UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > General Vintage Technology Discussions

Notices

General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc.

Closed Thread
 
Thread Tools
Old 7th Mar 2004, 3:35 pm   #1
roger_a
Retired Dormant Member
 
Join Date: Sep 2003
Location: Croydon, London, UK.
Posts: 40
Default B7X14A Reverbeo (Survey)

Hi all, I hope this is in the most suitable section. (Please move if not)

B7X14a/65

Replacement/Modification 1.

I understand that early versions on this radio used two 6.3v scale bulbs, whereas later ones had an Electroluminescent lamp made by Philips. This was connected across the 245v AC secondary winding of the mains transformer. The circuit of the B7X43A (see further on) also shows the same high voltage, flat device being used.

From various websites I've found out that these " lamps " failed very early on in their lives. Oxygen penetrated the glass sandwich and reacted with the phosphor. This I understand radically reduced the light output. Usually, the suggestion was to revert back to the twin lamps with some sort of diffuser behind the scale (normal convention).

Having recently obtained one of these radios, I found that my scale had " mother of pearl " swirls travelling along the inside of the glass. The light output could just be seen with closed curtains. It also had a crack on the bottom edge which may have caused the chemical action mentioned above.

After trying bulbs/ LEDs/green acetate/ glow wires etc, I persued the possibility of obtaining a modern flat lamp replacement. This I have partially achieved and the radio is now working how the designers intended (green glow) and it really looks great. The " lamp " has been sandwiched between two pieces of glass, to emulate the original. Unfortunately, the device I obtained is of old technology, will not last long due the low frequency AC drive source, but at least it cost me nothing!

Further discussions with various manufacturers/suppliers indicate that new panels can be provided having identical dimensions to the original, but must be driven from a very small invertor running between 200 & 400Hz. This would be fed from a rectified heater voltage. I have been told that it would be unlikely that any oscillations, including generated harmonics would cause problems.

I have a couple of digital pics showing the old and new screens, if you want to see. Even if the old screen has been chucked out, this sandwiched replacement could still be used.

This new method is a very elegant solution and looks immpressive, but in my opinion, will mainly fail because of the cost of implimentation. The cost could never be recouped!.
------------------------------------------------------------------
Modification 2.

It's a shame that the radio doesn't have stereo FM as standard. Later released radios (perhaps not in the UK) like the B7X43A used the reverbeo system and also included a decoder.

I'm very intererested in researching the possibilty of obtaining parts and building such a decoder. I remember in the past that many IC designs were available. Obviously, it is unclear at this time if audio levels would matched, or if there would be sufficient FM drive from the discriminator etc.

As far as costs are concerned, this is difficult. To get the costs down we need to know what quantities are involved. To get a ball park cost figure, I need to know if anyone is interested in either, none or all of the above.

I see this as an ongoing project with a few problems yet to be solved.

By the way, I have always tried to be honest with my past restorations, to try and maintain the " history/design " of the radio. But I do replace the mains cable and provide some safety features around the PSU. However, this Philips radio (late 50's) is now my main listening radio and my pleasure would be increased if the stereo conversion worked Ok.

I am happy to take on-board the initial research, with help from anyone else. I fully realise that the more suitable decoder ICs may be difficult to source. I've already sent out emails to suppliers for available stocks.

So if anyone is interested perhaps you could reply to ---

Question (1) Replacement illuminated screen.
Question (2) FM Stereo Decoder kit


Obviously, any other comments/advice/suggestions would be welcomed.

regards,

Roger

PS, I'll have to get Paul to do a training course on PCB/CAD programs for the decoder, or will veroboard come to the rescue!!.
roger_a is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 3:41 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.