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Old 27th January 2004, 10:35 PM   #1
arnoldc is offline arnoldc  Philippines
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Default Seeking advise on my EL34 amplifier

it's me again :lol:

last night i completed an EL-34 amp and i think it sounds decent with nice bass and i was thinking how to get more power from it without overhauling, i.e. SEP to PP, the amp.

it is currently wired as triode, with pin 1 strapped to K. i've seen a few schematics with pin 1 tied to plate instead. what is the difference?

according to SE Amp CAD, i should be getting around 2.8W from this amp. i'd like to get more power.

i would like to wire it for pentode mode and my other question is, at the voltages shown, should i just tie pin 4 to a 250V supply?

am i better off using an UL OPT?

your thoughts are most appreciated.

cheers.
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Old 27th January 2004, 10:50 PM   #2
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Default Re: Seeking advise on my EL34 amplifier

Quote:
Originally posted by arnoldc


according to SE Amp CAD, i should be getting around 2.8W from this amp. i'd like to get more power.

i would like to wire it for pentode mode

your thoughts are most appreciated.

cheers.

Hi alnoldc!!

If you put the EL34 in pentode mode you must use some global fedback if not the speaker will not have damping at all...so if you go to pentode a litlle change in the actual circuit is needed.

Regards!
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Old 28th January 2004, 09:42 AM   #3
arnoldc is offline arnoldc  Philippines
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hi jorge, thanks for the reply. feedback, ugh (i have no idea about that) time to dig up the morgan jones book
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Old 30th January 2004, 03:58 AM   #4
SHiFTY is offline SHiFTY  New Zealand
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I would seriously try pentode mode and see if you like it... A bit of feedback is not a sin...
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Old 30th January 2004, 09:16 AM   #5
arnoldc is offline arnoldc  Philippines
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i had it modified to pentode mode last night. i fed 250V into G2 and immediately noticed more power. i did not have any feedback as i don't know how to apply one.

it sounds "different" though, and i can't explain what it is. i was asking myself "is this the sound of a pentode?" the mids are different from a triode amp and when it was wired as triode.
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Old 30th January 2004, 08:31 PM   #6
SHiFTY is offline SHiFTY  New Zealand
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Feedback is easy to apply.

On the preamp tube, insert a 100 ohm resistor between the 1K resistor/bypass cap and ground. to this junction connect a suitable feedback resistor (for example 4.7K should work OK) to the secondary of the OPT. See diagram.

If the amp sqeals when you first turn it on, reverse the ouput transformer secondary leads.

Apologies for this dodgy sketch
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Old 31st January 2004, 02:30 AM   #7
arnoldc is offline arnoldc  Philippines
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hi shifty, thanks for the mod! i'll work on it now
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