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Old 25th October 2010, 05:21 PM   #71
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Default Correct

Quote:
Originally Posted by kavermei View Post
Looks like an interesting idea!, but make sure that the CCS can dissipate the required power (20 ... 25W if I calculated it correctly).

Kenneth
You are correct about the power dissipation. The circuit I came up with uses an LM317 as a CCS, and a BUX85 transistor is used to keep the voltage on the LM317 within its tolerance limits. The BUX85 can handle 450 volts on the collector and can dissipate 40 watts max. If it's well heat sinked 20 watts should be no problem. I already built this and tested it and it works.

The 1 ohm resistors make measuring the cathode currents easy. 1mA = 1 volt. The LM317 CCS is adjusted to sink 180mA and the 25 ohm pot is used to balance the currents at idle in the tubes.
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Old 25th October 2010, 10:22 PM   #72
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measuring cathode current over the 1 ohm resistor: 1mA = 1mV (not 1V).

Pieter
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Old 20th December 2010, 05:27 PM   #73
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Hi gentlemen,
After some more experiments, I ended up using this schem. Any ideas?

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Old 20th December 2010, 05:32 PM   #74
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Quote:
Originally Posted by hoangduongo View Post
Hi gentlemen,
After some more experiments, I ended up using this schem. Any ideas?
I like it!

Why didnt you use grid stoppers on V4, V5 and V6 ?
Also, i'd change the bias circuit (the pot meters) so that when one breaks (wiper loses contact) the voltage goes all the way down, and not to 0V
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Old 20th December 2010, 05:56 PM   #75
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Quote:
Originally Posted by hidnplayr View Post
I like it!

Why didnt you use grid stoppers on V4, V5 and V6 ?
Also, i'd change the bias circuit (the pot meters) so that when one breaks (wiper loses contact) the voltage goes all the way down, and not to 0V
Thank you hidnplayr for your comments.
I actually use grid stoppers for V5 & V6 (forgot to put them in the schematic). For V4 I think R8 already works as gird stopper, so no need for that.
Havent thought about the pots, talking about changing bias circuit, did you mean changing R27, R28 value and connect them to B-?
Thanks again.

Last edited by hoangduongo; 20th December 2010 at 05:59 PM.
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Old 20th December 2010, 06:10 PM   #76
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Quote:
Originally Posted by hoangduongo View Post
Havent thought about the pots, talking about changing bias circuit, did you mean changing R27, R28 value and connect them to B-?
Thanks again.
I was thinking something like this:
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Old 20th December 2010, 08:41 PM   #77
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Originally Posted by pieter t View Post
measuring cathode current over the 1 ohm resistor: 1mA = 1mV (not 1V).

Pieter
Sorry - typo.
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Old 10th October 2011, 02:51 PM   #78
adam2a3 is offline adam2a3  Greece
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Default GM70pp class A driven by RY50 SRPP and 6SN7

Hi, this is my GM70pp 80W per channel, class A amp that is powered by a pair of modified ISCO 494 power supplys (1100V 300mA each).
It is using 6SN7, SRPP RY50 pair at 1000V parafeed driving a LUNDAHL 1660PPZ as a phase inverter.
Comments on the schematic are welcome!
adam2a3
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File Type: jpg DSC00874.jpg (458.3 KB, 323 views)
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Old 10th October 2011, 04:22 PM   #79
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Hi Adam,

Nice amp & schem, below are some of my ideas:
- The ГМ-70s and ГУ-50s seem to be too close to each other, with my amp, even though being monoblocks but with total idle dissipation of ~300 W/channel, it's way too hot that you should not use it in summer days
- The OPTs are 10k p-p? From the pictures I think it would be better if those OPTs are bigger.
- The 68Rs at cathodes of ГМ-70 should be 3W.

Regards,
Duong
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Old 10th October 2011, 06:30 PM   #80
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Nice!

Maybe once my 4 month old boy no longer needs my constant attention I can finish my amp. I'm jealous.

Very nice build.
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