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Old 7th July 2013, 05:03 PM   #1
kgc-jr is offline kgc-jr  United States
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Default Palmer DREI - Three SE Output Tubes Together?

I was recently browsing the Web and found the Palmer DREI guitar tube amp on Youtube. It uses a combination of three single-ended power tubes mixed together via separate blend controls. It appears from the Palmer website photos of the amp that it uses only one output transformer.

My question is: how do you connect all three output tubes together on one output transformer?
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Old 7th July 2013, 06:49 PM   #2
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It is for guitar, so less worry about 'optimum' impedance. Just connect them together at a HT voltage that is OK for all valves. If you want, you can have an OPT with different taps on the primary for each type of power valve.
The difference in drive requirements for each type can be compensated or left to the player with 'blend'? pots.
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Old 9th July 2013, 09:31 PM   #3
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I think it just uses a regular OPT (with relatively low Ra winding) with all three tubes wired in parallel and individual cathode resistors to set the bias for each tube. All the reviews seem positive, so I will have to try to build one to check it out for myself.
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Old 9th July 2013, 11:37 PM   #4
multi is offline multi  Australia
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Default 3 X 2A3 amp

Circuit for a 3 X 2A3 amp has one of the best driver circuits.
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Old 10th July 2013, 01:51 AM   #5
kgc-jr is offline kgc-jr  United States
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Thanks Para & Multi for your replies.

Jaz, I think your right, and I would also like to give this configuration a try. I have an EL34, 6L6GC, and 6V6 laying around somewhere, along with a Hammond 125FSE (20W SE) output transformer. What's nice is that this transformer has a multi-tap secondary which you can configure for different prim. impedances (2.5K-10K). I'm sure I'll be able find a decent plate load match for all three tubes in parallel. And in a guitar amp it may not matter all that much anyway.

If you put something together that works, please post it on this thread, as I'll be checking periodically and I'd like to see what you come up with.

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