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

Hey,

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.

Thankyou!
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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
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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.

Dogie
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Old 17th July 2005, 02:25 AM   #4
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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
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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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