Pamphonic 610 Record Player

[Pamphonica]

(Today's job)

This record player was bought quite cheaply from a chap who had bought it new in about 1958. He was happy that it was going to a good new home. I have always fancied one of these machines. It's a bit like a Pye Black Box, but of course it's Pamphonic, which is my preference.

It has a highly polished case and a decent Collaro deck. It is a direct mains set with no mains transformer so needs treating with care. The valve lineup is a little unusual - as well as a predictable UY41 and a pair of UL41s in push-pull, there's an ECC83 used as a preamp and phase splitter. So the heater chain is a little unusual, with a 2240 ohm resistor in parallel with the three 100mA U-series valve heaters, to add a further 50mA, so the total matches the 150mA drain of the remaining ECC83 operating with a 12V heater.

I wanted to get it right, so did not attempt to run it until it had been restored. Lacking a circuit diagram, I started from scratch and drew the diagram out bit by bit. Some of the components had lost their markings but were able to be measured with one end desoldered. No real surprises, except a total lack of any by-pass capacitors on cathode resistors.

The main electronic problem was the collection of Hunts caps, used for coupling the cartridge, some of the feedback, and the tone controls. Plus another one to couple the metalwork to the neutral line. Luckily there is no danger of hitting live metalwork as it is is very well embedded. So all the Hunts were replaced, and some 470K and 56K Erie resistors as well, as they had drifted high. The electrolytic was reformed and is certainly working, but probably could do with re-stuffing at some point. The pots felt Ok so were just lubricated. Someone had kindly already replaced the inter-stage couplers (0.1uF) with good RS versions so those were retained.

The deck needed a good clean (with IPA) to get gunk off the non-mechanical surfaces. The mechanism was carefully de-greased and re-lubricated. At first the platter was not being driven at all and I suspected a totally hard idler, but after some exploration a small pawl was found to be stuck. A few minutes easing with oil got everything working again and the deck spun up. There's very little bearing friction, but the idler is a bit smooth so slips for a few seconds. And Pamphonic seem to have added a huge cast weight to the underside (is that a normal Collaro feature?). The cartridge is a Ronette SA-250.

The valves were all tested and the UL41s were tired. The rest were fine. Some spare (used but good) UL41s were pressed into service. And the 610 was finally powered up, gently at first via a variac just in case!

And a couple of minutes later I was listening to the vintage sounds of "Take a pair of sparkling eyes" from the Gondoliers, by the Band of the Coldstream Guards, on 78. An old recording but somehow fitting. And a great sound from the 7" speaker.

What a joy to get this machine, which has not been used for probably 30+ years back into full working order. It's a great addition to my small Pamphonic collection.

- Jeremy

[Pamphonica]

A few before and after photos of the innards

[Pamphonica]

and with the nice shiny lid closed!

[GrimJosef]

Originally Posted by Pamphonica

No real surprises, except a total lack of any by-pass capacitors on cathode resistors.

Nice job Jeremy ! Another pretty thing singing again .

If you can afford the loss in gain then leaving the capacitor off the cathode resistor adds some negative feedback to linearise the stage in question. It's unusual to see it done on every single stage, but at least you don't have to worry about the electrolytics going dry with age ! Is there any global feedback as well ?

Cheers,

GJ

[Michael Maurice]

That weight on the underside is definitely not Collaro

[Pamphonica]

Thanks GJ,
there is overall feedback from the speaker terminals. One terminal feeds back via a 47K to the first stage (ECC83) cathode resistor. The other speaker terminal is taken to 0 volts via 47K // 0.04uF. Odd!
And thanks, Michael, for the confirmation on the weight. It does add a lot of mass to the deck, which perhaps floats better as a result on the springs.
- Jeremy

[GrimJosef]

Originally Posted by Pamphonica

there is overall feedback from the speaker terminals. One terminal feeds back via a 47K to the first stage (ECC83) cathode resistor. The other speaker terminal is taken to 0 volts via 47K // 0.04uF. Odd!

Hmm. Does it have an external speaker socket ? I'm hoping not, given the earthing arrangements.

I see there's a common cathode resistor for the two UL41's. As long as the valves are running in Class A the voltage across that will be DC only. So it won't add any feedback and a capacitor there wouldn't do anything. 150 ohms seems a little high. The datasheet recommends 100 ohms http://r-type.org/pdfs/ul41.pdf. But that's for 170V HT and maybe your UY41 straight off the mains is giving you more than that.

Cheers,

GJ

[Pamphonica]

No external sockets at all! Well-insulated, solid knobs. (The same knobs as on the Pye 15A radio). Deck is earthed. Cross fingers!
I didn't measure the HT but it's got to be somewhere nearer 200V.
- Jeremy

[threeseven]

Nice job Jeremy. I have a Clarke and Smith with the same deck and need a new stylus and possibly new cartridge. Any ideas where I might find one?

[Pamphonica]

No ideas on cartridge or stylus I am afraid. It's a new one on me.

[mark_in_manc]

Originally Posted by Pamphonica

And thanks, Michael, for the confirmation on the weight. It does add a lot of mass to the deck, which perhaps floats better as a result on the springs.

The big mass is interesting - the same technique is used when mounting a vibrating or impacting machine on springs to reduce vibration transmissibility into the floor on which it sits - machine sits on large concrete inertia block, which then sits on springs. Same technique can be used to isolate a 'quiet' piece of kit from the ground on which it sits...such as the whole 5-story Bridgewater (concert) hall in this town.

The main idea for isolation purposes is to lower the resonant frequency of the 'thing' on its springs - there will be several resonances, translational and rotational and mixtures, but thinking about the vertical 'bouncing' mode is perhaps the easiest. You only get a reduction in vibration transmission from root2 x f_res and above - so it makes sense to have f_res as low as you can.

This either means soft springs or a heavy mass. Heavy mass is more useful because it makes for easier stability control ('thing' wobbles around too much on very soft springs), and also reduces velocity of the 'thing' in the mass-controlled region above resonance due to any force components in that frequency range (since here F is more or less = ma).

Any deck might benefit from this, I guess, though benefits dissappear once one's springs go stiff (coil-bound) due to their static compression by gravity. It's interesting thinking about what components of vibration might be controlled - external ones (my kids jumping around on a wooden floor!) yes - but internal ones (grumbly idler etc) perhaps not, as the heaver deck might give the motor something more substantial to push against (depending on its mounting), perhaps putting the grumble more effectively into the platter


cheers
Mark

[Pamphonica]

Paul Taylor, Pamphonic's co-founder was a long-time member of the various acoustical and sound engineering societies in the UK in the 50s and 60s. He was a real engineer, and left behind carefully written out notes on things like the calculation of the compound wavefront from line-source loudspeakers. This sort of detail (the extra weight under the deck) is just the sort of thing he would have contributed to customise an otherwise fairly standard setup.
- Jeremy