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Rare Bird
23-10-2009, 10:38
Calling all Leak 'Stereo 20' owners..

Anyone tried a 5U4G inplace of a GZ34..

How thin on the ground are NOS Mullard '5U4G' & Roughly how much?

anthonyTD
23-10-2009, 10:47
Calling all Leak 'Stereo 20' owners..

Anyone tried a 5U4G inplace of a GZ34..

How thin on the ground are NOS Mullard '5U4G' & Roughly how much?
hi andre,
as far as i know MULLARD did not make or brand any 5U4's, they are a directly heated rectifier,[ht comes up almost straight away] where as the mullard GZ34 is an in-directly heated type [time lag on HT] you can however substitute one for the other in most cases. 5U4's [apart from early types] are easier to come by than GZ34's at the moment.
hope this helps.
regards,anthony,TD...

Rare Bird
23-10-2009, 11:17
Thanks Tony

Ah right so your talking shorter life span for the '5U4' than the 'GZ34'..

Deffo Mullard '5U4G' seen a few..Swear bind i saw a 5U4G in a leak 20 other day somewhere

anthonyTD
23-10-2009, 12:18
Thanks Tony


Ah right so your talking shorter life span for the '5U4' than the 'GZ34'..

Deffo Mullard '5U4G' seen a few..Swear bind i saw a 5U4G in a leak 20 other day somewhere
hi andre,
not nescesarily, it just means that instead of having a soft start which is what an in-directly heated rectifier provides,[GZ30,32,33,34,37etc] the HT [high voltage] will be on the the rest of the valves in the circuit before the heaters have warmed the valves sufficiently to draw current! which is not so good for the life of some valves.
i hope this helps.
regards,anthony,TD...

pure sound
23-10-2009, 16:25
A 5U4G will drop the HT by maybe 30V so there may be a little less power on tap.
Modelling the ST20 power supply in PSUD shows a surprising level of ripple, something like 11V! It could've done with a choke really.

NB: the 5U4 also pulls an additional 1A from the heater winding so it may also cause the mains transformer some extra stress.

anthonyTD
23-10-2009, 18:02
A 5U4G will drop the HT by maybe 30V so there may be a little less power on tap.
Modelling the ST20 power supply in PSUD shows a surprising level of ripple, something like 11V! It could've done with a choke really.

NB: the 5U4 also pulls an additional 1A from the heater winding so it may also cause the mains transformer some extra stress

agree,
GZ34=1.8 AMP 5U4G= 3 AMP!
same issues when substituting GZ34 for GZ33 and GZ37 which also have 3 AMP heaters. people often disregard this when substituting rectifiers then wonder why their mains transformers are getting red hot!:doh:
A...

Rare Bird
23-10-2009, 20:16
So i'll not bother then

:lolsign: