Help fixing my clipped Twin Jet.....

[RJF]

Not positive, but I believe I found a picture here where you are supposed to clip the diode so that you can run EL34's. My TJ has EL34's and was like that when I bought it, and I want to get rid of them and put KT88's back in it. I think the original owner completely removed the diode instead of just clipping one end of it. Am I looking in the right spot and what do I need to get it fixed right so I can get the correct tubes back into this thing that belong there? EDIT, this is my amp pictured.

 

[glip22]

Not positive, but I believe I found a picture here where you are supposed to clip the diode so that you can run EL34's. My TJ has EL34's and was like that when I bought it, and I want to get rid of them and put KT88's back in it. I think the original owner completely removed the diode instead of just clipping one end of it. Am I looking in the right spot and what do I need to get it fixed right so I can get the correct tubes back into this thing that belong there? EDIT, this is my amp pictured.

That is actually good he desoldered it cleanly. I did mine that way also. It is the closest resistor to the edge of the board. Just piggy back solder the original one back on and you should be good to go. Or you can just be done with it and install a quad of Gold Lion KT77's. The best tubes bar none in this amp. No need to add the resistor back. The 88's are too glassy imo.

 

[RJF]

Not positive, but I believe I found a picture here where you are supposed to clip the diode so that you can run EL34's. My TJ has EL34's and was like that when I bought it, and I want to get rid of them and put KT88's back in it. I think the original owner completely removed the diode instead of just clipping one end of it. Am I looking in the right spot and what do I need to get it fixed right so I can get the correct tubes back into this thing that belong there? EDIT, this is my amp pictured.

That is actually good he desoldered it cleanly. I did mine that way also. It is the closest resistor to the edge of the board. Just piggy back solder the original one back on and you should be good to go. Or you can just be done with it and install a quad of Gold Lion KT77's. The best tubes bar none in this amp. No need to add the resistor back. The 88's are too glassy imo.

I know, through search I've ran across 10+ posts from you about how great 77's are. I will be putting 88's in, I want the ultra clear and tight bottom with the glassy high.

The problem I have is the resistor is completely gone, It did not come with the amp. What are the specs of the resistor?

 

[glip22]

Not positive, but I believe I found a picture here where you are supposed to clip the diode so that you can run EL34's. My TJ has EL34's and was like that when I bought it, and I want to get rid of them and put KT88's back in it. I think the original owner completely removed the diode instead of just clipping one end of it. Am I looking in the right spot and what do I need to get it fixed right so I can get the correct tubes back into this thing that belong there? EDIT, this is my amp pictured.

That is actually good he desoldered it cleanly. I did mine that way also. It is the closest resistor to the edge of the board. Just piggy back solder the original one back on and you should be good to go. Or you can just be done with it and install a quad of Gold Lion KT77's. The best tubes bar none in this amp. No need to add the resistor back. The 88's are too glassy imo.

I know, through search I've ran across 10+ posts from you about how great 77's are. I will be putting 88's in, I want the ultra clear and tight bottom with the glassy high.

The problem I have is the resistor is completely gone, It did not come with the amp. What are the specs of the resistor?

Alright But you should try them sometime. They hold the tightness, well you read my posts. Bottom resistor is 33k. You will need a 22k ohm piggybacked. You have the correct spot. As I said resisitor closest to the bottom of the pic is the one.

 

[RJF]

thanks

 

[zewango]

There was a thread where this pic was posted having a switch with KT88\El34 option.
It looks like the top resistor has it piggy backed. I've been debating on making the switch to el34's.

 

[leib10]

That's my Twin Jet. I highly recommend the double-throw switch. You're bound to get sick of either the KT88's or EL34's and want to go back to whatever you had. Otherwise a lot of soldering and desoldering is involved. Cost me $100 done by a good tech, or if you are good with resistors you can do it yourself.

 

[RJF]

I've been debating on making the switch to el34's.

Don't do it man. To my ears, the 34's sound boxy, currently mine is a VERY mid heavy amp and it's tough to dial it out. IMHO, it sure seems like the preamp was designed around 88's with the TJ, since just a hair less mids and a bump in the bass would make the amp sound more balanced to me, and easier to EQ.

UNLESS...... a guy wants to play classic rock or something, where really strong mids are common, but if you have a TJ, you're probably a metal player anyway.

 

[RJF]

I did mine that way also. It is the closest resistor to the edge of the board. Just piggy back solder the original one back on and you should be good to go.

I'm a little confused, as this sounds like you are saying to piggy back the bottom resistor of the two in the picture? With the pic from leib10's photo, it almost looks like it's the upper resistor that is being piggy backed.

So, do I piggy back the resistor marked in red or the one in yellow? Does that look correct?

 

[glip22]

I did mine that way also. It is the closest resistor to the edge of the board. Just piggy back solder the original one back on and you should be good to go.

I'm a little confused, as this sounds like you are saying to piggy back the bottom resistor of the two in the picture? With the pic from leib10's photo, it almost looks like it's the upper resistor that is being piggy backed.

So, do I piggy back the resistor marked in red or the one in yellow? Does that look correct?

His is done differently. I imagine you can do either. I am almost positive mine was the bottom one 402 This is what was piggybacked originally. I could be wrong but I don't think so. The value of the bottom one should be 32k. I can't tell if the one above it is also 32.

 

[RJF]

I did mine that way also. It is the closest resistor to the edge of the board. Just piggy back solder the original one back on and you should be good to go.

I'm a little confused, as this sounds like you are saying to piggy back the bottom resistor of the two in the picture? With the pic from leib10's photo, it almost looks like it's the upper resistor that is being piggy backed.

So, do I piggy back the resistor marked in red or the one in yellow? Does that look correct?

His is done differently. I imagine you can do either. I am almost positive mine was the bottom one 402 This is what was piggybacked originally. I could be wrong but I don't think so. The value of the bottom one should be 32k. I can't tell if the one above it is also 32.

Got it, thanks.

 

[zewango]

I have to check my amp again, but I thought mine also had the upper resistor piggy backed from Bogner and it's all still stock.

 

[glip22]

Heres a post from Steve K. I am doubting myself now. I really though it was the bottom but I did my amp a good while ago.

Easy to do. Get you a set of SED Winged C's or if you are a JJ guy, E34L's. Make sure the quad is matched and a PC in the high 30's to low 40's. The quad of SED's I used was a 42.

1. In the chassis, adjacent the bias screw, look for two piggy backed resistors at R402. Next to the fuse holders.

2. Take some small wire snips and clip the resistor off near the body. Leave the tails in case you want to go back with another.

3. As delivered, it has a 33K on bottom and a 22K on top. This gives an Req-13.2 ohm for the 88's.

4. Flip the chassis back over. Set the bias adjust about mid range.

5. Swap the tubes out. Hook up a speaker/power. Is using a Bias rite, set it up.

6. Turn it on, and you should see about 30mA bias without doing anything. I measure my PV @ 500V. Then biased up to 35mA.

This takes no more than 10 minutes or so and you are ready to go. Someone questioned why Bogner piggybacks the bias resistors. It so you can clip the top one off, which is parallel, not series, and be able to use 34's fairly easy. It would be easy to rig a switch to the chassis wired straight to the PC and remove that other resistor and put the resistors on the switch. You could then change between 34's, 88's or whatever you wanted to do

 

[RJF]

Update:

I FINALLY got around to actually getting this done and I think I've ran into a problem. R402 is NOT the spot where the 22K resister goes, it's R401. I put it on R402, as stated by Steve K and glip22. When I turned the amp off stand by the bias shot up and up until it blew the main fuse in the amp. Realizing there was a problem, I figured that R401 was actually where that piggy back resister goes. After removing the resister from 402 and putting it onto 401, everything seemed normal with the stand by off, but I had not checked the bias yet. I went to touch leg number 3 on one of the power tubes to get a plate voltage and I got a pop and blew the fuse in my multi meter from forgetting to take it off of miliamps. After fixing my multi meter, I was able to get my first bias reading which was only 15-20ma on tubes 1,2,3, and nothing on number 4. No matter which way I turn the bias control, it does not change, which is really weird.

In the dark, I can see tubes 1,2,3 have a light purple "heugh" to them, but number 4 does not. I am not sure if I damaged something from putting the 22K resister in the wrong spot, or from touching number 3 leg with my multi meter on one of the power tubes ( actually touched #1, not #4.) Unless it's something simple and you guys have a good idea, looks like this thing is going to have to go to Bogner.

 

[RJF]

Just got it back from my local tech, I blew a screen grid resister which is why one power tube was down.My "matched" set of Sovteks aren't very matched at all, but are biased between 40 and 53ma depending on the tube. My tech thought that putting the bias resister in the wrong spot and the bias climbing sky high might have hurt the tubes a little bit, causing the biasing difference between the bunch.

Regardless, now that everything is right again with this TJ, it is WAY better than before with the EL34's. Bigger tighter bass, less spiky mids, all around better.

 

[leib10]

I agree. It's just a much ballsier tone and it's so much more aggressive than with EL34s. The highs are a bit jagged, but you can dial that out.

 

[Trippled]

Hmmm that's weird.
I'm also interested in getting 88's on mine recently, I took the chassis out to have a look
and found out that there are 3 resistors in that spot, 2 seating next to each other and another one soldered
on top of one of them, supposedly this was done by jorg at bogner as I oredered my TJ with 34's.

When I asked jorg what to do he responded: " I think it's either the two yellow or orange wires, what ever is hooked up now, use the other color".

Couldn't really understand what he meant, he didn't respond back till now, anyone has an idea?

 

[glip22]

Hmmm that's weird.
I'm also interested in getting 88's on mine recently, I took the chassis out to have a look
and found out that there are 3 resistors in that spot, 2 seating next to each other and another one soldered
on top of one of them, supposedly this was done by jorg at bogner as I oredered my TJ with 34's.

When I asked jorg what to do he responded: " I think it's either the two yellow or orange wires, what ever is hooked up now, use the other color".

Couldn't really understand what he meant, he didn't respond back till now, anyone has an idea?

He was referring to your power transformers wires. I think there is a lower voltage option.

 

[Trippled]

How come he didn't mention the resistor change?
Here's the full sentence:


Hi Daniel,

You need to rebias the amp, you also have the choice to hook up the higher plate voltage, I think it's either the two yellow or orange wires, what ever is hooked up now, use the other color.

Regards,

j o r g

Sorry, I'm bugging you guys with this, I just wanna get the 88's in there allready and he won't respond back,
looks like they're busy there.