hey larry

I see trouble with the bypass caps on the LM317 regulator. They have
opened up and now the adjust pin, which is an op amp input, isn't
bypassed, letting in massive quantities of rf and overloading the op
amps ability to compare the reference voltage to the adjust pin
voltage.

73 OM
n8zu



On Nov 4, 5:06 pm, "Larry Gagnon" wrote:
Hello. I have a homebrew linear 13.8V 20A power supply I have been using
for some years to power an IC-735, a 2M rig and some accessories. The PS
has these characteristics:

- well filtered (35000uF)22AMP, 21 volt DC output from diode bridge circuit
- LM-317 regulator circuit (as per LM-317 datasheets)
- MJ2955 NPN feeder transistor from regulator driving 4 - 2N3055 PNP power
transistors in parallel
- large heat sinks (I don't think heat is a problem)
- good air circulation with fan

I have the regulator set to 13.7 VDC out. Lately however, I have had some
problems with voltage drops: while drawing 20 amps the voltage drops to
about 11.3 volts and I have had reports of a rough CW signal as a result.

I have tested the reg circuit and even replaced the LM-317 to no avail. I
cannot see where the problem lies, unless perhaps the MJ2955 feeder
transistor is not working as it should? (I don't yet have a replacement
transistor to test that idea, hence this post).

Any ideas greatly appreciated.

Larry VE7EA

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