1966 service advice to replace all HUNTS caps

[trobbins]

I recently came across this 1966 service letter for Selmer organs (of which I have a 1958 Concert). Check out the last two paragraphs for a good laugh about the reliability reputation of Hunts caps even back then.

[Kentode]

Fascinating. Any idea who Selner/Selmer and Jennings are? Discrete components suppliers perhaps?

I've found Hunts caps that have split in two along the length, although this is in a 1960's radio so sixty years old.

[Refugee]

I can remember in the 1970's an engineer doing a homer that had gone bang and puffed out a cloud of smoke. It was a valve TV and it carried on working. The owner wanted to make sure it was still safe.
The cap across the power switch was blown in half cross ways.

[Aub]

I assume it means the Selmer who made instruments and amplifiers in the fifties and sixties?

Aub

[trobbins]

Yes Selmer made instrument and guitar amps, as did Jennings I think (Vox I think). Selmer also made a small range of electronic organs.

[Alistair D]

Originally Posted by Kentode

Fascinating. Any idea who Selner/Selmer and Jennings are? Discrete components suppliers perhaps?

I've found Hunts caps that have split in two along the length, although this is in a 1960's radio so sixty years old.

Selmer and Jennings were organ and amplifier etc manufacturers to the music industry. Jennings used to sell a lot of their equipment under the JMI brand.

Al

[paulsherwin]

It appears to be the service department of an electronic organ dealer. Selmer certainly made those.

[wd40addict]

I have an Ultra FM950, which from the factory had all Hunts *except* the output valve grid cap which was a disc ceramic! Even ex-factory there were obviously reliability concerns.

Needless to say all the Hunts have been replaced. It was actually done in two waves, I originally just changed all the larger values, smaller tested ok. After 4/5 years of steady use I noticed performance had deteriorated. Changing the rest of the Hunts restored it!

[Hartley118]

Has anyone encountered a brand of paper capacitor that doesn't actually leak after 70 years or so? I have various examples of Dubilier and TCC etc brands that leak so much that you could use them as cathode resistors, whereas a Hunts might only serve as a grid leak (literally).

I'll admit to something of a soft spot for Hunts' capacitors because they were the readily available brand in the 1950s/60s which provided the magical fix when used to replace the then common wax version of 'that capacitor' back in the day. Of course, if that outer coating is cracked, then all bets are off. I've never found out what that coating consists of - such a distinctive smell when you catch it with the iron!

I do still use every day a 1960s Heathkit valve preamp with an untouched interior full of immaculate looking black Hunts paper capacitors. Yes, they all leak just a little bit, but not sufficiently to much upset circuit conditions (cathode bias is pretty tolerant). I'm sufficient of an originality fan not to replace them on sight, particularly as it was very nicely built by an avionics colleague of mine.

Martin

[The Philpott]

-Aussies telling it like it is. We could do with more of that here.

[Leon Crampin]

Probably the best post-war paper capacitors were made by Sprague in the US. Many appeared over here in the late '40s and were used by Murphy in some sets.

Using a metal can with well sealed end disks, these capacitors still generally exhibit reasonably low leakage. Possibly, the paper dielectric was oil impregnated, further reducing moisture ingress.

Leon.

[trobbins]

Here is a link to original (better resolution) scan of that letter: https://www.dalmura.com.au/static/1966%20letter.jpg

Here is a link to the Selmer-Hoffner website with the best compendium of the range of equipment that Selmer put out, including the electronic organ I have. Sadly the organ range never came with a crocodile skin covering - so missed out on that Selmer marketing style. http://www.vintagehofner.co.uk/amps/concert1.html

The letter is from the Australasian importers of Selmer to their regional service centres - with that letter being in the service manual sent to NZ agent SPACE AGE ORGAN SALES, Auckland. With a business name like that in 1966, they were likely riding the wave of the Gemini program, but I doubt organ sales kept skyrocketing.

In a time context, Selmer appear to have started making electronic organs in the early 1950's, but its likely manufacture stepped up in 1957 with the release of the Concert/Minster models, so with less than 10 years service life the Hunts had quite a reputation. In the circa 1958 organ I restored I did swap out 96 Hunts caps with datecodes from late 1956 to mid 1957 - most are in the 60 oscillator/divider stages and the tone-shaping networks for the 28 registration/stop tabs, where cap leakage could well play havoc. Luckily nearly all of the Mullard valves were still ok, as that included 64x 12AX7's.

[Maarten]

Originally Posted by Hartley118

Has anyone encountered a brand of paper capacitor that doesn't actually leak after 70 years or so?

Not necessarily a brand, but the best chance of a paper cap working after 70 years would be one in an oil filled, soldered tin can with glass leadthroughs. And then only if it was made using the best quality of paper and oil and the seal is actually hermetical.

[trobbins]

More mirth - probably at the expense of Hunts - a clip from a website with history of West Croydon Methodist Church at 93 London Road, Croydon:

"When the old church was demolished, the old church organ was removed and sold as scrap, and the money put towards the purchase of a new organ — “a Selmer ‘Minster’ electronic two-manual” which cost £560 (£11,801 in 2015 prices). This was dedicated at a special service on Saturday 22 February 1958, with Norman Hunwick of Shirley Methodist Church as guest organist.

This, unfortunately, proved not to be the wisest of purchases, as the new organ seems to have rapidly deteriorated. Just over a decade later, the Croydon Advertiser characterised its sound as “a queer noise”, and reported that it “would give up the ghost halfway through the service and a piano would have to take over.” Eventually, “even the organist gave up and refused to play the instrument.”

https://london-road-croydon.org/hist...st-church.html

[Heatercathodeshort]

To be fair to Hunts they were dealing with insulating materials that were available at the time. Their electrolytic range had a good reputation.

All wax insulated capacitors suffered leakage to a very small extent even when new. Modern capacitors are so well constructed that occasionally small value changes have to be made in television timebase circuits, especially the frame linearity feedback loop to accommodate the zero leakage from modern 'perfect' capacitors.
Old style capacitors had a life expectancy of around 10 years, the average life of the equipment they were fitted in.

Some makes were slightly better than others. Dubiliar made excellent capacitors of all types including the .1uf 7kv types used in the mains derived EHT circuits of early television receivers. TCC had a good reputation but suffered problems with the 'Plastiseal' range in the mid to late 50's. they leaked terribly when they warmed up! Their oil filled metal cased capacitors were satisfactory but the EHT Visconol types did suffer leakage and breakdown. It was all early technology stuff!

Generally EMI produced quite good wax capacitors that remain solid with only slight leakage even today. Who remembers the advert for Hunts Tonic Water? Call for Hunts!
John.

[Radio Wrangler]

Waxies and then Hunts paper capacitors fed and clothed a couple of generations of repairmen's families.

David

[wd40addict]

I suspect being used in an organ oscillator is the very worst possible place for a leaky cap - the tuning drift would probably be noticed by the player pretty quickly. In comparison radio or TV would be a longer process before the average customer noticed anything.

£500 organs being reduced to junk after 5 years is pretty sobering!