Damn modern rectifier tubes

[Randall]

I had a spell a while back when I got a couple of bad right out of the box JJ GZ34s. So I switched to Rubys from Valve Queen, since she had a 6 month warranty, that I never had to claim. She has since gone out of business, so I switched to TAD on the advice of some here. Well, I just had one of those bad out of the box, which caused me to think I had either a bad GE 6L6 or a funky non- factory replacement PT. But nope, that shiny new Selected Premium 5AR4/GZ34-STR is shorting out, fresh from the supplier, which is in this case CED. These puppies are up to $31 my cost plus shipping. What a shame!

Good thing for clip on 2 amp circuit breakers to save on fuses while determining what is at fault in spark infested waters.

[pdf64]

So many amps incorporate a hot switching standby. If that’s the case here, it doesn’t seem fair to blame early rectifier valve failure on the valve manufacturer.

[Helmholtz]

What exactly is a hot switching standby?

...and what is the failure mode of the bad GZ34s?

[pdf64]

What exactly is a hot switching standby?

It describes the arrangement in which the standby switch is between the rectifier and the reservoir cap.
Causing a current surge via the rectifier to charge up the cap when the standby switch is closed.
http://www.valvewizard.co.uk/standby.html

[Helmholtz]

It describes the arrangement in which the standby switch is between the rectifier and the reservoir cap.
Causing a current surge via the rectifier to charge up the cap when the standby switch is closed.
http://www.valvewizard.co.uk/standby.html

I see, thanks.
But wouldn't the Fender way ( https://www.thetubestore.com/lib/the...-Schematic.pdf) be "hot" switching too?
No current surge and safe for the tube rectifier.

[pdf64]

…
But wouldn't the Fender way ( https://www.thetubestore.com/lib/the...-Schematic.pdf) be "hot" switching too?
No current surge and safe for the tube rectifier.

The magnitude of the current surge there will be lower in magnitude, as the reservoir cap is already charged, and the charging current drawn by the rest of the HT caps will be limited by the choke / dropper resistors. And the reservoir cap will also supply some of it.

[Helmholtz]

The magnitude of the current surge there will be lower in magnitude, as the reservoir cap is already charged, and the charging current drawn by the rest of the HT caps will be limited by the choke / dropper resistors. And the reservoir cap will also supply some of it.

Yes, I think the rectifier will not have to deliver anything that could be called a surge current in the Fender circuit.

But my question is more linguistical: Why is one circuit "hot" switching and the other not? Isn't "hot" typically related to voltage rather than current?

[pdf64]

… Why is one circuit "hot" switching and the other not? Isn't "hot" typically related to voltage rather than current?

Merlin explains

Valve (vacuum) rectifiers should always be allowed to charge the reservoir naturally from cold. If the valve is preheated before the reservoir is allowed to charge, the valve will have to supply the full inrush current when the switch is finally thrown. This is called hot switching and causes sudden cathode saturation that can lead to catastrphic arcing inside the tube. Hot switching of rectifier valves was usually forbidden by valve manufacturers

[Helmholtz]

So no explanation for "hot" .

[The Dude]

Maybe "hot" because filament power is there and the tube is heated fully before the caps are connected to charge?

[pdf64]

‘Hot‘ as in the rectifier cathode is at working temperature when the switch via which it charges the reservoir cap is closed.

[Leo_Gnardo]

I had a spell a while back when I got a couple of bad right out of the box JJ GZ34s. So I switched to Rubys from Valve Queen, since she had a 6 month warranty, that I never had to claim. She has since gone out of business, so I switched to TAD on the advice of some here. Well, I just had one of those bad out of the box, which caused me to think I had either a bad GE 6L6 or a funky non- factory replacement PT. But nope, that shiny new Selected Premium 5AR4/GZ34-STR is shorting out, fresh from the supplier, which is in this case CED. These puppies are up to $31 my cost plus shipping. What a shame!

Good thing for clip on 2 amp circuit breakers to save on fuses while determining what is at fault in spark infested waters.

Ruby's 5AR4C has been my choice for quite a while now. BUT they seem in short supply currently, as in nonobtainium. I also lament the demise of Valve Queen's tube biz. She seemed so on-the-ball, now on to other things. Good luck to her.

I remember a couple years ago, maybe 4 or so, our long missing Stan from California then Russia said he helped Ruby develop their 5AR4C. Made me feel even better buying a good product one of our MEFsters had a hand in creating. What's left? Last Super Reverb I had here left today with a used oldie but goodie RCA 5AR4/GZ34. Some of the AR/GZ's I have in the 'other than new' bin make sizzling or rattling noises in use. Those ARE new, but not desirable in a guitar amp. Your story about TAD's crummy tube doesn't exactly make me want to go there, nor does their cost. If I'm not mistaken TADs are Chinese. Premium Selected, you would think that means actually tested, maybe rigorously by fanatical German quality control personnel. Meh, not so much. These days those words likely mean as much as Special Design on speakers in Fender Amps. Specially Designed to assure a bigger profit for the distributor/dealer/manufacturer.

I guess there are the Russian TungSols - pricey and not all that special, and "Gold Lion" even more pricey and what's the advantage other than digging a bigger hole in my and my customers' pockets.

"determining what is at fault in spark infested waters" Randall you win this month's prize for clever turn of phrase, I'm likin' that, good one!

[g1]

So no explanation for "hot" .

I can see the confusion as to why the Fender arrangement is ok. Maybe 'hot charging' would be more accurate.

[nevetslab]

Merlin explains

Valve (vacuum) rectifiers should always be allowed to charge the reservoir naturally from cold. If the valve is preheated before the reservoir is allowed to charge, the valve will have to supply the full inrush current when the switch is finally thrown. This is called hot switching and causes sudden cathode saturation that can lead to catastrphic arcing inside the tube. Hot switching of rectifier valves was usually forbidden by valve manufacturers

The stock Vox AC30-6/TB I think is a good example of Hot Switching. The heater of the 5AR4 tube is heated, but the plates have not yet been closed....the Standby switch accomplishes that. This has traditionally led to premature failure of that rectifier tube in those amps. Just had one fail on me today, changed the wiring so the plates and heaters are in circuit when the amp is powered up, so the tube warms up while slowly charging the HT supply caps. S/B mute now done by shorting the grids of the power tubes together.

[trobbins]

I retrofitted a 1N4007 in series with each 5AR4 anode in my son's AC30 CC2 combo as the simplest and best way (imho) to alleviate poor valve rectifier life due to the standby switch.