#1
so im looking at getting a new sovtek 12ax7lp for my 5150 ii for the phase inverter. but i see all these warnings about cathode followers. right now i have jjecc83s across the board in the amp. will the sovtek not work well as a phase inverter for the 5150 ii? also what is a cathode followers pupose?
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#3
A phase inverter can't be a cathode follower, they're two completely different things. You can use a Sovtek as a phase inverter in your amp.

A cathode follower is a type of buffer, usually used to drive EQ stages. You see them a lot in modern amps.
#4
i read most of that article on cathode followers....good reading. if its a buffer why cant some tubes handle the voltage of a buffer?
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#5
Quote by iheartgun
i read most of that article on cathode followers....good reading. if its a buffer why cant some tubes handle the voltage of a buffer?


I believe its the current associated with them. The tubes can't handle the wattage.
Quote by DeathByDestroyr
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#6
It's heater to cathode voltage. A cathode follower has the cathode elevated above ground. If you don't also have elevated heaters (which few do) some tubes will shit their pants.
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#7
Quote by Cathbard
It's heater to cathode voltage. A cathode follower has the cathode elevated above ground. If you don't also have elevated heaters (which few do) some tubes will shit their pants.


Isn't there a grid current as well that must be taken into account?

I thought I read somewhere that the grid wattage was lower on the "non" cathode follower recommended tubes. It pushed them too close to the wattage rating and shorten their lifespan.

Or should I put the crack away?


Edit:Everything in above in my statement should be ignored. See below.


Edit:

I read a few things along these lines previously as well.

Spiral filament tubes do not work well in cathode follower circuits and are prone to failure. This appears to be due to the closer spacing of the spiral filament to the cathode. Spiral filament tubes include the 12AX7LPS, 12AX7EH, Tung-Sol 12AX7, Mullard 12AX7 reissue, and JJ ECC83s/12AX7

^ pulled from TGP.
Quote by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
Last edited by R45VT at May 3, 2013,
#8
Why would the grid current change? You do tend to run more plate current through a cathode follower but that isn't the issue, it's the voltage on the cathode.
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#9
Quote by Roc8995
A phase inverter can't be a cathode follower, they're two completely different things. You can use a Sovtek as a phase inverter in your amp.

A cathode follower is a type of buffer, usually used to drive EQ stages. You see them a lot in modern amps.


They also add compression.


Quote by Cathbard
Why would the grid current change? You do tend to run more plate current through a cathode follower but that isn't the issue, it's the voltage on the cathode.


It's not that the grid current changes, it just a higher quiescent current.
Quote by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
Last edited by R45VT at May 2, 2013,
#10
Ah. But it should still be designed within spec. It's class A, you'd design it up near full current handling at quiescent regardless of it's topology.
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#11
Well hopefully my ramblings didn't confuse anyone.


TS: Roc nailed it- for your PI you can use any tube without the cathode follower into consideration.
Quote by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
#12
Quote by R45VT
Isn't there a grid current as well that must be taken into account?

I thought I read somewhere that the grid wattage was lower on the "non" cathode follower recommended tubes. It pushed them too close to the wattage rating and shorten their lifespan.

Or should I put the crack away?


Edit:

I read a few things along these lines previously as well.

Spiral filament tubes do not work well in cathode follower circuits and are prone to failure. This appears to be due to the closer spacing of the spiral filament to the cathode. Spiral filament tubes include the 12AX7LPS, 12AX7EH, Tung-Sol 12AX7, Mullard 12AX7 reissue, and JJ ECC83s/12AX7

^ pulled from TGP.


first of all i love this... this is where i learn the most shizz from stuff like you guys just did so thank you. with the literature that was posted earlier and what you guys are saying its starting to make a little sense.

now the bolded area is my concern. like i said i have jj ecc83s in all positions except the PI right now. what position is the cathode follower in the 5150 II?
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#13
Quote by iheartgun
first of all i love this... this is where i learn the most shizz from stuff like you guys just did so thank you. with the literature that was posted earlier and what you guys are saying its starting to make a little sense.

now the bolded area is my concern. like i said i have jj ecc83s in all positions except the PI right now. what position is the cathode follower in the 5150 II?


I don't see any cathode followers in your amp.

Here is more reading:

http://www.thegearpage.net/board/showthread.php?t=543091


I am concerned myself now as I am going to modify one of my amps... it will now have a cathode follower driven tone stack - I can't float my heaters... 6VAC with no center tap. I guess if the JJ blows out I will have to get a non spiral heater...
Quote by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
Last edited by R45VT at May 3, 2013,
#14
The JJ ECC83S & ECC803S do not crap themselves in the CF stage. The ones prone to dying there suddenly are primarily the Tungsol RI 12AX7 & Sovtek LPS tubes. The EXH 12AX7 used to be a long plate tube until they changed it to a shorter plate design(not sure which happened in the right order, don't really care for these tubes anyway), but that particular one is also to be avoided if possible. The Mullard RI 12AX7 I've found to be most reliable recent Sovtek tube but I've not gone about trying to see if it is capable of surviving in the CF stage(it's an expensive tube!) although tonewise rather flat, an excellent PI tube IMO.

EDIT: The chinese tubes in most stock mass produced amps can also survive the CF stage.
Last edited by steven_ferns84 at May 3, 2013,
#15
I have read the same thing across a few different forums. No one is saying the JJ's have shit on them, that was a response from New Sensor which makes Sovtek and tung-sol if I am not mistaken. They were commenting on the spiral filament design being the root source of the problem.


Thanks for the input.
Quote by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
#16
^Yeah the New Sensor stuff is not spec'd right. Actually I've spent $90 total on 6 Tungsol RI 12AX7 last year hoping that atleast 4 out of 6 would be without problems and all for the V1 spot only. Sadly after 2 weeks or a month each of them developed this buzz/hum that gets really annoying. I could have just gotten a single NOS Tungsram 12ax7 from KCA for $89 w/shipping that would not only be reliable but sound great
Right now I've given up on current production stuff, the reliable ones don't sound all that great while the somewhat good sounding ones haven't been reliable to me at all.
#17
Off-topic, but reading threads like this causes me to wonder: which denizen of the GG&A Forum has been zapped the most times as a result of monkeying with this stuff? Electrocution is a bitch, and I'll bet some of you have some great war stories!
"Maybe this world is another planet's hell?" - Aldous Huxley
#18
i have yet to zapp myself and i intend to TRY and keep it that way.

back to topic.
i see that CF's are or can be a buffer for an eq stage or they work with higher voltage for the tube heaters. instead of playing the guessing game with tubes why havent the manufactoring companies made a CF only tube?
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It is NOT trash metal it is tHrash metal...get it right
#19
Quote by iheartgun
i have yet to zapp myself and i intend to TRY and keep it that way.

back to topic.
i see that CF's are or can be a buffer for an eq stage or they work with higher voltage for the tube heaters. instead of playing the guessing game with tubes why havent the manufactoring companies made a CF only tube?


They don't need to if its built to the 12AX7 specs. The ones thy fail aren't built up to spec.
Quote by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
#20
Quote by FatalGear41
Off-topic, but reading threads like this causes me to wonder: which denizen of the GG&A Forum has been zapped the most times as a result of monkeying with this stuff? Electrocution is a bitch, and I'll bet some of you have some great war stories!
I've zapped myself more times than I could count. I almost enjoy it now, the rush afterwards is almost like doing a line of speed.
The most common one is my pinky finger touching the 240V side of the transformer. Ouch!
Gilchrist custom
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Marshall JCM900 4102 (modded)
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