Twin Jet- Switch between KT88's and EL34's?

[leib10]

So it seems that the EL34 conversion for the Twin Jet is really popular; however, my tastes are somewhat fickle and I could see myself going back and forth between EL34's and KT88's. Is there any way to rig a switch so that I could change between the two tube types without having to clip off and resolder resistors?

 

[se7en]

If I were you I would try 6550's before those two tubes.

 

[leib10]

I'm not really familiar with 6550's. Are they interchangeable in KT88 amps?

 

[steve_k]

I'm not really familiar with 6550's. Are they interchangeable in KT88 amps?

They are generally drop in replacements for KT88's. The TJ does not have much bias range though. Make sure you buy 6550's with the a current match around the same as the 88's that are in it. Bogner is usually nice enough to mark the tube bias on the tubes when they ship.

If you go to 34's, you will have to clip off the piggy-backed bias resistor. Do a search in here where I posted some photo's if you need to. It is definitely worth the effort. And, yes - you can put a double throw switch in the back with the bias resistors on it. I saw that on the Bogner forum.

Steve

 

[leib10]

Here's another question. My Twin Jet came in today, but for the second time now, V8 was cracked after being banged against the transformer (I think). So I've heard that it's possible to run an amp on two tubes instead of four (at the expense of tone); is this possible with the Twin Jet? It would only be for a few days until a matched quad gets here.

Also, what is the normal range of bias (in mA) for the Twin Jet? It no longer says the bias range on the top of the chassis.