On Sat, May 18, 2024 at 09:11 PM, W7WRX wrote:
The best appears to be from CTR engineering.? There are two plants that make 3-500 tubes in china. These are the best of the two.? They are fully Hi pot tested and guaranteed.? ?Mine have been rock solid.
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I have had very bad luck with Penta.? Over and over failed or gassy tubes out of the box.? I ended up just getting a refund, They were nice to deal with, no trouble.? I was told they likely just got a bad batch.? Maybe they are better now. This was a year or two ago.?
CTR gets his 3-500Z's from the exact same chinese factory as Pentalabs....and also RF parts.? ?These are the ones with the white bases.? ?Factory #2 is junk, with a 70% failure rate....and those all have brown bases.?
Even tubes from the good factory all? just 1 kv hi-pot test? between grid and cathode.? (Eimac's are typ 5 kv from grid to cathode...and 16 kv from anode to grid).? ?The good chinese tubes have higher grid to cathode C? vs? eimac.? It appears the chinese tubes? have spaced the grid closer to the cathode vs eimac.?
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A month ago, everybody and their dog got a severe bad batch of chinese 572B's..... like the entire production was screwed up...... but the 572B is another, all together scenario.?
