Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mresistor on October 12, 2018, 12:54:22 pm
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Since I have to replace the ot in my ampeg B15S amp.. I ask for your consideration of this option ..
Hammond 1650HA 40 watts
Hammond 1650PA 60 watts
the amp uses two 7027A power tubes and the Plate v could be a high as 570 v due to high wall v https://drtube.com/datasheets/7027a-rca1959.pdf
MM has one for $260 and Mojo has one for $299 very expensive
I think I can mount this hammond under the stock transformer can without potting and still have the stock look..
btw anyone know how to de-pot a potted transformer from the 70's? I think I would warm it up in the oven and then dump the goo out.. but I don't know
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According to what I have learned that primary impedance of the stock OT is 6K .. and resistance of 300 ohms.
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Is the mojo OT potted? If so that costs more to pot the OT.
It's a bass amp so I would go with a larger/higher wattage OT, given a choice.
Many guys here have used Hammond iron, with great results.
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.....the amp uses two 7027A power tubes and the Plate v could be a high as 570 v due to high wall v https://drtube.com/datasheets/7027a-rca1959.pdf (https://drtube.com/datasheets/7027a-rca1959.pdf)
The data sheet shows 600dcv max for the plate and 500dcv max for grid 2/screen. It also shows 600dcv max for both plate and grid 2/screen if using a tap from the plate wind (UL). UL taps limit the screen grid current.
All 4 schematics in Doug's library show 575dcv plate and 580dcv on screens with 470ohm 2w screen R's.
So use at least a 1K 5w R for the screens to help limit the screen grid current.
Real 7027's will take the dcv in your amp, so the data sheet say's and new 7027's? :dontknow:
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Thanks Willabe - for sure I will change the screen resistors. Crazy high voltages in this amp.