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Old 22nd December 2012, 12:04 PM   #1
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Default Sakuma's bleeder tubes and series connected transfomers

Hi!

I just browsed Sakumas website and found some of his latest works. Sakuma is known for his unconventional circuits. He added some new twists to his latest builds.

There are 'bleeder tubes' added to provide some load to the power supply. Probably for stabilisation. But why use tubes instead of a plain resistor? He even uses expensive DHTs for this purpose like a WE300B here:

12AT7 / 841 SE phono preamplifier

There is even a transformer added as a load to the tube, with the secondary just grounded on both ends.

Here he uses a 50:

5691 / WE-102D SE phono preamplifier

This time even with an input transformer.

There is probably some reasoning behind it, did anybody read the MJ magazines in which these circuits got published? Was there an explanation why this was done?

Also quite interesting the use of several transformers connected in series as a load to enable transformer coupling of high rp tube like the 841:

841 SE Tone control and buffer amplifier

Best regards

Thomas
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Old 22nd December 2012, 02:07 PM   #2
DF96 is offline DF96  England
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Reasoning? An unusual circuit with expensive components used in non-standard ways must surely sound better than a bog-standard circuit that any competent engineer/DIYer could design.
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Old 22nd December 2012, 02:14 PM   #3
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Seems like a good way to boost Tamura's sales.
Any affiliation?

I see it as a consequent further development of "tube amps" with tubes that have only the heater connected (usually they come in bundle with many blue LEDs).
Including DHTs and transformers seem like a naturally "step up" from these designs.
No other idea that I could provide...

Martin
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Old 22nd December 2012, 02:19 PM   #4
12B4A is offline 12B4A  United States
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I can think of far better circuits to use rare vintage tubes in which they would actually be amplifying an audio signal.
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Old 22nd December 2012, 02:39 PM   #5
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Surely there is an alternative explanation to this. The arrangement is too elaborate to be designed to simply increase the ps loading. Let's not jump to conclusions and speculate how silly Sakuma is.
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Old 22nd December 2012, 02:46 PM   #6
Zen Mod is offline Zen Mod  Serbia
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crude shunt reg ?
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Old 22nd December 2012, 02:46 PM   #7
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My only non-cynical explanation that I can come up with is that these are parts of possible "upgrades" for the future. Everything already wired in the amp, just connections to the outside world have to be added.
This way, an additional line stage could be added to the existing (and already paid) amp fast and at low costs.
Too weird to be true?

Martin

PS: Is the schematic actually correct? Shouldn't the left PS diode also be connected to choke and first cap?

Last edited by bayermar; 22nd December 2012 at 02:48 PM.
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Old 22nd December 2012, 03:08 PM   #8
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I think Sakuma's finally gone off the deep end. Although I have seen UTC transformer primaries used as a delay line in a preamp to compansate for transition speed when used with SS power amps. Seems bizarre to me.
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Old 22nd December 2012, 04:40 PM   #9
jlsem is offline jlsem  United States
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Quote:
PS: Is the schematic actually correct? Shouldn't the left PS diode also be connected to choke and first cap?
Yes. Looks like an oversight on the publisher's part.

John
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Old 22nd December 2012, 05:24 PM   #10
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Hi!

My intention was not to give any judgement about these circuits. I'm interested if Sakuma wrote anything bout this, probably in MJ mgazine. Anybody read about this who can post a translation?

Thomas
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