[morzh]

Arran

I thought you suggested the smoking occurs due to the field coil being disconnected.

If it is connected, anything can be the reason, and I thought of RF 78 tube shorts.
Part #19 short (if the field coil IS connected) would require also some short in the Det. oscillator tube, but even this will not reault in #7 smoking as it is serialized with some 50Kohms resistance and the drop on it (again, if #19 is at fault) would be so small (0.5% of the total voltage), it is far from causing anything like 200 Ohms resistor (also probably 1/2W) to smoke.

If #61/62 do smoke, this indeed may be (potentially) due to the field coil missing; #7 - unlikely.

I would say, if #7 smokes with the field coil removed, it will smoke with the coil in place too.
I would look for shorts in wiring - the schematic does not show any path that can do it.

Well then you explain it? You are shooting down one of my theories, which is little more then a guess anyhow, but you haven't come up with any other explaination that hasn't been though of, as to why part #7, the 200 ohm resistor, is burning up. I did also mention that there may be a wiring error or a stray blob of solder etc. that could cause it. Part number #19 is directly in the path of the B+ voltage along with part #21, part #22, and part #14, there is no other path for the B+ voltage to get to part #7 as part #7 is in the cathode circuit of the 78 and 6A7 tubes.
With no load on the B+ line in that branch of the B+ circuit the voltage will be high and behave like the resistors #21 and #22 weren't even there and possibly cause the dielectric of part #19 to break down and short out. Again short of a wiring error there is no other direct path to that 200 ohm resistor. Another possibility is that the field coil being missing, somehow caused the cathode current to increase, but that doesn't make much sense since the only way that could happen is if the plate and screen voltages were there and the grid bias voltages were not. But when it comes to antique radios, the age of the components and tampering by former service persons means they sometimes do whacky things that are not easy to explain.
Regards
Arran

Arran,

I was saying something before (mentioning shorts in wiring) that completely agrees with your notion of wiring error: it is, like you said, either wiring (error/short due to old wiring) or solder blob.

But if you look at the sch, if the wiring is intact, you yourself can see that there's no way in heck the absence of the field coil can create the smoking of #7, unless there are pre-existing conditions (just mentioned by you and me). A tube short is possible also, but first there have to be other shorts, so a shorted tube can create this if the plate power is absent.

I mean no disrespect.

Mike.