#1
I bought a JCM 800 2205 that has KT88 power tubes. Very very unattractive and sterile sounding. I want the lush warm sound that you get from EL34/E34L power tubes.


I've been reading that people that switch from EL34's to KT88's are required to modify their amps. It's more than simply adjusting the bias.


Is this true? Will I need to modify my amp to go from KT88 to EL34 power tubes?
Mesa Single Rectifier
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#2
Quote by touji-za-nai
I bought a JCM 800 2205 that has KT88 power tubes. Very very unattractive and sterile sounding. I want the lush warm sound that you get from EL34/E34L power tubes.


I've been reading that people that switch from EL34's to KT88's are required to modify their amps. It's more than simply adjusting the bias.


Is this true? Will I need to modify my amp to go from KT88 to EL34 power tubes?


Yeahup. EL34s have a different pinout that requires a change.

You could switch to 6L6 or KT77s...the KT77 is like an EL34 only w/ tighter low end. Good stuff.
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#3
what does it mean that they have a different pinout?

how would I go about modifying that.

edit: They are both 8-pin octal sockets, if that's what you are talking about.
Mesa Single Rectifier
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Last edited by touji-za-nai at Feb 22, 2009,
#4
Quote by DLrocket89
Yeahup. EL34s have a different pinout that requires a change.

You could switch to 6L6 or KT77s...the KT77 is like an EL34 only w/ tighter low end. Good stuff.

6L6s and EL34s are interchangeable in Marshalls. Going from KT88s back to EL34s is no problem at all in a JCM800, but you will need to change the bias range resistor on the board.
#5
Quote by al112987
6L6s and EL34s are interchangeable in Marshalls. Going from KT88s back to EL34s is no problem at all in a JCM800, but you will need to change the bias range resistor on the board.


I'm sorry I am asking so many questions, I've only been playing guitar for about 4 years, and I've been just recently educating myself on the more advanced side of it.

changing the bias resistor is the same thing as adjusting the bias, right?

It's just turning the little dial to the right range. Not actually changing a physical part in the amp or replacing it?
Mesa Single Rectifier
Marshall 1960A vintage
Rg3exfm1 w/ EMG 85/81
Big Baby Taylor Acoustic
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Last edited by touji-za-nai at Feb 22, 2009,
#6
Quote by al112987
6L6s and EL34s are interchangeable in Marshalls. Going from KT88s back to EL34s is no problem at all in a JCM800, but you will need to change the bias range resistor on the board.


hrm..cool...they have pin 1 going to ground or the raw bais supply? (ground if it's a Marshall)...
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#7
Quote by touji-za-nai
what does it mean that they have a different pinout?

how would I go about modifying that.

edit: They are both 8-pin octal sockets, if that's what you are talking about.


The EL34/E34L has it's supressor grid coming out on pin 1, most tubes (KT88 included) have it grounded to the cathode internally. So...if it's set up to only run KT88, there is no connection on pin 1 because that connection is made inside the tube. BUT, if they set it up to run an EL34, then you're good to go.

If you open up the amp, does pin 1 have a connection? If it doesn't, it needs to be tied to pin 8.
Quote by kcdakrt
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#8
Quote by DLrocket89
The EL34/E34L has it's suppressor grid coming out on pin 1, most tubes (KT88 included) have it grounded to the cathode internally. So...if it's set up to only run KT88, there is no connection on pin 1 because that connection is made inside the tube. BUT, if they set it up to run an EL34, then you're good to go.

If you open up the amp, does pin 1 have a connection? If it doesn't, it needs to be tied to pin 8.


Is it even possible for my JCM 800 to be running KT88's and still be set to run EL34's?
Mesa Single Rectifier
Marshall 1960A vintage
Rg3exfm1 w/ EMG 85/81
Big Baby Taylor Acoustic
Ibanez TS808
#9
it is technically possible, but not very good for it at all.

KT88's require a higher bias point, they need to be running "hotter" than EL34's which is probably why it sounds very sterile
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#10
Quote by touji-za-nai
Is it even possible for my JCM 800 to be running KT88's and still be set to run EL34's?


yeahup. tie pin 1 to pin 8. KT88 has no pin 1 connection, so you're fine. EL34 needs pin 1 tied to pin 8, so you're good to go there too.
Quote by kcdakrt
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#11
Quote by Khoifish321
it is technically possible, but not very good for it at all.

KT88's require a higher bias point, they need to be running "hotter" than EL34's which is probably why it sounds very sterile


very true...I was talking about pinouts, not biasing points and whatnot.
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#12
ah I was just talking in general terms

I know for my Splawn Nitro that I can't just stick KT88s in there, I need to solder a resistor on the board somewhere and then bias the KT88's to the correct bias point, and it is hotter than the EL34s.

I'd assume that if he bought it with the KT88s, it is probably installed correctly but not biased correctly.
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#13
Quote by Khoifish321
ah I was just talking in general terms

I know for my Splawn Nitro that I can't just stick KT88s in there, I need to solder a resistor on the board somewhere and then bias the KT88's to the correct bias point, and it is hotter than the EL34s.

I'd assume that if he bought it with the KT88s, it is probably installed correctly but not biased correctly.


yeah...and we haven't even got to transformer impedence matching yet...
Quote by kcdakrt
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#14
Its preamp tubes are a combination of 12AX7EH, 12AX7-A, and ECC83S tubes.

Would I be able to replace those with a set of stock ECC83S preamp tubes w/o changing the power tubes or adjusting the bias?

I'm trying to get an Underoath type of tone. Lots of smooth modern style distortion w/o being overly saturated, still lots of clarity.

I assume 90% of the tone will be coming from the preamp tubes considering it's a heavy distortion tone. Maybe that's what I need.
Mesa Single Rectifier
Marshall 1960A vintage
Rg3exfm1 w/ EMG 85/81
Big Baby Taylor Acoustic
Ibanez TS808
#15
Quote by touji-za-nai
Its preamp tubes are a combination of 12AX7EH, 12AX7-A, and ECC83S tubes.

Would I be able to replace those with a set of stock ECC83S preamp tubes w/o changing the power tubes or adjusting the bias?

I'm trying to get an Underoath type of tone. Lots of smooth modern style distortion w/o being overly saturated, still lots of clarity.

I assume 90% of the tone will be coming from the preamp tubes considering it's a heavy distortion tone. Maybe that's what I need.


yeah...replace them all with JJ 12AX7s. no biasing or other funn stuff required.
Quote by kcdakrt
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#16
replace them with 12AX7's? 3 out of the 5 tubes are 12AX7's. Wouldn't changing them all back to ECC83's make the amp sound more like it was suppose to?

I had a JCM 800 2203 for about a week and I want that tone. I know 2205s have a slightly different tone, but not this much.
Mesa Single Rectifier
Marshall 1960A vintage
Rg3exfm1 w/ EMG 85/81
Big Baby Taylor Acoustic
Ibanez TS808
#17
12AX7A = ECC83 = 12AX7EH

Replace them all w/ JJ 12AX7s (or ECC83s in you're in Europe). Don't worry about power tubes.

Crank it up, maybe throw a pedal in front...
Quote by kcdakrt
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#18
one thing about the JCM 800 is you really have to crank it to get a decent level of gain and use an OD
Ibanez PGM100
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Peters Chimera
Orange PPC212 w/ Celestion V30 and Celestion G12-75
#19
Quote by DLrocket89
hrm..cool...they have pin 1 going to ground or the raw bais supply? (ground if it's a Marshall)...

They do. At least my JTM45 does and I know the 1959 and 1987 designs did as well. I imagine they continued to do so with the JCM800s.
#20
Quote by al112987
They do. At least my JTM45 does and I know the 1959 and 1987 designs did as well. I imagine they continued to do so with the JCM800s.




sounds good. doubt they re-engineered something to remove capability from it...
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