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Post subject: Old Hi-Fi Tube Amps, Suitable for Guitar Amps?
Posted: Sat Oct 30, 2010 6:32 am
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I have heard that some of the old '50's & '60's Hi-Fi Tube amps can be used as guitar amplifiers. My father was a hi-fi enthusiast, and back in the late fifties and early sixties he built several of these with kits purchased from Dynaco, Heathkit, etc., which was apparently a common practice at that time. I believe there are still a few at the old homestead down in Georgia. I see these old amps frequently gathering dust in hock shops here in Charm City, and they are always cheap. Some are of a piece, and some have separate pre-amp and power amp components. Many have at least a couple of 1/4" jacks. Just wondering if any one has any experience using old tube hi-fi amps as guitar amps, and if so, what sorts of things to look for/at when exploring these as a possible power source. As always, any input is always appreciated. Thanks,...O.


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Posted: Sat Oct 30, 2010 9:00 am
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Most of these amps are designed to run "clean", right up to their max rated power. And their tone control stacks do not have the extreme boost/cut treble and bass capabilities typical of the average guitar amp. Thus, while they're often quite loud they're usually pretty "sterile" sounding, with very little compression or odd-order harmonic distortion. However, with modern pedal technology you can get pretty much any tone you wish with some strategically-selected stompboxes. The old hand-wired Macintosh, Dynaco, Fisher, and Harmon-Karden amps were built like proverbial Patton tanks using the finest iron and components available -- either then OR now. In fact, the old Dynaco "mono 70" formed the basis for the original Sunn amps back in the early '60s and Phil Lesh of the Grateful Dead swore by his Macintosh 275's. Skip Simmons out in Sacramento modifies many vintage hi-fi amps into some primo harp amps......

http://www.skipsimmonsamps.com/index.html

Summing up, yes -- these amps are certainly worthy of consideration.

HTH

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Posted: Sat Oct 30, 2010 10:40 am
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Thanks, Arjay, I knew you had the experience to give an informed insight into my latest crazy idea. As I said, I frequently see old tube hi-fi amps in pawn shops here in the $20-$40 range, and they just sit on the shelves forever. I guess the lighter weight Class A/Optical low watt stuff is all the rage with the high-end stereo guys these days; given the compressed frequency response of modern recordings (CD's, mp3's, etc.) I kinda wonder why they bother-try listening A/B to a quality vinyl recording and a cd of your favorite record and you know what I mean. My only small practice amp right now is a solid state Peavy, but I've got a few single speaker cabs that I'd like to try matching with an old tube hi-fi amp for home use-"porch weasel piggyback", as it were. Mostly the stuff I see is Dynaco, Fisher, Heathkit, Philco, Western or GE. Macintosh, even the old stuff, is always at a premium, and snapped up toot suite by collectors. I'd forgotten that the Dead's '60's equipment was based on Macintosh power amps-I think their improper grounding curtailed their Woodstock appearance. Thanks for your help...O.


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Posted: Sat Oct 30, 2010 5:57 pm
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When I first got into piddling with guitar amp, about 20 years ago... rebuilding Dynacos for guitar use was kind of a fad. The iron and EL34 power tubes of the ST-70 lend fairly well to guitar use. I think Ken Fischer used Dynaco iron and some of the amp's topology in his early Trainwrecks.

I'm not sure about McIntosh, though. They usually run UL taps on the OPT. May need to do more tweaking to get the tone you want.

BTW... Old PA amps sometimes make good DIY guitar amp projects (like old Bogens). FWIW. Good luck!


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Posted: Sat Oct 30, 2010 6:04 pm
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I know a lot of guys who grab up these old chassis just for the tube complement -- a $20 Dynaco might yield a hundred bucks' worth of glass depending upon the model. If you find one cheap enough that works I'd say grab it up. Look for something as an integrated (ie: pre- and power-amp as a single chassis) unit to simplify the logistics. Most of the old Heaths and even the older tube stuff from Lafayette Radio and Tandy (Radio Shack) were good proven designs with quality components.

HTH

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Posted: Sat Oct 30, 2010 6:09 pm
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BMW2002Ti wrote:
I'm not sure about McIntosh, though. They usually run UL taps on the OPT. May need to do more tweaking to get the tone you want.


Correct. Which is the primary reason the tube Mac's ran so clean at rated power and even beyond. They're beautiful for PA/SR use though and bass guitar applications where max clean is desired.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Posted: Sun Oct 31, 2010 5:18 am
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Thanks for all the responses, gentlemen! I'm gonna be investigating some of the local pawn shops this week to see what looks interesting/applicable to this project. Integrated amps seem like the way to go, as having separate pre- and power amp chassies (pl.? sp.?) sitting on top of a small speaker cab would be pretty unwieldy. A couple of you have mentioned tweaking these amps for guitar use. Is this strictly for greater tonal control, or is there something that must be done to make them actually able to function as a guitar amp? With 1/4" jacks, I was assuming (hah!) that I could just plug and play, providing impedances aren't too far off. Thanks for all the help and any suggestions...O.


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Posted: Sun Oct 31, 2010 7:08 am
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Many of these amps have their pre-amp/gain stage/PI tubes idling right in the middle of their voltage swing. This gives the amp the best linear response. But sometimes, not the best response for guitar use. You may need to play with plate voltages, idle bias settings, and local & global feedback to tailor the tone to what you want. There are sites on the Net about these things in general (like RG Keen's stuff). And also specific mods for specific units. I find playing with the gain stage and PI section affects the tone the most. I usually keep these unit's power section stock.

Best to try out unit, stock (after replacing needed parts---like lytics). Then, mod each stage bit-by-bit... as needed. First gain stage and PI seems to make the most difference to the tone. As well as the global feedback. It's all empiric, really. Your ear is the best judge. As long as the unit doesn't smoke too much. 8^)

Good luck! Keep us posted.


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Posted: Sun Oct 31, 2010 9:48 am
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BMW2002Ti wrote:
First gain stage and PI seems to make the most difference to the tone.


+1

As well, cap values in the amp's EQ section can be swapped out to tailor the response curves.

BMW2002Ti wrote:
As long as the unit doesn't smoke too much.


:mrgreen:

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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