[Hallicrafters] SR-150 Restoration - short signal loss & noise

[WA2CLX]

I'm bringing up an SR-150 in great physical shape. It has been offline 
for at least 5 years or so. This afternoon, I slowly brought power on 
using a variac, pausing for about 15-20min at each successive voltage 
level without anything going haywire (no excessive current rise or 
fluctuations) or caps shorting.

After full power was restored, and I listened on all bands, it seemed 
whenever there was a particularly strong signal, the unit went dead for 
a short period, accompanied after a moment by a series of stacatto 
noises, almost like you'd hear a furnace electronic ignition source 
start or car ignition noise, etc. Then just as soon as it came, the 
receiver returned to normal again. Tune the band, get a reasonably 
strong signal, and it would go through the same routine. Other than 
that, reception was great, and the receiver had very little background 
noise.

Both RF and AF gain perform normally when signal is present and the rig 
didn't go silent (probably obvious). I recall varying the AF gain, when 
the unit went dead and it didn't affect it. I also tried backing off on 
the RF gain before tuning another medium or strong signal, and the same 
'silent treatment' started again shortly after the signal was tuned. The 
medium-strong signal sounds great for a skosh before the rig plays dead 
for a bit, does the noisy thing, then returns to operating normally 
again while tuned to that same signal.

I just got the rig and haven't been through the schematic and possible 
causes, but thought I'd put it out there in case someone has been 
through the same thing, or has an idea on possible cause.

I did notice with the RF gain off, and the audio gain full up I could 
hear a pronounced AC hum, which I pretty much expected. I'd planned to 
replace the electrolytic in the PS-150 supply anyway.

As noted, I haven't been through the rig yet to check tubes, caps etc.

Thanks for any ideas or recommendations on diagnostics.

Phil WA2CLX