You are forgetting the grid to cathode test specs.
The China tubes usually hi pot to 1kv grid to cathode at best maybe a hair higher. Inter-electrode capacitance is roughly double of the Eimac spec. This screws the input swr up a bit on the higher bands for amps with a tuned input.
This goes for all the China white base tubes.
When one fails or bad to begin with 99.9 percent of the time it is from a grid to cathode short. I have only seen a couple fail anode to grid but was due to shipping damage.
I have handled thousands of white and brown base China 3-500z tubes.
Jim can explain the test jig Tom and Ameritron uses to weed out the tubes with a grid issue.
Scott
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On 2024-05-22 10:16, W7WRX wrote:
I dont think you are in his group? He has been selling and testing
these for 4 years now. Since you might not be in there, I can post
the Hi pot data here:
"These tubes all tested good, 24 out of 24. The highest high pot
anode to grid was 15 kV, the lowest was 11 kV.
The highest grid current for emission saturation at 2800V anode was
190 mA, the lowest 170 mA. The lowest peak output at emission limiting
at 2800V was 1050W at 5V filament, the highest was 1200 W.
Grid high pots were 1500-5000V at 10uA leakage, with most around
2000V. The 5kV tubes had ~15 kV anode. They must have a really hard
vacuum."
-------------------------
From: [email protected] <[email protected]> on behalf of
Jim VE7RF via groups.io <jim.thom@...>
Sent: Wednesday, May 22, 2024 7:17 AM
To: [email protected] <[email protected]>
Subject: Re: [ham-amplifiers] 3-500 tubes
On Tue, May 21, 2024 at 05:54 PM, W7WRX wrote:
<The tube He sells clearly a white base tube. Check this link. He
had them change specs on these and had to purchase hundreds of them
to test before they finally got a good batch. These exceed Eimac
spec now.
## Tom dumped the tubes from factory #2 (with it's 70+ %
failure rate and brown base) and went to factory #1 (with it's 13%
failure rate...and the white base).
## Test any chinese 3-500Z with a hi-pot tester. You won't measure
5 kv between grid and cathode....like you see on any Eimac 3-500Z.
The best you will measure is 1 kv, if that....and sometimes as low as
600-700v.
## You won't measure 16-18KV, from anode to grid, like on any Eimac
3-500Z.
## The measured C between grid and cathode on the chinese 3-500Z's
is far more than an eimac. The chinese tubes have the grid spaced
closer to the cathode vs Eimac. The MU on the chinese tubes is 200.
The MU on the eimac 3-500Z is just 130.
##Per JI, the chinese tubes need at least 5 vac bare min, on the
socket, to function correctly....and 5.2 vac, to meet IMD specs.
The chinese 3-500Z's will work fine.... as long as they have the
white base...and are matched correctly, if a 2 x tube amp used. On
eimac 3-500Z's.... grab any random pair of new eimac 3-500Z's.... and
they are matched up.... since they were built to exact specs.
Links:
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[1] /g/ham-amplifiers/message/40406
[2] /mt/106173952/8135091
[3] /g/ham-amplifiers/post
[4] /g/ham-amplifiers/editsub/8135091
[5] /g/ham-amplifiers/leave/12941173/8135091/773995006/xyzzy
