tighter filtering and stiffer rectifyer?

[Bluefinger]

Hi,

I would like to try tighter filtering and maybe a 5U4 in my 5E3 based build. How far up can I go with the filter caps before I run into trouble? Is there anything else I would have to change if I use a 5U4? It is equipped with vintage style heyboer trannies. It also has a fixed/cathode switch and the plate voltage already is at the limit in fixed mode ... can I expect a lot higher voltages with the 5U4?

thanks!!!!!

[MWJB]

I'd make sure that the PT has a 3A 5V rectifier winding, if not, then a 5V4 rectifier will work, the 5V4 voltage drop is usually between a 5U4 & GZ34. I usually find a 330ohm cathode resistor is required with a 5V4 in a 5E3.

In fixed mode you might need to stick with modern, higher voltage 6V6s if the B+ is high, rather than NOS 6V6.

[Bluefinger]

Thanks ... I'll check the specs of the tranny

What about the filtering? At this time I have 33, 22, 16 but I wonder how high I can go up ...

[MWJB]

First filter is the most important, but screen supply could also do with bumping up, I'd leave the preamp at 16-22uf.

So 50-100uf at the main B+ filter, 40-50uf at the screen supply. Going bigger at the 6V6 cathode bypass cap will also tighten things up, 100uf/100v should do here.

[Bluefinger]

ok, thanks .. I'll try that

[pdf64]

5R4 (WGB are toughest) have electrical performance very close (equivilant?) to 5U4 but only take 2 amps heater current.
The couple of Philips JAN 5V4 from the 80s that I've got seem to perform the same as GZ34, in terms of volt drop; maybe vintage ones would drop more.
So maybe a 5R4 would provide a smaller step up in V B+. Pete.

[diagrammatiks]

you probably can't go higher then 32-40 if you're using a tube rectifier for the input filter.

[pdf64]

Quite a good article on the mercury magnetics site
Mercury Magnetics
I don't know about 'Install a luf 600-1000V non-polar plastic capacitor across the last decoupling electrolytic in the line' helping with ghost notes (anyone?) but the other stuff seems good.
Pete.

[MWJB]

Diagrammatiks wrote: "you probably can't go higher then 32-40 if you're using a tube rectifier for the input filter." this is untrue. 5Y3/5U4G/5V4G/5AR4 all will take 100uf at the first filter, don't fancy that much? Then stick to 50uf, safe as houses all day long.

[pdf64]

5Y3/5U4G/5V4G/5AR4 all will take 100uf at the first filter

Mark, just to clarify, you may have specified this before but does this hold true with both vintage and current production tube manufacture?
Pete.

[MWJB]

Hi Pete,

Yes, true for both. Sure there is the odd duff tube, but there isn't any particular model that seems any more prone to failure with 100uf at the first filter. Best to wire them to the hot side of the standby (if it interrupts the B+), rather than the cold side (as on the RI 59 Bassman, which eats the odd 5AR4).

[Bruce / Mission Amps]

I'm running a 47uF@500v in section one, followed by two 22uF@500v caps of mine.
If you are worried about the cap drawing too much current at start-up and stressing the rectifier tube, simply solder a 22 to 47 ohm 2 watt Mtl-Ox resistor in series with the wire from the rectifier to the standby switch.