Orbit 10 channel, 6 volt Tx and system

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jmendoza
Posts: 167
Joined: 18 Feb 2018, 23:07

Orbit 10 channel, 6 volt Tx and system

Post by jmendoza »

OK, now working on another of Selcuk's reed sets, this one is a 6 volt Tx, solid state Orbit 10 channel.
Four of the five Transmites needed to be opened up and components replaced; one had a bad one-shot,(Q3,4) it would not neutralize, another drove in one direction only, bad Q1, one had no drive in either direction, bad Q1,2, and one would drive very slowly with the reeds, but drive fast when the reeds were actuated by hand, bad C1/2 input filter cap. The last Transmite drove slowly in one direction, leaky drive transistor Q6. C1/2 is actually a dual capacitor; it is two 5uF caps in a three lead package, as they both share a common positive lead. I replaced it with two individual 4.7uF tantalums. For the transistors, I used 2N3904 for the NPNs and for the PNP drivers a 2N4403 works fine. No need to try and source the original metal cased Germanium types, as the modern silicon versions work fine. I recommend replacing Q1 and 2 as a pair, the same goes for Q3,4 and Q5, 6.

The original 1959 Transmites lack a protection diode that prevents shorting the transistors if both reeds are actuated at once. It is a simple matter to add the diode: The diode's Cathode goes to Q1 collector, and the anode to the orange wire from the reed (negative end of C1).

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