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Help with 6B4G PP amp.
Help with 6B4G PP amp.
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Old 16th July 2005, 05:46 PM   #1
AudioGeek is offline AudioGeek  United States
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Default Help with 6B4G PP amp.


Currently my amp is a Sovtek 6B4G PP Class A amp.

output stage is at around 340v (300v plate to cathode). OPTX is a 5K:8 unit.

bias is shared cathode and driver is a ECC99 with VR150 tube regulation into a 1:1/1 phase splitter tranny.

Now i want to upgrade it a bit.

What is a good bias point for Class A PP using these sovteks? I heard you can push them a little hotter....?

Should I use seperate filament supplies and seperates bias for each output tube?

Power supply is CLC with a small 3uF input cap a large 5H choke then I think over 180uF at output. Input stage is tapped from this through a dropping resistor to the VR tube...

I am looking for a bit more power and a little more musicality.. (isn't everyone).

So basically I am looking for ideas and advice on what I can do to this amplifer... I am open to changing the input tube and biasing of both input and output and changing PS... but the phase splitter tranny and OPTX stay.

It is not you... you are it.
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Old 16th July 2005, 06:29 PM   #2
Yvesm is offline Yvesm  France
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Could you show your schemo ?
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Old 17th July 2005, 12:11 AM   #3
Dogie_Hogan is offline Dogie_Hogan  Netherlands
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Default pp-6B4G

I would suggest:

- replace the ECC99 driver-tube by the latest version of the 6CG7-EH from Electro Harmonix orsome more sonical a RCA 6CG7, the SITE-GETTER version!
- an input-stage with the 5965 (E188CC) improves also the sound. (Ra 100K, Rk 1K6, Ub 260-280V.)
- Every 6B4G should have it's own Rk (1K/20W.)

With above chanches the sound has at a lower level allready more "body"/drive. No need for more output power.

With the nice Sovtek 6B4G, I think Ub 350V. is maximum with Ia 50mA.

Above experiences were with a PP-6B4G with floating-pharafase ("Hafler"), input tube 5965 (improved 6072A), , 6CG7 EH driver (Ra 27K, Rk 470R, Ub 315V.), Ub 6B4G's 320V. and Raa 5K/6R.

Amazing the 6CG7 EH: clean, open, natural and live soundstage. The RCA 6CG7 with site-getter is a little bit better in the mid-range.

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Old 17th July 2005, 02:25 AM   #4
zarniwoop is offline zarniwoop  United States
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I'm getting nice power out of PP sovtek 6b4g amp. Running them hot. Not sure if its truly class A, but it sounds very good. ~350V p-k, 75mA. 5K a-a load, but I have 8R nominal speaks. on the 4ohm 2ndary.

Driver headroom/linearity is important or you just get a lot of the driver tube's distortion dominating the output. I have a differential 6sn7 driver, with direct coupled, 6fq7 CCS loaded input stage. Not that this is great.. just a tweaked amp, and thats how it ended up for now.

don't really have any great advice, but you can push the sovteks pretty hard if you want more power.
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Old 17th July 2005, 02:53 AM   #5
Dogie_Hogan is offline Dogie_Hogan  Netherlands
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Default more output with a PP 6B4G

More power with a PP-6B4G.

Do you hear the difference between 12 or 15 Watts for instance?
I expect no... , and in dB: 10 Watts => 40 Watts.

Improving connectors, speakercable (Vandenhul D-352 for instance) and a better driver/inputstage may give more body/drive at a lowe volume-level. And speakers with a flat-impedance of course.
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