The AM Forum

hello all, I'm looking for a quick way to drive the exciter stages of the
Westinghouse MW-2 which require a low-power signal in the 1.8-5 Mc
range (the input 6ag7 stage of that unit is shown in figure 2 below).

Since I have a bunch of 160/80/40 xtals I am thinking of building the
xtal oscillator/buffer shown in figure 1. It is from the TMC GPE-1A exciter.

I have three questions, one question being "am I smoking something funny ?"
The other two questions are on figure 1.

What say the expert pool ?

73 de Peter

#1...If it is old transformer varnish, ground up with something else flammable that you are smoking, then yes. :P

#2...No, they are in parallel to 'tweak the freq' as it were.  The actual ground connection for each crystal is not very well shown, but it is sorta thru the shield of the cable between them, the caps, and the tube.

#3...Sure, why not.  Alternative DC isolation might be in order, but only playing with it will tell.

73DG

my supplier only had flux !


well, the xtal switch feeds the top of the crystal but the bottom of the crystal is
on the braid and the caps to ground are attached to the braid...so they should be
in series  with the xtal ???

Peter

I see...Is the braid bare or insulated from the chassis?  It might just be a way to peak rather than tweak the freq.

Are we geeks?

73DG

The circuit diagram indicates the braid is not grounded except through the
capacitors. Maybe someone with TMC equipment experience can chime in ?

The manual says to adjust the trimmers (which appear to be in series with the
xtals) in order to center the measured frequency on the indicated-on-crystal
frequency after the oven has been in operation for a while.


that's for sure, but I also do this in order to consume the time that I would
otherwise use to watch/listen to the (so-called) news.

I guess I'm really asking if I can use the circuit in figure 1 as a fundamental
crystal oscillator without having to worry about tuning the plate of the oscillator.
The multiplication chain I want to drive was covered in this thread

http://amfone.net/Amforum/index.php?topic=25432

Peter

Why not just use the existing 6AG7 as a xtal osc?  The 6AG7 has been used a bazillion times for that purpose.

in the multiplier chain the 6AG7 is an untuned amplifier and is inextricably linked
(considering my abilities to modify  :-[) to a keyer. So I would prefer to leave
that part intact.

Am I reading the circuit in figure 1 correctly when I say that the xtal tune caps are in series with the xtal to ground ?

And JN, pick a Sunday morning and go to the bazaar area in downtown Athens
(Monastiraki) and look up the store of "POP 22 WATT" (if he's still around).

Kalispera de Peter

Crystals??

YUK!!

Monastiraki has pretty much nothing for radio equipment.  There's one old buzzard with a tiny shop that has some old components and that all I've found.

All that keyer toob does is switch the screen of the 6AG7.  No need for a tooned circuit on the plate of the 6AG7 but you could easily do so.

The MW-2 transmitter system had a crystal oscillator section. It is a very simple system and I'll see if I can get the manual apart to scan it.

The MW-2 was designed to have an output of 2.5 KW on phone. They also had an amplifier 10 KW for it but I can find little information in it.

you can see my MW-2 here...  https://picasaweb.google.com/Captionmarvelous/W2PFYStationPhotos# (https://picasaweb.google.com/Captionmarvelous/W2PFYStationPhotos#)

if you could do that it will be greatly appreciated (in addition to elevating you
to super-Godly status !)