[Hallicrafters] Hallicrafters FPM 300 mkII service notes

[Kenneth Laine Ketner]

Hallicrafters FPM 300 mk II service notes
KA5ELD

The set was acquired showing good receive, but only a few watts out on
transmit.

Inboard power supply showed only 300 volts (should be 700) going to PA
plate.

This suggested attention to the power supply board. To remove it, from
the bottom of the rig, unscrew the 2 jacks (1 for mic and 1 for phones)
on the side of the chassis. Don’t disconnect the wires, but take the
mounting nuts off and the jacks will come out of their mounting holes
and can be set aside still connected. Carefully remove the two wires
pinned on the right side of the power supply board - these pop straight
up off the gold pins on the board (be sure to mark the pins and
re-connect them the same way, swapping them could be a bummer). Desolder
the two yellow wires coming to a solder lug in about the middle of the
board. Remove the 4 mounting screws on the board. With careful and slow
fiddling, the board can be drifted to the right and rear and when it
comes free of the wiring harness, it can be hinged from its left side
wires to a vertical position, and while held in that position, front and
back of the board can be serviced. When you first look at it, that looks
impossible, but with slow caution it can be readily done.

I checked the rectifier bridge module associated with high voltage, D301
(original part number, W06, which matches to a contemporary ECG 5307). I
noticed generally bad soldering practices on the underside of this
board, and sure enough, the negative lead of D301 had been weakly
soldered - almost no solder - and the wire had finally arced through the
little solder it had, creating an open circuit in the negative lead of
D301. Thus only the general B+ was getting to the PA plate which now
lacked the additional voltage boost that D301 was intended to provide.
Although D301 tested ok, I replaced it with a ECG 5307 because the
latter has a 1000 PIV rating instead of the W06 PIV of 600.  I tested
the other PS board components, and they were all good.

I resoldered any suspicious solder joints, then carefully re-laid the
board and re-connected everything.

I fired up the set, re-set the PA bias, then keyed the transmitter. Now
150 Watts out. Wow, and that is with one 6KD6 PA tube! Wonder how the
transmit will sound over the air?

Very nifty radio. Probably one of those Northrop guys (they had bought
Halli by this time) fell asleep at the soldering gun over on the power
supply assembly line.

--

Ken Ketner
ARS KA5ELD (Extra Class)
  Personal Webpage: http://www.wyttynys.net
  Office Webpage: http://www.pragmaticism.net
Email:
 home: ketner at arisbeassociates.com
 office: b9oky at ttacs.ttu.edu

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