I noted color codes on all the transistors and pulled
them for testing. Other than the color codes, the
germanium transistors had no part numbers, just a Texas
Instruments logo on the side made with a rubber stamp
(Figure 6). I have read that the coding was primarily to
show junction capacitance, so, the better units could be
used in the converter and IF stages, and the higher
capacitance transistors in the less critical audio stage.
When I tested them, all the transistors showed a huge
amount of reverse leakage compared to later transistors. I
chose the best transistors and set them aside. I then
replaced the bad output transformer. The next issue was
Of the four electrolytic capacitors, three were open
and one was shorted. My first attempt was to drill out the
tubular units and slip a modern capacitor in the cardboard
sleeve. It was important to keep the cardboard-sleeved
capacitors, as all the early units used that type. Later units
(starting around serial number 20,000) alternated between
cardboard and ceramic sleeves.
Figure 7 shows the two types. I couldn’t drill out the
units without destroying the sleeve, so I went to plan B. I
located some tiny electrolytics and mounted them on the
back of the board (Figure 8) — they are not visible when
the unit is assembled. For the shorted capacitor, I drilled a
hole through the printed circuit board (PCB) the size of
the lead that just misses the board trace on the rear. The
important part of this is that the new capacitors can
be removed without a trace if a buyer wanted this
unit in all-original condition.
I installed the transistors and held my breath as I
brought up the voltage on my bench power supply.
At about 14 volts, I heard some noise from the
speaker and saw that current was about as
expected. I cranked it up to 22 volts and rotated the
tuning dial. While I live in a poor area for AM radio,
our one good AM station came in “loud and clear.”
Well, maybe not so loud, but it sounded quite good
considering that the speaker was still not in the
Sensitivity was not so great, so I decided to do
an alignment. Having replaced one IF transistor
justified a trim, considering their lack of uniformity.
If you had a bad transistor when this was under
warranty, Regency would replace the transistor and
neutralizing capacitor as a pair.
I melted the wax off the IF transformer slugs
44 May 2017
FIGURE 7. Early and later capacitor types.
FIGURE 8. Miniature capacitors were needed for the 1/4" space.
FIGURE 6. Color-coded TI transistors.