U78 Valve or equiv - UK Vintage Radio Repair and Restoration Discussion Forum

bigfathairyvika · 19th Nov 2023, 10:50 pm

Having read that rectifier valves can sometimes start introducing hum, I'm looking to try a quick change to compare..
But, U78's ( full bridge) used in the BC5645 appear to have become audiophool priced items at 60 quid plus each!

Is there a similar and cheaper valve?
Does anyone have one they wouldn't mind parting with?

Mark

CambridgeWorks · 19th Nov 2023, 11:03 pm

6X4, EZ90, CV493, CV4005 all sensibly equivalent according to r-type.org.
http://www.r-type.org/exhib/aaa0870.htm
Osram Marconi or Mullard brands are the expensive ones.
The likes of Brimar or Pinnacle seem to be unloved!
Rob

Diabolical Artificer · 20th Nov 2023, 7:55 am

Might have a 6X4 Mark, will check later when it's light.

Andy.

Station X · 20th Nov 2023, 10:14 am

My inventory is showing a used U78 and two used 6X4WA's.

If you're interested in any of these I'll test them. I don't expect audiophool prices.

Station X · 20th Nov 2023, 10:25 am

New 6X4WA's are going for £12.00 on eBay.

https://www.ebay.co.uk/itm/271111353278

bigfathairyvika · 20th Nov 2023, 6:13 pm

Thanks all for pointing out the many alternatives and the link to a new one.
I did initially look on langrex for the u78 and gasped at the 150 quid ish price.
The link shows that they have cheaper versions and new at that.
Andy, see what you have, I may have to pop over again or may buy a new one at 12 quid.

Sideband · 20th Nov 2023, 10:19 pm

£150 !!!

it's only a rectifier, not particularly robust either but reliable enough. Rated at only 60mA. I've probably got a couple if all else fails. If you don't mind enlarging the hole slightly and changing the base, you could fit an EZ80....same rating.

paulsherwin · 20th Nov 2023, 10:36 pm

The 6X4 was very common in the US in both domestic and military equipment, and remains easily available today from the usual sources.

bigfathairyvika · 28th Nov 2023, 6:25 pm

Bought a new old stock 6x4 from langrex.
And it really is new old stock. Looks like it was only just made.
Thanks to station x for the link.

19th Nov 2023, 10:50 pm	#1
bigfathairyvika Hexode Join Date: Nov 2009 Location: Cambridge, Cambridgeshire, UK. Posts: 375	U78 Valve or equiv Having read that rectifier valves can sometimes start introducing hum, I'm looking to try a quick change to compare.. But, U78's ( full bridge) used in the BC5645 appear to have become audiophool priced items at 60 quid plus each! Is there a similar and cheaper valve? Does anyone have one they wouldn't mind parting with? Mark

19th Nov 2023, 11:03 pm	#2
CambridgeWorks Nonode Join Date: Jun 2010 Location: Spalding, Peterborough, Cambridgeshire, UK. Posts: 2,750	Re: U78 Valve or equiv 6X4, EZ90, CV493, CV4005 all sensibly equivalent according to r-type.org. http://www.r-type.org/exhib/aaa0870.htm Osram Marconi or Mullard brands are the expensive ones. The likes of Brimar or Pinnacle seem to be unloved! Rob __________________ Used to be robinshack. New name pays tribute to the old Pye factory in Haig Rd/St Andrews Rd

20th Nov 2023, 7:55 am	#3
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,372	Re: U78 Valve or equiv Might have a 6X4 Mark, will check later when it's light. Andy. __________________ Curiosity hasn't killed this cat...so far.

20th Nov 2023, 10:14 am	#4
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 20,662	Re: U78 Valve or equiv My inventory is showing a used U78 and two used 6X4WA's. If you're interested in any of these I'll test them. I don't expect audiophool prices. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

20th Nov 2023, 10:25 am	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 20,662	Re: U78 Valve or equiv New 6X4WA's are going for £12.00 on eBay. https://www.ebay.co.uk/itm/271111353278 __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

20th Nov 2023, 6:13 pm	#6
bigfathairyvika Hexode Join Date: Nov 2009 Location: Cambridge, Cambridgeshire, UK. Posts: 375	Re: U78 Valve or equiv Thanks all for pointing out the many alternatives and the link to a new one. I did initially look on langrex for the u78 and gasped at the 150 quid ish price. The link shows that they have cheaper versions and new at that. Andy, see what you have, I may have to pop over again or may buy a new one at 12 quid.

20th Nov 2023, 10:19 pm	#7
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,445	Re: U78 Valve or equiv £150 !!! it's only a rectifier, not particularly robust either but reliable enough. Rated at only 60mA. I've probably got a couple if all else fails. If you don't mind enlarging the hole slightly and changing the base, you could fit an EZ80....same rating. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

20th Nov 2023, 10:36 pm	#8
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,177	Re: U78 Valve or equiv The 6X4 was very common in the US in both domestic and military equipment, and remains easily available today from the usual sources.

28th Nov 2023, 6:25 pm	#9
bigfathairyvika Hexode Join Date: Nov 2009 Location: Cambridge, Cambridgeshire, UK. Posts: 375	Re: U78 Valve or equiv Bought a new old stock 6x4 from langrex. And it really is new old stock. Looks like it was only just made. Thanks to station x for the link.