.

crane

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Re: tube amp attenuator
« Reply #12 on: October 27, 2010, 11:39:47 AM »
Quote
I can get 6P14P (russian el84) dirt cheap here (for about 2$ a piece)
*Very* interesting, can you provide any links?
Thanks.
No links, sorry. I live in Latvia, which used to be in USSR, so we have plenty of russian stuff here at local flea market. It is not easy to get 50 of them, but if you only a few it's easy.
12AX7 substitutes (6n2p) ar about 1-2$ but they're less fun because the pinout differs and there is no 12.6V heater possibility while 6p14p ->EL84 substitution is "plug and play".


melvin - thanks for sharing your expirience, I will try to google some more on this :)

J M Fahey

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Re: tube amp attenuator
« Reply #13 on: October 27, 2010, 11:48:22 AM »
Thanks.

bry melvin

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Re: tube amp attenuator
« Reply #14 on: October 27, 2010, 08:50:20 PM »
Quote
Hi bry melvin,
                  You say you have to *Rebias* when pulling 2 tubes?
You must have a strange amp? headscratch.

Well probably not HAVE to...but pulling the 100W's tubes (which we only so when a 50W JCM breaks down and the place is too small) changes the tone...colder ..soooo