[GreenKeys] Flesher TU-170 Loop Key Transistor

[w9ddd at tapr.org]

It can't hurt.  I don't recall specifically what Irv Hoff's ST series may or may not had for a snubber.  

Looking at the schematic for DT500, I see a 0.1 cap in series with a 470 ohm resistor connected from emitter to collector.

Do you have the TU-170 manual?  I don't have mine handy, but I don't recall any mention of a need for anything external.  Perhaps they have something internal to the box?  Or a bunch of folks have been lucky over the years. 

John, W9DDD


> On Oct 30, 2020, at 11:02 PM, hwhall at compuserve.com wrote:
> 
> I've built keyers using that transistor and always had an RC snubber across them.
> 
> Wayne
> WB4OGM
> 
> -----Original Message-----
> From: Harold Hallikainen <harold at mai.hallikainen.org>
> To: Green Keys <greenkeys at mailman.qth.net>
> Sent: Fri, Oct 30, 2020 8:20 pm
> Subject: [GreenKeys] Flesher TU-170 Loop Key Transistor
> 
> 
> I'm looking at the manual for the TU-170 and see that it keys the loop
> with an MJE340 which has a maximum Vce of 300 V. 152950 loop supply has a
> loaded output voltage of 125 V. Can the MJE340 take the inductive spike
> when it opens the loop, or should a clamp be added?
> 
> Thanks!
> 
> Harold
> 
> 
> 
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