Power tubes plate resistor
Moderators: pompeiisneaks, Colossal
Power tubes plate resistor
Hello. Does it make sense to drop the power tubes anode voltage by connecting suitable resistors between the tubes pins and the output transformer?
Amateur
Re: Power tubes plate resistor
It depends what the intention / goal is?
I can't think of any benefits from doing that.
I can't think of any benefits from doing that.
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Stevem
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Re: Power tubes plate resistor
In a 4 or more output tube amp a low value low wattage one is used as a blow out resistor which will allow the amp to work with one dead tube on each leg of the OT and not blow the HT or mains fuse.
Check out a Ampeg SVT output stage as that amp uses such a set up!
Check out a Ampeg SVT output stage as that amp uses such a set up!
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Power tubes plate resistor
If the resistor blew on a good tube, I think that the screen grid current might shoot up and damage it.
May be mitigated by the low screen grid supply of the SVT.
But may be better to put such a fuse in the cathode circuit?
However, perhaps if they're mounted near / at the tube socket, such resistors are being intended to act as plate stoppers, especially when there's multiple high mu tubes in parallel?
May be mitigated by the low screen grid supply of the SVT.
But may be better to put such a fuse in the cathode circuit?
However, perhaps if they're mounted near / at the tube socket, such resistors are being intended to act as plate stoppers, especially when there's multiple high mu tubes in parallel?
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Re: Power tubes plate resistor
Have some problem with B+ voltage. Amp have 6ak6 tubes, push pull. They need less plate voltage. Now i put 1k power resistor after bridge rectifier. Now power tubes plate voltage is ok. And i must put lower resistor to b3 and b4.pdf64 wrote:It depends what the intention / goal is?
I can't think of any benefits from doing that.
Bad english, sorry
Amateur
Re: Power tubes plate resistor
Just make sure that dropping resistor does not operate beyond it's power rating as it could cause a fire.
I see the 6AK6 is only a 1.1 watt tube.
So a large power resistor should work or a zener diode.
I see the 6AK6 is only a 1.1 watt tube.
So a large power resistor should work or a zener diode.
Tom
Don't let that smoke out!
Don't let that smoke out!
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gingertube
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Re: Power tubes plate resistor
The plate resistors you see in some old amp schematics were there for a different reason. They are "plate stopper" resistors for stability. After you have fitted appropriate grid stops and screen stops and STILL (GRRR!) have parasitic oscillations in the output tubes the next thing to try is plate stop resistors. They are generally no larger than say 100 Ohms.
Cheers,
Ian
Cheers,
Ian