[TMC] VOX-2

[Roy Morgan]

On Apr 1, 2009, at 11:37 PM, Telegrapher at att.net wrote:

> Couple of things i've noticed in playing/working on this unit.

Here are my comments, not based on a lot of experience with the things:

> 1: I was complaining about the excessive amount of leakage  from the  
> unit.  ... turning the "XTAL" switch at the bottom of the front  
> panel from "VMO" to "1" or other position that the leakage from the  
> unit went almost to zero.

It SHOULD go to zero.  In crystal position 1 the thing should be  
operating on the frequency of whatever crystal is in position 1.   
There should be NO output on whatever frequency you had the variable  
oscillator set to.

> 2: Drift.  ... i switched the "XTAL" switch from postion 1 back to  
> VMO.  WHAT!  There was a 63 cycle shift in the frequency.

You unsettled the thing.  These are meant to sit on one frequency 24/7  
forever.  No changes.  Even high stability crystal oscillators won't  
restart on the frequency they settled onto after long operation.

>  Not sure why that's happening because all three of the HFO outputs  
> on the panel have some sort of termination on them.

That may be not very relevant.  There is some buffering between the  
oscillator and the HFO outputs, right?  The load should not affect the  
operating frequency much if at all.

>   ...  It happens every time i change the switch position so it's  
> not just a fluke occurance.

You are turning off the variable oscillator and then turning it back  
on again.

> 3: Output.  ...half scale ...  Way more than needed as i only use .2  
> mc to drive the GPE-1 exciter

You mean 0.2 watts, I think.  The TMC transmitters are meant to get to  
full output with 200mw input, and I'd expect most to not need that  
much at all.

> .... according to the manual .9 ma should be the norm.  May be  
> something to that, will have to investigate.

The transmitters and oscillator amplifier states all operate at an  
extremely linear region of the tubes involved, for the conditions the  
tubes are operated at.  So  I suggest you simply set the gains (output  
controls) at more or less the same level and let every thing run at  
low levels.

> 4: Ovens.  My Outer Oven light remains on constantly.

This is not good.  The tripple oven arrangement depends on each oven  
being run at it's stable point.  If the outer oven is not up to  
temperature, then the middle one is taking over and providing too much  
heat.  Occasional, short periods of ON should be happening in all  
three ovens.  You can't expect stable operation if any one oven system  
is not operating correctly.

>    I am measuring one of the inner oven loops open and did indeed  
> find some open wires

Those wires are tungsten or the like and may not solder at all  
easily.  I have a Northern Electronics master oscillator of similar  
sort with mouse-pee corroded heater elements.  I don't know the right  
fix yet.  It may involve a mess of high value resistors spread out on  
some sort of circuit board to replace the defunct heater element.  (In  
the Northern, the heaters are square pads of heater wire all cemented  
together in a sheet about 4 inches square.

Roy

Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073