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Feeding a 300b (JJ2A3) to drive a GM70 (via Monolith Magnetics IT)
Though the 76 has that magical sound, it needs a preamp to drive to full power. Gain is about 10x on the 76, need more like 20x.
Any ideas on a tube without losing the triode magic?
Pulling off a 400v supply with dropping resistor.
Thinking of the following
5687- Just a tad more gain but not enough. Might be microphonic
7788- Triode wired, should easily get 20x gain.
6E5P- Triode wired
I have a couple 5842 tubes (417A) as well, these probably won't swing enough Voltage...CCS?
Any other ideas?
Follow Ups:
You mentioned the 5687. A similar high gm/ low R P type. with a μ of 22, is the ECC99. With CCS loading, you'd get the gain wanted.
FWIW, Lynn Olsen has used the ECC99 in his 300B designs.
Eli D.
A little tweaking and this might work well.
About 1 volt input for full A1 power output
Or should I use the other half of 5687 for CCS?
Edits: 11/27/16
Wire the 2 channels asymmetrically. Use section 1 in a channel and section 2 in the other channel. When the tubes show signs of wear, flip/flop them.
The "sand" device is (IMO) better at the CCS job than a triode.
Eli D.
The problem may be you want that magic that dht bring to the party. The solution may only be 4 stages vs 3. Went down this path with 845's. Years ago started with a 5842 two stage then 3 then 4 each time it by got more dynamic and with 2a3 300b 26 845 46 etc... Things just sounded more like real live music.
There is a reason that dht are used and it not because they are cheap, powerfull, or easy to work with. I realize this requires more room, time and money. So much for the KISS principal!!!
Enjoy the ride
Tom
You are so right Tommy ......DHT's rule!
Have fun!
Willie
Yeah, probably why I never liked my 300b amp with two stages.
76-26-300B was magic
A few possibilities...6N6
6A6
12AY7
12AV7
EF86 triode mode
--------------------------
Buy Chinese. Bury freedom.
Edits: 11/26/16
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