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Post by holytrain on Jul 2, 2022 18:26:41 GMT
Group looking for substitute power transistors for a Rockola 40218-2-A. It originally had (4) 2N2869 and (4) 2N2147 and help would be appreciated.
Thanks
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Post by jukenorman on Jul 2, 2022 19:25:49 GMT
Hi Holy,
It would be useful when posting queries like this if you identified the Rock-Ola model number - but OK, I have discovered that it's a 424! I have this in my notes:
"Rock-ola 424 amplifier, silicon can replace germanium outputs. Replace all eight metal TO-3 transistors with 2N3791 PNP silicon. Change the four 2.4 ohm resistors in the base circuit of the outputs to 10 ohm, 1 watt. Adjust the bias pots for 35 to 60 ma and 22.5 volts or half the supply as shown in the manual."
I hope that helps!
Norman.
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Post by Ron Rich on Jul 3, 2022 4:25:26 GMT
Hi Norman,
Does this work for (m)any other RockOla amp(s) ? Ron Rich
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Post by jukenorman on Jul 3, 2022 9:23:52 GMT
Hi Ron,
I think that it would work in any Rock-Ola amp with germanium output transistors. The issue is that in the 60s', Rock-Ola (and AMi) jumped about a lot with their amp designs - tubes, germanium transistors, tubes, silicon transistors etc. All over the place really! I was sure that a query like this had come up here before so I did a quick search and it was for a 47160-A in a model 448 RO.
Norman.
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Post by Ron Rich on Jul 3, 2022 12:00:40 GMT
Thanks, Norman !
Ron Rich
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Post by holytrain on Jul 3, 2022 20:20:55 GMT
Norman Thank you for your reply I will give it a try.
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