GaryM wrote:
I recently posted a similar message to the boatanchors newagroup, but I
have had no reply, so I hope that perhaps a different readership of this
newsgroup might be able to help.

At a recent radio rally I picked up a Hallicrafters S-118 receiver. It's
a bit tatty, but I was interested since I have never owned a valve
(tube) receiver. I've located a scan of the service manual on the BAMA
website, but the schematic was unreadable. I've found a number of US
websites which sell the manual, but the cost plus postage is about the
same as the rx cost! I will go this route if nothing turns up.

If anyone can help with the schematic or information on the power supply
I would be very grateful. I have no idea what voltages the power supply
is supposed to generate, but one idea is to replace the US transformer
with a UK equivalent. The power supply appears to have a semiconductor
doubler on the output side. I am quite happy to remove this and use the
correct secondary voltage from a UK transformer. I may be possibly
offending the purists, but I am happy to replace as much of the PSU as
necessary just to get the rx going again. I do have some high voltage
transformers in my junkbox despite never having constructed any tube
equipment.

During the various searches it appears that the S-118 has a mk1 and mk2
version. If anyone could explain the difference (so that I can order the
right manual) I would be grateful
================================================== ======
Suggest you keep the rx as is an feed it with 115-120 V ,either from a
variac or a sturdy 230/240 V transformer with a centre tap , using only
the primary winding as an auto-transformer (not using the secondary
windings) (Large) transformers can often be found at Junk sales or flea
markets . Another possibility is using 2 transformers ; one being
230/240 to 12 V or about and the second one 230/240 to 24V or about
By connecting the the secondaries you can get 115/120V.

Of course you have to ensure that the transformer(s) can handle more
than 100 W to be on the safe side . The Hallicrafters rx will highly
likely not consume more than 100 W

If the rx has not been used for considerable time ,the electrolytic
capacitors might have to be reformed . Do that (preferably) with a
variac or with a few transformers with say 12 -24 V secondaries,
starting with say 12 V connected to the rx power input ,after a while
increasing the voltage by series connection with another low voltage
secondary ,either from the same or a different transformer ( ensure that
phasing is OK by checking output with voltmeter) .
To minimise power required while reforming the electrolytics you can
remove the valves(tubes) (but of course not the HV rectifier valve if
fitted

There is 1 potential snag using equipment designed for 60 Hz (USA) on a
50 Hz supply system . If the transformer of the rx is marginal capacity
wise , it could become rather warm when connected to a 50 Hz supply
system , because the higher frequency permits less transformer iron.

Note: During the valve(tube)equipment era ,aircraft required AC .
To minimise weight the transfomers used had to be as low in weight as
possible , that's why the onboard supply system operated at 400 Hz.


Good luck with your vintage RX

Frank GM0CSZ / KN6WH