Im no big amp tech, but the amp listed is pulling in the contacts and killing receive once the tube section power in engaged, any ideas or thought would be appreciated.
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Black Cat JB76b
- Thread starter Wky Gatekeepr
- Start date
Typical failure begins when someone tries to use a radio that's just too big for the amplifier. This is a 1970 design meant for 1970 radios that would bust a gut to dead key 3 and swing 14 Watts PEP on AM. Anything bigger than that tends to be unhealthy for it.
The keying transistor is the usual cause of this symptom.
Original type number for the keying transistor is 2N2222, or PN2222. A lot of other numbers will substitute, like 2N3904, 2N4401, NTE123A and many others.
There is a small glass diode feeding into the base terminal of the keying transistor. A generic 1N4148 or 1N914 works, along with a long list of close equivalent types. Just needs to be a small glass diode that's fast enough to rectify RF voltage. The black-epoxy rectifier diodes used in a power supply won't work, they are meant for 60 Hz frequencies, much to slow for this keying circuit. Whenever the keying transistor gets overloaded, this diode usually gets hammered along with it.
Here's the schematic of the base version.
73
The keying transistor is the usual cause of this symptom.
Original type number for the keying transistor is 2N2222, or PN2222. A lot of other numbers will substitute, like 2N3904, 2N4401, NTE123A and many others.
There is a small glass diode feeding into the base terminal of the keying transistor. A generic 1N4148 or 1N914 works, along with a long list of close equivalent types. Just needs to be a small glass diode that's fast enough to rectify RF voltage. The black-epoxy rectifier diodes used in a power supply won't work, they are meant for 60 Hz frequencies, much to slow for this keying circuit. Whenever the keying transistor gets overloaded, this diode usually gets hammered along with it.
Here's the schematic of the base version.
73
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