PI tube type concerns.

[joesatch]

I have a number of Mullard Reissue tubes and have some in the PI's of a few of my builds. I came across this in the forum universe. Any credence to this? Got me worried.

[joesatch]

The post is inconsistent with this page on sweetwater which says the Mullard is specifically suited for the PI. What's the deal? How do i know if my Mullards are spiral filament or if i should use them in the PI?



https://www.sweetwater.com/store/detail/EHX12AX7M--mullard-12ax7-russian-preamp-tube

[acheld]

I don't know the answer . . . .

But, have you had problems with the tube?  I have two builds with these in the PI position (both LTPs) which have been used daily for years w/o problems.   

I have little trust in statements made on the internet, especially when "a guy" is quoted.

[shooter]

from ValveWizard;

Heater ElevationIt is important not to exceed the maximum rated heater-to-cathode voltage. Since the cathode is at a high voltage it is often necessary to elevate the heater supply to a cathode follower. Exceeding the rated figure can lead to increasing heater hum and noise as the heater insulation degrades at an accelerated rate. The ECC82 datasheet states Vhk(max) is 180V. In this case the load line indicates an anode-to-cathode voltage of 140V, meaning the cathode-to-ground voltage must be 280 - 140 = 140V. This is within limits, but it wouldn't hurt to elevate the heater by 30V or so, all the same.Don't forget that an output coupling capacitor will be needed to block the cathode voltage from watever we happen to be plugging the cathode follower into.

follow this rule, shouldn't be any problem

[joesatch]

from ValveWizard;

Heater ElevationIt is important not to exceed the maximum rated heater-to-cathode voltage. Since the cathode is at a high voltage it is often necessary to elevate the heater supply to a cathode follower. Exceeding the rated figure can lead to increasing heater hum and noise as the heater insulation degrades at an accelerated rate. The ECC82 datasheet states Vhk(max) is 180V. In this case the load line indicates an anode-to-cathode voltage of 140V, meaning the cathode-to-ground voltage must be 280 - 140 = 140V. This is within limits, but it wouldn't hurt to elevate the heater by 30V or so, all the same.Don't forget that an output coupling capacitor will be needed to block the cathode voltage from watever we happen to be plugging the cathode follower into.

follow this rule, shouldn't be any problem

If I'm not doing DC heaters i elevate the heaters on all my amps (65vdc)