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In Reply to: RE: I Made a Mistake Once... posted by Triode_Kingdom on September 08, 2014 at 00:33:12
TK
"I Thought I was Wrong Once…But I was Mistaken"
said by Oscar Wilde
In my situation ...
Using the Tent Labs Bias Supply would
give me the regulation needed.
It can source or sink 1.5mA.
DanL
Follow Ups:
"...the Tent Labs Bias Supply ... can source or sink 1.5mA."
According to the simulation, source current is very small, less than 100 uA. However, sink current might be more problematic. I added a simple shunt regulator to get an idea of what's required. In the circuit below, if the grid is driven hard, Q2 must sink 3-4 mA in order to maintain a constant DC voltage level at the bypass capacitor.
This doesn't mean the Tent supply won't work, but its effectiveness will depend on how hard the 845 is driven. It appears that if you input a sine wave at full A2 power, bias voltage will increase if the sink is limited to 1.5mA. However, if the amplifier only experiences brief A2 operation on transient peaks, the 1.5 mA sink should be satisfactory. Also, the larger the value of the bypass cap (or reservoir cap, as Naz referred to it), the longer it takes to charge up when grid current is drawn. That provides a larger window over which grid current can be drawn without significantly disturbing the amplifier's operating conditions.
I could try to simulate this with a 845 if you're interested. However, I've found that many tube models don't draw grid current properly. The 211 I'm using now was the third one I tried.
--------------------------
Buy Chinese. Bury freedom.
From the pic on the website ...
It looks like a PP complimentary transistor pair
directly to the output with no cap.
So I guess a IRF9610 CCS loaded follower
would be the answer to my needs.
Source to Ground
Drain to CCS to -300V
Tent Labs to Gate
Output from Drain
Modest 10mA on CCS
Peaks would draw more from IRF9610
DanL
I need an N channel not a P channel FET.
I have 2SK2700s on hand that are overkill.
Same FET the Power Drive uses.
Same circuit as described above.
DanL
There are a number of ways to get this done. I like the simplicity of bipolars for this sort of thing, so I'd probably use the Tent to drive a NPN high voltage Darlington, maybe the NTE2540 or similar. Whatever works!
--------------------------
Buy Chinese. Bury freedom.
Edits: 09/08/14
Dan, are you married to the Tent labs Bias supply or could you get a little more current by using something else? I'm not familiar with what you are using but my thought is that it would open up your circuit configuration options.
Naz
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