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Old 22nd August 2003, 05:16 PM   #1
zxx123 is offline zxx123  United States
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Default Anybody Has 6b4g Se Power?

1. I am planning to build 6B4G.
Can you explain 6B4G power amp's characteristics?
Compared to 2A3, how is it?

2. Can I use 12AX7 for pre-part?
I can only find the schematics which use
some expensive tubes.


Thanks.
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Old 22nd August 2003, 07:44 PM   #2
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Default ...Quick reply...sorry busy!

6B4G (and 6C4C - russian equivalent) are electrically the same as a 2A3 except for the heater requirements. i.e 6.3V at 1A c.f. 2.5V at 2.5A.

I have sets of both and find them very similar sounding. My favorite if the 60s & 70s Svetlana 6B4Gs but I haven't tried RCA 2A3s yet....

Yes you can use a 12Ax7 for the pre-amp part but I wouldn't. The input capacitance of the valve requires at least 3mA to drive it properly (I prefer twice that - it sounds better). Not everyone agrees on this...so try it and see.

Cheap valves that drive the 6B4G well are 6SN7 family at 8mA or more (I like 12-15mA). My favorite is 6N6P at 20mA or more.

I built a guitar amp using three parallel 2A3s for output and drove them from a 6AS7. This sounds superb (but is a little over the top...).

What tubes do you have available? The family here can come up with some designs to try using almost anything! Even (gasp) pentodes

ciao

James
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Old 22nd August 2003, 07:50 PM   #3
Fuling is offline Fuling  Sweden
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I drive my 6B4G SE with choke loaded 6SN7´s (parallell sections)
I use Hammond 150H 8mA chokes, and they work fine.
Before I convertet to choke loading I used 6SL7 with one section as gainstage and the other as cathode follower...

Would love to try IT-coupled 6C45´s.
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Old 22nd August 2003, 07:55 PM   #4
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Hi Fulling,

I've driven 6B4Gs with IT coupled 6C45 in SE and PP. It's good but not as good as 6N6Ps in this role. (I prefer the 6C45 in PP driving 845SE via an IT). Pete Millett has posted some interesting tests on the 6C45 distortion spectrum on AA that might explain this...

ciao

James
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Old 23rd August 2003, 06:57 AM   #5
SHiFTY is offline SHiFTY  New Zealand
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I have built the Angela SRPP 2A3 amp at http://www.angela.com/catalog/how-to/EZ.2A3.html using 6B4G. It sounds very nice indeed, I really prefer the SRPP driver, and you can use a 12AX7 instead of 6SL7.

One thing you will need to do is use a DC filament supply for each 6B4, AC supply causes too much hum.
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Old 23rd August 2003, 07:25 AM   #6
Fuling is offline Fuling  Sweden
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James,

I took a look at a 6N6P datasheet and yes, it looks like an excellent driver tube!

ShiFtY,

You´re right about the filament hum.
I converted to DC heating a while ago (choke filtered non-regulated supplys) and that took away most of the hum.

I think some extra caps (both in the filament PSU and in the HT rails) will take care of whats left.

By the way I didn´t notice any difference in the sonics between AC and DC heating.
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