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Old 2nd February 2009, 09:33 AM   #11
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I don't think I should post it here, as that would make the people at AX probably a bit unhappy...

For the 6528 you need Va-k to make it work, of course. depending on the load, but surely more than 50V IIRC. Should be clear from the data sheet. OTOH, using a FET for the pass device, that runs with much less Vd-s, much cooler.

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Old 3rd February 2009, 01:42 AM   #12
phi70 is offline phi70  United States
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Default Re: Re: Thanks for the confirmation

Quote:
Originally posted by disco

How do you calculate the voltages for the error amplifier?
No I didnt calculate the voltages, it was not a real DIY effort but an investigative effort to FIX bad sound of a commercial product.
The original circuitry of the audio section was a close model of a famous Wada Shigeru SRPP follower added to a Marantz 7 gain stage. The power supply as far as I know is just textbook stuff, the final output B+ is tuned using a trimpot (with resistors on each side) connected to the cathode of the 12BH7 that adjusts the grid bias to the EF86.
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Old 3rd February 2009, 01:45 AM   #13
phi70 is offline phi70  United States
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Quote:
Originally posted by janneman
20mV ripple from a regulator is just a bad regulator. And then to add injury to insult and add an L-C after it....

My tube HV reg has <500uV over audio band (<50uV over most of it). Will be published in AudioXpress in March or April issue.

Jan Didden
Interestingly enough this manufacturer of my preamp keeps adding more and more post regulation chokes to his newer offerings!
I am not sure where the 20mV ripple came from, Didnt see it in the raw B+ going into the regulator so I am inclined to think it came from the regulator filaments or bad tube choice.

Will definitely look at your design @ AudioExpress. Thanks and best regards.
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Old 6th March 2009, 01:42 AM   #14
phi70 is offline phi70  United States
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Default Tube regulator circuit on AudioExpress

I came across an article on Audio Express on tube based regulators published earlier:

http://www.audioxpress.com/magsdirx/...cknell2890.pdf


I tried to model the basic regulator circuit (figure 1) which is quite similar to the one that is in the preamp I am working on. I discovered that the g2 of the EF86 has a noticeably higher voltage than the control grid g1 and g3 being tied to cathode is referenced by the zener stack.

As a result the plate voltage of the EF86 is in the order of more than 100V below the
output tube's cathode. This leads me to suspect that the output tube is not really turned on.

May I ask if anyone has had experience building a similar regulator with an EF86 control
and if so whether the voltage on the EF86s screen grid (g2 between R5 and R6 in the diagram) really should be higher than the anode?!

Any pointers appreciated. Cheers,
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Old 6th March 2009, 06:51 AM   #15
phi70 is offline phi70  United States
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Default never mind... the screen grid G2 of the EF86 was wired wrong

It was wired to the regulated B+ which is substantially lower than raw B+,
rendering current starvation on the EF86 which makes the plate output too low
and as Morgan Jones describes in his valve amp book I was getting the exact
"sulking effect" when wiring the screen grid to regulated B+ instead of unregulated B+
(which is the proper way as depicted in the AudioExpress diagram).
Sorry for the confusion.
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