EFK 8/1/2018 6:42 AM
Anyone familiar with OLD octal triodes?
I'm having a bit of an issue and I'm hoping there might be some "old timer" around who might be familiar with this situation. I have an amp that can use a 6N7 or 6Y7 (or 6Z7 but I don't have any of those) as a paraphase inverter. If I use a 6N7 either metal shell or glass, I flip the switch to start up the amp and all is well. Meanwhile, if I use a 6Y7, I have to sit through about 1 to 2 full minutes of assorted static, crackles etc. Once the amp has run for a few minutes all is then well and it runs perfectly. Now I have on hand about 6 or 7 different 6Y7 tubes and they all, without fail, do this. I have repeatedly gone through the data sheets including the sheets for the type 79 (earlier 6Y7 with different base) and don't see anything indicating an especially long warm up, but this is what it seems to me is going on, as if the tube itself just needs a really long warm up to operate properly.

I would simply stick with the 6N7 tubes but I believe the 6Y7 is making a bit more audible gain here, or I should say I can hear a difference and for a guitar amp prefer a 6Y7 in this position. While the tube is going through it's crackle routine and warming up, I do not measure any weird fluctuations in voltage or anything like that.

Just a wild hair, wondering if anyone out there still even remembers a 6Y7?
 
Enzo 8/1/2018 9:06 AM
We once bought 100 brand new GE 12AT7 tubes. Came in a nice styrofoam thing. Every single one of them popped and crackled the first minute or so after power up. But only the first time, after that they were flawless.

We are used to 11 second warm up, but that is not your beef here. Tubes are mechanical things, metal structures can expand and contract as they heat up.

It wouldn't be a spec, you just have tubes that are noisy at warm up. Any amp circuit will tell you to have an amp running for 20 minutes before making adjustments like bias, because the tube warm up is not merely the time until it makes audio. I'd live with it myself, but customers would probably gripe.
 
EFK 8/1/2018 5:10 PM
Quote Originally Posted by Enzo View Post
I'd live with it myself, but customers would probably gripe.
Well you sure nailed it! Thanks for offering some insight Enzo. This is exactly how I see it - a minute or so of the crackles doesn't bother me in the least, but if I choose to sell it, it's hard to sell anything that needs "an explanation" and I'm not the kind of person to sell it without the explanation. I was just wondering if there was something notorious about the 6Y7. I have 3 Sylvania and 4 Philco, plus two just completely label-less, and they all do exactly the same thing, even after all being tested (in the amp) and running for a bit. Just seems really weird.
 
mozz 8/1/2018 6:04 PM
You want to go here and ask. Many old timers with tons of knowledge.
http://antiqueradios.com/forums/index.php