Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: svejkist on March 22, 2022, 01:30:10 pm
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I've been building a Maggie 213 Troubadour, using Martin Manning's brilliant MOV varistor hack. So far so good, except I find conflicting information on the B+ I should be targeting (and nothing on any other voltages). I don't have a Troubadour handy to measure, or even compare the sound at different voltages, so I am flying blind. If it were for me, I would just do what sounds best, but this is for a customer, so I would like it to sound as close to a real 213 as possible. The MM replacement PT is 378-0-378 @80ma, but the only marked schematic I have found calls for a Hammond 291BEX (330-0-330) with a 25V voltage reducer .That is a pretty big disparity. The second sounds more reasonable, especially for the 6
LV6s of that era.
Does anyone know what I should really be targeting? Thanks in advance.
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This link may lead to some good info about the 213. There was a lot of discussion about this amp (building, repairs, etc.) when Yahoo magnatone-valco group was still around.
https://groups.io/g/magnatone-valco
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From what I could glean a few years ago, the B+ was about 350-360Vdc, dropping to about 300V at feed 'A'. The total idle load on B+ is approaching 100mA, with circa 20-25mA going to screens and pre stages, and the 6V6's have about 12W plate dissipation. PSUD2 indicates the PT secondaries are circa 300-0-300V, which would align with those using a 330-0-330V secondary and then a voltage reducer.
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Thanks guys!