z rt 66....no choke?

[funkmeblue]

how does z get away with not having a choke or a large resistor on his rt 66?

[Sonny ReVerb]

Probably because the Rt. 66 uses an ultra-linear OT.

...a blend of triode and pentode, in which the screen-grid has a percentage (between 0% and 100%) of the plate's output signal impressed on it. This is the basis of the "ultra-linear" circuit, and is usually achieved by incorporating a suitable "tap" on the primary winding of the output transformer that the vacuum-tube (valve) is connected to.

[M Fowler]

I think because he is running higher voltages than normal.

He is using 370-0-370 to GZ34 recto having 445VDC to the OT at A (B1).

Between B1 and B2 you could run a choke some have in their modified versions. If you wanted to get lower voltages and a different feel like the JTM 45 you sure could run the choke.

He uses a 50uf-50uf can cap some Rt66 have used 40-20-20-20 can cap with 33uf on the board. Between B1 and B2 there is a 27k resistor dropping B down to 306vdc to V1 EF86 which is running high voltage and also the V2 12AX7 has high voltage of 353.

PT has 50 or 70V bias tap our make your own bias tap. Not shown on layout but is in the pictures add a 47pf mica cap between the junction of .15uf/91k and junction of .15uf/82k on the long tailed PI.

OT is running ultralinear taps but I used JTM 45 PT and OT on mine.


Mark

[Sonny ReVerb]

I believe the winding between the plate and the screen of the UL OT acts as a choke. Check out the Bassman 70 or the Bassman 135. They're both UL sans choke.

[funkmeblue]

right on, I've been looking into building a kt66 amp and going ultralinear, I did not know that about the ul windings, thanks. I'm thinking lower voltages than z and an 8k output. Anyone know a good output? would triodes dynaco clone z565 be enough? I'm going to check out them fender schematics, thanks again!

[M Fowler]

I had done some research in past posts as well as other posters had suggestion such as Dyanclone trannies but I decided to do another search tonight and will attach my limited search.

The JTM 45 OT I used of course is does not have ultra linear taps and the JTM 45 PT I used does not have bias tap.

Mark

[funkmeblue]

did you use a choke with your jtm45 output?

[M Fowler]

I did not use a choke. I did have to play with the bias resistor to get a good setting without red plating the KT66s since I did not have bias tap off PT.

edited

I attached a poster's different version using 12AX7 instead of EF86 in V1 it uses a choke and JTM trannies.

Also see this thread https://tubeamparchive.com/viewtopic.ph ... highlight=