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Old 11th September 2012, 02:49 PM   #11
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Quote:
Originally Posted by ruben alstad View Post
screen grid seeing 416 volts?
but the GU50s have a max 250volt screen grid.
operating waay over spec, are they ok with it?
In UL mode they may survive. In triode you may use up to 450 V, in pentode maximum 300V (in audio amp).
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Old 11th September 2012, 03:05 PM   #12
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Quote:
Originally Posted by palmas View Post
KT88 is a different bugger, not that well built and prone to faillure
sorry, i meant to make the kt88 amp use GU50s instead.
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Old 11th September 2012, 03:07 PM   #13
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Quote:
Originally Posted by ruben alstad View Post
sorry, i meant to make the kt88 amp use GU50s instead.
Do you mean KT88 in this particular amp instead of Gu-50?
Yes, in such regimes they would be happier.
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Old 11th September 2012, 03:30 PM   #14
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Quote:
Originally Posted by Wavebourn View Post
Do you mean KT88 in this particular amp instead of Gu-50?
Yes, in such regimes they would be happier.
it may need a new thread, but GU50s can operate on kt88 amps with a rebias?
push pull UL/triode 430/450b+ driven by 12au7 phase splitter.
this amp is going to be rebuilt anyhow, might aswell make it run on gu50s.
also the phase spliters are probably going to be replaced by either 6CG7,12bh7 or a 6sn7.
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Old 11th September 2012, 03:32 PM   #15
palmas is offline palmas  Portugal
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Quote:
Originally Posted by ruben alstad View Post
it may need a new thread, but GU50s can operate on kt88 amps with a rebias?
push pull UL/triode 430/450b+ driven by 12au7 phase splitter.
this amp is going to be rebuilt anyhow, might aswell make it run on gu50s.
also the phase spliters are probably going to be replaced by either 6CG7,12bh7 or a 6sn7.
They might, but you'd have to check case by case and sockets are not exactly same size

Last edited by palmas; 11th September 2012 at 03:44 PM.
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Old 11th September 2012, 03:43 PM   #16
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Quote:
Originally Posted by palmas View Post
They might, but you'd have to check case by case and sockets are to exactly same size
gu50s use their own socket.
kt88 uses octal.
6sn7 uses octal
12au7 12bh7 and 6CG7 uses noval.
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Old 11th September 2012, 03:51 PM   #17
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Some idea for improvement: If the PI's tail resistor is returned to the second filter cap of the bias voltage supply, the 560k/150K divider, the following 68k resistor and the 0.1µ cap from pin 7, second tube, could be omitted. Pin 7 and the grid leak must be grounded in this instance.

This would lead to a bigger possible output voltage swing for the PI - not too bad for GU50 finals.

Best regards!
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Old 11th September 2012, 03:55 PM   #18
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Quote:
Originally Posted by ruben alstad View Post
it may need a new thread, but GU50s can operate on kt88 amps with a rebias?
No. I meant in this particular amp KT88 may work better than GU-50. GU-50 likes higher anode voltage and load resistance, and lower G2 voltage than KT-88.
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Old 11th September 2012, 11:51 PM   #19
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Quote:
In UL mode they may survive. In triode you may use up to 450 V, in pentode maximum 300V (in audio amp).
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So I would be better off running in triode mode to increase the survival rate?
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Old 12th September 2012, 12:15 AM   #20
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Quote:
Originally Posted by wazza220951 View Post
So I would be better off running in triode mode to increase the survival rate?
Yes, but you will get less power than in UL mode. But it should be cleaner power.
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