Nearly two years ago, Eli coached me on starting this amp, providing some "hen scratches" for the various sections. I had asked the forum about driving 6y6GT tubes in push-pull, and Eli responded with the idea of using a 6922. He also knew of several transformers and passive components that I already had on hand in my bins. (I'm frugal when possible.) So he sketched out the stages with those components in mind.
Besides using available parts on hand, I added some new parts options in the event that others might be interested in building this. For example, I found a couple of nice Edcor power transformers that are cheaper than purchasing both the Triad N-77U isolation transformer AND a needed booster transformer. These Edcors have sufficient specs at a good price, and they come with end bells if you need the cosmetics. :-)
This amp was also designed to allow experimentation with some other features I had either not yet built or had not experienced by listening. Here are some of those features:
- CSS on the 6922 anodes
- MOSFET concertina splitter direct coupled to the 6922 plate
- AC balance control for the splitter legs, in order to optimize wave symmetry and reduce distortion.
- Fixed bias, adjustable for each 6Y6GT output tube
- Regulated screen supply using a VR tube (0C3A)
- Near-class-B biasing ("deep class AB"?) for efficiency and low current draw as well as allowing higher B+ voltage on the finals
The result is a great-sounding amp that is highly tunable on the bench.
In this thread, I'll report the bench measurements of a working breadboarded amp along with the current schematics. The original thread with Eli's hen scratches is here:
Driving 6Y6GTs with El Cheapo 12AT7 front end?
Thanks also go to Michael Samra, Jim McShane and Don Sachs for their input and help as well. Miles Prower, Tim Robbins and Mark Weiss on diyAudio helped with on-bench 'scope measurement questions, too.
--Jeff Yourison
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Topic - A 6Y6GT/6922 P-P Amp with MOSFET Concertina Splitter - jyourison 10:32:15 03/28/15 (26)
- 6Y6GT - FenderLover 06:55:02 03/30/15 (3)
- RE: 6Y6GT - jyourison 10:55:28 03/30/15 (2)
- 6Y6G coke bottles - FenderLover 06:48:44 03/31/15 (1)
- RE: 6Y6G coke bottles - jyourison 07:34:41 03/31/15 (0)
- RE: A 6Y6GT/6922 P-P Amp with MOSFET Concertina Splitter - drlowmu 22:57:04 03/28/15 (2)
- RE: A 6Y6GT/6922 P-P Amp with MOSFET Concertina Splitter - Eli Duttman 08:08:14 03/29/15 (0)
- RE: A 6Y6GT/6922 P-P Amp with MOSFET Concertina Splitter - jyourison 06:49:48 03/29/15 (0)
- 6Y6GT/6922 Link to larger schematics and PDF file - jyourison 11:52:01 03/28/15 (14)
- RE: 6Y6GT/6922 Link to larger schematics and PDF file - jyourison 12:06:26 05/14/15 (0)
- RE: 6Y6GT/6922 Link to larger schematics and PDF file - Tom Bavis 11:00:33 03/30/15 (12)
- Results with lower current in the 6922 (6.5mA) - jyourison 21:17:46 03/30/15 (0)
- Could you expand on this statement? - jyourison 14:04:40 03/30/15 (4)
- RE: Could you expand on this statement? - Eli Duttman 17:09:31 03/30/15 (3)
- RE: Could you expand on this statement? - jyourison 17:37:13 04/1/15 (2)
- RE: Could you expand on this statement? - Eli Duttman 19:02:16 04/1/15 (1)
- RE: Could you expand on this statement? - jyourison 20:16:46 04/1/15 (0)
- RE: 6Y6GT/6922 Link to larger schematics and PDF file - Eli Duttman 13:05:43 03/30/15 (5)
- I plumb forgot the larger decoupling capacitors on the schematic - jyourison 14:21:58 03/31/15 (0)
- Effects of Source to Ground adjustment - jyourison 14:32:43 03/30/15 (3)
- RE: Effects of Source to Ground adjustment - Eli Duttman 17:15:10 03/30/15 (2)
- Reduced 6922 Current (6.5 mA) results are good! - jyourison 21:05:11 03/30/15 (1)
- RE: Reduced 6922 Current (6.5 mA) results are good! - Eli Duttman 08:12:53 03/31/15 (0)
- 6Y6GT/6922 Bias supply and anode load CCS - jyourison 11:31:35 03/28/15 (0)
- 6Y6GT/6922 Power Supply Option 2 - jyourison 11:09:41 03/28/15 (0)
- 6Y6GT/6922 Power Supply Option 1 - jyourison 10:59:02 03/28/15 (0)
- 6Y6GT/6922 Amp Channel - jyourison 10:42:05 03/28/15 (0)