sovtek 5ar4 v 5u4

[Princo]

Can i use a 5ar4 as a direct replacement for the 5u4 in wad 300bpse

thanks

[bob orbell]

Google FRANKS VALVE DATA, this is a fantastic site and you can see if there is any difference. Bob

[John Caswell]

Yes you can, there will probably be a slightly lower voltage drop across the valve and also the heater voltage will be a bit higher because of the lower heater current consumption. On the upside the 5AR4 is indirectly heated so will warm up slower.
You will also need to check the resistance in the anode circuit to see that it matches the recommendations that Mullard state, and that the following smoothing electrolytic on the cathode of the 5AR4 also does not exceed Mullard's recommendations.
John

[Princo]

thanks john

[bikerhifinut]

Equivalent to GZ34.
It's a better valve overall on paper. A more modern design if you like.
slightly superior current handling, capable of withstanding 60uF on the cathode against the 5U4G which generally has a maximum capacitance of 16uF off the cathode, this is assuming no current limiting resistor in series with the reservoir capacitor but all the same.............
Heater current 1.9A vs 5U4 3A so the mains transformer will have an easier time of it.
As Noted by JC, as it's indirectly heated you get a useful slow start feature also.
Just watch for the increased HT voltage in case you exceed the working voltages of any R and C downstream of it.
As to any perceived sound quality differences that can't be explained by the lower voltage drop, I have no comment.
I'd take the maximum allowable volts and amps with a pinch of salt with modern variants, the original Mullard etc valves were undoubtedly more electrically robust when pushed to their limits. Hence the eye watering prices of even used Mullards on the market.
Andy

[Princo]

Thanks Andy, i have a couple of Sovtek 5AR4 i plan to use, so your comments very helpful

[Princo]

hi

i completed one of the 300b pse monos and just testing, installed 5ar4 but no other valves, rectified voltage directly out from valve pin is 554v, would this be about right for no load voltage with all valves removed.

thanks

[John Caswell]

I would expect the voltage to be about ^2 ie 1.414 times the transformer voltage so if the tx voltage is 300V ct to rectifier anode I would expect 300 x 1.414 let's say x 1.5 (to make it easier) = 450.
Without any load the tx secondary volts will be higher, so rectified volts will be higher. You will need to measure both to get a sensible answer.

John

[Princo]

thanks john,
with a 380v secondary then 550vdc seems about right

[Princo]

im in the process of testing 300b pse, using 5ar4 rectifier, im a little nervous about the increased B+ voltage of the ar4 compared to the 5u4 and was thinking to install a resistor each on the rectifier plates, can anyone advise me regarding this, good idea or not? size?

thanks