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 > Success Stories

Notices

Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

Reply
 
Thread Tools
Old 24th Nov 2021, 11:34 am   #1
AD360 Rob
Hexode
 
AD360 Rob's Avatar
 
Join Date: Jun 2012
Location: Chester, Cheshire, UK.
Posts: 403
Default Odd DAC90A fault cured

Morning all,

The latest DAC90A on the bench was an ivory one bought from eBay.
It was described as working and indeed it was to some degree.

As it was filthy and had a damaged loudspeaker grille it was duly stripped down for a full clean and inspection.
This revealed that someone had carried out the odd capacitor replacement and had fitted a non Celestion loudspeaker.
I decided to treat it to the usual work, replacing all the waxed capacitors, doing the UL41 pin 4 mod, tuning gang grommets and any wildly out of spec resistors. Also, the crumbly wiring around the dropper section was replaced too.
As a matter of course with these, I remove and check the dial lamps both for continuity and rating as I have been caught out in the past with a flasher bulb being fitted to one holder on another set (that had me scratching my head a bit)
Anyway, all work done, power up time came and I was rewarded with dial lamps so dim that they barely lit the filaments. Weird I thought as I had already changed the shunt resistor for a 180ohm and with the standard spec lamps this results in a pleasantly warm glow from the scale. Voltage checks revealed hardly any volts (1 or 2 hundred milivolts at best) across the lamps so I set about rechecking all my work just in case and measuring heater chain voltages in case there was an unexpected high resistance or leak to chassis but all appeared well here with al voltages correct apart from V1 heaters which were quite low and the valve envelope only warm to the touch but the radio did actually work which was even more puzzling.
I had noted that the original dial lamps were 6.5volt ones at 300mA and there was the clue which I had missed. I did some research on here and found a post that said you could use 6volt lamps in parallel if you couldn't get the originals and indeed someone in the past had rewired the lamp holders to be in parallel rather than series ! I simply didn't spot this as all the wiring looked to be original in that area. Re-wiring them to be in series restored normal dial lamp operation and V1 heater voltage.

Just goes to show that even on a set that is very familiar, the phantom can still trip you up. (said phantom had also had a twiddle of the aerial and oscillator trimmers but had left the I.F. transformers alone)

Rob
AD360 Rob is offline   Reply With Quote
Old 24th Nov 2021, 4:34 pm   #2
stevehertz
Dekatron
 
stevehertz's Avatar
 
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 5,965
Default Re: Odd DAC90A fault cured

Nice catch, well done.
__________________
A digital radio is the latest thing, but a vintage wireless is forever..
stevehertz is offline   Reply With Quote
Old 24th Nov 2021, 10:59 pm   #3
Uncle Bulgaria
Octode
 
Join Date: May 2016
Location: Cornwall, UK.
Posts: 1,399
Default Re: Odd DAC90A fault cured

I can see why people like having little pieces of paper inside saying what they'd changed. It seems like the Twiddler had done a good enough job for you to think the wiring was original, and presumably it provided some benefit relative to the lamps available when it was in use. Well done. It's always the bits that look fine that are the last to be checked...
Uncle Bulgaria is offline   Reply With Quote
Old 21st Dec 2021, 3:17 pm   #4
telstar
Octode
 
Join Date: Dec 2003
Location: Leeds, West Yorkshire, UK.
Posts: 1,355
Default Re: Odd DAC90A fault cured

Hi Rob.
Nice repair.
I have also a Bush DAC90A in cream cabinet. Mine did not have the original loudspeaker, but it does work O.K,
Also, I may check the lamp shunt resistor on my radio as the bulbs are not as bright as they could be,
Cheers
Mike
telstar is offline   Reply With Quote
Old 21st Dec 2021, 7:14 pm   #5
Radio1950
Hexode
 
Join Date: Apr 2017
Location: Buderim, Queensland, Australia.
Posts: 420
Default Re: Odd DAC90A fault cured

Thanks for sharing.
Sometimes these things are not obvious at all, as it might appear that the first repairer had just resoldered some lampholder tags that had heat dodgy joints.
Radio1950 is online now   Reply With Quote
Old 22nd Dec 2021, 2:55 pm   #6
telstar
Octode
 
Join Date: Dec 2003
Location: Leeds, West Yorkshire, UK.
Posts: 1,355
Default Re: Odd DAC90A fault cured

Hi. Another item to remember is that the wiring leading from the ballast resistor unit will no doubt need replacing as the sleeving will have crumbled with the proximity of the heat dissipated from the resistor.
Cheers
Mike
telstar is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 5:13 am.


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 - 2022, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.