COLIN LAMB wrote:
> You may simply be able to connect the scope on the outside of the amp.
> Watch it on 15 meters. You might also try looking at the other end (power
> supply), including cable lengths.
> It sounds like overheating is the problem rather than instantaneous spikes.
> Perhaps rf is coming in the power supply leads. It even might be something
> from the power supply going to ground.
Well, you nailed it! On all bands except 15 meters, the scope shows a drop of
about 0.2v on keying; nothing else. On 15, a BIG (35v p-p) sine wave appears!
The power cables are 10' lengths of 00 gauge welding cable, which is like a 1/2
wl dipole on 15m. I wrapped some #4 wire around a toroid and put it in series
with the + wire, and it cut the sine wave down to about 20v p-p. Then I
bypassed the + terminal of the amp with a total of about 3 uf, and that got rid
of it altogether.
It's interesting that the RF appeared equally whether I was transmitting into my
antenna or into my (shielded) dummy load. This indicates that the RF wasn't
being picked up on the power cables, but rather that the 'dipole' was taking RF
out of the amp box.
We'll see if the decoupling capacitors in the amp will hold up now.