Ei 12AX7 in Cathode Follower?

[FourT6and2]

Talking about reliability here.

Good tube for CF or no? I have two that aren't microphonic. I have a Chinese AC5 in there now. Sounds good but I want to experiment a bit. I also have an AC5 as the PI. Ei Good for that position too?

 

[C1-ocaster]

Talking about reliability here.

Good tube for CF or no? I have two that aren't microphonic. I have a Chinese AC5 in there now. Sounds good but I want to experiment a bit. I also have an AC5 as the PI. Ei Good for that position too?

I've heard that the Yugoslavian made EI's are great tubes/valves.
I found a source online and he had some that had funky looking glass, but he said they sounded just like the better/proper looking ones.
Cost was considerably lower like between $25-$45.
I'm planning on looking him up again and getting a couple to try out.

Let us know how they sound in your rig.

 

[FourT6and2]

Talking about reliability here.

Good tube for CF or no? I have two that aren't microphonic. I have a Chinese AC5 in there now. Sounds good but I want to experiment a bit. I also have an AC5 as the PI. Ei Good for that position too?

I've the Yugoslavian made EI's are great tubes/valves.
I found a source online and he had some that had funky looking glass, but he said they sounded just like the better/proper looking ones.
Cost was considerably lower like between $25-$45.
I'm planning on looking him up again and getting a couple to try out.

Let us know how they sound in your rig.

Well before I pop them in I need to know if they can hold up in CF and PI positions.

 

[C1-ocaster]

Talking about reliability here.

Good tube for CF or no? I have two that aren't microphonic. I have a Chinese AC5 in there now. Sounds good but I want to experiment a bit. I also have an AC5 as the PI. Ei Good for that position too?

I've the Yugoslavian made EI's are great tubes/valves.
I found a source online and he had some that had funky looking glass, but he said they sounded just like the better/proper looking ones.
Cost was considerably lower like between $25-$45.
I'm planning on looking him up again and getting a couple to try out.

Let us know how they sound in your rig.

Well before I pop them in I need to know if they can hold up in CF and PI positions.

Ah, I see.
For PI I'm sure they'll be fine.

Why would you think any pre tube might not work in your amp?
Is there something odd about the amp?
What amp is it?

 

[OUTLAW1969]

Talking about reliability here.

Good tube for CF or no? I have two that aren't microphonic. I have a Chinese AC5 in there now. Sounds good but I want to experiment a bit. I also have an AC5 as the PI. Ei Good for that position too?

I've the Yugoslavian made EI's are great tubes/valves.
I found a source online and he had some that had funky looking glass, but he said they sounded just like the better/proper looking ones.
Cost was considerably lower like between $25-$45.
I'm planning on looking him up again and getting a couple to try out.

Let us know how they sound in your rig.

Well before I pop them in I need to know if they can hold up in CF and PI positions.

Ah, I see.
For PI I'm sure they'll be fine.

Why would you think any pre tube might not work in your amp?
Is there something odd about the amp?
What amp is it?

It would "work", but he is concerned about how long they would hold up in those slots. The CF and PI slots are tricky....

 

[FourT6and2]

Talking about reliability here.

Good tube for CF or no? I have two that aren't microphonic. I have a Chinese AC5 in there now. Sounds good but I want to experiment a bit. I also have an AC5 as the PI. Ei Good for that position too?

I've the Yugoslavian made EI's are great tubes/valves.
I found a source online and he had some that had funky looking glass, but he said they sounded just like the better/proper looking ones.
Cost was considerably lower like between $25-$45.
I'm planning on looking him up again and getting a couple to try out.

Let us know how they sound in your rig.

Well before I pop them in I need to know if they can hold up in CF and PI positions.

Ah, I see.
For PI I'm sure they'll be fine.

Why would you think any pre tube might not work in your amp?
Is there something odd about the amp?
What amp is it?

It would "work", but he is concerned about how long they would hold up in those slots. The CF and PI slots are tricky....

Yep. Cathode Follower circuits are notorious for destroying certain tubes. Just trying to find out if anybody has experience with the Ei Yugo in this position.

 

[MississippiMetal]

Just elevate the filament supply and put whatever you want in there.

 

[FourT6and2]

Just elevate the filament supply and put whatever you want in there.

Elevated heaters would be interesting. Isn't it all about the heater to cathode voltage ratio?

 

[MississippiMetal]

Just elevate the filament supply and put whatever you want in there.

Elevated heaters would be interesting. Isn't it all about the heater to cathode voltage ratio?

Yep. I had to elevate the heaters in my last build because I was trying to get the preamp B+ up to Diezel's 400vdc range. Interestingly enough, you elevate a Centre Tapped heater supply by referencing it to the high voltage side. I use the screen node. Of course you need a couple of resistors and a cap to create a stable voltage divider. You can't just jumper the screens to the filament. You're using the voltage divider and the HT voltage to give the filament rail a DC reference higher than 0v ground but not so high as to fry it either. H-k voltage refers to the DC potential between the two electrodes. We're talking about altering that to keep the tube within safe limits.

 

[FourT6and2]

Just elevate the filament supply and put whatever you want in there.

Elevated heaters would be interesting. Isn't it all about the heater to cathode voltage ratio?

Yep. I had to elevate the heaters in my last build because I was trying to get the preamp B+ up to Diezel's 400vdc range. Interestingly enough, you elevate a Centre Tapped heater supply by referencing it to the high voltage side. I use the screen node. Of course you need a couple of resistors and a cap to create a stable voltage divider. You can't just jumper the screens to the filament. You're using the voltage divider and the HT voltage to give the filament rail a DC reference.

Hmm, not sure I want to go to that much trouble in someone else's amp design. If it were an amp I built, sure. If it were that easy to make CF stages safe to run every tube why wouldn't the builder run elevated filaments to begin with? Is there a downside? Other than maybe adding like 20 minutes to the amp's build time and an extra $1.00 to parts cost.

 

[MississippiMetal]

Well what kind of h-k voltage are we talking about here? Not all amps with a CF are running the kind of B+ that would kill a tube in that position.

You can't assume that just because someone designs and builds an amp that they have all the kinks worked out and there are no design flaws. Friedman has apparently been having issues with his production models popping when channel switched and hasn't yet figured out why.

 

[FourT6and2]

Well what kind of h-k voltage are we talking about here? Not all amps with a CF are running the kind of B+ that would kill a tube in that position.

You can't assume that just because someone designs and builds an amp that they have all the kinks worked out and there are no design flaws. Friedman has apparently been having issues with his production models popping when channel switched and hasn't yet figured out why.

I haven't measured the various preamp socket pins. So I don't know what kind of voltage is running on them. I can check at some point though. I know tubes that use spiral filaments like the New Sensor Russians tend to go bad in CF positions and are generally not recommended. But then most JJs (even the ECC803S with spiral filament) and Chinese tubes hold up just fine. So I was just curious about Ei.

As far as design goes, I can't speak to that because I'm not that versed in amp/circuit design to know one way or the other.

 

[O'Rourke]

According to the data sheets I have the Ei is rated for a 180 volt heater/cathode max differential, same as the Shuguang Chinese 12AX7's. You should be fine as long as you don't exceed that. Sovtek's are only rated for 100 volts h-k difference which is why people say don't run Russian tubes in a cathode follower stage.

As far as the PI spot you can run whatever you want. Good read here, 9th question down-

http://www.aikenamps.com/index.php/technical-q-a

 

[FourT6and2]

According to the data sheets I have the Ei is rated for a 180 volt heater/cathode max differential, same as the Shuguang Chinese 12AX7's. You should be fine as long as you don't exceed that. Sovtek's are only rated for 100 volts h-k difference which is why people say don't run Russian tubes in a cathode follower stage.

As far as the PI spot you can run whatever you want. Good read here, 9th question down-

http://www.aikenamps.com/index.php/technical-q-a

Perfect, thanks! I'll measure the preamp sockets in my amp at some point. But I've been running a Shuguang in the CF slot without any problems.