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RH807 with a pentode driver?

jaymanaa said:
Did you get any of the Micah CCS boards? I may have one pair I could "loan" you for awhile.:yes:
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I missed out on that. What are they and what parts do they use?

I've got the parts laying around here for a 10M45 based ccs but I've been too busy to actually build anything for a few months. I was originally going to use a pentode as the ccs load but I can't think of any reason to add to the complexity without gaining any real benefit.
 
Has anyone played around with a pentode driving the output tube using Shade feedback? I was wanting to give that a try as well when I put together my 807 SE pentode amps. My initial experiments with the 807RH design weren't as good as I was hoping for.
 
Scuzzer said:
Has anyone played around with a pentode driving the output tube using Shade feedback? I was wanting to give that a try as well when I put together my 807 SE pentode amps. My initial experiments with the 807RH design weren't as good as I was hoping for.
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I have three now. Two with 6AC7's and one with the faux-pentode 6H6/FQP1N60 cascode( triode on the bottom ). They're E-Linear so the plate-to-grid ratio is set by the tap percentage. That varies between 20 and 50%( 20% for the 813/cascode, 40% for the W6m, 50% for the 16446's in the Mk.iii's). Absolutely *NO* intention of ever taking them apart.

On the next set( 6CB5A pentodes with EL84's in 50% E-Linear )I expect the same sort of result. The S258Q outputs only have 50% taps; I plan to clone them and have them made with lower percentage taps.
cheers,
Douglas
 
Andyman said:
Jay, you have no idea of the magnitude of such a project. :D
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I think both ov them have equal bench 'depth'...LOL

I've pulled a fine set ov parts out of my pile to make an amp. The only stuff I need to arder is the trivial stuff like plate load resistors and some zener diodes for the voltage ref on the screen regulator.
cheers,
Douglas
 
BTW, I'm a moron, the 7C7 triode strapped specs I was looking for were right on the sheet with the curves. Not bad specs, but probably not enough gain, I'd guess.
 
Yah Dave both the GM and gain of the 7C7 is pretty low.

If wanting to stick to Loctals there are a few I've found.

EBL21
KT81

Then you've got the Grandaddy of all loctal drivers, C3G!
(C3O as well)

Myself I would go C3G, you can get them for $15-25 each
not cheap but not to expensive either, they'll work trioded
or as a pentode pretty dam nicely.

Douglas turned me onto these a while back, they come with
a metal cover but can be taken to the glass envelopes here.
http://www.jacmusic.com/nos/C3g-C3m-info.html

Tubedepot even sells them..
http://www.tubedepot.com/nos-c3g.html
 
I'm building a 2A3 stereo amp right now with Kegs 6EJ7 driver setup with Hammond 156C as a plate choke load and the JJ tubes.... good stuff! :)
 
Right! I forgot about the C3G, that's a nice tube. C3M is another, I believe, but I'd have to look at the specs.

C3m-Inside.jpg


Very cool.

C3G is nice looking, as well.

C3g-picture1.jpg
 
I talked to Kegger tonight and discussed some of the options listed in this thread. I'm liking the C3g more all the time with the 5B/255M operating in UL mode.
 
None of those being what you would call, inexpensive. Seeing as you were going off the main path. The 3g certainly looks good, though.
 
I believe I have a dozen or so 5B/255M'sand don't have much invested in them. The C3g is definitely a little more than I'd like to spend, but as Keg mentioned, it would get me into TOTL type performance. Some with the inclination could copy the circuit with a 6DJ8 and some 6L6s.
 
$25 a pop I wouldn't call expensive though either, you'd certainly spend that or more for
many tubes used in a lot of peoples gear, an most wouldn't come close there performance.
(sure there not dirt cheap keg specials, but hey) :)

If you look you may find a source that has them at better prices, if you do I'm interested. ;)
 
Just go for it Dave. The tube cost will probably pale in comparison to the rest of the parts you'll need anyway :).
 
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