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Old 30th January 2008, 09:55 PM   #31
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Ok. 222.7 is VOLTAGE, not CURRENT.
It is an effective voltage while an amplitude is 1.42 times higher.

What maximum power dissipation you may allow for your output tube?
George (tubelab.com) have plenty of them so he tortures tubes to see if they are alive on certain power; if you have only few of them you probably have to trust the manufacturer that specifies the max power, right?
So, how much are you going to dissipate?
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Old 30th January 2008, 09:58 PM   #32
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Default The 813

90mA @ 900Vdc per 813 Tube...single ended.
_________________________________________Rick..... ......
pardon , yes of course it is volts...we commonly say wall "current" poor grammer.
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Old 30th January 2008, 09:59 PM   #33
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Default Re: The 813

Quote:
Originally posted by Richard Ellis
90mA @ 900Vdc per 813 Tube...single ended.
_________________________________________Rick..... ......

Ok, do you have a MOSFET that can survive twice more?
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Old 30th January 2008, 10:02 PM   #34
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I would have to look up some Mosfet ratings......These "sand blocks"...I have few. No Mosfets here.
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Old 30th January 2008, 10:18 PM   #35
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Quote:
Originally posted by Richard Ellis
I would have to look up some Mosfet ratings......These "sand blocks"...I have few. No Mosfets here.
____________________________________Rick........
The idea was, to get a SE sound from a PP transformer. It will be even better than SE because the transformer needs to be smaller, with less of iron and copper (both are expensive in South America and in China, right?), so capacitance between windings will be smaller, the same about stray inductance. You'll get a sound from a PP amp similar to a sound from SE amp that is not practically possible if to use an "inside of the box" approach. My approach is to go out of the box and look from outside.

You'll need also an opamp to drive a FET. do you have some?
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Old 30th January 2008, 10:26 PM   #36
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Ok, do you have a BJT from an old TV?

MOSFET is what come to my mind because of availability.

Do you have a BJT that was used for horizontal deflection in an old TV?
They usually survive high enough voltage that is needed for vacuum tubes.

PN junctions on high voltages (ANY PN JUNCTIONS!) work like Zener diodes: from some point they start conducting. It means, a transistor is a transistor until you supply it with a certain voltage, after that it is a Zener diode!!!!

Back in 1970'th I used to select transistors for my custom amps from devices that were rated for 25V when I need more than 100 Volts.

Do you have an idea how to measure your transistors?
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Old 30th January 2008, 10:42 PM   #37
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Gentlemen;
if you have any questions please ask.
I am aware that nobody knows analog electronics like me it is not a shame because I myself don't know everything, and the more I know the more I understand how much don't I know; so please don't hesitate and ask. If both of us don't understand I'll learn together with you continuing the discussion. We'll gain both.
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Old 30th January 2008, 10:48 PM   #38
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Sorry wavebourne...my boy is buggin me to tear apart a wall wart so I can get some 9Vac out of a 12Vdc so I can power up his Nintendo (Down since we got here).
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Old 30th January 2008, 11:20 PM   #39
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Gentlemen,

This looks like fun! Can I just use rubber gloves rather than using one hand with the other behind my back (fingers crossed of course)?

I like the idea of a Russian-American DIY Tube amp over a Chinese one!

We covet a lot of electronic components from Russia anyway and quite a few of their tubes! So this is a worthy undertaking and I hope to learn too!

Thanks guys!

Regards//Keith
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Old 30th January 2008, 11:51 PM   #40
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Bernardo,
Talk to Eduardo at Audio Pax. He builds excellent tube amps and he is in Brazil. His web site is www.audiopax.com. He should be able to help you out.
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