Home–Built Timer Counter Project?

[Chris55000]

. . .Can anyone tell me if this home–built counter–timer was featured in one of the UK Construction Magazines?

. . .If anyone can tell me anything about this evacuated B7G quartz crystal, that says "CRL 708 111 K" on it, that would be very helpful!

Chris Williams

[Chris55000]

. . .You were a bit too quick Sir, the pictures were still uploading when you posted – there's more here!

. . .I've a feeling Practical Wireless did something like this but I can't remember when – it appears to be quite professionally built internally!

Chris Williams

[Chris55000]

. . .One final one showing a close–up of the evacuated B7G crystal!

Chris Williams

[Chris55000]

. . .All the Nixie Cathodes lit up at once giving only a faint orange haze throughout the four tubes when I switched the unit on, either they're counting very fast and the display isn't being latched or there's a fault on one or more of the four Nixie Driver Boards – I haven't started to draw anything out yet!

Chris Williams

[Radio Wrangler]

That looks a good bit older than the PW 'Robin' project which was in their Rob Mannion editorship era. I think Practical Electronics published one in the late sixties.

David

[Chris55000]

. . .A quick prod inside reveals the power comes from an "RS Midget Mains Transformer", 6.3 V at 1.2 A L.T. and 125–0–125 V at 50 mA H.T., half–wave rectified, with +325 V H.T. for the four Nixie Veroboards, but no L.T., I only measured 0.15 V coming out of the W01 rectifier, so me thinks a new rectifier is needed!

. . .The rest of the L.T. supply is a perfectly normal emitter–follower series reg. that feeds +5 V to the various other Veroboards in this unit! There was a small self–adhesive label on the front of the unit that said "+5 V Supply Intermittent!" – me thinks this duff rectifier is why!

Chris Williams

[Chris55000]

. . . Circuits to follow later when I've worked it all out!

Chris Williams

. . .PS!

. . .I've also got a professionally home–built and lettered Laboratory Oscilloscope Members might like to see as well!

[Chris55000]

. . .I know why all the Nixie Tube cathodes were glowing – +325 V is far too much H.T. for the anode of a Nixie Tube, given that there are 68 V clamp diodes across each output of the '141 cathode drivers, then assuming each cathode is drawing 1.5 mA, then there would still be +180 V at each anode leg of the tube, (which is what I actually measured!) – more than enough to allow the gap between the mesh anode and each cathode to strike – using full wave rectification from the H.T. secondary of the mains transformer would still provide enough to strike the anode–cathode gap when the internal decoding circuits of the '141 turn on that output, but 160 V wouldn't be enough to strike the gap across a switched–off output – the 68 V clamp diodes would prevent the gap striking when the output is disabled!

Chris Williams

[Chris55000]

. . .The design uses TTL and most of the chips have "71xx" date codes on them – did Practical Electronics or the RSGB Radio Communication Handbook feature anything like this?

Chris Williams

[Terry_VK5TM]

Practical Wireless August to December 1971 and the Nixie HT is 300V.

[factory]

All the cathodes glowing is a standard fault with 74141 based equipment, when the TTL supply rail fails low or to 0V. I've had this happen with Racal & Advance stuff, I've seen it happen enough times to know the cause.

David

[Chris55000]

. . .Thank you for that Terry – you certainly seem to have the knack of finding the dates and titles of Original Construction Plans in the Constructor's Magazines!

. . .I've ordered two replacement W04 rectifiers for the H.T. and L.T. rectifiers!

. . .Power Supply circuit to follow when I've filled in all the correct component values!

Chris Williams

[Chris55000]

. . .Power Supply Circuit!

. . .To follow next are the circuit and layout diagrams for the four identical display boards, Boards C to F!

. . .Because World Radio History provided very poor quality scans purposely in order to stave off the wrath of it's current publisher, I will be issuing new circuits and layout diagrams with this project!

. . .This Project won the "Practical Wireless" Autumn 1971 "Constructor's Design Trophy Competition" for its Author!

Chris Williams

[Chris55000]

. . .The resistor in my Power Supply Circuit Diagram shown as "R15" should be labelled "R24" – I only noticed the slip–up after I uploaded it!

Chris Williams

[Terry_VK5TM]

Just for interests sake, there is a similar unit with much expanded functionality in Radcom (or Radio Communication as it was then) in the 70's.

I'll dig up exact year and month a little later.

[Terry_VK5TM]

March 1976

[Radio Wrangler]

1976 is a few years later than I'd have dated it from the design, and I know Graham, G3MFJ quite well! He's been one of the activists of The G-QRP club for many years on the committee and running their component sales operation, but has recently retired to ease off under the accumulation of years. He's still around.

David

[Terry_VK5TM]

Yes, know Graham also as part of the GQRP club (I'm the Australian Rep).

Considering how long publication can take, it may predate the publication date by a couple of years, especially considering it looks like a lot of work went in to it.

[Chris55000]

. . .Hmmmmmmmmm!

. . .That definitely appeals Terry!

. . .Just as well I thought of getting another "Midget Mains" h.t. Nixie Transformer then!

Chris Williams

[See_Mos]

I have an RS midget mains transformer here on the shelf. It's not quite the same as the one in your pictures and there is no part number on it so I don't know the details. I can power and test it if you are looking for one