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Old 5th February 2012, 05:35 PM   #1
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Smile suggestions for driver tube for 2A3

Greetings!

I bought a pair 2A3's and just finished winding my OPT's and now i want to start making the amplifier!

I am searching for a driver tube and i am thinking for the 12BH7 or 6CG7..
Does someone has experience with them and can share his findings of them or if there is something better i am open to any suggestions...
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Old 5th February 2012, 05:48 PM   #2
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Yes, i have. 12BH7 and ECC99 are intended for this purpose and both excellent. I personally like JJ ECC99 and would use them to drive 2A3. They show very low distortion, are reliable and will be available in the future (or similar tubes like 12BH7).
I used them for driving transformers at line level signals.
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Old 5th February 2012, 05:50 PM   #3
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ECC99 was made exactly for this purpose. They are excellent tubes and will be available in the future (or similar tubes like 12BH7). They sound good too.
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Old 5th February 2012, 06:47 PM   #4
djn is offline djn  United States
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A friend of mine built a 2A3 using 6SL7s for drivers. I think it sound VERY good.
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Old 5th February 2012, 08:21 PM   #5
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Are you going RC coupled or are you also winding input and driver transformers? The better designs of yesteryear used push pull drivers in to transformers with push pull drive. RCA advises separate coils (bring out both wires instead of just a center tap) since separate bias adjustment is usually needed for balance. Cathode adjustment is possible too but that requires separate filament windings. To get the full power of vintage designs, the bias feeds to the drive transformer are low impedance and it's a step down transformer so you can get the added power of class A2 or AB2 on peaks without drive distortion or bias shifts.. The smaller vertical output twin triodes and similarly made tubes not marketed for high voltage are all good choices for transformer drive. 6BL7 12BH7 6CG7/6FQ7 6SN7 6GU7. There are a number dissimilar vertical triodes that will work well using the bigger half for the driver and smaller for the input stage. Some of the larger ones have capability near that of the 2A3 (6GF7A etc). If using RC coupled drive you'll get less power and blocking distortion when overdriving, but much lower currents work then with the choice being limited mostly by the miller capacitance of the output. The 6SL7 suggested was no doubt used in that mode, being low current like a 12AX7. If you want Class A2, AB2 capability with RC and direct coupling, look at the drive section of the Heathkit W6A or W6M. A 6SL7 and 6BL7 or 6SN7 will replace the 12AX7 and 12BH7 if you want the more vintage octal look.
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Old 5th February 2012, 09:12 PM   #6
kevinkr is offline kevinkr  United States
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You might also want to consider the 5842/417A particularly if you are interested in using choke loading or interstage transformers.

Other potentially interesting choices include the D3A and C3G although in most applications the gain will likely be too high.

The Russian 4P1L DHP driving an IT in triode connection or in pentode RC coupled might be worth investigating .. I've not yet gotten around to doing something with the ones I have, but will..

If you need little gain and like American dhts the 26, 30, 31, and 112/12 might also be worth looking at.
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Old 5th February 2012, 09:46 PM   #7
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Why no Pentode driven 2A3 ?
12HG7,12GN7, 12HL7, EL802, 6Sh52P, D3A, E280F, E810F, EFL200, ECL200,...

Quote:
Originally Posted by GlowSignal View Post
12BH7 and ECC99 are intended for this purpose and both excellent.
No, 12BH7 was intended as vertical deflection amp in TV sets. And yes, it works well for other purposes, too
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Old 5th February 2012, 09:58 PM   #8
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Currently i possess two D3A and the perfomed very nice!
I know that the gain is two much
I am thinking about CCS load. In all testing i have seen the D3A perfoms very good.

What about a cascade driver?

Last edited by nomiconxp; 5th February 2012 at 10:12 PM.
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Old 5th February 2012, 10:44 PM   #9
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I will try D3A and 12GN7A in triode mode 180V 16-18mA bias point with rc coupled.

kevinkr i will try too the 4P1L a friend has and i will borrow.
Has anyone used the cv181??
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Old 5th February 2012, 10:47 PM   #10
mos57 is offline mos57  Italy
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56 have same filament voltage, very good linearity and look like 2A3, but gain is not high.
I would suggest the family tubes 5687/7044/6900 or the russian 6H30DR.
But I think that the D3A in triode connection is a very good choice.

Best regards, Francesco.
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