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Old 23rd Dec 2019, 2:27 pm   #104
Pinörkel
Pentode
 
Join Date: Jun 2019
Location: Dortmund, Germany
Posts: 161
Default Re: Telequipment D75 scope.

Quote:
Originally Posted by mhennessy View Post
For what it's worth, the serial number of my vertical unit is E543428 and the date codes I can see on the transistors are 1974 for both 2N2369s and 1977 for the TFD1551. Of course, I've no way of knowing if the JFET is original or a replacement. I can look up the details for the X unit when I next go up in the attic. But having said that, I doubt we'll be able to gather any meaningful data about how these units evolved, given the small numbers out there today.
The serial numbers of my units ar similar to yours, 543091 for the 067-672-00 and 541073 for the 067-673-00.
Quote:
Originally Posted by mhennessy View Post
You might be right - does the soldering on that resistor give any clues?
The soldering looks unsuspicious. However, the cutting angle of the R1015 resistor is the only one that is not parallel to the board, which could hint at it being installed after the board was put into the frame.
Quote:
Anyway, on Les's unit, I can see that the 910R resistors do look like your top one. And they measure high (around 1k1). Which suggests that they are carbon-composition rather than film.
Just measured my resistors with a somewhat decent LCR-meter at 100hz. The R1015 measures 0.9261 kΩ and the R1012 0.9106 kΩ. Unfortunately there is no way knowing if swapping R1015 for a better matching one is a good idea or not, because the unit might or might not have been calibrated against the currently installed resistor.
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