TFL5005D: carbon between contacts on solder side of output tube socket?

[Silvertone Jockey]

The TFL I have apparently has a history of eating power tubes before I acquired it. The output transformer had obviously gone bad in a very violent manner judging by the stains on the chassis. It had the wrong output transformer in it as a replacement (the larger one for 4 6l6's) which I replaced with the proper size (actually the correct primary impedance for the circuit and 4,8, and 16 ohm taps, from a Conn organ that I had on hand, heavier iron than stock)

Anyway I hadn't noticed the carbon which appears to look exactly like arc flash traces, when I first worked on it but something just wasn't right, and I kept smelling something so I gave it another look this evening. Tell me this probably happened when the output xformer went south..........which is my theory. I checked the resisters on the sockets and they were pretty tight except the 470 ohm resisters which were about 510 on one and 560 on the other, which I will replace both. with hand selected replacements. Anything else I should check?

Thanks for helping out people with your experience like you do, this forum and an armature telescope making forum I also hang at gives me some hope for humanity

[Silvertone Jockey]

Found out what that smell was when I heard 'that sound' while testing the amp.

You know the one, the one that sounds like speaker destruction?

And if you've ever heard it before you will never ever forget it, because it's like

Hollie crap!!!..........WTF was that?

So you never know about an old junkbox transformer that you didn't even know you had, before you looked for one to see if you did.

I tested it, smelled it, re-insulated it

I guess I just really hate it when that sound happens and it takes more than 2 seconds to get to the amp and turn it off

[Justin Thomas]

Just for clarity, is this a Bandmaster Reverb?

Justin

[Leo_Gnardo]

Anyway I hadn't noticed the carbon which appears to look exactly like arc flash traces, when I first worked on it but something just wasn't right, and I kept smelling something so I gave it another look this evening. Tell me this probably happened when the output xformer went south..........which is my theory.

Could well be the other way around. Tube sockets with carbon tracks should be replaced. I've been lucky a couple times and managed to Dremel-grind the affected parts away, then test thoroughly for a couple of days with all sorts of loads including mismatches. But the sure fire way is - replace socket.

Tubes sitting in arcing sockets also get carbon tracks. Best to replace.

Hi voltage breakdown rating of air is 8000 volts per inch, dry air, sea level pressure. Derate for humidity and altitude. Even with "ideal lab conditions" 8000V/in is 500V across 1/16 inch and that includes anything conductive not just metal. Includes carbon tracks and any other conductive debris. Distance between tube socket pins is what, looks like a little less than 1/8 inch to me.

Also a good idea to install anti-flyback rectifier string as suggested by Ken Fisher in The Trainwreck Pages. Find and read the appropriate part. A buck's worth of insurance here may save lots of headaches down the line. This technique prevents the voltage at plate pin from exceeding B+. Flyback spikes can hit 3000V. Why take a chance on setting up a lightning storm right where you don't want one. You can turn this amp with a bad reputation into a good citizen.