Kiwahl -
First, that's a 2N3858 in the Buffer position, a 2N3904 will replace.
The 2N706 is still available from Mouser and others. Other transistors
'may' work, but 'may' also corrupt the linearity. I don't know.....
I've been looking for a defunct PTO to conduct these sorts of
experiments on, and can't bring myself to mess up a working unit! :-)
There are several other, more likely, causes of PTO failure.
Top of the list is bad solder joints, particularly the tap on the coil.
The 10V Zener sometimes shorts.
Leaky or shorted Dur-Mica (brown, dog-bone) cap.
Leaky or intermittent disc ceramic cap.
Roughly in that order!
The Buffer should read about 8 VDC on the Collector, 2.5 VDC on the
Base, and 1.9 VDC on the Emitter.
The Oscillator should read about 9 VDC on the C, 5.6 VDC on the B, and 5
VDC on the E. The Collector reading may be 'anything', depending upon
the characteristics of your meter probe. It may kill the oscillations
completely. The important reading here is the Base to be about 0.6 V
above the Emitter. If this is true, the transistor is almost certainly ok.
Let us know what you find!!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Kihwal Lee wrote:
The PTO in my R-4A failed a few days ago. I replaced it with a spare I
had, but I still want to fix it as it has better linearity. In case
the transistors are bad, what are the proper substitutes? It has a
2N3058 and a 2N706.
Kihwal, K9SUL
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