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In Reply to: RE: curious posted by Dave Davenport on September 21, 2014 at 18:27:58
The VR150 and the 47K resistor will be deleted in the modified schematic. A SEDHT circuit should be as simple as possible. It is no good construction practice to introduce resistance by hammering down the B+ voltage with a series resistor. The rectifier tube will be a RGN1064 followed by C-L-C-L-C. Film caps.
Each filament supply will employ Lundahl LL1694 double chokes in common mode rejection coupling and 2 x 15.000 microf. for zero AC.
There will be no feedback.
A switch for cathode current adjustment make it possible to use both 4101D and 4104D.
How does it look? Any critical and constructive suggestions are appreciated.Johnny
Edits: 09/21/14Follow Ups:
You asked :
(1) Simplify, get rid of the series coupling cap, and direct couple the the two audio stages.
(2) Avoid a C input filter, puts spikes on B+. I like best of all .... L1/C1/L2/C2. Ls 20 Ohms or less in DCR, prefer under 10 Ohms.
Jeff Medwin
Hello Jeff,
1. It would have been fine to skip the coupling cap, but what are the consequences?
I don't want to destroy the tubes and OPT's.
How to make protection circuit?
2. Partially L input filter, only a very small C to get the B+ on the mark.
30 ohms each choke, the best I had.
Johnny
A properly designed direct-coupled two-stage amp is hugely bulletproof. Start to study Loftin-White iterations on line.
Usually B+ to the Finals is 450-500 VDC which most output tubes and transformers can take. I can send you information if you email me .
Jeff Medwin
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