Curious Marc repairs the HP5245 Nixie counter

 These videos were mentioned on the Soldersmoke blog:

part1 source: https://youtu.be/B-4cUGSsGPQ

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part 2 source: https://youtu.be/mgi34ogzbvY

 

part4 source: https://www.youtube.com/watch?v=01GzduUaLOE

Several things of note:

1) reading the state of neon lamps with photo sensitive resistors ?  WOW

The photo resistors reminded me of how an HP ink jet printer head looks.

2) Step recovery diodes to generate a 100 ps blip every 100 ns (10 MHz rate) for the comb generator.  double WOW

The narrow blip results in only a 2 db spread of harmonic amplitude !  If only the SRDs were cheap, they could be used in a crystal calibrator !

3) the cavity tuned LC filter to select individual harmonics in the range 10-500 MHz (or higher) from the comb generator ?  triple WOW  

Silver plating, fancy glass discs but ultimately done in by grease seizing up the gear train.  This reminded me of the infamous Ten-Tec PTO grease problems.  Something about grease wants regular maintenance.

4) Marc found 6 bad transistors in the main counter.

   This reminded me of Field Day in a curious way :)

One year Morrie, WB9JHW arranged to bring two SB-104 rigs on the Glen Gates Gang Field Day (we usually went 2A).  One SB-104 was his, the other was from the Heathkit store in Milwaukee where he worked.  Great !  Using a rig with digital readouts was a first for me.

But Todd, WB9HJG, mentioned one thing that I've remembered to this day:  he didn't like the fact that Heathkit used those snazzy Beckman gas discharge planar displays.  The reason was that the high voltage required to light the displays wasn't a good design mix with the low voltage ICs and transistors used in the rest of the SB-104.

Now I own both an SB-104 and a MR-1010 receiver which also uses the Beckmans but haven't ever had high voltage damage problems.  The MR-1010 display is iffy(it sings) but it's probably the capacitors in the high voltage going bad - the ICs and transistors are OK.

So those Nixie tubes (or the high voltage power required for them) might be part of what caused those 6 transistor failures for Marc in the HP counter.

The moral: don't mix high and low voltage parts :)

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm