McMurdo Valve Bases - UK Vintage Radio Repair and Restoration Discussion Forum

jonnybear · 2nd Jul 2014, 4:40 pm

For what it's worth, broken contacts in McMurdo valve bases can be a pain, sometimes you can reform them with a needle, but more often they are brittle and snap. this is something I came across, If you have an old scart socket cut the pins out and with a nail file or the like, file the slot out slightly, take out the old broken contact, two of these scart pins side by side slot back into the base giving good contact just need a bend on the solder tag to keep them in position. I do not know if it is a long lasting repair but it seems to work.
John

G6Tanuki · 2nd Jul 2014, 7:23 pm

That's a nice fix - using easy-to-acquire parts, too.

The McMurdo type valve-sockets do seem a major fail after a few decades: I wonder if anyone's ever done an analysis of the brass composition and compared it with the brass used for the contacts on Amphenol-type Octal bases?

jonnybear · 2nd Jul 2014, 7:44 pm

The composition of the brass is probably the same, fatigue is more than likely caused by temperature changes, octal valves have less heat transfer through the thin connecting wires to the pins, where b8a & b9a do not, just my theory anyway.
John

McMurdo · 2nd Jul 2014, 9:53 pm

My username is in honour of these things!
One small aspect of my day job is restoring valved musical electronics; the famous company Vox (Jennings) used McMurdo and a single organ can contain scores of bases with broken pins, no good for a professional musician. I've always opted to replace the holder complete, though it's not in the spirit of this forum and is a very time consuming affair.

Hermit6345 · 8th Jul 2014, 1:33 pm

What a good idea. The B7G bases in 1.4 volt portables seem to be the most unreliable possibly due to something coming from the batteries. I have changed a lot of single contacts and a few whole valve bases which can be a pain.. The larger bases, like octal etc. seem to be better.

2nd Jul 2014, 4:40 pm	#1
jonnybear Octode Join Date: Nov 2010 Location: Cullompton, Devon, UK. Posts: 1,435	McMurdo Valve Bases For what it's worth, broken contacts in McMurdo valve bases can be a pain, sometimes you can reform them with a needle, but more often they are brittle and snap. this is something I came across, If you have an old scart socket cut the pins out and with a nail file or the like, file the slot out slightly, take out the old broken contact, two of these scart pins side by side slot back into the base giving good contact just need a bend on the solder tag to keep them in position. I do not know if it is a long lasting repair but it seems to work. John Attached Thumbnails

2nd Jul 2014, 7:23 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: McMurdo Valve Bases That's a nice fix - using easy-to-acquire parts, too. The McMurdo type valve-sockets do seem a major fail after a few decades: I wonder if anyone's ever done an analysis of the brass composition and compared it with the brass used for the contacts on Amphenol-type Octal bases?

2nd Jul 2014, 7:44 pm	#3
jonnybear Octode Join Date: Nov 2010 Location: Cullompton, Devon, UK. Posts: 1,435	Re: McMurdo Valve Bases The composition of the brass is probably the same, fatigue is more than likely caused by temperature changes, octal valves have less heat transfer through the thin connecting wires to the pins, where b8a & b9a do not, just my theory anyway. John

2nd Jul 2014, 9:53 pm	#4
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,271	Re: McMurdo Valve Bases My username is in honour of these things! One small aspect of my day job is restoring valved musical electronics; the famous company Vox (Jennings) used McMurdo and a single organ can contain scores of bases with broken pins, no good for a professional musician. I've always opted to replace the holder complete, though it's not in the spirit of this forum and is a very time consuming affair. __________________ Kevin

8th Jul 2014, 1:33 pm	#5
Hermit6345 Rest in Peace Join Date: Oct 2006 Location: North Wiltshire, UK. Posts: 638	Re: McMurdo Valve Bases What a good idea. The B7G bases in 1.4 volt portables seem to be the most unreliable possibly due to something coming from the batteries. I have changed a lot of single contacts and a few whole valve bases which can be a pain.. The larger bases, like octal etc. seem to be better.