UU4 rectifier - UK Vintage Radio Repair and Restoration Discussion Forum

Busman1950 · 2nd Mar 2015, 5:02 pm

Hi all.
Can anyone advise me whether a UU4 rec can be substituted with an MU14.
It's from an Ultra 203 and it circuit states UU4.
The valve data is very similar and pin out is identical.
Many thanks in advance.

Leon Crampin · 2nd Mar 2015, 6:55 pm

Theoretically, the UU4 is rated for 350V rms max. per anode and the MU14 for 500.

Mazda made a UU5 to cover 500V applications, and MOV made the U12 for 350V.

In practice, it is widely accepted that the 350 and 500V valves are the same, although selection could have been made before type identification. MOV rather confusingly produced an MU12/14 which to some extent bears this out.

Most vintage radios with energised 'speakers use a 350-0-350V transformer, in which case any of these valves will work within their published ratings. Beware using a directly heated rectifier such as the U12 in applications specifying an indirectly heated device; the reservoir and smoothing capacitors could be damaged.

Mazda valves are of far better quality than anything MOV produced - so a UU4 or UU5 would be my choice. The Brimar R2 and R3 are also excellent devices.

Leon.

Busman1950 · 3rd Mar 2015, 12:16 pm

Hi Leon.
Many thanks for your reply.
Methinks I'll hold out for a UU4 rather than risking the Ultra as it's in superb condition.
Regards
Bob

jonnybear · 3rd Mar 2015, 2:51 pm

One here Bob.
http://www.ebay.co.uk/itm/A-GOOD-USE...item27fa4824a0.
John

ukcol · 3rd Mar 2015, 3:52 pm

In the Ultra 203 both anodes are strapped together to form a half way rectifier via a surge limiter resistor from the mains. The mains voltage on the anodes is well with the MU14's ratings. The MU14 is designed for a maximum reservoir capacitor of 32uF, it is 16uF in the Ultra 203.

The heater current of the MU14 is slightly higher at 2.5 Amps. The UU4 has a 2.2 Amp heater. This extra 14% of heater current is unlikely to be a problem for the mains transformer.

An MU14 will be fine.

Busman1950 · 3rd Mar 2015, 3:54 pm

Cheers John.
Just had a look and the seller is only a few miles from me so will save on postage, as long as I win it.
Regards Bob

Hi Colin.
Many thanks for the advice, I may go for the MU14 as they seem more plentiful and much more reasonably priced.
Regards Bob

2nd Mar 2015, 5:02 pm	#1
Busman1950 Retired Dormant Member Join Date: Feb 2015 Location: Bracknell, Berkshire, UK. Posts: 11	UU4 rectifier Hi all. Can anyone advise me whether a UU4 rec can be substituted with an MU14. It's from an Ultra 203 and it circuit states UU4. The valve data is very similar and pin out is identical. Many thanks in advance.

2nd Mar 2015, 6:55 pm	#2
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,874	Re: UU4 rectifier Theoretically, the UU4 is rated for 350V rms max. per anode and the MU14 for 500. Mazda made a UU5 to cover 500V applications, and MOV made the U12 for 350V. In practice, it is widely accepted that the 350 and 500V valves are the same, although selection could have been made before type identification. MOV rather confusingly produced an MU12/14 which to some extent bears this out. Most vintage radios with energised 'speakers use a 350-0-350V transformer, in which case any of these valves will work within their published ratings. Beware using a directly heated rectifier such as the U12 in applications specifying an indirectly heated device; the reservoir and smoothing capacitors could be damaged. Mazda valves are of far better quality than anything MOV produced - so a UU4 or UU5 would be my choice. The Brimar R2 and R3 are also excellent devices. Leon.

3rd Mar 2015, 12:16 pm	#3
Busman1950 Retired Dormant Member Join Date: Feb 2015 Location: Bracknell, Berkshire, UK. Posts: 11	Re: UU4 rectifier Hi Leon. Many thanks for your reply. Methinks I'll hold out for a UU4 rather than risking the Ultra as it's in superb condition. Regards Bob

3rd Mar 2015, 2:51 pm	#4
jonnybear Octode Join Date: Nov 2010 Location: Cullompton, Devon, UK. Posts: 1,435	Re: UU4 rectifier One here Bob. http://www.ebay.co.uk/itm/A-GOOD-USE...item27fa4824a0. John

3rd Mar 2015, 3:52 pm	#5
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: UU4 rectifier In the Ultra 203 both anodes are strapped together to form a half way rectifier via a surge limiter resistor from the mains. The mains voltage on the anodes is well with the MU14's ratings. The MU14 is designed for a maximum reservoir capacitor of 32uF, it is 16uF in the Ultra 203. The heater current of the MU14 is slightly higher at 2.5 Amps. The UU4 has a 2.2 Amp heater. This extra 14% of heater current is unlikely to be a problem for the mains transformer. An MU14 will be fine.

3rd Mar 2015, 3:54 pm	#6
Busman1950 Retired Dormant Member Join Date: Feb 2015 Location: Bracknell, Berkshire, UK. Posts: 11	Re: UU4 rectifier Cheers John. Just had a look and the seller is only a few miles from me so will save on postage, as long as I win it. Regards Bob Hi Colin. Many thanks for the advice, I may go for the MU14 as they seem more plentiful and much more reasonably priced. Regards Bob