[Johnson] Viking I durability?

[Carl]

it seems like that would be easy to fix with a phase splitter circuit. throw away the transformer. I don't see why a Viking one would be any less durable than any other AM transmitter.


** A phase splitter for AB2 allows better control of the audio passband but requires more power to overcome losses while a restrictive transformer limits the passband. 
As far as durability they survive well when regularly maintained and not modified beyond safe levels.The VI and II were designed to a spec and barely make it.



I wonder what the shortcomings of the transformers 
Johnson used were. Skimped cores can cause overheating which 
may in turn cause failure of the insulation or the 
insulation may have been skimped causing arc overs and 
shorting.


** The driver transformer is very reliable but also very restricted and the only solution is replacing it with a better one. Running DC thru the primary plus audio limits its signal handling. Here is where bigger is better for both bandwidth and power handling.


     It was common for years to design modulators, even in 
broadcast transmitters, on the basis of the rather low 
average modulation in unprocessed or lightly processed 
speech and music.  When fed with a processor that has heavy 
compression or worse yet clipping the whole modulator may be 
overloaded with consequent transformer failure.


** Obviously not the case in the Vikings as the CDC model has an always on clipper yet reliability is no different than the standard model. The driver stage simply cannot supply enough power to go beyond about 80% modulation and above that distortion is 25% and up.


     While the 807S in the modulator seem to be run on CCS
ratings the transformers may still have been in adequate to 
cope with abuse from heavy processing or clipping.

** The mod transformer can fully modulate a 100W carrier but with distortion since the driver and 807's are still the limiting item. About a 80-85W carrier by reducing loading increases the modulation impedance while remaining in AB1.



> 
> Don't know if you are familiar with the circuit but it uses two 6AU6's one as the speech amp and the other as the driver for the 807's. In it's stock from it barely makes enoght drive to do anything. I guess that's why there has beem so many articles on the matter.
> Terry N3GTE


** I strongly suggest that those replying at least look at the schematic before commenting about the audio. And also having the 3 ER issues handy to see what can be done that actually works and is not piecemeal as are so many other mod articles for these rigs.
I did an as built evaluation of my V-II after overhauling, then the Stage I mods in the ER article, and my own take on a part of the Stage II mods.
Since the CDC has an extra 7 pin socket for the no longer used clipper I took the easy way out and changed the second audio stage to a 6J6 phase splitter driving another 6J6 as the PP driver stage with plenty of power handling capability for low distortion full audio. The 6J6 is a very cheap and under utilized tube that can easily provide voltage or power gain
Test equipment and on the air confirmed that it now sounds very nice.

My V-1 just has Stage I mods as I reduce the RF power anyway to drive an amp and there is more than enough AB1 audio.

Carl
KM1H