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Chinese 300B

142.119.53.183
Posted on January 22, 2021 at 10:40:45
vetmedrobert@gmail.com
Audiophile

Posts: 453
Location: Ontario
Joined: September 20, 2007
 I recently finished a project that uses 300Bs. They are Gui Guang 300B that I purchased a few years ago as backup. The amp uses fixed bias and according to the WE data sheet 70 ma is the maximum plate current. So I adjusted the current to 70ma, with about 385 volts at the plate. From the WE plate curves I would have expected ~-80 grid volts. Instead I measure around -70 grid volts. If you look at 2A3-40 plate curves this is what you might theoretically get. I have a pair of EH 300B which I will try but in the meantime is this something that is common with Chinese tubes? FYI I posted on another discussion group but have gotten very little response. I appreciate any thoughts and comments, TIA

 

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RE: Chinese 300B, posted on January 22, 2021 at 16:33:47
Tre'
Industry Professional

Posts: 17296
Location: So. Cal.
Joined: February 9, 2002
 " From the WE plate curves I would have expected ~-80 grid volts. Instead I measure around -70 grid volts"

That would lead me to think the tube are soft (wearing out) but that just may be the way there were made.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Chinese 300B, posted on January 22, 2021 at 19:40:52
vetmedrobert@gmail.com
Audiophile

Posts: 453
Location: Ontario
Joined: September 20, 2007
 Well, these ones have not had until recently more than 10 hours use. So it would seem that they were not well made to begin with. OTOH I swapped in a pair of EH 300b which came with the original Bottlehead Paramounts and despite having many thousands of hours of use they measure much better than the Chinese tubes that are essentially new.

 

RE: Chinese 300B, posted on January 22, 2021 at 20:27:26
Paul Joppa
Industry Professional

Posts: 7295
Location: Seattle, WA
Joined: April 23, 2001
 Many tubes will drift during the first 100 hours or so, as the cathode finishes forming I presume. It's worth checking again when they are run in.

 

RE: Chinese 300B, posted on January 22, 2021 at 21:11:52
vetmedrobert@gmail.com
Audiophile

Posts: 453
Location: Ontario
Joined: September 20, 2007
 Assuming they last 100 hours, of course.

 

RE: Chinese 300B, posted on February 1, 2021 at 07:53:24
Acoustic-Dimension
Distributor or Rep

Posts: 26
Location: Delft, the Netherlands
Joined: December 17, 2009
 That -80V negative bias is for the "average" tube. Even many WE tubes will not test like that. Some will need more negative bias and some want less.
And that is according to the WE datasheet, these are a different brand tubes. Not all copies will follow the original datasheet exactly.

So they are just a little different.

 

Has anyone tried the LinLai 300Bs?, posted on February 10, 2021 at 18:48:56
ishmael39@earthlink.net
Reviewer

Posts: 10
Location: Brooklyn
Joined: March 11, 2017

 

RE: Chinese 300B, posted on February 22, 2021 at 19:11:45
ishmael39@earthlink.net
Reviewer

Posts: 10
Location: Brooklyn
Joined: March 11, 2017
 don't worry if it plays music it is fine.

with 300Bs the only measurement that matters is transconductance

when we bought used WE300Bs we would measure all the used loose ones (in a cardboard box) and pay the owner so much for every micromoho

but you need a tube tester that takes 4-pin tube and measures not just 'conductance' but transconductance

just enjoy them

herb

 

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