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The new 300B+ 1st cut...

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Thorsten

(M)

In Reply to: The new 845 and 300B+ posted by bcherry on March 17, 2005 at 19:02:24:

Hi,
The first thing I did was to hook up the 300B+ to my lab PSU and test Brians remark of 3.6A heater current had me scared.
Well, alarm bells off, both draw a short peak of 3A+ on switchon but settle at < 2.4A, the LD+ Heater supply is designed to cope with that.
Okay, I happen to know that Master Liu runs the 300B+ "low & Hot", that is loads of current, low anode voltage, low load, sorta 350V/160mA/1K5.
So, just to be perverse I'll try the opposite, namely 450V/120mA/2K5. This according to P-Spice simulations with a VERY ROUGH model for the 300B+ (Brian, do you have Sofia curves for the 300B+?) should allow 20W+ for 5% THD limit.
The 310A from the 91 Frontend looks servicable if we crank up the Anode Voltage to 250V with 135V screengrid voltage (slight change in cathode R).
If I find the time this WE I'll give this whirl.
Ciao T

Follow Ups:

Re: The new 300B+ 1st cut... - bcherry 01:12:36 03/22/05 (1)
Maybe some variation with the filaments then as Liu confirmed he was getting 3.6 current draw with his.
Liu has it set up to run 120ma/400v/1k5 with the big cores.
No curves for the new 300B+ yet. In fact no Sofia anymore as replaced it with an Amplitron. Will do some curves soon as I get some pending issues out of the way.
Will be neat if you can implement the 310a. We're really in a groove with this tube.
Brian

Take control! DIY.
- Re: The new 300B+ 1st cut... - Thorsten 01:18:39 03/22/05 (0)
  Hi,
  > Maybe some variation with the filaments then as Liu confirmed
  > he was getting 3.6 current draw with his.
  Hmmm. They PEAKED at 3.6A, but dropped to 2.4A once the heaters had stabilised....
  > Liu has it set up to run 120ma/400v/1k5 with the big cores.
  Well, I have decided on 120mA/450V/3k myself and to accept that at really low frequencies the OPT will saturate.
  > No curves for the new 300B+ yet. In fact no Sofia anymore as
  > replaced it with an Amplitron. Will do some curves soon as I get
  > some pending issues out of the way.
  Thanks. I used the curves from old 300B+ Datasheet, not sure how close this matches.
  > Will be neat if you can implement the 310a. We're really in a
  > groove with this tube.
  Looks like we need a little bit more swing into a little bit more capacitance than the 310A is happy with.
  See my new post up there:
  http://www.audioasylum.com/forums/DIYHiFi/messages/4943.html
  for my current ideas.
  I'm butchering a dreadfully build Amp from Dared for the chassis, driver 76 & 5687.....
  Ciao T

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