Phil here, introducing myself and my plan`

[pjd3]

lucky for me I'm keeping my first build simple, may not even use all my preamp tube holes. But definately good to know that there room for more in case. (incase of what I wouldn't know, yet).

Hey, surprised to see there are still yellow Mallory 150's in stock. I was expecting to see white. Not that it matters much to me but, thought yellow may have been getting thin. Just got those from vintage fender amp repair with a handful of preamp cathode resistors. I measured them and it was nice to see that they were all .5% to 2% tolerance, with a few at 1%. The claim was that things go better with tight cathode resistors and I was convinced they did measure and sort as claimed. May round up for an assortment of F @ T filter caps. I decided to go with individual even though there is a cap can hole in the chassis. Should be a fun task figuring out how to arrange those.

Have a great weekend everyone, thanks,

Phil

[Lynxtrap]

And I'm really interested in using KT66's for this project. I just like the clips I've heard and everything I've heard about them.

I don't have a Princeton to look at, but one thing to consider: You might want to check the distance between the output tube sockets. KT66's are big bottles.
I was about to put KT66's in a 6L6GC amp, but the Gold Lion bottles almost touched each other so I didn't feel comfortable with it.
I can imagine that it might be even tighter in a Princeton.

[pjd3]

I'm going to check on that right now as we speak. If it is an issue, I would either consider fabricating a means where the KT66 would fit, or Just use 6L6GC. I like 6L6GC and have no complaints there. And even a good set of 6V6's I could probably live with. I don't plan on having a very loud stage volume. Its all good.

Hey, a little question. since a pair of KT66's tend to want a primary impedance of closer to 8K and a pair of 6L6's like to have more around 4K, And, the primary of an output transformer reflects the load impedance of the secondary, is it proper to conceive that with an OT of 8K primary and 8ohm secondary with KT66's, that in putting in 6L6's and using a 4ohm speaker you would provide the 6L6's with a 4K impedance? According to articles and video's it appears you can creating better matches like that if you are aware of how an OT reacts.

By the way, I've been out of action for a few weeks, got in a car accident with a concussion and stitches. Thanks for all your feedback, and I'm back in action.

Thanks,

Phil

[martin manning]

since a pair of KT66's tend to want a primary impedance of closer to 8K and a pair of 6L6's like to have more around 4K, And, the primary of an output transformer reflects the load impedance of the secondary, is it proper to conceive that with an OT of 8K primary and 8ohm secondary with KT66's, that in putting in 6L6's and using a 4ohm speaker you would provide the 6L6's with a 4K impedance? According to articles and video's it appears you can creating better matches like that if you are aware of how an OT reacts.

You can indeed miss-match the speaker and OT secondary tap impedances to get multiples of the specified primary impedance. It works, but isn't ideal. Marshall may have run KT66 into higher impedances in the '60's, but the data sheet curves suggest 4k is a better match at idle voltage around 400-450V plate and screen.

The KT66 envelope is a bit over 2" in diameter, so I would want to have them spaced at least 3" on center.

[pjd3]

Thank you Martin, I guess I was a bit mistaken about the KT66's. I'll need to learn better how to make out the specs on the data sheets. (single vs pair, etc..). I had my eye on the Allen TO26 which has a primary impedance of 7000.

As far as the spacing and dimensions go, the KT's would be touching each other in the chassis I have now unless I get carefully creative in modifying one of the existing holes or, if design and layout permit, placing the rectifying tube in between the power tubes. That would dimensionally allow the 3 large tubes to fit with some breathing room, its a matter of how much and if an electrically acceptable wiring layout is feasible. If that all gets too crazy I'll just bite the bullet and stick with common fitting tubes. The KT66's Max diameter is 2.08" while the GZ34 rectifier max diameter is 1.31".

Thanks for stopping by,

Phil