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In Reply to: The new 845 and 300B+ posted by bcherry on March 17, 2005 at 19:02:24:
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.
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.
> 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:
for my current ideas.
I'm butchering a dreadfully build Amp from Dared for the chassis, driver 76 & 5687.....
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