Any reason I shouldn't...

[yankeerob]

put an 8.2nF cap (2kV) across the anodes on a tube rectifier? Sorry I've been away for a while but I have been working my butt off - putting a lot of good advice gathered here to good use

I don't seem to be able to find any info on it and I'm guessing that either a.) nobody's ever felt the need to try it but it wouldn't hurt the tube or b.) everybody else knows the tube's gonna flip me the bird and take a permanent powder but haven't bothered to publish anything to that effect.

It's something that works quite well on silicon rectifiers in making the transition from STANDBY to ON really smooth and quiet... I have had an issue or two with new tube rectifiers, especially JJ's (to the point that I now refuse to use them) and occasionally get the odd flash when taking the amp out of standby which is greatly reduced by putting a 47nF from the cathode to ground... I've been rubbing my chin for a while about this and am sorely tempted to see what'd happen but don't particularly feel like blowing up a perfectly good tube to find out it's not a good idea

One thing I can share is that we now routinely put a diode in series between the power tranny and anodes on all tube rectifiers to reduce sag - not eliminate it - just reduce it. We have found that without them modern tube recto's produce a pretty unpleasant artifact when you get them into 'brownsville'... the diodes virtually eliminate said unpleasant sound, give us a good coupla extra watts into the bargain and the amps are still more dynamic than most... only a purist would notice or moan about it... most modern guys and gals have never heard a proper tweed circuit do it's thang...

[stokes]

That flash is the tube arcing internally.What tube is it?Maybe those JJ's just suck.How much capacitance do you have at the output of the rectifier?I havent seen any issues with "over filtering" any tube rec's I've experimented with,but to be honest I havent tried a 5Y3.

[yankeerob]

Hey Stokes...

As far as can make out JJ just can't make rectifiers... but I digress...

Old spec sheets vary and you can't get a straight answer out of New Sensor 'cause no one will speak to you - probably because they're afraid to publish a spec sheet as no one seems to be able to produce consistency out of the former USSR and Eastern bloc... if you're a mftr you're stuck with them so...

I only use 5Y3's in our little 5E3 clones... on the general whole we use mainly 5AR4/GZ34's - Sovtek and EH's and they are pretty solid. We occasionally use a 5U4 if we need to lose some voltage or think we might like a little more current capability... as you would!

But I'm building a monster on the same circuit (5E3/5E5) with a bigger transformer set - PT has 200mA 380-360-340-0-340-360-380 sec and the OT a 60W 5K pri - I can build 60W 5F6A and 2204 clones all day long with them but many who have tried the little tweed Pro we do would like a little more power... we use a 150mA 340-0-340 into a 35W 5K6 and get 28W clean out of 'em but you know how it is - everyone wants to be the loudest...

So - my thinking is - we put an 8n2 across the input of our silicon rectifiers on the big boys (well the biggest we do at present) and makes the 'Standby/ON' really quiet and smooth - almost like the 'soft on' in some better power amps - would this have a similar effect on a valve rectified power supply... I now routinely put a coupla 1n4007's in series between the transformer and the anodes on the little guys and had planned on doing the same with 1n5408's on this guy... I also tag a 630V 47nF from the cathode to the deck... All I really want to do is try and make sure we don't get any majorly frightening pops and farts out of it when we take it out of standby.... I try to stick to 40uF or less for a cap input - 33uF is typical and they're always F&T's

Many thanks for replying...

Regards, Rob

[stokes]

Cant really help you with the cap across the plates thing,I've never tried a cap across the plates of a tube rectifier,but to be honest I've never had any issues as you describe.I'll give you some observations,if you dont mind,tho.The "pop" on going from standby to power on,to my understanding is the first cap charging up.If you have the standby between the rectifier and the the first cap in the B+ rail this can be remedied by moving the standby after the first cap,allowing the cap to charge during the "warm-up" while the amp is in standby.The arcing you describe is most likely a bum rectifier,which to me,is all current production rectifiers,if you've read any of my comments here you probably know that I am a "NOS snob",wont use anything but in my own gear,but I do often install them at peoples request and havent found any,rectifiers or other tubes, that I am happy with.In my mind arcing in a rectifier can be attributed to 2 things,either a bad or marginal tube,or way too much filtering on the first stage,although I've done extensive tests with various rectifiers and havent found a NOS 5V4,5U4,5R4,5AR4 that cant take up to 220uf.So that narrows it down to a marginal tube,and to me calling JJ's marginal is a compliment.As I said before,I havent tested any 5Y3's because I dont use them at all,anything that calls for a 5Y3 gets a 5V4,as I have a good supply of them on hand.Putting diodes between the PT and the tube rec is a good safety feature,but really shouldnt affect the sag,after all the tube is still the limiting factor between the PT and the rest of the amp,at least I havent seen this to be the case.I also dont see how the cap across the plates of the rec is going to affect the arcing or the annoying pop as it is before the point where this symptom is coming from.Another trick to keeping the power supply clean,is to put a .1@1kv across the first cap in the rail,helps keep out RF interference as well,but that isnt really relevant to your post,just a FYI in case you didnt know.I dont see how the cap across the plates of the rec would hurt anything,unless the cap itself shorted out,but I dont see how it will help anything at that point of the circuit,but who knows,give it a shot,after all,tube guitar amps do defy manuals and the limitations and "specs" they recommend.