[Amps] Fwd: Question about 4-1000A operation

Sun Jul 15 08:35:24 EDT 2007

Bob:

I have SPICE models for various tube amps that I have created over the years.  I have a 4-1000 model.  You are welcome to it if you want it, but you'll need LT Spice from Linear Tech, which is free (www.linear.com).  It is by far the best free SPICE.  I don't even renew the SPICE software license at work anymore because it is that good.

BTW: Anyone else is welcome to these SPICE models and the Matlab code I use to generate the tube transfer funtion.

I ran a simulation and I see vrtually no plate current drawn for a grounded grid 4-1K with Ep = 1500V. You did not give the bias, but with 0V between grid and cathode, and the screen grid at ground, there is no current (~ 1 ua).  I then referred to my 4-1K datasheet.  Eimac only has one constant current characteristic plot for screen voltage of +500V, therefore, I can't directly compare your result.  However, when I change the screen voltage to 500V from 0V (floating it from the control grid), the quiescent Ip is 820 ma, which agrees with the constant current plot in the datasheet (it has to, my 4-1K model was derived from that datasheet constant current plot).  If you want a copy of the datasheet, I can email it to you.  A British ham has these on a website (g8wrb.com).

I have checked my models carefully against the load lines for many tubes.  I have validated other operating cases, and use it for amplifier design.

Therefore, I don't think the 4-1K is bad, you just need to compare opereating points to the datasheet.  Try other biases and plate voltages, and see if you emulate load lines in the constant current plot in the datasheet.

Suffice it to say, a 4-1000 in grounded grid (screen and control grid at DC ground) has very low gain.

Email if you want the SPICE and Matlab files.  The SPICE file already has the 4-1K model in it.

73,

Steve, K0SF

----- Original Message -----
From: "Robert Groh" <rgroh at swbell.net>
To: amps at contesting.com
Sent: Sunday, July 15, 2007 12:43:17 AM (GMT-0600) America/Chicago
Subject: [Amps] Question about 4-1000A operation

Well, I've got a bit of a problem and would like some opinions. Another ham tried out one of my 4-1000A tubes and reports the following:
Filament fine, tube lights up fine

He ran it with filament only for 4 hours and then applied 1500V to the plate

Result: no grid current

Another 4-1000A tube was tried in same circuit and gave 50 mA idling current.

I'm not sure what exact circuit he is using - probably grounded grid. No idea of what screen voltage.

So it seems that my tube is no good.  Any other possibilities we should try before converting it into a table lamp?

73
Bob, WA2CKY

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