Valve-base Cement. - UK Vintage Radio Repair and Restoration Discussion Forum

G6Tanuki · 11th Oct 2014, 1:35 pm

Just out of interest, does anyone know the precise makeup of the brown(ish) cement used to attach[1] glass valve-envelopes to their bakelite bases?

I'm thinking that it was some sort of Urea-Formaldehyde resin base bulked out with wood-flour? I've today been recovering the bakelite Octal-plugs from a slew of gone-to-air or otherwise unserviceable valves, and have noticed a wide degree of variance in how easy it is to dig out the remaining cement. A lot of US valves have a really hard brown shiny variety whereas that used by Mazda seems to be somewhat greener, duller, and crumblier.

[1] for not-necessarily-very-permanent meanings of 'attach'.

SurreyNick · 11th Oct 2014, 1:59 pm

I believe it was shellac.

Andrewausfa · 11th Oct 2014, 2:57 pm

Having done the same as you recently, it reminded me of Cascamite wood glue which is what you mention, UF resin with additives.

David G4EBT · 11th Oct 2014, 5:47 pm

Fro my experience it was generally shellac and wood flour, which is quickly dissolved with methylated spirits. I've done this often when replacing damaged valve bases on otherwise good valves, and when converting EBL1 (side contact base & 3/8" top cap) valves to EBL31s, which use an octal base and 1/4" top cap.(The two valves are electrically identical). Genuine EBL31 valves are quite rare and are required for Ecko A22 radios. (The so-called 'EBL31' valves on offer from UK valve dealers are invariably too tall to fit into the A22 and also have a 3/8" top cap).

If you wish to refit a valve base you can make a mixture using woodflour and shellac. Unless you have a bandsaw, (in which case you'll know that you're constantly clearing woodflour out of it), you can simply use 80G sandpaper on a piece of scrap wood and will soon collect enough. Easier of course to use two-part epoxy products such as car body filler or two-part woodfiller. (But probably not Araldite).

If you have a loose valve base (or top cap), you can usually re-secure it by dribbling shellac around the base, but bear in mind that if you buy ready-to-use bottled shellac French polish, it is quite thin and will probably need more than one application if the gap is wide, so maybe a couple of elastic bands from top of the valve to the base will pull the base back into position while the shellac sets.

There have been several warnings on the forum cautioning against the use of superglue ('CA') for re-fixing valve bases, as allegedly it can crack the glass when it heats up. Don't know if that's just an 'urban legend' but maybe best to err on the side of caution.

Hope that helps a bit.

11th Oct 2014, 6:21 pm

I steal some of the wifes nail varnish (the clear stuff) and dribble a bit down the gap.

SurreyNick · 11th Oct 2014, 9:01 pm

I would strongly advise mixing your own than buying off-shelf. For adhesion I would opt for a 5lb cut (proportionately 5lb of shellac to 1 gallon of meths). You can't buy ready mix 5lb cut, well I've never seen it. Standard mix is 2 or 3lb cut. 5lb is thick and dries very quickly.

Billie the Boss · 12th Oct 2014, 6:48 pm

I use Glass Glue. Works fine for me. I find super glue can go white ish.

11th Oct 2014, 1:35 pm	#1
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Valve-base Cement. Just out of interest, does anyone know the precise makeup of the brown(ish) cement used to attach[1] glass valve-envelopes to their bakelite bases? I'm thinking that it was some sort of Urea-Formaldehyde resin base bulked out with wood-flour? I've today been recovering the bakelite Octal-plugs from a slew of gone-to-air or otherwise unserviceable valves, and have noticed a wide degree of variance in how easy it is to dig out the remaining cement. A lot of US valves have a really hard brown shiny variety whereas that used by Mazda seems to be somewhat greener, duller, and crumblier. [1] for not-necessarily-very-permanent meanings of 'attach'.

11th Oct 2014, 1:59 pm	#2
SurreyNick Heptode Join Date: Apr 2014 Location: Wigton, Cumbria, UK. Posts: 728	Re: Valve-base Cement. I believe it was shellac.

11th Oct 2014, 2:57 pm	#3
Andrewausfa Octode Join Date: Dec 2010 Location: St Ives, Cambridgeshire, UK. Posts: 1,180	Re: Valve-base Cement. Having done the same as you recently, it reminded me of Cascamite wood glue which is what you mention, UF resin with additives. __________________ Invisible airwaves crackle with life. Or they should do. BVWS Member

11th Oct 2014, 5:47 pm	#4
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,763	Re: Valve-base Cement. Fro my experience it was generally shellac and wood flour, which is quickly dissolved with methylated spirits. I've done this often when replacing damaged valve bases on otherwise good valves, and when converting EBL1 (side contact base & 3/8" top cap) valves to EBL31s, which use an octal base and 1/4" top cap.(The two valves are electrically identical). Genuine EBL31 valves are quite rare and are required for Ecko A22 radios. (The so-called 'EBL31' valves on offer from UK valve dealers are invariably too tall to fit into the A22 and also have a 3/8" top cap). If you wish to refit a valve base you can make a mixture using woodflour and shellac. Unless you have a bandsaw, (in which case you'll know that you're constantly clearing woodflour out of it), you can simply use 80G sandpaper on a piece of scrap wood and will soon collect enough. Easier of course to use two-part epoxy products such as car body filler or two-part woodfiller. (But probably not Araldite). If you have a loose valve base (or top cap), you can usually re-secure it by dribbling shellac around the base, but bear in mind that if you buy ready-to-use bottled shellac French polish, it is quite thin and will probably need more than one application if the gap is wide, so maybe a couple of elastic bands from top of the valve to the base will pull the base back into position while the shellac sets. There have been several warnings on the forum cautioning against the use of superglue ('CA') for re-fixing valve bases, as allegedly it can crack the glass when it heats up. Don't know if that's just an 'urban legend' but maybe best to err on the side of caution. Hope that helps a bit. __________________ David. BVWS Member. G-QRP Club member 1339.

11th Oct 2014, 6:21 pm	#5
Guest Guest Posts: n/a	Re: Valve-base Cement. I steal some of the wifes nail varnish (the clear stuff) and dribble a bit down the gap.

11th Oct 2014, 9:01 pm	#6
SurreyNick Heptode Join Date: Apr 2014 Location: Wigton, Cumbria, UK. Posts: 728	Re: Valve-base Cement. I would strongly advise mixing your own than buying off-shelf. For adhesion I would opt for a 5lb cut (proportionately 5lb of shellac to 1 gallon of meths). You can't buy ready mix 5lb cut, well I've never seen it. Standard mix is 2 or 3lb cut. 5lb is thick and dries very quickly.

12th Oct 2014, 6:48 pm	#7
Billie the Boss Retired Dormant Member Join Date: Oct 2009 Location: Dingle, County Kerry, Ireland. Posts: 86	Re: Valve-base Cement. I use Glass Glue. Works fine for me. I find super glue can go white ish.