Recent Clementine Projects

sweet & juicy SE amp for 1626 Darlings and the 6L6 family

Postby 20to20 » Thu Sep 20, 2012 7:15 pm

Ty_Bower wrote:The Valve Wizard explains it better than I...

http://www.freewebs.com/valvewizard/flo ... phase.html


That is some ....cheww...yy....chuuu..wyy...cheww...ww...www...yyy....
....chuuu..wyy...cheww...ww...www...yyy....cheww...yy....chuuu..wyy...cheww...ww...www...yyy.......chuuu..wyy...
chuuu...ww...www...yyy...cheww...yy....chuuu..wyy...cheww...ww...www...yyy.......chuuu..wyy...chuuu...chuuu..chuuu...ww...www...yyy....

Still chewin' here Boss....
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Postby 20to20 » Thu Sep 20, 2012 8:09 pm

Ty,

Just looking at the diagram and seeing the inverter output being equal to the first tube output, it seems as it passes back through the FB resistor, it would just null the other signal to 0. I guess I gotta read up on how feedback works, AGAIN, to see how the signal finally balances at unity gain... Circular logic makes my brain hurt and my stomach (sick) (sick) (sick)
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Postby EWBrown » Sat Sep 29, 2012 2:42 pm

I finally tried the floating paraphase 12V6GT PP circuit out, with a 275-0-275V power trannie (for a B+ of 340VDC, and approx 20V drop through the 500 ohm cahtode resistios, for approx 40 mA per 12V6GT. and a Hammond 1608 (8K P-P to 4/8 ohms)PP OPT, connected for ultralinear operation.

It actually worked, and sounded pretty good, but I could get only about 4-5 Watts out of it, before it started noticeably clipping.

The next step would be to use a CCS for the 12SL7 cathodes joined together, to make it more like a classic long-tail phase splitter.

Rather than start hacking up the board, I'll just let it be, and I decided to revert it back to being a stereo SE amp, and I'll go with the original intended purposing of a trioded, or UL 12V6GTs, as this has worked very well for me, in an earlier completed project.

FWIW, I referred back to the original 1949 ARRL Amateur Radio Handbook modulator circuit (6B4Gs and 12SL7 floating paraphase), and the construction article stated that it was good for about 6 watts, before distortion. So perhaps 4-5 watts with 12V6GTs was about what I should have expected.

/ed B
Last edited by EWBrown on Tue Oct 07, 2014 4:37 pm, edited 1 time in total.
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Postby 20to20 » Sat Sep 29, 2012 7:00 pm

EWBrown wrote:I finally tried the floating paraphase 12V6GT PP circuitout, with a 275-0-275V power trannie (for a B+ of 340VDC, and approx 20V drop through the 500 ohm cahtode resistirs, for approx 40 mA per 12V6GT. and a Hammond 1608 (8K P-P to 4/8 ohms)PP OPT, connected for ultralinear operation.

It actually worked, and sounded pretty good, but I could get only about 4-5 Watts out of it, before it started noticeably clipping.


/ed B


Scoped clipping? What was your dummy load? Or do you have your speakers run out to the barn?
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Postby EWBrown » Sun Sep 30, 2012 1:44 pm

No fancy test equipment, just a JBL 2600 (89 dB efficiency) bookshelf speaker and my ears, as I increased the volume, it went from nice to nasty pretty quickly. I did check the B+ just to make sure it wasn't drooping, the tranny is more than sufficient for a single PP channel (or two SE channels, I've used this same combination previously), with 275-0-275 @ 120 mA, plus 2 X 6.3V, 2A filament windings.

I did try two differrent pairs of 12V6GTs, just in case I had a bad one, and I also tried two different 12SL7s.

I'd wouldn't call it a "failure" just yet, more like a "work in progress", I'll do up a point to point version, and then I'll mess around with the resistor values, maybe it just needs some more fine tuning / tweeking. The board's too nice just to turn it into a "lab rat" for experimentation.

/ed B
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Postby 20to20 » Sun Sep 30, 2012 7:34 pm

EWBrown wrote:No fancy test equipment, just a JBL 2600 (89 dB efficiency) bookshelf speaker and my ears, as I increased the volume, it went from nice to nasty pretty quickly. I did check the B+ just to make sure it wasn't drooping, the tranny is more than sufficient for a single PP channel (or two SE channels, I've used this same combination previously), with 275-0-275 @ 120 mA, plus 2 X 6.3V, 2A filament windings.

I did try two differrent pairs of 12V6GTs, just in case I had a bad one, and I also tried two different 12SL7s.

I'd wouldn't call it a "failure" just yet, more like a "work in progress", I'll do up a point to point version, and then I'll mess around with the resistor values, maybe it just needs some more fine tuning / tweeking. The board's too nice just to turn it into a "lab rat" for experimentation.

/ed B


All your numbers on that seem to jive with the data sheet power spec for about 14W. (???) (???) Of course if we're in the BoSox ballpark, then all bets are off. (lol) (lol)
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Postby EWBrown » Mon Oct 01, 2012 7:23 am

At this point, it was just a quick "roll of the dice", and it definitely merits more research / experimentation. I'll put it in the "rainy day" or "(next) winter project" queue,

It's weird how the sound quality transitioned so quickly from "clean" to "nasty", while not producing any greater output power. I'll drag out the scope and distortion analyzer, etc and get it figured out, sometime...

Plan B would be to use a CCS diode for the 12SL7 cathodes, and re-work the circuit to a more traditional LTPI design.

/ed B
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