5AR4 Orange lightening bolt

Just noticed an orange "lightening Bolt" run down the inside of the 5AR4 envelope when the relay energized. Don't recall noticing that before. But the amp works just fine. Your thoughts on this please (I do have the "yellow sheet diode mod" installed).

CletusB wrote:Just noticed an orange "lightening Bolt" run down the inside of the 5AR4 envelope when the relay energized. Don't recall noticing that before. But the amp works just fine. Your thoughts on this please (I do have the "yellow sheet diode mod" installed).

This is not what the tube wants, it's slow or fast destroying it. The cause is that
a relay closes and the rectifier tube takes a surge to charge large caps.

Sudden application of large currents is the cause.
See http://www.tronola.com/html/maximize_tube_life.html for a discussion.

Here it is in real-time followed by two attempts at slow motion.

I guess I'll just order a couple Chinese 5AR4 tubes. I do have a Weber WZ68 that I've never used.

.

Ok, a Gold Lion GZ34 is on order from uncle Jim McShane.  In the meantime, I've retired the 5AR4 and stuck the Weber WZ68 in there (that sucker runs as hot as a tube) and re-biased the rig.  These old ears cannot detect a sonic difference at this time, will audition it more acutely tonight.

C, FMI ; why a delay relay when you are running a TUBE rect? Thanks, Dale

Dale Stevens wrote:C, FMI ;  why a delay relay when you are running a TUBE rect?  Thanks,  Dale

It will delay B+ until the output tubes are fully warmed up. The 5AR4 is a slow-onset rectifier tube - or so it was back in the day. I am not so sure it remains as slow an onset tube as it was, today. What with all the burn-outs and failures reported here after only a relatively few hours, I have to question their quality in general. The Dynaco-marked tube in my very vintage 70 has many thousands of hours on it as to my Siemens 6CA7s and RCA 7199s.

To keep the B+ off the outputs till they have arrived at operating temperature, but if using a tube rectifier or the Weber WZ68 , you don't really need it. But more importantly, insurance that power can't be cycled between off and on states without a 17-sec delay, as when a brief power outage occurs, which is VERY common in my area.

Gold Lion GZ34 from Jim McShane came in today. Got it plugged-in and re-biased the KT-88s. Bass response sounds a tad more pronounced, but have not really listened enough, so that can't really be confirmed at this point.

The Gold Lions work nicely on the M125s as well.

I think I am starting to dislike the relay board. I do also have a GFCI "latch-out" on the mains should there be a power failure.
Maybe, Bob or Jim can correct me if I had too many beers here (LOL). 
Even with this new rectifier, I see an ever so  tiny arc at the base when the relay kicks-in (really disturbing). I think the relay kicks in and the rectifier sees a sudden "dead-Short" instantaneously as the depleted caps receive B+
Will study the diagrams tomorrow again, maybe I'll flip the amp over and bypass the B+ carrying contacts allowing the voltage to rise slowly, as the suite of tubes, especially the rectifier, come up to temperature.
Nonetheless, still the sweetest amp I've ever had!

you only need a TDR if you are not using a rectifier tube.
Also, check to see what the timing of the relay is.
Standard is about 17 seconds. The longer the time, the greater the current surge when it does kick in.

Yup, I think I'll shunt those two relay switch-points with the unused mono/stereo switch. That way I can have no TDR when using the tube and TDR active when using solid-state rectification.
Just hate the idea of chopping into my perfectly running amp.

UPDATE:
Easier way to defeat the TDR:  Switching-in a 1K resistor across R3 would energize the relay almost instantaneously on power-on, T = 1.1 * R3 * C3 (0.036 secs)    ....think I'll go this route

Ok, just implemented the latter TDR bypass method and it works a peach!
I can now use the otherwise useless stereo/mono sw to go between "instantaneous" or 17-sec delay, depending on weather I'm using a GZ34 or some solid-state tube look-alike (the WR68 does have a short delay built-in).
No more tube arcing!

I also just bypassed my TDR relay.  After swapping the SS for a tube rectifier (didn't like the SS sound) I watched it faintly flash white when starting up once.