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In Reply to: Looking for a GOOD 211 / VT4-C Schematic posted by Super_BQ on July 17, 2003 at 23:47:58:
Don't believe everything you read about high B+ and transmitting triodes. Many folks have been using 845's at low B+ with good results.I played around with 211's and finally settled on a B+ of 825v, 60ma as an operating point. It gave me all of the power I needed and sounded wonderful. It also allowed me to use some "reasonable sized" 15uf/1000v oil caps instead of a few much larger parts I had.
I was more impressed at the sonic differences made by altering the current than the B+. Also the power supply made a substantial difference - liberal use of swinging/smoothing chokes and smallish oil caps sounded way better than larger banks of electrolytics. I'm not sure the 866jr's made any sonic difference, but they sure looked better!
My circuit is very similar to PAE's (see link below)
The single stage driver is sweet and works well.
Mikey's FS-100's are fantastic.
Follow Ups:
The power supply for your 211 looks incredibly complicated. Making a PCB for that cathode supply module will be a task on it's own. Actually, where would I find such a module? It would seem that to build a 1.3KV power supply with simple C-L-C would be much easier.Another point I should bring up is i've seen most are running DC on the 211 filament heaters. This is a big concern for such a DHT. or is it not in the case of the 211?? - how long will the tube last? And does running 10V AC cause that much noise that one would only think to use DC and live with replacing 211 tubes more often?
Acutally my power supply is very different than the one on PAE's site. I use individual AC transformers for each 211 filament, the 866jr and the 6C45 filament. The large Acro TP-550 provides 825-290-0-100-290-825 as well as additional 5 and 6.3v filament taps.At turn-on the individual filament transformers for the 211, 6C45 and 866jr's are started. There is a 2 minute delay to allow the 866jr's to come to full temperature before the TP-550 is started. This is done with a digital delay board.
When the TP-550 comes on it feeds the 825-0-825 to a pair of 866jr's, which go thru a damper diode for slow turn-on. This is choke loaded with a swinging choke --> 15uf/1000v oil ---> smoothing choke ---> 30uf/1000v oil with a small bleeder resistor for the B+
The power supply for the 6C45 is a 6106 (bendix indirect 5Y3GT with a very slow turn-on) into 12H, then 100uf for the driver stage.
The 100V tap provides bias voltage thru a 1N4007 and simple filter/divider network.
All said, it's pretty simple. First pre-heat 866jr's and filaments on 6C45/211's and bring up the bias. 2 minutes later start B+ which has a slow turn on because of the damper diode. Lastly the B+ for the driver stage comes up.
Even with AC on the 211's I get very reasonable hum levels. The power supply actually has a bridge rectifier and cap to filter the 10V supplies installed, but I never wired them up. AC was plenty quiet - even on Altec speakers.
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