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Decca XMS heads

 
FIXITNOW2003
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picked up 2 off these in red in there boxes plus a spare boxed stylus anyone got a spec sheet for them please

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Topic starter Posted : 17/05/2015 8:22 pm
Nuvistor
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Not a spec sheet but an interesting post about head shells for the XMS.

http://www.lencoheaven.net/forum/index.php?topic=8513.0

Frank

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Posted : 18/05/2015 4:01 pm
FIXITNOW2003
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thanks

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Topic starter Posted : 19/05/2015 9:58 am
FIXITNOW2003
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have measured them with a fluke 1 is 2K9 sadly the other is o/c . i think this will need rewinding any tips or hints on how too? never tried this before

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Topic starter Posted : 19/05/2015 1:27 pm
Hartley118
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Congratulations on finding a high impedance XMS head with a working coil - so many of them go open circuit because the very fine coil wire gauge is inclined to self-destruct of its own accord.

I remember first being intrigued by these heads when our school music department bought a shiny new Deccalian record player in the early 50s. I guess they were the ultimate evolution of those heavy magnetic pickups that served the industry from the 1920s to the 1940s. I believe they're a development of the Decca type D, designed for playing the post-war extended frequency range FFRR 78s and found in the first single-speed Deccalian. The XMS 78 heads are coloured brown and had a diecast metal upper shell giving a tracking weight of 15-20 grams - relatively light in its day! LP heads, as you describe, are red and are of all-plastic construction and hence lighter, automatically reducing the tracking weight to around 10 grams for the more vulnerable vinyl.

The 78 heads include a link between two pins which automatically switches in the correct 78 equalisation in the amplifier.

They were made with a surprising range of specified impedances, and therefore output levels, denoted by the colour of the bottom 'seal' plate:
gold 30 ohms
red 170 ohms
silver 1300 ohms
green 4200 ohms

It's quite common to find the 78 head with a silver plate and LP with a green plate, these then giving similar voltage outputs in a Deccalian or Decola because 78s tend to be modulated louder than LPs.

As far as I know, the low impedance heads were used with a step-up transformer in the 'push-pull throughout' Decola balanced input. Why there should be such a variety of impedances does though remain a mystery to me. There was even a blue plate model made specially for KB, though I've never seen one.

I've also come across a version of the LP head in white plastic and one in magenta with a black plate, which uses the slightly lower mass type H stylus and claims improved performance.

For playing 78s, the XMS head ranks among the best, with a frequency response well maintained above 10kHz. They were certainly used in broadcast studios into the 1970s. I use one in a Deccalian plugged into my stereo system and it gives a good 78 performance.
The performance of the LP head is though best described as 'interesting'. The compliant vinyl record material brings the resonance of the rather heavy armature down below 10kHz, resulting in a rather characteristic HF peak. Perhaps it compensated for the HF roll-off in those 12-inch speakers in the Decola! The XMS also lacks any significant vertical compliance, so is inclined to groove jump and 'needle talk'.

Spare styli are getting hard to find. I think the 'H' is still available from Musonic. It's physically shorter, so it may be necessary to remove the seal plate. If your spare stylus has good soft rubber, that's great - so many have gone hard over the years.

I guess that the XMS remains the only LP head which can be dismantled and serviced on the bench with nothing more than screwdriver and pliers! Rewinding the coil is another matter. I've managed to rewind a 30-ohm coil with reasonable results, but any higher impedance has so far defeated me and my rather agricultural coil winder.

Incidentally, any fans of Flanders & Swann's 'Song of Reproduction' will be familiar with the reference to the 'red head pickup' double entendre - no doubt an XMS!

Best of luck with your own 'red head pickup' All you need now is the rest of the Decola!

I'd be very interested to hear other members' experience of these interesting products from the early days of hi fi.

Martin

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Posted : 31/05/2015 3:01 pm
Cathovisor
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There was even a blue plate model made specially for KB, though I've never seen one.

The 'blue plate' ones are wired differently to the standard Decca XMS heads: KB fitted a much more elaborate pick-up equaliser on the 'grams and disc reproducers that used these heads compared to Decca, where the wire link merely adds an extra capacitor in shunt with the input. As a result, the KB heads pass the audio through different networks for microgroove and standard recordings.

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Posted : 31/05/2015 9:23 pm
Hartley118
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Interesting that KB used more sophisticated EQ than in the Deccalian. Do the KB heads have a different connector with more pins?

In the Deccalian, the link in the 78 head does double up the capacitance in the LF boost EQ, lowering its turnover frequency to suit the 78 curve. I guess it's not an ideal bit of design to lose so much signal by putting a passive EQ straight after the head, thus requiring the mighty gain of a 6SL7 and 6V6 to drive the speaker. As far as I can see, the Decola circuit was different, with separate manual EQ switching after the first amplification stage. There's also a hum snag with the Deccalian arrangement: when the red LP head is plugged in, it just leaves the EQ pickup lead floating which, even though screened, can act as an antenna for hum pickup.

I think we were more tolerant of hum in the 1950s!

Martin

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Posted : 01/06/2015 4:58 pm
Cathovisor
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Interesting that KB used more sophisticated EQ than in the Deccalian. Do the KB heads have a different connector with more pins?

No, absolutely the same as the XMS connector matched the pre-existing Garrard 3-pin connector. The difference is that whilst the lower pin remains common, the LP head output is taken via the opposite pin to the 78 output (the 78 head is a standard one) - but both heads have a shorting link wired to the other pin so in KB's case, it also shorts the unused equaliser to earth.

My own preference is actually for the Type D pickup that Decca created, as used in the 78-only Deccalian: I also wonder how many dealers (and later enthusiasts) who fitted a 3-speed machine in a 78-only Decola also carried out the mods to alter the frequency response?

The 3-speed Deccalian arrangement is actually very bad practice as when heads are changed, the control grid is left floating as the DC path between grid and cathode is broken by the removal of the head: I added a 470kΩ resistor between grid and cathode (many times higher than the load intended or needed for the XMS) to preserve the DC conditions.

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Posted : 01/06/2015 11:35 pm
Brian Cuff
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No one has mentioned the EMI high sensitivity pickup released in 1937/8. This pickup has a straight response to over 9kHz with a resonance at around 12kHz. There is no armature in the normal sense as the very small needle itself comprises most of the moving mass. I believe that these were used in the old BBC record play-in decks (Cathy?). There is one fitted to my Marconiphone 703 Mastergram and it really does sound good. Tracking weight is also very low (I haven't measured it yet!).

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Posted : 02/06/2015 12:33 am
Cathovisor
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There is no armature in the normal sense as the very small needle itself comprises most of the moving mass. I believe that these were used in the old BBC record play-in decks (Cathy?).

Yup - the EMI Type 12 pickup, a.k.a. the "Hypersensitive". The BBC modified them with a small cut in the armature mounting plate to remove the aforementioned resonance.

The BBC seemed to have a penchant for needle armature pickups: prior to this the chosen pickup of the BBC was the Burndept needle armature pickup. A review carried out by the Wireless World in the early 1930s demonstrated that the Burndept output was free of any of the resonances that were normally present in the standard type of pickup: the downside was that the Burndept needed longer needles to work as a standard short needle would get lost in the magnet assembly (and just to add to your frustration, the tip of the needle then gets stuck against one of the pole pieces)! Typically the usual pivoted reed assembly produces a resonance at about 3-4KHz and on some cheap pickups, it can be quite dramatic. I have a 1930 Burndept radiogram which uses their needle armature pickup: as a result I have been accumulating tins of Columbia "Duragold" needles which, apart from being eminently suitable for autochangers, have sufficient length for the job in hand. Like the EMI Type 12, the Burndept also needed a transformer as they are low output devices and as I have more than one of these Burndepts, I am very tempted to pair one with a Garrard 201 I have just to see what they sound like with modern amplification.

In a 1930s issue of The Gramophone, there is a picture of Christopher Stone at work at the BBC in which he explains that the pickups are Burndept, and needles are either Duragolds or 'Golden Pyramid', but used only once.

Murphy also used a needle-armature pickup made by BT-H in the A26RG: the problem for some users of course is that they discovered the hard way that their beloved 'fibres' wouldn't work....

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Posted : 02/06/2015 2:09 am
FIXITNOW2003
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great info thanks :aad

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Topic starter Posted : 02/06/2015 10:20 am
Hartley118
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Marconiman - Good to hear of your success in restoring and improving your Deccalian. Never seen a walnut cabinet model. Perhaps as well, otherwise I'd be tempted to add it to my already-too-big collection!

The early years of the Deccalian were marked by impressively rapid innovation in turntable design, starting with the 78-only Garrard governor motor in 1948, soon superseded by idler drive units - some of the best quality products that BSR ever made. With their long precision centre bearings and relatively heavy turntables, they must rank as some of the earliest transcription turntables, predating the Garrard 301 by 2 or 3 years. There was the two-speed unit with a 'Decola-style' speed change knob, followed by the 3-speed model which was then in turn superseded by the Garrard TB. I do find it more difficult to get a decent rumble and wow performance from the Garrard TB than from the earlier BSRs that I guess were custom-built for Decca. I still use the 3-speed BSR model regularly.

You're so right to recall the staggering innovative culture in Decca around that time of the late 40s/early 50s. I gather much of the credit goes to Harvey Schwartz, a great engineer and salesman who came over to Decca UK with the US Brunswick acquisition. Also Chairman Ted Lewis, stockbroker, was rare among financial men as appreciating the importance of investing in innovation. I guess we shall never know names of the actual inventors and designers of the 'D' and 'XMS' heads and the Deccalian itself, but they deserve awards.

Those exciting post-war times at Decca compare brilliantly with the turgid technical conservatism at EMI, so slow to improve the performance of their records and issuing only 78s until 1953. I guess they missed Alan Blumlein!

Martin

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Posted : 05/08/2015 2:58 pm
Cathovisor
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I thought the Decca pickup was attributed to Arthur Haddy?

I gather much of the credit goes to Harvey Schwartz, a great engineer and salesman who came over to Decca UK with the US Brunswick acquisition.

He certainly created some interesting designs in the early 30s when he arrived: I have a 1932 Decca radiogram (model 29) that is a TRF on long wave, and a superhet on medium wave!

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Posted : 05/08/2015 3:32 pm
Hartley118
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I always associated Arthur Haddy's name with the clever extended range disc cutter developments at Decca Studios and associated microphones and amplifiers. To quote the Deccasound website (which may or may not be authoritative) . "In June 1945, Decca formally introduced its new recording process, dubbed “Full Frequency Range Recording” by Decca’s American-born engineer Harvey Schwartz (who also developed the Decola)." However, it's difficult to imagine there being no communication between the disc cutting guys and the disc player team. I guess that the original Decca type D pickup was the one designed to play those WW2 sonar recordings that began the FFRR story.

My one disappointment with FFRR 78s is the typically heavy surface noise which tends to mask those extra octaves in the high frequencies. Surprising that Haddy didn't introduce a quieter disc material like the Columbia 'New Process' from the 1920s. But I guess he had no influence in that area of the company. Steel needles still reigned supreme for most customers and needed robust grooves!

Martin

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Posted : 05/08/2015 4:41 pm