jerry amp

Postby tigerstrat » Sat Feb 02, 2008 7:01 pm

jenkins wrote:I seriously doubt that how much the amps wieghed, their reliabilitiy, changing the tubes, or the resale value mattered at all. These are things that people who play in bars consider.

They were the grateful dead playing huge shows. He always had backups of everything ready to go, so reliability shouldn't matter. He had roadies to carry his equiptment, and he wasn't selling his old gear. He was either keeping it or woud give away a lot of it.
I cant see the weight or resae value coming up in jerry's mind when considering amps


I'm sorry but that's ridiculous to me. Reliability ALWAYS matters. Or do you want to be in the middle of a two hour set with failing, farting equipment? You don't think that's a traumatic interruption no matter if there is a backup somewhere, which will take several minutes to replace? You are right they WERE the GD, playing huge shows- all the more reason to pick the best gear that won't go tits up in the middle of Bird Song, or start sounding funny somewhere in the middle of a tour because a set of power tubes is moving through the natural arc of their lifespan.
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Postby jenkins » Sat Feb 02, 2008 7:12 pm

your right tigerstrat reliablity does matter. They certainly did not use any shitty amps.
What i was trying to say (maybe didnt do it very well) was that he had techs to do all the maintanence needed and he had backups ready to go if somethng shit the bed.

So at that point reliability is obviously still important but not much of a factor when trying to make your tone perfect.

Would seem to me that getting two of everthing and haveing it ready to go at a minutes notice(which jerry had for his amps and power amps) pretty much solves the problem of reliablity.

And when you read interviews with the jerry and the roadies it seems like their equiptment was constanly being repaired and maintained.

would u agree that tone was more important to him than reliability?

U are right, it doesn't matter how great something sounds if it shits the bed in the middle of a set.

That is something I worry about because I cant afford to buy 2 of everything.
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Postby tigerstrat » Sat Feb 02, 2008 10:27 pm

jenkins wrote:would u agree that tone was more important to him than reliability?


I would think it was at least equal, but the thing with power amps in particular is that at a fairly early point I believe he... really THEY (Healy, Bear, Garcia etc) decided they wanted absolutely no coloration of tone from the power amps, and as much as possible from the guitar itself. The MC3500's were tube and 350w mono and 125lb. McIntosh discontinued making them right after JG and the Dead got several of them in 1972, so they started buying the new model- the MC2300 which was the same size and weight but 2x300w or 600w bridged solidstate- nearly twice the punch per pop!
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Postby Chuckles » Thu Jun 19, 2008 11:50 pm

Just revisiting this and other power amp threads, as I'm thinking of going to a rack unit with either the Alembic or Trio pre into some SS power amp.

So, my quesiton is, are the earlier McIntosh tube power amps (3500.. or the earlier lower powered units they used) that much cleaner than the 6L6 end of a Twin... or is it just a question of more power?
Seems like I've been here before...

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Postby Jon S. » Sat Jun 21, 2008 8:25 am

As a fan of really cheap fixes that cost little and sound good, an overlooked option for folks who want a bit more of the Jerry tone from what you already own is to actually lower the power tube bias a bit from its optimal level. Try it sometime, see what you think of its impact on your amp's edge/smoothness and dynamic range - you might be surprised at what you hear.
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Postby bucketorain » Mon Jun 23, 2008 5:08 am

Jon S. wrote:As a fan of really cheap fixes that cost little and sound good, an overlooked option for folks who want a bit more of the Jerry tone from what you already own is to actually lower the power tube bias a bit from its optimal level. Try it sometime, see what you think of its impact on your amp's edge/smoothness and dynamic range - you might be surprised at what you hear.


could you explain that a bit further please?
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Postby waldo041 » Mon Jun 23, 2008 6:09 am

bucketorain wrote:
Jon S. wrote:As a fan of really cheap fixes that cost little and sound good, an overlooked option for folks who want a bit more of the Jerry tone from what you already own is to actually lower the power tube bias a bit from its optimal level. Try it sometime, see what you think of its impact on your amp's edge/smoothness and dynamic range - you might be surprised at what you hear.


could you explain that a bit further please?


the power output tubes are either a fixed or adjustable bias. fixed bias a tech needs to physically change out a couple resistors to lower or raise the bias to the tubes. adjustable bias uses a potentoimeter to bias the tubes. the hotter a tube runs the faster it breaks up ie.. less headroom. the colder a tube is biased the later it breaks up ie.. more headroom.

peace,
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Postby Jon S. » Mon Jun 23, 2008 7:46 am

With Waldo around I hardly need to provide any specifics at all! :)

Perhaps not quite so black and white but essentially exactly what I meant.
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Postby jonarobb » Mon Jun 23, 2008 1:22 pm

waldo041 wrote:
bucketorain wrote:
Jon S. wrote:As a fan of really cheap fixes that cost little and sound good, an overlooked option for folks who want a bit more of the Jerry tone from what you already own is to actually lower the power tube bias a bit from its optimal level. Try it sometime, see what you think of its impact on your amp's edge/smoothness and dynamic range - you might be surprised at what you hear.


could you explain that a bit further please?


the power output tubes are either a fixed or adjustable bias. fixed bias a tech needs to physically change out a couple resistors to lower or raise the bias to the tubes. adjustable bias uses a potentoimeter to bias the tubes. the hotter a tube runs the faster it breaks up ie.. less headroom. the colder a tube is biased the later it breaks up ie.. more headroom.

peace,
waldo


Not entirely accurate....

Technically all output sections with tubes are either fixed bias or self(cathode) biased. All amps are adjustable in one way or another. It's just a matter of how labor intensive it is. The play on words came with the introduction of variable resistors, pots, trimmers, etc, on the bias circuit. It's a mistake to refer to an amp with a trimpot as "Adjustable Bias" but it has become so commonplace that it's become the acceptable term. It's still a "Fixed Bias" circuit. There are many amps that are cathode biased that have a trimmer in circuit as well and these amps are referred to as self biasing even though you can adjust the range in which the cathode swings.


As for how hot or cold you push a power tube, this does not follow any hard fast rule such as a hot tube equals less headroom, or a cold tube equals more headroom. It has more to do with the type and quality of the tube construction and type of bias scenario, fixed or cathode. Example being a GE 6550. If you were to run this tube at 45-55 percent of it's plate dissipation, it would be quieter and exhibit a harsh clipping. Pushing it up into the 60-70 range raises the perceived headroom and the tube operates much more efficiently.
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Postby waldo041 » Mon Jun 23, 2008 5:34 pm

jonarobb wrote:
Not entirely accurate....

Technically all output sections with tubes are either fixed bias or self(cathode) biased. All amps are adjustable in one way or another. It's just a matter of how labor intensive it is. The play on words came with the introduction of variable resistors, pots, trimmers, etc, on the bias circuit. It's a mistake to refer to an amp with a trimpot as "Adjustable Bias" but it has become so commonplace that it's become the acceptable term. It's still a "Fixed Bias" circuit. There are many amps that are cathode biased that have a trimmer in circuit as well and these amps are referred to as self biasing even though you can adjust the range in which the cathode swings.


thanks for straightening the play on words out. i do understand fully that all of them are fixed bias whether cathode or fixed. a tube runs on a bias setting and that setting is set to a point or fixed, while still adjustable whether easy or not.

jonarobb wrote:As for how hot or cold you push a power tube, this does not follow any hard fast rule such as a hot tube equals less headroom, or a cold tube equals more headroom. It has more to do with the type and quality of the tube construction and type of bias scenario, fixed or cathode. Example being a GE 6550. If you were to run this tube at 45-55 percent of it's plate dissipation, it would be quieter and exhibit a harsh clipping. Pushing it up into the 60-70 range raises the perceived headroom and the tube operates much more efficiently.


running a ge 6550 at 45-55% of it's plate dissipation is probably running the tube too cold and causing your scenario. running the same quality tube at 90-95% of it's plate dissipation will run the tube hotter and if not built that well, WILL create less headroom. not too mention lessen the life of the tube itself. i know there are some other parameters that also need to be looked at, but a colder bias versus a hotter bias will change the headroom altogether whether more or less either way.

peace,
waldo
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Postby Jon S. » Mon Jun 23, 2008 7:08 pm

FWIW, in my original suggestion that instigated this sidebar I was referring to fixed bias push-pull (i.e., Class AB) amps as personally I don't associate Garcia's tone with any commonly used cathode-biased circuit. But maybe that's just me.

As for headroom, it's a slippery concept. What an oscilliscope tells you is max headroom and what you perceive as such may or may not align due to psychoacoustical properties that include how humans perceive different frequencies differently.

In general - let me say that again, in general - my experience hearing push-pull circuits is that lowering the bias slightly but significantly from what your oscilliscope will tell you is optimal for the power tubes in question, while it usually affects the wattage only slightly, affects the tubes' dynamics and frequency response in a manner that, absent hard clipping, leads to a relatively smoother, less edgy, softer sound. (At and past clipping, the "hotter" tube may sound smoother.)

Here is a real life example. The amp in question is my Reverend Hellhound. The top setting is the "60" setting on the 60/40 switch, the bottom the "40" setting. Notice how little of a difference the bias change has on the output wattage. 3 watts difference is not even audible to me. But the psychoacoustical difference is quite audible.

That was what I meant in my original post which in retrospect I could have explained better the first time. But I sure do enjoy these discussions! :)

Reverend Hellhound
Electro-Harmonix 6L6EH
Vac = 120.8

"60W" power setting:

V+ = 475V
Vp = 473V
Vs = 459V
Vg = -52.0V
Ik = 31.0 mA (avg)
Po = 42W @ 8 ohms at onset of clipping
40W @ 4 ohms

"40W" power setting:

V+ = 477V
Vp = 475V
Vs = 462V
Vg = -52.0V
Ik = 26.4 mA (avg)
Po = 39W @ 8 ohms at onset of clipping
36W @ 4 ohms
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Postby jonarobb » Mon Jun 23, 2008 9:22 pm

Jon S. wrote:FWIW, in my original suggestion that instigated this sidebar I was referring to fixed bias push-pull (i.e., Class AB) amps as personally I don't associate Garcia's tone with any commonly used cathode-biased circuit. But maybe that's just me.

As for headroom, it's a slippery concept. What an oscilliscope tells you is max headroom and what you perceive as such may or may not align due to psychoacoustical properties that include how humans perceive different frequencies differently.

In general - let me say that again, in general - my experience hearing push-pull circuits is that lowering the bias slightly but significantly from what your oscilliscope will tell you is optimal for the power tubes in question, while it usually affects the wattage only slightly, affects the tubes' dynamics and frequency response in a manner that, absent hard clipping, leads to a relatively smoother, less edgy, softer sound. (At and past clipping, the "hotter" tube may sound smoother.)

Here is a real life example. The amp in question is my Reverend Hellhound. The top setting is the "60" setting on the 60/40 switch, the bottom the "40" setting. Notice how little of a difference the bias change has on the output wattage. 3 watts difference is not even audible to me. But the psychoacoustical difference is quite audible.

That was what I meant in my original post which in retrospect I could have explained better the first time. But I sure do enjoy these discussions! :)

Reverend Hellhound
Electro-Harmonix 6L6EH
Vac = 120.8

"60W" power setting:

V+ = 475V
Vp = 473V
Vs = 459V
Vg = -52.0V
Ik = 31.0 mA (avg)
Po = 42W @ 8 ohms at onset of clipping
40W @ 4 ohms

"40W" power setting:

V+ = 477V
Vp = 475V
Vs = 462V
Vg = -52.0V
Ik = 26.4 mA (avg)
Po = 39W @ 8 ohms at onset of clipping
36W @ 4 ohms


Hey now,

Again, just to clarify. The Hellhound ironically has a variable circuit on the cathode of the power tube. It has less to do with the bias circuit, and more to do with the cathode and overall transconductance of the tube. The slight change on the current draw of the power tube(Ik) is incidental of the real mojo that is taking place which is that the amp is a psuedo cathode(self) bias in the 40w setting. I've worked on many of these amps as well as other prototypes that Kager has unleashed on NYC. Your reading alone tells you that the control grid is fixed. Your B+ isn't changing on the plates. DING! Fender was so enamoured with a similar psuedo self biasing circuit back in the day that CBS era amps saw this type of circuit for all of what, 10 months in 1968? The 60/40 switch is tied to the cathodes lifting them from ground, and introducing a variable impedance. This was the magic of both very early Traynors, Ampegs and some Yorkvilles. Dennis Kager has about 20 or more patents on every variation of this circuit. I'm surprised the Reverend amps didn't last as long as they did. I really dig them and that very design. Take good care of that one. You probably want to get those EH power tubes out of there. You're selling yourself short on the tone in that 40 watt setting. The new Tung Sol 6L6-STR is about the sweetest current production tube going if you can't break the bank on some old American GE's or Sylvania's.


All of this is good conversation and I thoroughly enjoy it. I, in no way mean to one up anybody or knock someone else's amp and guitar expertise. I'm always looking for new tricks and tips myself. I repair amps, effects and guitars for a living so I'm pretty much knee deep in the tinkering on a daily basis.


Waldo, always dig your posts and I worship your unearthing of all the great info about Jer's rig, thanks! But man, if you're gonna run a 6550 at 90-95 percent plate dissipation, which is basically Class A, I don't want to be in that room. ;)


Oh, and this just in. Hot off the wire: http://news.yahoo.com/s/nm/20080623/en_nm/boygeorge_dc
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Postby Jon S. » Tue Jun 24, 2008 5:48 am

That's very helpful info., jonarobb. Would it be OK with you if I cut and pasted your response into a pair of ongoing threads on the Reverend Discussion Page and The Gear Page (with appropriate credit, of course)?

P.S. I love my Hellhound, I really do. Among the mods I've done to it (Pete Cage did the actual work, I just asked for 'em! ;) ) are hooking the Schizo (US/UK) switch up to a footswitch and adding a trim pot to allow me to dial in as much or as little of the mid-boost (you'll probably tell me now it's more complicated than that but it's what I hear :) ) as desired. It's really nice, setting the mid-boost low gets me legitimately into the tweed zone with that amp which it certainly was never advertised as having the capability of (whether so designed or not).

I've never tried it with NOS tubes, primarily because I'm happy with it now with the EHs. According to Naylor, it was designed specifically around current production Russian tubes and that's what he advises sticking with. I did try and test a pair of Svets in it. Interestingly, I could coax a legit 50+W out of the amp with the Svets but it totally didn't sound as sweet with 'em (sounded quite harsh to me).
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Postby jonarobb » Tue Jun 24, 2008 6:43 am

Jon S. wrote:That's very helpful info., jonarobb. Would it be OK with you if I cut and pasted your response into a pair of ongoing thread on the subject on the Reverend Discussion Page and The Gear Page (with appropriate credit, of course)?


That's absolutely cool. I dig The Gear Page myself. No real credit necessary. I learned it from opening up one too many amps and saying to myself, "What the @#$% is this?" And then being like, "Oh, cool, that's how that works!". The clarification was just a way to show you that although bias, and it's adjustment, obviously has an effect on tone, in this case, there is more than one way to milk a power tube for tonal variations and coloration. It's ironic that your amp has the circuit variation that it does. With the birth of the internet and the abundance of info out there sometimes it gets a little weird with everyone's opinion, etc. Example being how folks slam the Fenders from 1968 with the cathode lifted. If you get a chance to sit with one of those amps and really dig in you'll find it's actually very unique sounding and has a smooth clip to it, and a very violin sounding sustain/decay when pushed hard. Particularly the late 68'-early 69' Twins. It's also kind of telling that when Garcia stopped using that 4x10 Fender Concert right around that same era he moved over to a Twin Reverb full time. Before the whole McIntosh era he was using the tube output section from the amp. Maybe they were off the shelf cathode biased Fenders, who knows?

PS; Listen to Jerry's solo on any one of the 68-69 Death Don't Have No Mercy's. To my ear that is probably one of the best sounding guitar tones in music.
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