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Author Topic: Typical output of a GI-7b? (400W?)  (Read 4024 times)
N8CBX
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Posts: 130




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« on: March 03, 2013, 03:31:05 PM »

I have a one GI-7b, tube amp that I built and I was wondering what others are reaching in output power. On 40M and with about 30W drive, I get an honest 400W with 400mA Anode/100mA grid currents. I get about the same numbers on 80M too. I pushed Ia & Ig as far as I dare, as those are about the max according to the tube's spec sheets.
Anode voltage at the tube is 2162V unloaded; 1900V loaded. I know I'm a little short on HV filter capacitance, but there wasn't much room available.
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
K2DC
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« Reply #1 on: March 04, 2013, 03:09:36 AM »

With a little higher plate voltage, you should be able to get 500W or so out of it.  A data sheet I saw shows a typical CW operating point at 1.05KV plate voltage and 300 mA Ip.  At 60% efficiency, that would give an output of 525W.  You could probably squeeze a little more than that, but it might be pushing things.

73,

Don, K2DC
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W9GB
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« Reply #2 on: March 04, 2013, 11:23:50 AM »

Jan -

Your output is typical, and why this tube is often used in conversions of multi-band HF amplifiers using sweep tubes (350 - 500 watts RF output).
I sometimes compare the RF output of the Russian surplus microwave triode, GI-7b to the Eimac 3CX400 (8874) triode used in paging and broadcast industry (1970s-1990s).
IF the Eimac 8874 sold at the same price as the GI-7b, you would have seen far more usage after 1980s.
« Last Edit: March 04, 2013, 11:26:38 AM by W9GB » Logged
N8CBX
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« Reply #3 on: March 04, 2013, 12:54:28 PM »

Okay, thanks for the comments.
I did a little calculation on plate dissipation:
1900V * 0.400A = 760W
760W - 400W = 360W (plate dissipation)
400W/760W = 52% eff.
Advertised value for p/d is 350W, so it looks like I'm right on track with the specs. And with a better anode supply, I could get better efficiency too.
Jan N8CBX
73
« Last Edit: March 04, 2013, 01:00:19 PM by N8CBX » Logged

Dayton Ohio - The Birthplace of Aviation
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