EL34s in Twin Jet? UPDATE: Mod complete!

  • Thread starter Thread starter TheMagicEight
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TheMagicEight

TheMagicEight

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I'm not sure if I'm digging the KT88s. I don't really like the huge bottom end. The tone of the amp is excellent, and I love the gain structure in the preamp, but I've been going back and forth on the amp as a whole because of the huge low end.

What I'm wondering is if I can take the KT88s out and put EL34s in without switching out the resistor. I know it won't be right, but it should be safe, correct? Even if the amp is biased too cold with the EL34s, I should be able to hear the general difference between them.

Anyway, my main question is if I simply swap out the KT88s for EL34s without modding the amp, will it be safe?

Thanks

PS - has anyone tried the Twin Jet with the regular Bogner 4x12? Anyone get to compare it to the Uberkab?
 
You'll need to change out the resistor to get the bias in range, I would'nt just throw them in.
 
edgeofdarkness":1rsepbw4 said:
You'll need to change out the resistor to get the bias in range, I would'nt just throw them in.
Click to expand...
But if I don't change out the resistor, it shouldn't harm anything, right? Correct me if I'm wrong, but putting the EL34s in from KT88s should just run the EL34s too cold.
 
I inquired about having EL34s in a 20th Ann Shiva. Called up Bogner and asked them.

They said that it requires a resistor change, but more so, something about higher voltage from the bigger transformers (designed for use with KT88s) that would wear out the EL34s quicker.

How quick? I couldn't get a sttraight answer on that, and still cant.

I asked some amp techs/makers and they said that you should be fine - you might get 6 months out of an EL34, instead of a year... something like that.
 
RockStarNick":inf9qmu0 said:
I inquired about having EL34s in a 20th Ann Shiva. Called up Bogner and asked them.

They said that it requires a resistor change, but more so, something about higher voltage from the bigger transformers (designed for use with KT88s) that would wear out the EL34s quicker.

How quick? I couldn't get a sttraight answer on that, and still cant.

I asked some amp techs/makers and they said that you should be fine - you might get 6 months out of an EL34, instead of a year... something like that.
Click to expand...
Thanks!

I ended up trying it last night. Well, I couldn't get the idle current past .08mA!!!!! Even though it sounded like ass, I could hear the general difference in tone between the EL34s and KT88s. I would really like to try it out, but I'm happy for a little while. As it turns out, there were two things wrong that made the amp sound bad. First off, I had a dying preamp tube. I don't know what I was thinking when I last messed with the preamp tubes - if I was thinking at all - but I stupidly put a JJ ECC83 into V3, a cathode follower spot. The other thing was that the KT88s were set too cold from the factory, maybe around 20mA. I swapped the preamp tube, biased it a little higher, and now I'm getting somewhere!

I would still like to try out the EL34s biased correctly, though. If anyone knows what resistor value you'd need and where it should go, please inform me.

Thanks for the responses!
 
So I pulled the trigger today and went for it. Called up Bogner in the morning and they first told me that since the plate voltage was so high, I wouldn't get as much life out of the EL34s. I told him it was right around 530, and he said nevermind, that it would be 100% alright. Said that later Twin Jets had a higher plate voltage (does anyone know how the higher plate voltage would affect tone?). I swapped R401 (2 piggybacked resistors near the bias trim pot) for a 47k ohm resistor and now the range is a little on the hotter side - the lowest I can set the bias is about 30mA - but I think that's about where I'd have it anyway.

It sounds awesome!!! I might try and put together a clip at some point because the amp sounds like what I think of when I think Uberschall. Now I want to put out a disclosure that the amp is not as open as before, it doesn't have as "clean" a tone as with the KT88s, and it's not as tight and defined as before with the same low end. What it does have is a more harmonically rich - if there ever was a loaded term :lol: :LOL: - tone to it that I felt the KT88s couldn't offer. I've played a little on a Rev. Blue and the difference here seems to be that with the master presence and depth, the channel EQ becomes that much more usable. I can turn the master depth down a little and run bass up, then crank channel presence and turn mids up past noon, and I get this ultra heavy Uberschall tone that - to me - sounds like the best damn Uberschall I've ever heard!

For now, the mod will stay! I have JJ E34Ls in it. Those with knowledge on EL34 Uberschalls: which EL34s do / did you like best? I've never really been a fan of the E34Ls and am thinking =C=s will be an improvement.....
 
se7en":59wobdvl said:
Any chance you could record a clip for us?
Click to expand...
1. http://soundclick.com/share?songid=8791576 - Les Paul / Channel 2 / G12Ms
2. http://soundclick.com/share?songid=8791591 - Les Paul / Channel 2 / G12T-75
3. http://soundclick.com/share?songid=8791610 - Les Paul / Channel 1 / G12Ms
4. http://soundclick.com/share?songid=8793221 - ESP Horizon NT-II / Channel 2 / G12Ms
5. http://soundclick.com/share?songid=8793231 - ESP Horizon NT-II / Channel 1 / G12Ms

See the page for full details.
 
Sounds good man! Love the tone you get with the Duncan 59' split to a single coil . Real nice :)
 
I have a feeling I'm eventually going to do this with my 20th Anniversary Shiva too, when I get one. Sounds like it would be OK to do so.

I'd love to take it to a tech, and have them install a mini-switch, to go back and forth between KT88 and EL34 bias ranges.

I'd REALLY love for someone to install some external bias adjustments, but that's pushing it...
 
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