Has anyone used The Guiguang 300B? - Page 2 - diyAudio
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Old 22nd October 2010, 08:52 AM   #11
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The filament on the old sovtek 300B is much thinner than, say the JJ300B. It lights up quicker when heated with constant current.

Filament breakage is a real problem with much of the recent production DHTs, I hear that the Svetlana is worse than the Sovtek, and just about all factories have had problems with this. I think it is by far the biggest failure mode of 300Bs.

I just measured the cold-filament resistance of a 1998 Sovtek 300B and found 0.7 Ohms. With a high current secondary winding [ac heat], or large capacitors [dc heat] you get a 7A peak at switch-ON! This is not kind to the DHTs. Even high quality types will risk some mechanical distortion of the filament, and shorter life.

This is a quantified problem in the transmitter tube world, check out page 2 of

http://www.burle.com/cgi/byteserver.pl/pdf/voa.pdf


The solution is straightforward enough: use current-driven heating. A properly-implemented current heater starts the filament at normal operating current - no shocks or peaks - and it warms up very gently.

If that is not enough, You also get a remarkable improvement in the sound quality! we've been discussing current-heating at the 'New DHT Heater' thread for a while:

New DHT heater

Current drive modules for DHT filaments are available from Tentlabs, or you can obtain my regulators in kit form - please PM for details.
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Old 30th November 2010, 03:03 PM   #12
Mike H is offline Mike H  United Kingdom
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Quote:
Originally Posted by aldovan View Post
Friends

I see some Guiguang 300B tubes in ebay.
The look of this tube is fine.
Anyone have experience com this tube ? Sound fine ?


FWIW I'm a "recent convert" to the black carbonized (or whatever it is) plate and gold pins one, I presume that's the one you mean. I luv 'em. Good value for money IMO. Though really needs something like Rod's CCS DC reg heater supply to get the best out of them IMHO. So far mine come from citiysystems88 on eBay (Hong Kong).


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Old 1st December 2010, 02:33 AM   #13
Dave C2 is offline Dave C2  United States
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Quote:
Originally Posted by Mike H View Post
FWIW I'm a "recent convert" to the black carbonized (or whatever it is) plate and gold pins one, I presume that's the one you mean. I luv 'em. Good value for money IMO. Though really needs something like Rod's CCS DC reg heater supply to get the best out of them IMHO. So far mine come from citiysystems88 on eBay (Hong Kong).


What kind of 300Bs did you have before you bought the treasures? I've been thinking about getting some but need to hear more results for others that are using them. How wide is the soundstage by comparison to your other tubes?
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