Practicalities
No doubt correct connectors are available
but, as most T1154 ancillaries come at horrendously high prices,
junk box-based alternatives need to be made. The aerials used on the T1154 are not what most
amateurs are used to. Both the fixed aerial and the trailing
long wire have indeterminate impedances and do not use standard
co-ax plugs. The HF and MF outputs each have a single brass pin
which is about 4.5mm in diameter (probably 5/32 inch). In my
junk box I found a 2 inch piece of duralumin tubing which was
a snug fit so I tapped both ends 2BA and cut it in half. After
fitting each with a solder tag secured with a short 2BA screw
I now have a pair of mating aerial connectors. Adjacent to the
pair of aerial connectors is an earth pin having the same diameter.
I used a small piece of brass tubing, and enlarged the hole to
about 5/32 inch internal diameter, then cut a slot and squeezed
this so the tubing was a snug fit. Next, the HT supply. This
uses a special connector comprising a single pin similar to the
earth pin plus a polarising pin of about 0.13 inch diameter.
To make suitable lead for the HT connection I made a connector identical to that of the
earth connector. Next I found a quarter inch plastic rod and
drilled it with a hole to fit the polarising pin. I then cut
the rod to about an inch and a half and tapped the end to 2BA.
What about protecting the lethal voltage on the new connector
from the transmitter operator? I found an old relay fitted with
a removable square cover which I drilled to accommodate the tapped
end of the plastic rod. The HT lead was routed out the bottom
of the cover after drilling a hole to match the HT cable.
HT Connector: On the left the plastic rod drilled longitudinally
with a hole 0.13 inches in diameter and the end threaded 2BA
to be fitted with a plastic nut. The brass fitting is drilled
0.16 inches and the end tapped and fitted with a 2BA scew and
solder tag. Centre is an old relay cover. the top is drilled
for the plastic rod and a hole is drilled for cable entry on
the lower side.
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Wiring up the new Jones connector was
straightforward. I used heavy cables for the LT leads and high
voltage cables for the remainder of the leads. I used a tie wrap
to secure the wiring then fitted the cover using heatshrink sleeving
where the cables came through the cover. Ideally the connector
covers should have 90 degree cable exit but I was only able to
get types with a straight through cover.
The socket is labelled "D"
on the schematic. The pins correspond to the numbers on the moulding
and have the following connections:-
1 220V minus; 2 220V plus; 3 Start LT
PSU; 4 12V/24V for PSU start relay; 5 LT minus; 6 LT plus; 7
1200V minus; 8 Start HT PSU
I fitted heatshrink sleeving
over the solder joints. The inner surface of the cover is well
insulated.
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I tried the two new connectors and discovered
a strange problem. The mode switch knob hit the Jones plug cover
(and if it had passed this it would even foul the new HT cover
which doesn't protrude anything like as much). What was wrong?
After puzzling over the problem I noticed
the original connector securing bar posts matched the new Jones
plug cover (the securing bar itself is missing) so it's pretty
clear that the problem is not the plugs. In my T1154 example
the wavechange knob and the mode switch knob are identical. Both
are moulded with a pointer at right angles to the knob body.
I decided to look at pictures of the T1154 on the Net and found
that the knob fitted to my example was wrong. In fact many sets
used black coloured knobs of the same shape as the coloured types
used for the coil tapping switches for both the wavechange and
the mode switch. Maybe some have the wrong knob fitted to the
former? Certainly mine has the wrong type fitted to the mode
switch. The solution turned out to be simple. I have two R1155
receivers and both use the same knob that's used on the T1154
mode switch so I swapped the one on the R1155 wavechange switch
for the one on my mode switch... easy? Not so because the mode
switch itself has no end stops. Instead, the end stops are built
into the front panel and I'd inadvertently turned the switch
shaft without the knob being fitted. I did this when looking
for a replacement knob to see if there was significant turning
resistance. The switch has at least 12 positions when the knob
isn't fitted... of which only 6 positions are valid. Time to
peer at the circuit diagram and figure out exactly what the switch
does...
The mode switch is a Yaxley style thing
fitted at the rear of the T1154 and connected via a long quarter
inch rod which passes through the front panel and drilled for
a pin which mates with a slot in the back of the knob. The knob
can be fitted in either of two positions one of which is correct
and the other wrong, so putting the knob back on with the switch
180 degrees out might blow up the transmitter. I pictured a big
flash from the PT15s so it was vital for the correct orientation
to be found.
The switch uses three wafers with contacts
at the front and back sides of each wafer. The wafer sides are
labelled in the schematic as F, G, H, J, L and M which appear
to have (at least) the following functions:-
F & G: each has 2 wipers and 2 contacts
wired in parallel for switching LT to the PT15 filaments.
H & J: 2 wipers and 2 contacts,
Start LT; 1 wiper and 3 contacts for PT15 bias setting and MCW
L & M: 2 wipers and 5 contacts,
microphone switching; 1 wiper and 3 contacts, sidetone to R1155
headphones (Pin 6 on plug A)
Using this information I was able to
set the switch to OFF position and fit the replacement knob only
to discover it didn't work! It seems the T1154 knobs are a different
shape to those used in the R1155, and I had to cut off part of
the R1155 version so the switch can select all of its six positions
instead of just the three centre ones.
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Above shows an R1155 knob
above the knob fitted to my mode switch. The lower knob was correctly
used on the T1154 wavechange switch but a second identical one
was fitted to the mode switch which was fine until correct Jones
Plugs were fitted then it was too long and fouled the Jones plug
covers. The R1155 knob, of which I had a spare is not right either
because as you can see above those on the T1154 do not have a
flat underside. To operate correctly due to protruding end stops
the underside needs to be cut back like the T1154 wavechange
switch above. As the knob is made from solid material I was able
to cut it back by about 5mm to match the shape of the proper
knob. It then fitted and worked properly.
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