Guillermo -
Actually the 0B2 was a 'downgrade' that was only used in the first 1000 (s/n 7000 - 7999). It was
holdover from the R-4A which still had a tube based CALIBRATOR that needed the 'regulated' +150
VDC. Starting with the R-4B, the CAL circuit was changed to an FET with RTL dividers to provide 25
kHz markers, meaning the 0B2 was no longer needed. The lower voltage stages had their own Zener
regulator, (BAND, PTO and CAL,) and this was supplied direct from the 'un-regulated' +150V bus. I
guess it took the first 1000 units for Drake to realize that the 0B2 no longer contributed any
improvement and could be removed!!
So your R-4B is one of the first 1000, with a s/n in the 7000 range. There are other changes in
later versions, such as changing the oscillator in the PTO from bipolar to FET for improved stability.
If you can get me a good email address, I can send you the correct schematic.
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>
GGLL wrote:
Hello Garey, my name is Guillermo, LU8EYW/W in Puerto Madryn, Chubut
province, Argentina.
I'm troubleshooting my R-4B receiver and searching the schematic, the model which has the OB2
regulator voltage included (V11) and a PCB board not included in the first models (or at least,
different as I'm seeing in various different schematics already downloaded). In my receiver, this
regulator tube is located between front panel and V2.
So far, I've had no luck yet, but found and downloaded three
different copies, no one of these has the OB2 regulator tube.
Furthermore, I've supposed my R-4b to be a later serial number model, but looking photographs
at Drake virtual museum, I see one which has a larger serial number than mine, but no OB2!
(looking in detail, you can see just printed "OB2" onto the chassis, only).
Can you enlighten me about which version of this receiver had this upgrade?.
Many thanks in advance
Regards
Guillermo - LU8EYW/W.
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