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67' Bassman Project--KT66's?

1/16/1999 10:00 PM
67' Bassman Project--KT66's?
I'm slowly converting my 67' BLKface Bassman to BLKface specs. Got a nifty one that must have been transitional. I got the AB165 circuit instead of the AA864. Been thinking about tubes for this amp. Was planning on going with the Svetlana 6L6GC, but for awhile in the back of my head them Golden Dragon KT-66 have been bothering me.  
Looking in APittmans book, in his tube descriptions he lists the 6L6 AKA KT-66. Would this be a direct drop-in with just a bias adjustment. I printed out a KT66 spec sheet and notice the Heater draw is a bit higher. Seems with my little tube spec sheet reading knowledge they like to bias out a bit higher also. Anybody see or know any problems I might run into with this.  
I'm not going for any particular sound in general. Just something alittle different. And to play with my curiosity about these tubes. Anybody got some comments on how these might sound?  
1/16/1999 11:15 PM
MJ Harnish

I would check to see if you can fit KT-66's in the amp with the way the tube sockets are spaced since the KT-66's are quite a bit fatter aren't they? It's not a big deal with a Bassman though since I believe the chassis has a couple extra holes punched, so you could just slide on of the power tube sockets over one space to give yourself more space.  
What's the difference in heater current draw?
1/17/1999 1:37 AM

Hey MJ  
My chassis doesn't have the extra holes punched that you mentioned. As for the size I was looking at the picture over at Hoffman's web site--there isn't a side by side but the Golden Dragon look extremely comparable to the 6L6 in size. Now the Groove Tubes look huge next to the GD. Here's the page:  
As for current draw--the GEC sheets I printed out on the KT-66 states approx 1.3A. I believe a 6L6 is .9A if I'm not mistaken. Lookin' at a difference in .8A. I don't plan on using the bass channel, so I could pull the first couple preamp tubes to help make up the difference if need be. But, I'm kinda scheming to do something evil with one or both of those. No definate plans as of yet. I was hoping for some of overating of the power transformer.  
Anybody know the specs of that era?  
1/17/1999 9:11 AM
Benjamin Fargen

Long time no talk.....  
Sounds like you have a good little project going on there! I think your on to something with the KT 66' might get some of that Eric Clapton bluesbreaker tone. He used KT 66's during that era. All the talk I hear about the early Bassmans and Marshall plexis being a similar animal,it might be a fun test. As far as the heater draw, why don't you pull the bass channel 12ax7's like you said, run it hard and see what the temp is on the power tranny. Then do a quick test with the bass 12ax7's back in. The extra heat generated(if any)should be the determining factor. Wouldn't the main 2 amp fuse blow before your power tranny had a meltdown?  
Let us know what you decide to do!  
Have a good one, Benjamin.  
P.S. I have some pictures of my completed Clubman and a new project I am working on. (switchable tweed and blackface  
Princeton preamps with a single 6V6GT power tube and darker Vox style reverb.)  
I'll keep you posted!
1/17/1999 7:59 PM
Michael Tousek
The Bassman heads of the late 60's are great mod platforms. I've got an AB165 silverface, also, though the pot codes show it to be a 1968. I moddded this amp with a Marshall-style output section using EL34's about a year ago and haven't had any problems with the PT. EL34's draw 1.5 amps of heater current -- .2 amps more than KT66's. The PT does get hot, but not so hot that you can't lay your fingers across it. The range of the stock bias supply was broad enough to accomodate the 34's, and I'd guess it would work with KT66's, too.  
I measure around 450 volts on the plates with the stock PT, which to me is a pretty healthy figure. I was reading on another bulletin board, though, that the Bassman's PT is limited in current capacity compared to a Super's. Maybe they were talking about heater current, but I got the impression they meant primary current. This seems a little strange considering that the Bassman was designed as a bass amp -- can anyone verify this?  
I've been toying around with the idea of KT66's myself and would be curious to hear what you think if you decide to use them.  
Michael Tousek
1/18/1999 8:13 AM

I've got a set of the Golden Dragon KT66's in my bassman RI now. I've also got some of the new VA and GT KT66's in a couple of Marshalls. The golden dragons are somewhat similar in sound to the Svetlana 6L6GC only bigger sounding. More bass and high end. With both tubes biased a 35ma the GD's are noticably louder also. I don't have any specs on the golden dragons but internally they look more like a 6L6 than a KT66. I'm very happy with the sound of the golden dragons in the bassman. I've got them biased at 40ma and they give me a very dynamic sounding amp. just my .02 cents. Mark
1/21/1999 8:58 PM
MJ Harnish

Hmmmm.... That brings up the question: If it looks like a 6L6 and it sounds like a 6L6, maybe it is a 6L6? This wouldn't be the first time somebody's "mislabelled" a tube. For some reason I thought I remember some talk a while back about the fact that ONLY the GT and the VA tubes are really KT66's. Not that it matters if you like the sound... :O)

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