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Dean View Drop Down
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Points: 37575 		Direct Link To This Post Posted: March 02 2009 at 15:57
Originally posted by Trademark Trademark wrote:

Hughes   & Kettner used to make a little tube preamp (used a 12Ax7 I think) that had an output of around 5w when hooked directly to a speaker cab.  I practiced through mine a lot.  Don't know if you could get this onto battery current though.  I suspect not unless you raid the folks' car.
9V PP3 bateries would struggle to power the heaters, let alone supply enough power to juice-up the amp itself LOL - an inverter needed to convert 9V to 300V would be pretty inefficient, reducing battery life further.
 
I'd be curious to know the H&K model number - I'd love to know how they got 5W out of a 1W valve.
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Points: 37575 		Direct Link To This Post Posted: March 02 2009 at 16:06
Originally posted by N Ellingworth N Ellingworth wrote:

opps, yeah I did mean 384 (I'm was a little preoccupied with sourcing heatsinks at the time)

Yeah I just noticed that myself PP3 batteries really aren't suitable for this project unless I limit myself to a really low power chip like the LM386, which is going to be very disappointing.
The LM384 will be fine - just plan for 2.5W, it's only 3dB down from 5W and you'll hardly notice the difference - the reduced current will improve battery life and big decoupling caps will source all the current you'll need for transients giving you a pretty good peak power capability - just don't expect to sustain it for any length of time. Also, shop around for batteries - they don't all have the same ratings.
 
Not going overboard on the LEDs will also help LOL


Edited by Dean - March 02 2009 at 16:08
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Trademark View Drop Down
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Points: 1009 		Direct Link To This Post Posted: March 02 2009 at 16:07
Cant recall the model number, but I believe it was called the "Bluesmaster" or Crunchmaster".  It was a 1/2 rack unit with the H&K Red Cab circuitry for cabinet simulation (mid eighties style).  Can't help you on the tubes.  It may have another tube for power output (EL34 maybe?), I don't remember.  I haven't seen one in close to 15 years since I got rid of mine.
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Dean View Drop Down
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Points: 37575 		Direct Link To This Post Posted: March 02 2009 at 16:13
EL34 make more sense - they could have ganged up several 12Ax7's but it's not worth the effort due to reduced reliability, though many heads use 12Ax7 i/p stage and MOSFET o/p stage.
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Petrovsk Mizinski View Drop Down
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Points: 25210 		Direct Link To This Post Posted: March 02 2009 at 19:47
Originally posted by Trademark Trademark wrote:

Hughes   & Kettner used to make a little tube preamp (used a 12Ax7 I think) that had an output of around 5w when hooked directly to a speaker cab.  I practiced through mine a lot.  Don't know if you could get this onto battery current though.  I suspect not unless you raid the folks' car.


It would have had to have had a built in power amp somewhere down the line.
5 watts suggest it would have used a single EL84 or 6V6 power tube somewhere in there.
As for the preamp tube, the only 3 that spring to mind immediately are 12AT7s, 12AU7s and of course, the 12AX7, the AX7 being the highest gain preamp tube of the bunch.
You don't recall the exact name of the H&K preamp you used do you?

Edit: nevermind, didn't see the extra posts when I posted mineEmbarrassed


Edited by HughesJB4 - March 02 2009 at 19:48
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Points: 25210 		Direct Link To This Post Posted: March 02 2009 at 19:52
Originally posted by Dean Dean wrote:

EL34 make more sense - they could have ganged up several 12Ax7's but it's not worth the effort due to reduced reliability, though many heads use 12Ax7 i/p stage and MOSFET o/p stage.


There's no way Trademark's H&K preamp would have been sporting an EL34 (or a 6L6 for that matter)
About the minimum amount of power a single EL34 will make is generally about 20 watts.
If you look around in guitar shops/guitar catalogues etc you'll see those little 5 watt tube amps are typically loaded with a single EL84 or 6V6, since those can go down to about 5 watts, in a class A configuration much of the time too.
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Dean View Drop Down
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Points: 37575 		Direct Link To This Post Posted: March 03 2009 at 02:19
^ you can always take less of a valve, but never more, there is no minumum wattage Wink - but an EL34 would have been an (expensive) overkill - well spotted.
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