3 Questions about a valve radio - UK Vintage Radio Repair and Restoration Discussion Forum

Dick Glennon · 22nd Sep 2010, 9:04 pm

Hello again, More questions, No 1 ,What ohms is used in coax cable in the wave-change-tuning area of a radio. No 2, What if any lubrication can be used on the wave-change contacts (slider type). No 3, Is it possible to repair slots in a paxolin strip that have become worn with work,ie.OFF switch slider. Hope someone can help. Regards Dick.

Steve_P · 22nd Sep 2010, 9:19 pm

1: Usually 75 Ohms. Just had the back off one of mine and that looks like 75 Ohms to me,
2: Not WD40! I use Servisol. I don't know about Ireland, but over here you can get it from Maplin.
3: Depends what's happened. Pictures would help. A brush would clean, Glue might mend or it may just need refitting.

Cheers,

Steve P.

Dave Moll · 22nd Sep 2010, 10:39 pm

Just to clarify re no. 2, what you want is to clean the contacts, not lubricate them - this is what Servisol (as Steve suggests) does.

PJL · 23rd Sep 2010, 8:54 am

Any type of RF coax would be fine. The frequencies are too low and cable length too short for any transmission line effect. Needs to be RF to be low capacitance.

G8HQP Dave · 23rd Sep 2010, 12:49 pm

Within a radio coax may cause problems due to its capacitance, so replace like with like. If there is coax it is probably 50ohms, but wiring around wavechange switches and tuning capacitors is rarely coax but just ordinary wire.

murphyv310 · 23rd Sep 2010, 1:37 pm

Hi.
Servisol will clean the contacts, remove tarnish etc, but the contacts will be more prone to wear, a couple of drops of electrolube is the best answer after cleaning the contacts or an ultra light touch of vaseline (petrolium jelly).
Incidentally I have been usng WD40 for years with absoulutely no problems.

DAVEHALL · 23rd Sep 2010, 10:06 pm

I'd suggest a bit of caution and test first .Reason , in ye olde GPO we used old valve amps ,with the gain pot in the feedback path and when it/switch contacts got dirty , AMP used to howl . One cleaner /lubricant from a reputable source caused no end of contact problems.We even ended up replacing a switch or two .

Dick Glennon · 26th Sep 2010, 2:05 pm

Hello again, I got sorted with the radio, I used servisol, 50 ohm coax cable and I had an old bit of paxolin so, I cut off fine dust with a hacksaw, mixed it with evostik and and filled the slot with it.I filed it off when set. So far so good. Thanks for all the help, Dick.

22nd Sep 2010, 9:04 pm	#1
Dick Glennon Hexode Join Date: Oct 2006 Location: Edenderry, Republic of Ireland. Posts: 428	3 Questions about a valve radio Hello again, More questions, No 1 ,What ohms is used in coax cable in the wave-change-tuning area of a radio. No 2, What if any lubrication can be used on the wave-change contacts (slider type). No 3, Is it possible to repair slots in a paxolin strip that have become worn with work,ie.OFF switch slider. Hope someone can help. Regards Dick.

22nd Sep 2010, 9:19 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: 3 Questions about a valve radio 1: Usually 75 Ohms. Just had the back off one of mine and that looks like 75 Ohms to me, 2: Not WD40! I use Servisol. I don't know about Ireland, but over here you can get it from Maplin. 3: Depends what's happened. Pictures would help. A brush would clean, Glue might mend or it may just need refitting. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

22nd Sep 2010, 10:39 pm	#3
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,130	Re: 3 Questions about a valve radio Just to clarify re no. 2, what you want is to clean the contacts, not lubricate them - this is what Servisol (as Steve suggests) does. __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

23rd Sep 2010, 8:54 am	#4
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: 3 Questions about a valve radio Any type of RF coax would be fine. The frequencies are too low and cable length too short for any transmission line effect. Needs to be RF to be low capacitance.

23rd Sep 2010, 12:49 pm	#5
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: 3 Questions about a valve radio Within a radio coax may cause problems due to its capacitance, so replace like with like. If there is coax it is probably 50ohms, but wiring around wavechange switches and tuning capacitors is rarely coax but just ordinary wire.

23rd Sep 2010, 1:37 pm	#6
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: 3 Questions about a valve radio Hi. Servisol will clean the contacts, remove tarnish etc, but the contacts will be more prone to wear, a couple of drops of electrolube is the best answer after cleaning the contacts or an ultra light touch of vaseline (petrolium jelly). Incidentally I have been usng WD40 for years with absoulutely no problems. __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

23rd Sep 2010, 10:06 pm	#7
DAVEHALL Retired Dormant Member Join Date: Jan 2010 Location: Coventry, Warwickshire, UK. Posts: 339	Re: 3 Questions about a valve radio I'd suggest a bit of caution and test first .Reason , in ye olde GPO we used old valve amps ,with the gain pot in the feedback path and when it/switch contacts got dirty , AMP used to howl . One cleaner /lubricant from a reputable source caused no end of contact problems.We even ended up replacing a switch or two .

26th Sep 2010, 2:05 pm	#8
Dick Glennon Hexode Join Date: Oct 2006 Location: Edenderry, Republic of Ireland. Posts: 428	Re: 3 Questions about a valve radio Hello again, I got sorted with the radio, I used servisol, 50 ohm coax cable and I had an old bit of paxolin so, I cut off fine dust with a hacksaw, mixed it with evostik and and filled the slot with it.I filed it off when set. So far so good. Thanks for all the help, Dick.