4CX350f valves - UK Vintage Radio Repair and Restoration Discussion Forum

G4YVM David · 22nd Feb 2019, 8:45 am

I'm considering a vintage vhf amplifier but I am.pretty sure the valve, a 4cx350f, is now part of the vast array of materials known as unobtanium. Is this so? It might make me reconsider...

Radio Wrangler · 22nd Feb 2019, 9:02 am

There are some around, but old Eimac ceramic toobs were known to sometimes be a bit leaky. 4CX250B and 8877s seem to have been more common.

Try asking on an EME forum, or an ad in Dubus.

David

G4YVM David · 22nd Feb 2019, 9:12 am

Thanks

Radio Wrangler · 22nd Feb 2019, 9:19 am

There are also the G3SEK triode and tetrode control boards which are worth investigating, also Ian did the VHF/UHF DX book for the RSGB and if you don't have a copy, it's well worth hunting one.

David

G4YVM David · 22nd Feb 2019, 9:42 am

Coincidence...i worked GM3SEK a couple of weeks back on 2m tropo from Salisbury. I was dead chuffed.

HamishBoxer · 22nd Feb 2019, 10:16 am

I bought a spare 4CX350F a year or so back for Nagi at a good price (new) off eBay.

dodgy-dxer · 22nd Feb 2019, 10:19 am

The VHF/UHF DX book is now available as a free download, I think from Ian's web site. (I know its "not the same" as a book but you can get it!)

They warn the info is dated but it provides excellent background material

73 Fred
G4BWP

Quote:

Originally Posted by Radio Wrangler

There are also the G3SEK triode and tetrode control boards which are worth investigating, also Ian did the VHF/UHF DX book for the RSGB and if you don't have a copy, it's well worth hunting one.

David

dodgy-dxer · 22nd Feb 2019, 10:26 am

Plenty around Europe on eBay including NOS (£39) and one sealed in a US military can £128 or offer

73 Fred
G4BWP

Quote:

Originally Posted by G4YVM David

I'm considering a vintage vhf amplifier but I am.pretty sure the valve, a 4cx350f, is now part of the vast array of materials known as unobtanium. Is this so? It might make me reconsider...

G6Tanuki · 22nd Feb 2019, 11:28 am

The G3SEK boards are definitely worth studying: a point often missed by some designers of amplifiers using the 4X-series of tubes is that the screen-grid supply needs to be able to both source *and sink* current.

The valves are still available - new - from CPII in the 'states [the company which now owns what us oldtimers still call Eitel McCulloch] but the prices are very much aimed at the military/industrial-sector purchaser!

The "care and feeding of power grid tubes" design-application notes - essential reading for anyone using these valves - are also available to download from

https://www.cpii.com/library.cfm/9

G4YVM David · 22nd Feb 2019, 11:28 am

Thanks chaps.

The control boards from Ian seem very reasonably priced although he warns this is their final year of production.

22nd Feb 2019, 8:45 am	#1
G4YVM David Heptode Join Date: May 2014 Location: Salisbury, Wiltshire, UK. Posts: 998	4CX350f valves I'm considering a vintage vhf amplifier but I am.pretty sure the valve, a 4cx350f, is now part of the vast array of materials known as unobtanium. Is this so? It might make me reconsider... __________________ David, G4YVM.

22nd Feb 2019, 9:02 am	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,864	Re: 4CX350f valves There are some around, but old Eimac ceramic toobs were known to sometimes be a bit leaky. 4CX250B and 8877s seem to have been more common. Try asking on an EME forum, or an ad in Dubus. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

22nd Feb 2019, 9:12 am	#3
G4YVM David Heptode Join Date: May 2014 Location: Salisbury, Wiltshire, UK. Posts: 998	Re: 4CX350f valves Thanks __________________ David, G4YVM.

22nd Feb 2019, 9:19 am	#4
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,864	Re: 4CX350f valves There are also the G3SEK triode and tetrode control boards which are worth investigating, also Ian did the VHF/UHF DX book for the RSGB and if you don't have a copy, it's well worth hunting one. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

22nd Feb 2019, 9:42 am	#5
G4YVM David Heptode Join Date: May 2014 Location: Salisbury, Wiltshire, UK. Posts: 998	Re: 4CX350f valves Coincidence...i worked GM3SEK a couple of weeks back on 2m tropo from Salisbury. I was dead chuffed. __________________ David, G4YVM.

22nd Feb 2019, 10:16 am	#6
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: 4CX350f valves I bought a spare 4CX350F a year or so back for Nagi at a good price (new) off eBay. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

22nd Feb 2019, 11:28 am	#9
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	Re: 4CX350f valves The G3SEK boards are definitely worth studying: a point often missed by some designers of amplifiers using the 4X-series of tubes is that the screen-grid supply needs to be able to both source and sink current. The valves are still available - new - from CPII in the 'states [the company which now owns what us oldtimers still call Eitel McCulloch] but the prices are very much aimed at the military/industrial-sector purchaser! The "care and feeding of power grid tubes" design-application notes - essential reading for anyone using these valves - are also available to download from https://www.cpii.com/library.cfm/9

22nd Feb 2019, 11:28 am	#10
G4YVM David Heptode Join Date: May 2014 Location: Salisbury, Wiltshire, UK. Posts: 998	Re: 4CX350f valves Thanks chaps. The control boards from Ian seem very reasonably priced although he warns this is their final year of production. __________________ David, G4YVM.