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Vintage threads from the first ten years
Dual OT circuit
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 4/25/2006 5:31 AM |
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Chris@CMWamps |
Dual OT circuit Hi all I have to design and build an amp with two OTs and two speakers, same concept as the very early 100 Watt Marshalls but using a different circuit and other tubes. How is the neg.feedback resistor wired from the PI, to which tap or are there two resistors used? According to some guys/info on the net it's possible to use just one output without the unused one being loaded with a speaker or load. Is this true? In any case: many thanks for all help and ideas, Chris |
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| 4/25/2006 2:51 PM |
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| dai h. |
IIRC, there was a bit of info on the plexi palace marshall board(?) on how those old dual OT 100s had their output transfrmrs. hooked up. You might also look at the reiss. dual OT 100 from Marshall(the HW--handwired--one). I think someone put up pics from their amp at the picture site for the yahoo jtm45 group. I also have some pics of somebody's original so if you need them just send me a note. |
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| 4/25/2006 3:00 PM |
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| Chris@CMWamps |
Hi Dai Many thanks, I'll send you an email in a few seconds. Chris |
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| 4/25/2006 3:15 PM |
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| Satamax | Hi Guys! Chris, i don't know anything about the dual OT circuits, but i'd think i would use a dual standby, so you could use it as a half power, or may be even HP switching  Something démential to try would be a bridged dual OT amp See what i mean? One preamp, feeding a concertina, spliting it into two long tail PI, feeding the two output stages, working bridged, hot of the top trany into the hot of the speaker, cold of this trany on the hot of the second trany, and the cold of that trany onto the cold of the speaker 200 watts with two 50 watt tranies
Bye. Max. |
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| 4/30/2006 8:35 AM |
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| Mark | Chris, I have an old twin reverb that uses 2 vibrolux sized output transformers. Phase inverter to power tubes is standard Fender, but each pair of tubes is wired to its own output transformer, output jack, and speaker. I added a switch which lifts the cathodes of one pair of power tubes from ground for 2 tube/1 speaker operation. Each output jack has an 820 ohm feedback resistor connected to its tip. The free ends of the resistors are joined and the combined feedback is run back to the bottom of the phase inverter. Simple, works well. Good luck. Mark |
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| 5/1/2006 2:52 AM |
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| Chris@CMWamps.com |
'51 Jensen P12P clones? Hi Mark & all Many thanks. Dai did email some info and links and after hours of midnight-emailing between London, Amsterdam, Japan and me (and some emails after that) it was totally clear to me. Mark: thanks for your dual OT TR notes. The idea from Satamax is pretty cool but requires a very hefty PT. The customer did talk about ordering a double GA40. So right now I'm wondering about replica's from a '51 style Jensen P12P speaker. Did have a look at WeberVST.com but didn't see those. Anyone got experience with such speakers and/or existing clones? Many tia! Chris |
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