No.121 - Racal 835 Universal Counter Repair

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This 835 has been sitting for many years and is missing parts! So, I set about trying to get it up & running.
I have about 15off these Huhne heaters as shown in the video, brand new unused. I am selling them, so if you want 1 then contact me via my website. I will ship internationally.
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[@user-pf3ye6yi9n]

The mystery component in the original crystal oven is a bimetallic strip to control the temperature - the symbol is a switch contact next to a representation of a strip.

[@IanScottJohnston]

Ahh yes, had to be old school of course!

[@elsaarmstrong-zp6ng]

The power in socket at the back is called a Bulgin socket! I used to have a Leak TL 50 valve power amp back in the 50’/60s with that type of connected! Many musical amps and organs like Hammond etc used that socket. It was very hard plastic or Bakelite! Not sure. TL 50 was superb sound with soft clipping even harmonic distortion and KT88 output valves. Wish I had kept it but valves were getting too expensive to replace! I think they are about £150 a matched pair now although 6L6’s are direct replacements and slightly cheaper! Massive mains/Output tranny with valve anodes around 700 volts you had to watch what your hands were doing! Original valves were Mullard but I think Russian valves are available nowadays! Superb sound with presence , sounded like you were listening to a l live band! With a pair of large speakers like Tannoy Westminster’s you could feel the low bass notes (32 ft or 16ft) pipe organs playing Bach’s Tocatto and Fugue full blast! p.s. neighbours didn’t like it! 😂Fraser

[@VEC7ORlt]

Really like the flowy and organic traces on those nixie driver boards.

[@simontay4851]

All drawn by hand. No of that autoroute rubbish here.

[@somewaresim]

Another great repair Ian. Thanks.

[@robharley9838]

Fun stuff Ian! Enjoy your work, thanks for sharing it.

[@dan77ring3]

Thanks for the video!, Nice instrument!!

[@johnwatson8820]

nice neat job on the crystal/heater mod,worked out great!!

[@joelkist6493]

Nice job Ian

[@andymouse]

Awesome stuff !....cheers.

[@GadgetUK164]

Brilliant improvisation =D What a lovely repair =D

[@SeanBZA]

Heater does need a small thin tube of insulation around it, and also you do need to solder a ground between the case of the crystal and the socket, the original has a pin for ground, and this will reduce the jitter from mains hum modulating the oscillator slightly. Depending on the crystal it might be needing a little more capacitance, so either grab a pair of 4p7 capacitors and solder across the pins to the ground, or if the frequency is still low you might need to have a larger capacitor to get in the adjusting range of the trimmer.

[@Batmule]

Nice video. Thanks!

[@colinstamp9053]

The mains input connector is a Bulgin PX0430. CPC still sell them!

[@IanScottJohnston]

Excellent, I'll tell the owner of the unit.

[@PeetHobby]

It's an interesting construction with that backplane board sitting diagonally.

[@allthegearnoidea6752]

I managed to get a tickle off one of these once. It looks to share parts with the Advanced brand counters. Another great and interresting video. Regards Chris

[@PeterCut62]

Hello Ian. You're becoming a real electronic archaeologist with this thing 😄. Cheers mate !

[@TheEmbeddedHobbyist]

Nice meter. I've got a Racal SA520 with a bank of 10 bulbs for each digit. 🙂

[@donepearce]

Brasso for tarnished BNCs. And it would have been an Arklone bath to clean it, back when that was legal.

[@IanScottJohnston]

I got away with Deoxit on a cloth in the end. Funnily enough I have Brasso on the shelf.....oh well!

[@andymouse]

Brasso and Arklone ! awesome smell and worked properly ! not like the rubbish they produce today. Sad day when we had to shut down our vapour Trich 111 tank !

[@TheDefpom]

You could put a small capacitor across the crystal to drop its value down a bit, even a few pF can make a difference depending on the crystal's designed load, one like that I would start with 10-20pF.

[@IanScottJohnston]

That would throw the reading higher. The crystal frequency needs to go up to bring the front panel reading down, so maybe playing with caps to ground on the xtal pins would do this but not nearly enough I think. I’ve left it as-is till the owner decides if they want to source an original ovenized oscillator.

[@TheDefpom]

@@IanScottJohnston crap you are correct.. but you can put a cap in series with the crystal to increase its frequency opposite rule though, higher value for less reduction, so start with 220pF first, if not then try 150pF etc.

[@sefarkas0]

There is no self check of its own frequency. the oscillator is measured with a time base of it's own oscillator. The test is to see if the counter is counting something. Add some capacitance across the trimmer, maybe you'll get the range for the time base.

[@IanScottJohnston]

Adding a cap increases the readout unfortunately. That wee polystyrene cap across the trimmer already I tried removing but it’s not enough.

[@markp7129]

Awesome video, really enjoyed it 😃😃😃. The one question that hits me is, is the temperature correct for the crystal? This is how crystal ovens work, adjusting the temperature to change the frequency.

[@Recoils-electronics-repairs]

i have a racal 9837 on my test gear shelf love the glow from the nixie tubes.

[@IanScottJohnston]

They are nice displays I gotta admit!

[@Recoils-electronics-repairs]

i would like to get a nixie tube voltmeter on my shelfs at some point

[@TheEmbeddedHobbyist]

Was going to say in the old days we used to solder a transistor to the crystal can to provide the heat and a foam sleeve over the top for a bit of insulation. this looks like a more modern version

[@IanScottJohnston]

Years ago when I bought these crystal heaters I tested them thoroughly and they regulate pretty good. Performance on a larger crystal like this one I don't know.

[@user-pf3ye6yi9n]

Pretty sure the original would be in its own enclosure so it wasn't trying to maintain a constant temperature in the whole instrument, at least any ovened crystal I've seen has been like that. How would a pilchard tin do for size?

[@TheEmbeddedHobbyist]

@@user-pf3ye6yi9n that's why I put a bit of foam as thermal insulation. You could put it in a tin and suck the air out to reduce thermal air flow in side.

[@capriracer351]

I thought of a few places where those crystal heaters would be useful for me. One is a Beckman Industrial frequency counter from the late 1980's or early 1990's I have. They mounted the crystal between a couple heat sinks for the power supply that generate a fair amount of heat. Problem is, it takes about 2 hours for the enclosure to reach equilibrium. The heater shown in your video should stabilize the frequency in about 5 or 10 minutes, I would think.

[@IanScottJohnston]

I've got 19 of them brand new, if you want any then contact me via my website.......will be much cheaper than via KUHNE themselves.

[@capriracer351]

@@IanScottJohnston OK, sounds good. I sent you a message.

[@zx8401ztv]

That's a nice looking counter. A prescaler could be added to cope with higher frequencys sorry im saying the obvious. The mains plug is a belkin but they are not cheap, there has to be a cheap plug/socket.

[@IanScottJohnston]

Somebody posted in the comments that the Bulgin PX0430 fits, £2.99.

[@zx8401ztv]

Ooow that has become cheap :-D @@IanScottJohnston

[@daveturner5305]

The connector reminds me of the old Belkin or Bulgin connectors.

[@IanScottJohnston]

Somebody posted elsewhere in the comments CPC are still selling the connectors…….wow!

[@fredflintstone1]

Hmm! wires taped they look like they are laced I used to do that years ago in the GPO(telecoms now) when grouping cables inside panels the days before tyraps 🙂

[@andymouse]

Squeak ! and yeah wax coated lacing cord, I was passed that skill down from an old wireman many moons ago don't know if I could do it now !

[@fredflintstone1]

@@andymouse Cheese!!!!! you would be fine it is just a Knack and a few minutes you would be fine 🙂 have you done anything with that light I sent you, apart from bining it

[@andymouse]

Well I have just seen it actually! I got as far as a bit of reverse engineering and first thought to change out the mike and then tried in vain to find the chip neither of these came to anything so its still in the 'continue' pile so will pick it up again someday !! I did send an email sometime ago I guess it never got to you I will check! Squeak :) !!@@fredflintstone1

[@TheDefpom]

Nice old unit, you might want to move that capacitor further away from the heater to reduce its ageing.

[@IanScottJohnston]

40.8 degC heater so no worries, it's probably not so far off that inside the unit anyways when up to temp. 105degC cap fitted, she'll be fine.

[@DrFrank-xj9bc]

you can' t trim 90ppm off. The XTAL seems to be operating in a wrong mode. Maybe the original one was a 333kHz , 3rd overtone. Therefore, if you have the oscillator schematic, try to analyse , which type it is, and maybe you have to redesign it.

[@IanScottJohnston]

I don't have a manual, but the Radiomuseum.org spec for the units says a 1MHz Crystal Oven, and the main schematic backs that up as it just switches between an internal and external Xtal via an XOR gate. The small schematic for the oscillator doesn't show a value. I suspect it's the old 2nd hand Xtal I used, if say 10ppm per year typical drift (from spec.) then this Xtal could easily have drifted by 90ppm I guess. I never measured it, but I did feed in a 1MHz external sig and the display was spot on. I have another 2nd hand 1MHz Xtal I could try, different brand.

[@ivolol]

How much trim range the trim capacitor will have will depend on the load capacitance your particular crystal is designed for. That said there might be a fixed cap in a pair with the trimmer you could change out to adjust the placement of the trim.

[@IanScottJohnston]

There is 2 caps in parallel with the trimmer, one polystyrene cap you can see bodged over the trimmer, removing it only got the display a little closer, the other mounted on the pcb next to the trimmer but very hard to remove due to that angled Pcb. I’ll have another look and see, but I did ask the owner of the unit, for originality, would be nice to get an original crystal oven and start from there.

[@ivolol]

@@IanScottJohnston A more significant option might be to pull out the circuitry from the crystal until you get to a plain logic-level frequency signal (hopefully) and just insert a 1Mhz or 10Mhz/10 OCXO in there or similar. Depends how much you love it :D Quite nice having the schematic Your DIY OCXO is quite quaint though. Nice to put those boards to use if you have a bunch of them

[@IanScottJohnston]

@@ivololit’s not my unit, just repairing for my faulty test gear supplier friend.

[@PapasDino]

Did you try the external reference? Nice work as usual!

[@IanScottJohnston]

Yes, it’s spot on running external 1MHz.

[@OmarMekkawy]

First comment. Thank you Ian for the video :D