Champ KT88 PT choice ?

[worth]

Hi evereyone.. can someone recommend a Hammond PT that would be right for ( A ) Champ with one KT88 , and (B) Champ with parallel KT88's ? I've got the Doberman/Heyboer 20 Watt SE output transformer , and an old Bandmaster PT , which I believe would be okay for one KT88, ( not entirely sure ). Thanks

[worth]

Well , after doing some reading , maybe the Bandmaster pt , with a HV secondary of only 325V, wouldn't be the best choice for a KT88.

[thermion]

also consider the huge difference between what voltage the plates want to see (500-600) vs. what the screens want to see (250-300). voltage doubler power supply or seperate supplies for screen and plate are options.

[rzenc]

KT88 spec sheet says it's similiar to 6550: see attached gif file.

Hope this helps.

Best Regards

Rzenc

[bigdaddy]

I looked at the tube data sheet. For SE class A operation operation most tubes say much less voltage for a power tube, the KT-88 did not provide that information, only push pull. But in reality it really doesn't matter all that much. It's more if the PT can handle the tubes in terms of amperage on the heaters which is 1.6A for a KT-88. How much can an original bandmaster PT handle? I wouldn't push it with 2 KT-88s. New replacements should be able to handle it as long as you don't have too many pre-amp tubes.

For one KT-88 that tranny should be fine. I have the same amp but use a Hammond PT and the doberman OT and it sounded great, too loud to really use now. I forgot which Hammond is in there but I think it's 300-0-300.

As for using 2 KT-88's in an SE amp I think that's kind of strange and going away from what a SE Champ amp is as a guitar amp. As it is your really aren't using even one KT-88 to it's full potential and the size of a PT for 2 would be expensive and heavy. I can see using a KT-88 or a pair of JJ 6V6 or even a pair of 6L6GCs, switching them back and forth depending on how you feel. For that matter with that OT it has different taps so you can use any tube or tubes you want, KT-66, KT-77, 6550, even a 7591a which sounded pretty goo to me. That would all work great with the Bandmaster PT and the Doberman Heybore OT IMO. I think in any configuration the amp would sound awesome. There are so many things you can do with an amp like that. I have made many variations with different power and preamp tubes and preamp designs.

[bigsbybender]

That Bandmaster PT will work. Something with more High voltage and current output would maximize power output. It's a crapshoot, whether the old Schumacher Bandmaster tranny can handle the heater current. I've stuffed 6550's and EL34 current hogs into old Fender amps and gotten lucky. I'd measure and compare the voltage drop from the original 6L6GC to the other tubes. If the heater voltage stayed the same in comparison, I'd consider it ok. If the voltage noticeably dropped more than .1v, I'd err on the side of caution and not use those tubes.
 So it comes down to your goal. Do you want the kT88 for it's tone or maximum power? The Bandmaster tranny will not eek out every last watt out of the 88's but it should work. If heater current is a concern, use the center tap off of a radio shack 12.6v transformer to heat one of the tubes.


J.

[rzenc]

I don't know how much current a Bandmaster P.T. might be able to handle on the H.T. winding... maybe 250mA's D.C.?
However, 6L6GC chart calls for 0.9A's for heaters, so 2x6L6GC = 1.8A's plus 3 or 4 little bottles which needs between 0.9A's ~1.2A's adding all them together we get 3A's for heaters... If you plan 1xKT88/6550 + 2 small tubes = 1.6A's + 0.6A's = 2.2A's. 2xKT88 = 3.2A's. No room left for small tubes.

Hope this helps.
Best regards,

Rzenc

[worth]

Thanks for the replies. I was thinking of using the Bandmaster PT for one , ( not two ) KT88 , but then again , I probably need a PT with a higher secondary voltage to get the most out of that tube. I've built a 2X6L6 parallel Blackface Champ , with an Allen PT and a Hammond 125ESE , that I really like , but I'm still thinking................