01-27-2017, 06:55 PM
To elaborate on what Mike said...
If you really want a reliable 89 or 19, switch the 36 tube for a 6A7 as outlined here.
However, that is taking things to unnecessary extremes. Usually, an 89 or 19 can be made to work with the stock 36 tube. You have to do the following:
* remove the oscillator coil and bake it at 200 degrees for 30 minutes; preferably before rewinding the tickler winding which is always open;
* reduce the value of the 15K resistor between the oscillator tickler winding and ground to 10K or even 7.5K;
* replace the mica cap in parallel with the same 15K resistor with a new 680 pF mica or C0G/NP0 ceramic cap.
If you really want a reliable 89 or 19, switch the 36 tube for a 6A7 as outlined here.
However, that is taking things to unnecessary extremes. Usually, an 89 or 19 can be made to work with the stock 36 tube. You have to do the following:
* remove the oscillator coil and bake it at 200 degrees for 30 minutes; preferably before rewinding the tickler winding which is always open;
* reduce the value of the 15K resistor between the oscillator tickler winding and ground to 10K or even 7.5K;
* replace the mica cap in parallel with the same 15K resistor with a new 680 pF mica or C0G/NP0 ceramic cap.
--
Ron Ramirez
Ferdinand IN
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