5U4G substitution

[Chris]

I did see those listed and thought the same!

"I ask you £362 for a U52/5U4G on eBay!!!!! Its only a b****y rectifier"



I have seen some NOS from Russia/Ukraine and thought it would be worth a try.


Is solid state a worthy substitute?

https://www.mojotone.com/support/kno...ate-Rectifiers


It's good that John is looking at future alternatives, valves will not go down in price, demand is high and all those valves amps out there will need continues replacement valves.

Chris.

[davebms]

hello all,, interesting stuff, I've not looked at valve prices for probably 2/3 years, But 5u4g really, some asking prices bonkers !! I run 5u3s winged C
(bless em )but there £50 ish a pair ,,plus I have 6D22S in stock looking forward to the info . I've had a magic smoke moment, so no amp at all this week

all the best dave

[bob orbell]

Thank you for the update and info John, I can now see the reason, mainly price, but also very slow start. Bob

[bob orbell]

Is solid state a worthy substitute? Well Chris, I did just that with my 6550 many years ago, I had to add a lot of resistance because of the increase in voltage (there is a big difference in voltage drop through thermionic compared to silicon) it worked, but sounded harsh compared to the 5U4G's, mind you, I did not increase the capacitance, which may have improved things, but it was very quiet. Bob

[bob orbell]

Very well laid out Richard, I am sure this mod will be a good move, one thing to add though, you do not mention KAT 6550 ( power amp ) the mod will of course apply to this model also. Bob

[Greg.]

Many thanks to John, Matthew and Richard for the new FAQ thread on converting 5U4 rectification to 6D22S for KiT/KaT6550 and KiT/KaT34. Well written, easy to understand instructions with good quality informative pictures.

When you have the time Matthew, it would be interesting to read your observations on any change to sound or performance, please

[Richard]

Thanks Bob and Greg. I just drew the circuit out from the photos and wrote it up. John and Matthew did a great job on the conversion - super neat! John planned it and sorted the parts and the wiring job and photos were done by Mathhew. Matthew checked voltages before and after and there was almost no change on any of them, so no point posting them, just expect what the standard build sheets show

FAQ article is here for anyone interested,
http://www.world-designs.co.uk/forum...ead.php?t=7971

[bob orbell]

That does look good and easy to implement too, I must say that the smaller rec. valves do not look invasive. Bob

[snowman_al]

Yes nice work there.
I do however have a concern. That is you now have 450 volts DC above the chassis and you could come into contact with it. OK if you understand this, But are you sure everyone you might implement the mod does?
I think there should be a Warning flash at the start of the procedure and repeated at the end. Like, ''High voltages are now present above the chassis. Do not disconnect the top caps with power on. Do not touch the top caps for 10 minutes after powering down.'' Or similar.

Oh, and I have tidied the schematic a little.
Alan

[bob orbell]

Interesting point Alan, I can see the danger may be a mesh cover over the two tubes. Bob