Bogner Twin JET + EL34 Conversion

[steve_k]

Easy stuff to convert. Bogner piggybacks two resistors for that reason in R402. The bottom is a 33 and the top a 22. Req = 14 when paralleled for a KT88 bias range. Snip the top resistor off and it puts you in the 34 range. But, you need to have a matched quad with PC range of 38-42 or close. The bias adjust is only about 180 degree's and it has a tight range. Go lower or higher on the tube rating, you will be out of range. So, get on to Laura and tell her you need Steve's SED Matched Quad of SED's for the TJ.

I feel like I got lucky when I converted mine. I threw in an old 90's (with relatively low hours) quad of Winged C 34's and after snipping the top resistor at 401 (402 actually corresponds to the single resistor position underneath the two piggybacked ones I think...at least on mine) was able to bias into the lower to mid 20 range as I like a colder bias then what most people prefer.

This particular quad of 34's was sourced to work within my old Dual Rectifier's '34 bias range believe it or not.

I am new to a lot of this stuff, regarding bias, etc... Can I ask why you prefer a colder range and tonally what difference does it make. Curious....

Biasing cooler (60-70% dissipation) will have the tubes breaking up a little later. They run a little cooler and may extend tube life somewhat. Biasing warmer (80-90%) will cause the tubes to brown and break up a little earlier and run warmer. Tube life subsequently will be decreased, maybe. I notice the amp gets to noisy too biasing too high.

As recommended, I stay around 70%.

Steve

 

[glip22]

Easy stuff to convert. Bogner piggybacks two resistors for that reason in R402. The bottom is a 33 and the top a 22. Req = 14 when paralleled for a KT88 bias range. Snip the top resistor off and it puts you in the 34 range. But, you need to have a matched quad with PC range of 38-42 or close. The bias adjust is only about 180 degree's and it has a tight range. Go lower or higher on the tube rating, you will be out of range. So, get on to Laura and tell her you need Steve's SED Matched Quad of SED's for the TJ.

I feel like I got lucky when I converted mine. I threw in an old 90's (with relatively low hours) quad of Winged C 34's and after snipping the top resistor at 401 (402 actually corresponds to the single resistor position underneath the two piggybacked ones I think...at least on mine) was able to bias into the lower to mid 20 range as I like a colder bias then what most people prefer.

This particular quad of 34's was sourced to work within my old Dual Rectifier's '34 bias range believe it or not.

I am new to a lot of this stuff, regarding bias, etc... Can I ask why you prefer a colder range and tonally what difference does it make. Curious....

Biasing cooler (60-70% dissipation) will have the tubes breaking up a little later. They run a little cooler and may extend tube life somewhat. Biasing warmer (80-90%) will cause the tubes to brown and break up a little earlier and run warmer. Tube life subsequently will be decreased, maybe. I notice the amp gets to noisy too biasing too high.

As recommended, I stay around 70%.

Steve

My PV is approx 515 with the 34's in. I biased to 30ma and it seems right.

 

[steve_k]

Easy stuff to convert. Bogner piggybacks two resistors for that reason in R402. The bottom is a 33 and the top a 22. Req = 14 when paralleled for a KT88 bias range. Snip the top resistor off and it puts you in the 34 range. But, you need to have a matched quad with PC range of 38-42 or close. The bias adjust is only about 180 degree's and it has a tight range. Go lower or higher on the tube rating, you will be out of range. So, get on to Laura and tell her you need Steve's SED Matched Quad of SED's for the TJ.

I feel like I got lucky when I converted mine. I threw in an old 90's (with relatively low hours) quad of Winged C 34's and after snipping the top resistor at 401 (402 actually corresponds to the single resistor position underneath the two piggybacked ones I think...at least on mine) was able to bias into the lower to mid 20 range as I like a colder bias then what most people prefer.

This particular quad of 34's was sourced to work within my old Dual Rectifier's '34 bias range believe it or not.

I am new to a lot of this stuff, regarding bias, etc... Can I ask why you prefer a colder range and tonally what difference does it make. Curious....

Biasing cooler (60-70% dissipation) will have the tubes breaking up a little later. They run a little cooler and may extend tube life somewhat. Biasing warmer (80-90%) will cause the tubes to brown and break up a little earlier and run warmer. Tube life subsequently will be decreased, maybe. I notice the amp gets to noisy too biasing too high.

As recommended, I stay around 70%.

Steve

My PV is approx 515 with the 34's in. I biased to 30ma and it seems right.

Yep, 34mA would be 70%.

 

[glip22]

Easy stuff to convert. Bogner piggybacks two resistors for that reason in R402. The bottom is a 33 and the top a 22. Req = 14 when paralleled for a KT88 bias range. Snip the top resistor off and it puts you in the 34 range. But, you need to have a matched quad with PC range of 38-42 or close. The bias adjust is only about 180 degree's and it has a tight range. Go lower or higher on the tube rating, you will be out of range. So, get on to Laura and tell her you need Steve's SED Matched Quad of SED's for the TJ.

I feel like I got lucky when I converted mine. I threw in an old 90's (with relatively low hours) quad of Winged C 34's and after snipping the top resistor at 401 (402 actually corresponds to the single resistor position underneath the two piggybacked ones I think...at least on mine) was able to bias into the lower to mid 20 range as I like a colder bias then what most people prefer.

This particular quad of 34's was sourced to work within my old Dual Rectifier's '34 bias range believe it or not.

I am new to a lot of this stuff, regarding bias, etc... Can I ask why you prefer a colder range and tonally what difference does it make. Curious....

Biasing cooler (60-70% dissipation) will have the tubes breaking up a little later. They run a little cooler and may extend tube life somewhat. Biasing warmer (80-90%) will cause the tubes to brown and break up a little earlier and run warmer. Tube life subsequently will be decreased, maybe. I notice the amp gets to noisy too biasing too high.

As recommended, I stay around 70%.

Steve

My PV is approx 515 with the 34's in. I biased to 30ma and it seems right.

Yep, 34mA would be 70%.

I found it odd that my PV with three KT88's installed was 523. I would have thought it would be higher with the EL34's, but it was actually a little lower with the 34's.

 

[steve_k]

88's and 6550's require a bias supply voltage 10V more negative than 34's. This is why you got to make the resistor change on most amps to compensate for the change in bias supply. When you made the change to 34's your voltage will increase by about 10V on the bias supply and subsequently decrease by 10V on the plates, cathode and screen. See?

Steve

 

[glip22]

88's and 6550's require a bias supply voltage 10V more negative than 34's. This is why you got to make the resistor change on most amps to compensate for the change in bias supply. When you made the change to 34's your voltage will increase by about 10V on the bias supply and subsequently decrease by 10V on the plates, cathode and screen. See?

Steve

 

[ttosh]

88's and 6550's require a bias supply voltage 10V more negative than 34's. This is why you got to make the resistor change on most amps to compensate for the change in bias supply. When you made the change to 34's your voltage will increase by about 10V on the bias supply and subsequently decrease by 10V on the plates, cathode and screen. See?

Steve

 

[mightywarlock]

Here's something I'm not exactly understanding here.

So...the Uberschall, is EL34.

The Twin Jet is KT88, but with a change can go to EL34.

So...if you take your Twin Jet, and make it EL34, couldn't you have saved some money and just gotten the Uberschall? I guess you lose the Presence and Depth that way...but...

I guess my real question is...
Is there really that big of a tone difference between a Twin Jet EL34 and a regular Uberchall?

 

[Mailman1971]

Here's something I'm not exactly understanding here.

So...the Uberschall, is EL34.

The Twin Jet is KT88, but with a change can go to EL34.

So...if you take your Twin Jet, and make it EL34, couldn't you have saved some money and just gotten the Uberschall? I guess you lose the Presence and Depth that way...but...

I guess my real question is...
Is there really that big of a tone difference between a Twin Jet EL34 and a regular Uberchall?

I was thinking this same question myself.
Or are there more tweaks to the TJ that the Regular Uber cant touch?

 

[DEWD]

Channel 1 on the TJ is completely different from any other version of the uber.

 

[steve_k]

What he said up there....

Channel 1 of the Uber is a clean channel. Channel 1 of the TJ is downright nasty and tasty. Channel 2 is similar to the Uber. Except, now you got the power section EQ control with depth and even more feckin presence (my favorite part of a Bogner) to kick it in the ball. The depth control will really test the back door of the cab and your speakers.

Steve

 

[steve_k]

What he said up there....

Channel 1 of the Uber is a clean channel. Channel 1 of the TJ is downright nasty and tasty. Channel 2 is similar to the Uber. Except, now you got the power section EQ control with depth and even more feckin presence (my favorite part of a Bogner) to kick it in the ball. The depth control will really test the back door of the cab and your speakers.

Steve

 

[steve_k]

there's an echo.....

 

[glip22]

there's an echo.....

Dude, I think you chewed on a few too many of those Psilocybins.

 

[ttosh]

I went with the Twin Jet because Channel 1 tones in the Tone Merchant Video sounded nothing like any Uberschall I had heard and I like the Shiva and heard some of it in there. With EL34's it is that much sweeter of a channel. It still cleans up well with a volume knob until you get pretty loud, then it has a bit of spank to the clean, but still workable. I guess Channel 2 is pretty much the same with a bit more tweakability with the depth and presence at the power level and presence at the pre level as well.

I am definitely not concerned with saving money at this point as this amp has finally taken away my amp gas. I can still say that and as much of an amp flipper as I am that is a big thing!!!

 

[glip22]

I went with the Twin Jet because Channel 1 tones in the Tone Merchant Video sounded nothing like any Uberschall I had heard and I like the Shiva and heard some of it in there. With EL34's it is that much sweeter of a channel. It still cleans up well with a volume knob until you get pretty loud, then it has a bit of spank to the clean, but still workable. I guess Channel 2 is pretty much the same with a bit more tweakability with the depth and presence at the power level and presence at the pre level as well.

I am definitely not concerned with saving money at this point as this amp has finally taken away my amp gas. I can still say that and as much of an amp flipper as I am that is a big thing!!!

You, an amp flipper. Nah!!

 

[TheMagicEight]

Channel 1 on the TJ is completely different from any other version of the uber.

+1

 

[steve_k]

there's an echo.....

Dude, I think you chewed on a few too many of those Psilocybins.

Grow season's over.....

 

[glip22]

there's an echo.....

Dude, I think you chewed on a few too many of those Psilocybins.

Grow season's over.....