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 > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Closed Thread
 
Thread Tools
Old 11th Dec 2021, 6:53 pm   #1
saddlestone-man
Hexode
 
Join Date: Mar 2009
Location: Cirencester, Gloucestershire, UK.
Posts: 391
Default Amplion Service Convette model S.142

Hello All

I picked up this S.142 at RWB last Sunday. I'd seen one a few years ago at a Radiophile meeting, but they seem to be pretty rare. I haven't checked the LT output yet, but I presume that it only covers 1.5V battery valves. I like the way the LT and HT outputs are connected to the various battery connectors likely to be encountered in valve portables.

Presumably not too many radio service departments invested in one, and most of the few that did threw them away when valve portables stopped coming in for repair.

Does anyone recall using one in anger, and does anyone have a schematic?

I had a look through the few Trader magazines I have to see if it was advertised or reviewed, but couldn't find any mention. Has anyone seen an advert?

best regards ... Stef
Attached Thumbnails
Click image for larger version

Name:	PC111673.jpg
Views:	208
Size:	88.7 KB
ID:	247672   Click image for larger version

Name:	PC111687.jpg
Views:	156
Size:	50.0 KB
ID:	247673  
saddlestone-man is offline  
Old 28th Dec 2021, 9:00 am   #2
Phil G4SPZ
Dekatron
 
Phil G4SPZ's Avatar
 
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,735
Default Re: Amplion Service Convette model S.142

A nice find! I suggest it will do 2 volts LT as well as 1.5 volts. The problem is that the LT voltage is controlled by a low-resistance rheostat in series with the LT supply. Thus you can only set the LT with all valves plugged in and drawing their rated filament current. A poor contact on the filament pins of one valve socket will cause the LT voltage to rise, with potentially devastating results to the remaining valves. So don’t wiggle the valves in their sockets!
__________________
Phil

Optimist [n]: One who is not in possession of the full facts
Phil G4SPZ is online now  
Old 7th Mar 2023, 6:12 pm   #3
Chrispy57
Hexode
 
Join Date: Mar 2020
Location: Rochdale, Greater Manchester, UK.
Posts: 439
Default Re: Amplion Service Convette model S.142

Hi Stef,
sorry I'm over a year late to the party, but I saw your original (closed) post recently while searching for information on my own S.142, and Radio Wrangler has kindly re-opened the thread.

I had picked this up on EBay several years ago, and whilst it was basically functional I had just made it electrically safe and put it to one side until I had a need for it, but your post inspired me to work on it.

I thought about Phil's advice, above, and decided to do a practcal updating, rather than a faithful period restoration with re-stuffing capacitors etc.

A previous owner seems to have fitted a new LT rectifier and tinkered with the wiring of the caps and inductors, as well as bodging the rheostat mounting, which may have been the cause of the original fault. I can see from the photo that yours has been bodged a bit too, with an extra blue cap and a dodgy mains lead.

I retained the iron-work and front-panel components (well, new HT pot reqd), but swapped over the two voltmeters to better associate them with their respective LT and HT terminals, after fixing the sticking HT meter and fitting new calibration resistors.

I have used a separate stripboard for each supply to incorporate 3 terminal voltage regulators; a pair of TL783 high voltage regulators in series to provide the range 45V to 120V, to match the old battery types, while staying well within the comfort zone of the TL783. For the LT supply the LM317 gives a range of 1.25V to 2V over the span of the original 16 Ohm rheostat, which I rather liked but needed some tidying up. Originally the brass shaft of the wiper connection made contact with the front panel cut-out, and had the potential to complicate the bias arrangement of a connected radio, once the front panel was earthed for safety reasons. Is yours the same? I widened the cut-out slot a couple of milimeters and fitted two layers of heat-shrink tube over the shaft, and inserted a fibre washer either side of the panel.

I have replaced the selenium rectifiers with silicon diodes, a 400V bridge for the HT and cobbled 4 1A Shottky diodes into a bridge for the LT, which was un-necessary really as there is voltage to spare. I also added a front-panel neon as a clear indication of "mains on", although the meters should make that noticable anyway.

I have replaced the caps and resistors across the front-panel vertical sockets, although I did actually test all the caps on my Hunts CRB-3 Capacitance Analyser (for fun really), and they were close enough to original values but with reduced insulation voltage - just above the maximum HT level but heading south after 70 years.

On the mains side of things; I have disconnected the now un-necessary voltage selector but left it in place to cover a hole, fitted a fuse to the rear panel, moved the mains switch wiring to the Live rather than Neutral, used a grommetted mains lead and fixed a terminal block and P-clamp on the mains cable.

The front-panel was covered with a nasty nicotine residue, that resisted all cleaning methods tried, except abrasion and Sani-Cloth CHG 2% medical device wipes, which unfortunately also wanted to dissolve the ink used on the lettering. So a laborious task ensued in an attempt to preserve what lettering remained, hence the strange label-like appearance!

Overall, I am quite pleased to now have a safe and functional bench power supply for any old valve based battery radios that come my way. I would be very interested to hear how you have been getting on with your own unit, since first posting about it a couple of Decembers ago.

Cheers
Chris
Attached Thumbnails
Click image for larger version

Name:	1 Before.jpg
Views:	59
Size:	100.2 KB
ID:	274528   Click image for larger version

Name:	2 Before .jpg
Views:	57
Size:	123.2 KB
ID:	274529   Click image for larger version

Name:	3 Updated 1.jpg
Views:	54
Size:	105.1 KB
ID:	274530   Click image for larger version

Name:	4 Updated 2.jpg
Views:	51
Size:	143.8 KB
ID:	274531   Click image for larger version

Name:	5 After.jpg
Views:	54
Size:	143.7 KB
ID:	274532  


Last edited by Chrispy57; 7th Mar 2023 at 6:24 pm.
Chrispy57 is online now  
Old 23rd Mar 2023, 12:09 am   #4
Phil G4SPZ
Dekatron
 
Phil G4SPZ's Avatar
 
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,735
Default Re: Amplion Service Convette model S.142

Great job, Chris. You have a useful (and safe) mains unit that will be an asset when servicing battery valve sets, and it’s a lot more versatile than the original.

I confess that I now prefer to power such sets from batteries whilst servicing them. For one thing, it’s more convenient, you’re not tied to the bench (I often work elsewhere) and the potential current available is restricted compared with a mains unit. I usually lash up ten PP3s in series for the HT, plus a C cell for LT, preferring Pound-shop zinc carbon cells that can easily supply the power required. Once working, a decent replica battery makes the set fully portable as was its original purpose.
__________________
Phil

Optimist [n]: One who is not in possession of the full facts
Phil G4SPZ is online now  
Old 23rd Mar 2023, 2:55 pm   #5
Chrispy57
Hexode
 
Join Date: Mar 2020
Location: Rochdale, Greater Manchester, UK.
Posts: 439
Default Re: Amplion Service Convette model S.142

Hi Phil,
thanks for your kind comments about my Amplion Convette S.142, which has now taken up residence alongside its similarly aged test equipment companions on my "mechanical/old wireless bench" ready for duty.
I did actually follow your currently favoured method of making up a battery box (PP3s and D cell) to restore, then use my Zenith Transoceanic a few years ago - in a Pringle socks gift box (the only useful Christmas present my MIL ever gave me!). Your post reminds me that I must check it out, in case those batteries have now corroded, as seems to have afflicted several other members in their recent posts.
Cheers
Chris
Attached Thumbnails
Click image for larger version

Name:	Bench.jpg
Views:	47
Size:	109.3 KB
ID:	275595  
Chrispy57 is online now  
Old 23rd Mar 2023, 3:01 pm   #6
Phil G4SPZ
Dekatron
 
Phil G4SPZ's Avatar
 
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,735
Default Re: Amplion Service Convette model S.142

What a nice tidy workshop, Chris! With a nice model engineer’s lathe too. Makes my shack look an even worse mess…

I have yet to experience leakage or corrosion from cheap zinc carbon cells. However it’s worth checking any that have been in place for any length of time.
__________________
Phil

Optimist [n]: One who is not in possession of the full facts

Last edited by Phil G4SPZ; 23rd Mar 2023 at 3:03 pm. Reason: Afterthought
Phil G4SPZ is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 1:48 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.