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

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Reply
 
Thread Tools
Old 7th Feb 2020, 9:38 am   #1
Beardyman
Pentode
 
Beardyman's Avatar
 
Join Date: Jan 2018
Location: Portsmouth, Hampshire, UK.
Posts: 171
Default Etronic RA640 re-visited

It was a while back when this radio was finished & lately I've been going through the collection doing a bit of cleaning/dusting etc. I never really finished the wooden case of the RA640 so I thought, "That's a good thing to begin with, should keep me quiet for a few weekends". Whilst I was seeing to the case I powered the chassis up on the bench & was listening to some 40's music via the pantry TX. After about maybe 10-15 minutes my inner supervisor said, "That sounds different!", it was very thin & reedy, virtually no bass notes at all then it would behave itself then thin & reedy again. To cut a long story short, I found the KT61 output valve had an intermittent heater/cathode short. Looked on line & could not believe the price these valves are going for! Ridiculous! Off to the valve museum & with a change of cathode resistor a Mazda 6P25 will be a good substitute at a far more reasonable price. Should be here early next week but all that aside apparently the KT61 had a bit of a history of this fault. With nothing to lose I applied a PSU set to about 3V but high current (>5A), it drew around 2-3A for a few seconds then cleared to zero. Thinking I'd either removed the short or blown the filament I checked again, no short & filament intact! Result I thought. No, within a few seconds it returned. I think that's the thing I like about valve radios, they just keep giving!
__________________
The difference between stupidity and genius is that genius has its limits. (Einstein)
Beardyman is offline   Reply With Quote
Old 7th Feb 2020, 6:59 pm   #2
Leon Crampin
Octode
 
Join Date: Nov 2005
Location: Surrey, UK.
Posts: 1,439
Default Re: Etronic RA640 re-visited

The poor quality of MOV valves never ceases to amaze me. Metallised types are now nearly always bare, and even when new, many MOV types barely make their specified gm on the tester.

Mazda, I think made the best valves apart from a few flaky rectifiers (U801 etc.) and most Philips and Brimar types were OK.

I would fit the 6P25 unless originality is important - a wayward output valve can damage transformers.

Leon.
Leon Crampin is online now   Reply With Quote
Old 10th Feb 2020, 11:21 am   #3
Beardyman
Pentode
 
Beardyman's Avatar
 
Join Date: Jan 2018
Location: Portsmouth, Hampshire, UK.
Posts: 171
Default Re: Etronic RA640 re-visited

Originality is sometimes important but in this case not. I refuse to pay 60+ for a valve that has an unknown history & doubtful construction. From what I've read the 6P25 has a better reputation & is significantly cheaper (approx. 18). If this set was a high end model I may have been tempted to "splash the cash". Yes, output transformers are easily damaged & I'll be keeping a weather eye on that when the new valve arrives. All the changes will be documented so if in the future the next owner wishes to put it back to original then they can. BTW, the case is looking much much better! Have a good day.
__________________
The difference between stupidity and genius is that genius has its limits. (Einstein)
Beardyman is offline   Reply With Quote
Old 10th Feb 2020, 11:35 am   #4
mark2collection
Hexode
 
mark2collection's Avatar
 
Join Date: Jul 2010
Location: Royal Berkshire, UK.
Posts: 351
Default Re: Etronic RA640 re-visited

Sound-wise, we had a similar thing recently with our Philco 444, reaching the point when warm, as through someone had 'flicked' an internal tone switch to make it sound quiet, dull, flat & no low frequency response at all. Imagine a pillow being placed over the loudspeaker.

Looking at the set yesterday, the output valve wasn't fully home & the centre of the 'speaker magnet was touching the voice coil former(?) The loudspeakers magnet assembly runs warm in use, I'd imagine the expansion was enough to upset the clearance, coupled with the lumpy/rusty bits too.

Having reseated the output valve, de-rusting the inner metal parts of the 'speaker & re-centering the voice coil, it's never sounded so good

My initial fear was, duff output valve.

They keep you on your toes, that's for sure.

Mark
__________________
Slowly turning the 'to-do', into 'ta-dah'
mark2collection is offline   Reply With Quote
Old 14th Feb 2020, 6:00 pm   #5
Beardyman
Pentode
 
Beardyman's Avatar
 
Join Date: Jan 2018
Location: Portsmouth, Hampshire, UK.
Posts: 171
Default Re: Etronic RA640 re-visited

Well, the 6P25 arrived today. Plugged it into the chassis and, after a few double checks, applied power. Everything looking good, no odd smells or smoke. Gradually a hiss from the speaker, tuned into the pantry tx, we have bass! Actually we have a very nice sounding radio again. Its been running on the bench for a couple of hours & nothing is distressed, mains & output transformers the same temperature as surrounding metal work. All in all I'm one happy bunny. Now to get to grips with the random pops, clicks & f*rty noise the Defiant is making! As I said before, I love valve radios, they just keep on giving! Have a good weekend one & all, keep safe.
__________________
The difference between stupidity and genius is that genius has its limits. (Einstein)
Beardyman is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 2:33 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 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.