KT77 a direct replacement in a JCM800 converted to EL34?

KFBR392

Silver Supporting Member
Messages
3,521
After having slept on it, I’ll keep running EL34s and look more into running my Boss GE7 into the front. Maybe set to Bass-heavy and a nice gain boost. That might be what helps this amp. It’s not a bad sounding amp at all, absolutely killer. I just want a little more bass than the circuit can give me.
 

big mike

Cathode biased
Platinum Supporting Member
Messages
14,525
After having slept on it, I’ll keep running EL34s and look more into running my Boss GE7 into the front. Maybe set to Bass-heavy and a nice gain boost. That might be what helps this amp. It’s not a bad sounding amp at all, absolutely killer. I just want a little more bass than the circuit can give me.

much better plan
People put too much emphasis
On the power tubes effecting the voicing
 

KFBR392

Silver Supporting Member
Messages
3,521
much better plan
People put too much emphasis
On the power tubes effecting the voicing
Any recommendations? Leaning towards Gold Lion but I’m all for bang for the buck. If there’s something cheaper that sounds 80% as good, I’m all for it.
 

big mike

Cathode biased
Platinum Supporting Member
Messages
14,525
Any recommendations? Leaning towards Gold Lion but I’m all for bang for the buck. If there’s something cheaper that sounds 80% as good, I’m all for it.
Yeah make sure what’s in there is biased right and add an eq pedal.

Expecting thick low end out of that circuit at low volumes is asking too much.
 

louis

Silver Supporting Member
Messages
4,300
I used to own a small box, JCM800 from Canada, so EL34s. That SOB was cut your head off bright! The bright cap on mine was actually on the volume pot IIRC, so lifting it was easy. It was still bright but not as damaging. I played it into a bunch of different speakers, the 65s were still pretty bright. G12M-25s were a little better. Jensens seemed a little less harsh. But I didn't shed a tear when I moved that amp on. Strange that my 82 vertical input is a completely different sounding amp.

Also worth saying that the MV Marshall JCM800s are NOT designed as a "get the distortion from the preamp" amp. They're designed for you to get the sweet spot at slightly less stage volume. I'm never happy trying to get distortion/overdrive on the 82 with the preamp knob. For that purpose, just get a pedal and set the amp fairly clean. In fact a REALLY cool 2 channel way to use the JCM800 is to plug into the low input and set it up for the typical warm, clean tone. Then do all the distortion with pedals!
I tried a beautiful 1981 JCM800 not long ago ,.....it was for sale but it almost cut my head in half !!
Piercing razor blade sharpness !!.......very different compared with the one I had years ago with it's honky low mid tone!
Don't remember the year though but not as nice looking as the 1981
 

alivegy

Member
Messages
1,176
I dont have a lot of experience with the later 800s but the 65 is a pretty dark speaker. If it is still very bright I dont know that a swap to a different tube is going to do it unless there is something wrong with the old tubes, especially if youre not driving the power tubes with a lot of volume.

Youre always going to lose some bottom end with an open back combo. Using an eq pedal may be your best option to shape the sound to your taste. I would also try a closed back cab to see if it is the character of the open back with the marshall that you dont like.
 
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7,422
Any recommendations? Leaning towards Gold Lion but I’m all for bang for the buck. If there’s something cheaper that sounds 80% as good, I’m all for it.
You could try some KT66 in it as long as the screens want to play along. Then the 77 can get pretty close.

Another option would be dropping the resonance of the amp circuit per modern specs.
 




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