Tube question

[zzmoore]

There are certain brandings of tubes from Reflektor, Mike Mathews, New Sensor, Electro Harmonix, (or whatever other name that company uses) that cannot tolerate the cat voltage when used as a Cat Follow.
Can any of you guys tell me what the problem is exactly.? Is it just a simple matter of materials not being up to the task.?
Thank You

[donnyjaguar]

Lack of insulation between the filament and cathode methinks!

[big mike]

I've heard it, but I've never seen it.
Supposedly they can't take the voltage in the cathode follower postion.

That said, Lots of companies still supply amps that way.
FWIW i always took that caution and stuck a JJ or Chinese in V2
The tungsol and Mullards and even EH are pretty good sounding for new production.

[zzmoore]

Lack of insulation between the filament and cathode methinks!
I have no real knowledge of parts in a tube, but is there insulation between the heater and the cat.?
I thought the Filament has to heat the Cathode in order for Thermionic Emission to occur. Will that happen with insulation between the two.?

[guiltless]

My understanding is that many newer tubes use a spiral filament for the heater. And, that filament is not as up to the task of surpassing the heater to cathode voltage differential as other filament winding types. Basically, in a CF stage you have much more than a few volts on the cathode, more like 180v! And the heater to cathode specs on older tubes is, at least for the GE data sheet I just looked at, 180v positive or negative difference.

New tubes being not as high of quality, can't run at the edge or beyond like the old production ones can. I have modded bassman with a Plexi/5f6-a CF in V2 and I am using a Telefunken smooth plate with great results in that spot. Much better sounding than the Matsushita or GE that I have tried.