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OP tube convertible PP amps?
OP tube convertible PP amps?
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Old 27th June 2005, 01:20 PM   #1
rick57 is offline rick57
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Join Date: Dec 2002
Location: dry ol Melbourne Australia
Default OP tube convertible PP amps?

Who has experience with “convertible amps”?

I’m considering a 45 PP, switchable to a
* DHT PP(300B) or
* 211/ 845/ EL34/ 6550/ KT88 PP
when the extra power is needed.

May need other set of OPTs?

Wiring more complicated?
Other issues??

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Old 27th June 2005, 04:33 PM   #2
Gluca is offline Gluca  Italy
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Location: Back to Italy
not me but ....

... what are you going to do with the power supply? 845/211 need an offensively high B+ while 45 are run at lower plate voltage

... and what about the heaters? ... hugely different voltages and currents

... and the bias? again, so different

... OPT? you can squeeze a very high power out of the 845 while the 45 give just a few watt and the loads are very different for each of these tubes. I don't believe a single OPT can offer all these options

Probably a selectable 45/2A3, just to stay with DHT's, can be a simpler/achievable project. And if you have separate 2.5V heater supplies you can switch to 300B. You could also add a DC (current) heater to have more flexibility and simpler wiring (You will just have to adjust the sensing resistor of the current regulator).

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Old 28th June 2005, 02:33 PM   #3
rick57 is offline rick57
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Join Date: Dec 2002
Location: dry ol Melbourne Australia

Yes - you’re right! I was beginning to come to the same conclusion.

I’m now investigating 845 PP as a *separate amp.


I'll condsider your ideas in a 45/ 2A3
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