Why would two 12AX7 bite the dust?

[wallythacker]

This is in my newly acquired TSL 60. I knew it sounded sick when I bought it hence the low price.

I have a Radio Institute of America tester that is very flexible and tests pretty much every tube ever to grace the innards of a musical amplification device.

Anyway, my Svetlana EL34 tubes (2000, January) are perfect, 100% on the tester. The 12AX7 closest to the output tubes was 90%, the 12AX7 under the metal cover was 98% and the other two12AX7 would both just slide into the replace zone when the test button was pushed.

The 12AX7 tubes are all Electro Harmonics and vary in date from late 1999 to mid 2000. The replacements I bought tonight are mid 2013.

Any thoughts on the matter?

PS. My TSL 60 was used as a workbench! I kid you not. Upon removal of the back plate I found a lot of sawdust. So I cleaned it out with a vacuum. Then I see some strange shiny material. I scrape a little with my fingernail to discover it's metal filings/shavings from some idiot cutting something metal over the TSL 60 head. I cleaned out all the filings I could see. Thankfully none of the sawdust/filings were on the chassis, transformers or tubes.

Anyhow, that's your laugh for the day. Some idiot used a Marshall head for a workbench.

Thoughts on why those two 12AX7 gave up and the others soldier on?

 

[ampmadscientist]

This is in my newly acquired TSL 60. I knew it sounded sick when I bought it hence the low price.

I have a Radio Institute of America tester that is very flexible and tests pretty much every tube ever to grace the innards of a musical amplification device.

Anyway, my Svetlana EL34 tubes (2000, January) are perfect, 100% on the tester. The 12AX7 closest to the output tubes was 90%, the 12AX7 under the metal cover was 98% and the other two12AX7 would both just slide into the replace zone when the test button was pushed.

The 12AX7 tubes are all Electro Harmonics and vary in date from late 1999 to mid 2000. The replacements I bought tonight are mid 2013.

Any thoughts on the matter?

PS. My TSL 60 was used as a workbench! I kid you not. Upon removal of the back plate I found a lot of sawdust. So I cleaned it out with a vacuum. Then I see some strange shiny material. I scrape a little with my fingernail to discover it's metal filings/shavings from some idiot cutting something metal over the TSL 60 head. I cleaned out all the filings I could see. Thankfully none of the sawdust/filings were on the chassis, transformers or tubes.

Anyhow, that's your laugh for the day. Some idiot used a Marshall head for a workbench.

Thoughts on why those two 12AX7 gave up and the others soldier on?

The cathode of the 12AX7 stops emitting electrons; after a certain time, it burns up like Halley's Comet.
There are only "so many" electrons to emit. When the numbers up, ya gotta go.
sayonara, electrons...

 

[chee16]

For current production gives those are pretty old. How does the amp sound now ? Current production tubes are hit and miss so trying to figure out a reason for them going bad is going to be hard without there being more of a pattern, like if v2 and v3 toasted again in a week, then you would start to think twice.

 

[wallythacker]

I guess I'm amazed the output tubes are still 100%.

I'm installing the new 12AX7 tubes tomorrow and I'll bias the amp while I'm at it. I don't think the bias has been touched or even checked in 15 years.

This should be a fire breathing dragon, not quite a Night Fury but fairly close.

 

[Dogs of Doom]

if you don't think the amp has been used in 10-15 years, you should have a tech look it over & bring up the voltage slowly, to make sure the cap's are in good shape...

 

[Gene Ballzz]

if you don't think the amp has been used in 10-15 years, you should have a tech look it over & bring up the voltage slowly, to make sure the cap's are in good shape...

D.O.D,
Sounds like it might be too late for that, as he already said it "sounded sick", meaning it's already been fired up. Oh well, "ce la vie!" I don't know the topography of the TSL, but if I recall correctly, I think I've heard it said that V2 & V3 take a pretty good beating in these amps? Either way, it might not be a bad idea to take a look at heater and plate voltages, especially in the preamp, while checking and/or setting the bias. I mean, even though he's a pretty new member here, if he's confident enough to tackle the bias, it's fairly likely that he's savvy enough to safely check those readings? No? Good idea to check wall power voltage before starting, for a good reference point.
Just My $.02 & Likely Worth Even Less,
Gene

 

[MartyStrat54]

V3 is the demanding slot in a TSL.

 

[wallythacker]

It's not a case of it not being used, it has been used by a kid for the last 3-4 years. He had no clue how a Marshall should sound and was running it through an Orange 2x12 cab. He had the impedance right, whether he knew how to configure it or it was just blind luck I don't know. I have no idea if he used instrument cables to connect the head.

I'll check the voltages as mentioned and maybe clean up the sockets while I'm at it. It was V2 and V3 that failed as expected. That's re-assuring, chances are everything else is good.

I'll be very pleased to hear it running properly.

 

[Alabama Thunderpussy]

V3 is the demanding slot in a TSL.

Yeah I mod those things to lower the h-k voltage.