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Old 2nd September 2007, 04:12 PM   #1
tubo is offline tubo  Philippines
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Default want to build a pentode driven drd 2a3!

hi folks,

i would like to build a pentode driven drd 2a3 or 300b, just like the one thorsten have but with e180f as the driver, as i have a quad given to me. im wondering if there is a schematic laying around on some of the threads. im fairly a newbie in ellectronics and tubes but i have built quite a few amps from schematics with parts list up until 400v.

will you guys be able to also specify the ps transformer and chokes if possible hammonds?
i would also like to use elctraprints for the plate chokes.

i already have some parts which are listed below.

transcendar 3k or 5k opts at 150ma
tj 2a3
tj 300b

thanks in advance!
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Old 2nd September 2007, 08:30 PM   #2
Klimon is offline Klimon  Belgium
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I'ld be interested to hear about pentode driven drd's too. How do pentodes behave with a choke load btw; not such a natural combination as triode + choke or am I completely missing things?

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Old 2nd September 2007, 08:41 PM   #3
jane is offline jane  Norway
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Pentodes have quite high internal resistance which, together with a reactive load, might affect the low frequency response.

Jan E Veiset
Life is hard - Then you die.
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Old 2nd September 2007, 10:17 PM   #4
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E180F is a great tube, but even better in triode mode. Would take care of the pentode high plate-Z issues Jane speaks of.
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Old 3rd September 2007, 01:28 AM   #5
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i would expect that you would need to resistively load the pentode and not inductively load it as typically done. Inductive loads and pentodes typically lead to very odd results.

the simple tasks is to find a pentode that is happy with the load it gets when you divide current by the needed bias. (10ma of current and a 45V bias would require a load resistor of 4K5)

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