UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

Chris55000 · 1st Dec 2019, 1:18 am

Hi!

Keith Skues's Sunday Night programme can still be picked up.on 411m m.w. in certain areas, and don't forget he has a "Wireless Of The Week" feature – there's no better programs for testing and enjoying old sets on!

Apart from that, my aim with vintage electronics is to try and get it working with h.t. line voltages as close as possible to those given on the maker's original service–sheet, it has been my experience, that valve (and transistor in some cases!) voltages, tend to be noticeably higher, sometimes as much as 50V over, on a typical valve radio h.t. line, which doesn't do elderly valves & components a lot of good!

Generally high mains voltages, along with silicon diode rectifiers and low e.s.r. h.t. smoothing electrolytic capacitors are the main case of this, and I found countless times that if you don't watch this point you'll.be chasing about after replacement valves or transistors more often than you ideally should be!

I'm also in total agreement about using modern components where appropriate – the yellow 1613 axials and good–quality carbon–film (power oxide for 1–3W types) and RIFA electrolytics, will provide stabilty and reliability of valve circuit operation to a far greater degree than was possible with the components of the time!

One really annoying troublesome vintage item, tho', is the "baretter" – this lightbulb like device has an almost constant–current characteristic over its rated operating voltage for the specific current it was rated to run at, but was also very fragile and replacements are almost impossible to come by new – the modern aluminium–housed metal–clad wirewound resistor bolted discreetly under the chassis with a suitable NTC in series is the best way of substituting this!

"Magic Eye" phosphors that degrade to the point of almost invisibility are another vintage restorer's annoyance, altho' my experience with the EM34 type has been that altho' they go dimmer very rapidly from new, their brightness is fairly steady over a much longer period – my Dad had at least six sets fitted with them and all were bright enough to be usable!

Sometimes too low a target–anode voltage can speed up deterioration as well as too high a voltage can, and a trawling of innumerable sets and bridge circuits, etc., suggests 210–220V is about the best voltage to use on most end–viewed types.

Old coils, I.F. transformers, etc., we're generally designed to have a very high 'Q' on account of the lower mutual–conductance of the valves then available, and short of obvious physical damage or obvious corrosion from a moisture–laden environment it should be virtually never necessary to replace such a coil or transformer!

Unfortunately the one thing that ultimately decides the future extent of our hobby, apart from our own lifetimes, is how long a.m. and f.m. radio transmissions remain operational for, and me thinks gentle pressure ought to be put on the powers–that–be to make them aware there is far more interest in analogue radio then they may realise!

Mains and output transformers aren't normally a problem these days, Ed can deal with "odd–ball" requirements and plenty are still being manufactured new altho' the prices have always been silly in my opinion!

Meter movements – the AVO CT160 is the most notorious one of all, the last one I saw was almost £400! – but I think you can still obtain movements of lower sensitivity that will fit the unit and have the same or similar appearance, but in the end the time may come when it may be necessary to rebuild a more modern movement about 50 or 100uA f.s.d. into the original case and rescale it together with a current amplifier.

Chris Williams

(I think Tonne's Meter software will reproduce a CT160 scale plate)

1st Dec 2019, 1:18 am	#62
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,867	Re: Nostalgia? Probably. Hi! Keith Skues's Sunday Night programme can still be picked up.on 411m m.w. in certain areas, and don't forget he has a "Wireless Of The Week" feature – there's no better programs for testing and enjoying old sets on! Apart from that, my aim with vintage electronics is to try and get it working with h.t. line voltages as close as possible to those given on the maker's original service–sheet, it has been my experience, that valve (and transistor in some cases!) voltages, tend to be noticeably higher, sometimes as much as 50V over, on a typical valve radio h.t. line, which doesn't do elderly valves & components a lot of good! Generally high mains voltages, along with silicon diode rectifiers and low e.s.r. h.t. smoothing electrolytic capacitors are the main case of this, and I found countless times that if you don't watch this point you'll.be chasing about after replacement valves or transistors more often than you ideally should be! I'm also in total agreement about using modern components where appropriate – the yellow 1613 axials and good–quality carbon–film (power oxide for 1–3W types) and RIFA electrolytics, will provide stabilty and reliability of valve circuit operation to a far greater degree than was possible with the components of the time! One really annoying troublesome vintage item, tho', is the "baretter" – this lightbulb like device has an almost constant–current characteristic over its rated operating voltage for the specific current it was rated to run at, but was also very fragile and replacements are almost impossible to come by new – the modern aluminium–housed metal–clad wirewound resistor bolted discreetly under the chassis with a suitable NTC in series is the best way of substituting this! "Magic Eye" phosphors that degrade to the point of almost invisibility are another vintage restorer's annoyance, altho' my experience with the EM34 type has been that altho' they go dimmer very rapidly from new, their brightness is fairly steady over a much longer period – my Dad had at least six sets fitted with them and all were bright enough to be usable! Sometimes too low a target–anode voltage can speed up deterioration as well as too high a voltage can, and a trawling of innumerable sets and bridge circuits, etc., suggests 210–220V is about the best voltage to use on most end–viewed types. Old coils, I.F. transformers, etc., we're generally designed to have a very high 'Q' on account of the lower mutual–conductance of the valves then available, and short of obvious physical damage or obvious corrosion from a moisture–laden environment it should be virtually never necessary to replace such a coil or transformer! Unfortunately the one thing that ultimately decides the future extent of our hobby, apart from our own lifetimes, is how long a.m. and f.m. radio transmissions remain operational for, and me thinks gentle pressure ought to be put on the powers–that–be to make them aware there is far more interest in analogue radio then they may realise! Mains and output transformers aren't normally a problem these days, Ed can deal with "odd–ball" requirements and plenty are still being manufactured new altho' the prices have always been silly in my opinion! Meter movements – the AVO CT160 is the most notorious one of all, the last one I saw was almost £400! – but I think you can still obtain movements of lower sensitivity that will fit the unit and have the same or similar appearance, but in the end the time may come when it may be necessary to rebuild a more modern movement about 50 or 100uA f.s.d. into the original case and rescale it together with a current amplifier. Chris Williams (I think Tonne's Meter software will reproduce a CT160 scale plate) __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!