30 W, P P, U L, opt. New build, Good, Better, Best, maybe Bestest.

drtool

It might get loud In Houston
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What opinions do you have. Front end, 80% chance, I will just copy the HF 22. Power tubes, 6BG6G super tubes. The 30 W ones. Thanks, Wayne.
 
I'd probably be real tempted to use new production Dynaco ST-70 transformers. They're said to be quite good.
 
Thanks G man. That was my first pick. But way to new to this. Price is not bad.
 
The Eico HF22 is great choice for a schematic!

If you want to continue with the plate cap theme of the 6BG6, you could replace the EF86 with a 6J7 and replace the two triodes in the 6SN7 with two 6J7s triode connected. The 6J7 triode connected has the same plate curves and operating points of a 6J5. There are two 6J5s in the 6SN7 bottle. Red wire is my favorite for plate caps. Make certain to use NOS USA plate caps; they are easy to find on epay.
 
Palustris, for the 6SN7, I was thinking of the 6F8G / VT99. Thanks for the 6J7 tip. I will look into that. Meters,plate caps and magic eyes are cool in my world. Oh, and the wire for the plate caps...well I think I will have something you will not see every day, week, month, year.
 
The Dyna A470 is good with EL34s, but not so good with 6L6 class tubes (which the 6BG6 is).

I've had good results with the Hammond 1650P transformer with 6L6GCs. It's 6600 ohm primary impedance is much more of a good match with 6L6s in UL with fixed bias. I got close to 40 watts out of the ones I used that way. About 440v B+ or so. I used the Dyna MK III circuit- so an Eico HF22 circuit would work even better (potentially more drive when optimized).

I used the "non-easy-wire" version- I just permanently paralleled the 4 ohm secondaries, so that the amp would have 4 and 8 ohm output taps.

Regards,
Gordon.
 
Thanks Gordon. I plan on only having 4 and 8 Ohm taps. My home made speakers are all 4 Ohm, so far. Left over car drivers.
 
These are a 6K5GT driving a JJ 2A3-40. They are equivalent to half of a 6SL7 and go for $10 - $15 on epay. Like the 6F8 they have cylindrical plates; you could use them instead of the 6J7 for less gain if you wanted to reduce negative feedback. I didn't mention the 6F8 since the prices are so outrageous. Don't forget a rubber grommet where the wire passes through the chassis. They are available from Antique Electronic Supply.

.2A3 amp 6K5 driver stereo photo.jpg
 
The Eico HF22 is great choice for a schematic!

If you want to continue with the plate cap theme of the 6BG6, you could replace the EF86 with a 6J7 and replace the two triodes in the 6SN7 with two 6J7s triode connected. The 6J7 triode connected has the same plate curves and operating points of a 6J5. There are two 6J5s in the 6SN7 bottle. Red wire is my favorite for plate caps. Make certain to use NOS USA plate caps; they are easy to find on epay.
Look at the Marantz amps post model 2 as a guide for elegance in Mullard drive with a triode connected pentode front end.
Imodel8man-4.jpg
 
Since you're going to be doing a ground-up build, reduce B+ enough to allow Class A operation.

The HF20 circuit was mentioned, and with some attention to some tuning of the OP's with Class A-level B+ it won't be bad. Consider also use of the 32004 OPT's as used in the HF20/22.
cheers,
Douglas
 
Thanks Douglas. I really wanted to try new OPT's. 1, any factory HF22 or 20 that needs a replacement OPT imo, should really get a 32004 rather then a rewind or new production. 2, I would like to compare my restored HF22 to a new build based on the same (or close to), circuit with new OPTs. I do believe it would be a lot less trouble just to plug in one 32004. I believe I will learn a lot more doing the build this way. I do have a friend that can give the stats when I am finished, He has a lot of test gear. Yes, I hope to put Dave's G fixed bias in the mix, so that changes things a little more. Speakers will be La Scallas and the Pioneer, BS 22's that were hot a number of years back. Class A, I might try on the next build when I am farther up the learning curve.
 
The only issue with UL, is that lower plate voltage also means lower screen voltage- which limits how low of a plate impedance you can use, without going out of the optimal range. In a UL setup, the screen voltage drops with the plate voltage- limiting the current available into low impedance loads.

This is why I suggested using a transformer with 6.6K primary impedance with the 6BG6s (which act pretty much like 6L6s, in terms of load lines) in UL.

4.3K could work well in Class A with 6BG6s- but only in pentode mode. The screens would probably have to be held at about the same voltage as the plates. Could be very good, with somewhere between 330-360v B+, both on plates and screens, fixed bias.

Regards,
Gordon.
 
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