Metropoulos Forum

What is your cathode voltage? I'm thinking possibly they're failing from high cathode heater voltage rather than too much current - you'll find 12ax7 datasheets actually state max 200V heater to cathode. A good idea is to reference the centre tap of the filament supply to above ground - just voltage divide tap off B+.

I agree that the Tung Sol 12ax7 reissue tubes sound great. But...I have had two which had a "hum" issue and I found out that this problem has not been uncommon with them.

Joe

Been running the Tung Sol RI in my V2 on my JTM45 and Marshall Vintage Modern for almost a year now and they still sound excellent. Did I just get a good batch or what???

weasel wrote:What is your cathode voltage? I'm thinking possibly they're failing from high cathode heater voltage rather than too much current - you'll find 12ax7 datasheets actually state max 200V heater to cathode. A good idea is to reference the centre tap of the filament supply to above ground - just voltage divide tap off B+.

^ +1

exactly what I was thinking when reading this thread too. referencing the heaters at around 50v will take the stress off the CF stage and makes the amp hum less too in my experience.

I have Tung Sol 12AX7 in all sockets of my 68 12xxx which has an extra tube for the effects loop and they sound great. However, I did have one go bad very quickly in v2 which I replaced with another Tung Sol 12AX7 that has lasted for months now with no issues. Maybe this is limited to just a bad batch of tubes.

How do the US made Tung-Sol compare to the re-issues?

Beserkr wrote:How do the US made Tung-Sol compare to the re-issues?

Like a Boéf Stroganoff to a Hot Dog.

Larry

novosibir wrote:

Beserkr wrote:How do the US made Tung-Sol compare to the re-issues?

Like a Boéf Stroganoff to a Hot Dog.

Larry

Would they work well as a PI driver?

What? The Hot Dog or the Boéf Stroganoff?

You aren't a friend of too many words, aren't you?

Larry

novosibir wrote:What? The Hot Dog or the Boéf Stroganoff?

You aren't a friend of too many words, aren't you?

Larry

LOL

Ok, you got me.. I would be wondering about the Boéf Stroganoff aka NOS Tung-Sol..

I keep the verbiage to a minimum, I don't want people to notice I haven't got a good grasp on the English language

had tung sol 12ax7's too, after about 1 year the tube in the cf stage died... so i'd recommend replacing them and saving them as a spare tube for V1 or whatever, as they could fail at any time, even after 1 year. anyway, i'm using nos miniwatts and telefunken in this amp now, but i only gig with the tung sol's and a gt 12ax7m in v2 that i had left, cause no one in the crowd will mention if there is nos glass in your amp.

Most of the 12AX7 types out of Sarotov (Sovtek, Electro Harmonix, Tung Sol, New Sensor) cannot handle the high cathode voltages.

Some of the design spec sheets I have seen on these tubes says the heater to cathode limit is 100volts, which is well below the 12AX7/ECC83 design spec of 180 to 200v.

Supposedly the Sovtek 12AX7WC can, but I have no experience or data on this tube.

this topic has not received the attention it deserves as people put the TS "RI" in the cathode follower all the time. even amp manufactures does this, selling something that will only last for a few days.

my 45/100 has 360v on v2 BTW

The first two samples of the Tungsol RI sounded great. I then bought more, only to find out that they don't hold up in the phase inverter spot. I also found out that when used in amps where the first gain stage has a low value Rk the tube will cause the scratchy volume pot effect. By the average they are more microphonic than JJs or Chinese. Conclusion: I won't touch 'em again.

I mostly use them in V1 of my cathode bias amps.
No issue (tung sol).