EL84 Monoblocks

for the DIY ST35, the Dynakit and every other PP EL84

Re: EL84 Monoblocks

Postby cdmawolf » Tue Jan 24, 2017 6:57 pm

A 6X4 rectifier will drop a PERFECT 20 Volts.
(cig)
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Re: EL84 Monoblocks

Postby corndog71 » Wed Jan 25, 2017 12:55 am

cdmawolf wrote:A 6X4 rectifier will drop a PERFECT 20 Volts.
(cig)

That's a good idea but I'd have to make a new layout. Possibly bigger box. Something to think about.
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Re: EL84 Monoblocks

Postby Stunch » Wed Jan 25, 2017 12:08 pm

corndog71 wrote:AC: 116
EL84 Plate 386 (For a stereo amp this should be 360-370)

AC:115
EL84 Plate 384


That's not too high, especially using the EFB circuit.
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Re: EL84 Monoblocks

Postby corndog71 » Wed Jan 25, 2017 1:02 pm

Stunch wrote:That's not too high, especially using the EFB circuit.


Ya think? Doesn't seem to negatively affect their performance. Each night they seem to get a little better sounding. If I really had any concern it would be that I might burn out the tubes too quickly. As I mentioned before, dissipation is right where it needs to be so perhaps they'll be fine. It's been a fun project. (banana)
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Re: EL84 Monoblocks

Postby Geek » Wed Jan 25, 2017 1:22 pm

EL84's are tougher than people give 'em credit for. The EL84M (pot-shot at a 7189 clone) is tougher yet ;)

Cheers!
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Re: EL84 Monoblocks

Postby Stunch » Thu Jan 26, 2017 3:29 pm

Just for fun, I checked my plate voltage and got 372VDC when in normal stereo mode. 370 is published spec by Dynaco. When I yanked the two outport tubes in one channel to force the amp into quasi mono, I got 398. I checked all other points and they were all up, very close to a factor of 398/372=1.07, being the difference between the plate voltages. For example, the stereo reading for the plate (pin 1) on the 12DW7 was 221 in stereo and 235 in mono. Cathode was 0.84 and 0.9 respectfully.

Wall voltage was around 117VAC.

And of course all the readings at the B+ points were up a factor of 1.07 as well. If I were to go the mono route, I kinda' know what to expect now. If I want to get close to Dynaco's specs, I would have to get a different power transformer - maybe a 310-0-310 - or possibly use a GZ34 rectifier or something.

Dammit Corndog, you've got me thinking now! (lol)
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Re: EL84 Monoblocks

Postby corndog71 » Fri Jan 27, 2017 2:23 pm

Stunch wrote:Dammit Corndog, you've got me thinking now! (lol)


I know! It never ends! This is my 4th attempt at building an amp based on the ST35. I've learned a lot since my 1st attempt and despite not having the best voltage numbers compared to the original design these monoblocks are my cleanest build and the best-sounding amps so far. The clarity and dynamics I'm getting are astounding!
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Re: EL84 Monoblocks

Postby DerekVa » Tue Mar 28, 2017 6:34 pm

Well done. I've thought about doing a monoblock version of my Stereo 35, but given how good my stereo version sounds, I'm afraid I'd muck something up...

-D
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Re: EL84 Monoblocks

Postby Geek » Tue Mar 28, 2017 11:45 pm

DerekVa wrote:....but given how good my stereo version sounds, I'm afraid I'd muck something up...


Ain't broke, don't fix ;)
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Re: EL84 Monoblocks

Postby corndog71 » Mon Apr 03, 2017 7:14 am

DerekVa wrote:Well done. I've thought about doing a monoblock version of my Stereo 35, but given how good my stereo version sounds, I'm afraid I'd muck something up...

-D


Keep the one you have and build new ones! (banana)
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Re: EL84 Monoblocks

Postby corndog71 » Wed Jul 12, 2017 7:12 am

My photo hosting site changed their policy so I'm going to find somewhere else to post my pics. Hopefully I can get them restored.
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