Philips Superinductance Radio

[Old Sparky]

On a thread to do with the return of Radio Caroline, the Philips SI radios were mentioned.  I am in process of repairing a 234A of that ilk, and know from the service manual that none of the many uninsulated tinned copper wires used to connect various parts of the circuit should be sleeved or otherwise insulated, presumably because the capacitance caused by the addition of sleeving would upset the alignment, but I'm sure that, if bare wires were used in anything made today in which mains and high DC voltages were present, it would, perhaps rightly, fall foul of safety regulations.  (admittedly no electronic equipment today would be built like the radios of 80 & more years ago, so the issue wouldn't arise)  However, many years ago I did see an early TRF radio (don't recall the make) of the type in which all components were connected together using insulated copper wires carefully bent at right angles where necessary and each component used screw terminals not soldered connections.  Radios of that type obviously worked (never heard the set in question working, though), so I wonder why the designers of the Philips SI sets felt it necessary to use bare tinned Cu wires rather than insulated ones.

[Murphyv310]

Hi.
Whether adding sleeving to the busbars would effect the sets performance is debatable. The construction is such that these "wires" are rigid and also when the chassis is boxed up in the cabinet, out of harms way.
Today we now rely on the HSE rules, have RCD trips and other safety devices which are there for our safety. The sad thing is we now rely far too much on these devices and take it for granted, same with modern cars with airbags etc. We now rely on technology rather than common sense.
I don't have issues with old sets, I know not to poke with fingers at unknown parts etc and I respect high voltages.

At the end of the day the set is 80 years old, it's done its job without killing anyone so why change it now?

[Old Sparky]

I wasn'nt thinking of changing it, Trevor, merely commenting along the lines of 'that wouldn't be allowed now'. In order to replace some items I've had to remove the tagboard with a row of resistors from the RH side (as viewed from the front) of the 234A, which, of necessity, meant de-soldering and moving some of the aforesaid wires, which I'm now in the process of re-connecting and re-positioning to the original layout, as I will do in other parts of the chassis after refitting the paxolin tubes containing replacement capacitors.

[Murphyv310]

I take lots of photos pre stripdown as its good reference on rebuilding.
Good luck with the restoration, a nice set to do with good performance for its type and age.

[ppppenguin]

Unshrouded high voltage wires and terminals are to be expected inside a piece of valve kit. ANd plenty of modern solid state kit too. The general rule is that they should only be accessible by use of a tool. Only skilled persons should be doing this. No real difference here between a 1930 radio and a 1990 TV.

OK, there are differences. Some old radios don't need a tool to get inside and high voltage points are often shrouded in modern kit. There are some prewar TVs with mains derived EHT on terminals that are all too easy to touch if you're working inside. This is not comfortable, even if you're suitably skilled and careful.

[Terry]

I wasn'nt thinking of changing it, Trevor, merely commenting along the lines of 'that wouldn't be allowed now'.  

Hmm. Would you consider a Mullard 5-10 built to Mullard's design with all of the components on tag boards with their exposed terminals, not to mention all the exposed valveholder pins, dangerous and 'not allowed now'?

Or a hand built printed circuit board? Mass produced boards have an insulating resist on them but it isn't there for safety - it is to save the enormous amount of money that would be wasted due to all the unnecessary, but expensive, solder deposited onto all of the tracks during the flow soldering process. Small scale hand soldered boards don't need such a resist so every single conductor (track) is uninsulated!

[Old Sparky]

Points duly noted, Jeffrey & Terry. For once I didn't take photos before dismantling (which I started over 2 years ago, then, for various reasons, put the SI radio to one side until recently. What I did do, however is make copius notes, including sketches of what goes where, besides obtaining the Philips Service Manual for the radio, so it's been mostly a case of getting my mind back into familiarity with the chassis after leaving it for so long, but I' getting there, albeit slowly!

[ppppenguin]

Philips were seeking to minimise all sorts of losses in the superinductance sets. Insulation was slightly lossy (very lossy at higher frequencies) before polythene and other modern plastics so perhaps there was some marginal gain to be had from leaving wires bare.

[Old Sparky]

Points duly noted, Jeffrey & Terry. For once I didn't take photos before dismantling (which I started over 2 years ago, then, for various reasons, put the SI radio to one side until recently. What I did do, however is make copius notes, including sketches of what goes where, besides obtaining the Philips Service Manual for the radio, so it's been mostly a case of getting my mind back into familiarity with the chassis after leaving it for so long, but I' getting there, albeit slowly.