The AM Forum

I am getting back to work, when I can, on the 813 rig.  I mounted the modulator chokes and mod tranny on a "platform" of plexiglass.

Finished it all up and went to see how it looked in the rack.  I can barely lift it!  Must be better that 100 lbs.  I CAN get it into the rack but only with careful prep and moving just so so as not to blow out the back. 

It is just heavy enough where I am waiting for the "boing" in the lower back.  Luckily I put rails in the rack otherwise it would be impossible.

Rich

more..........

Rich,

Pretty slick - I like the way you mounted the audio iron on the Plexi so that the bolts do not touch the chassis.

Is this the rig you will use with the GFZ MOSFET audio driver?  The 813 modulators are triode-connected?


Weight can be a BIG problem when racking it.  There are mini lifts available with wheels using hydraulyic hoists, something like an engine hoist.  They cost under $300. Using nylon straps as supports, you can position the rigs just like a helicopter does.   The cost of a bad back is much higher.... ;)

I solved my weight problem by making everything modular here. All big chokes and transformers simply sit on Plexiglass and can be pulled out individually. I use rails with a sturdy platform for each level in the racks. I use a chassis just for the small air sub-chassis for the finals - everything else gets mounted by itself.  The front panels can be tilted forward for servicing. The broadcash style of building has its advantages.


Hope you get it running FB soon, OM!

T

Looks very nice !

changing coils on the exciter looks like a death-defying act.

73 de Peter

Tom,
     Yes the GFZ driver is under the mod deck, I will try to get a picture.

Peter,
   Yeah, changing coils would be a pain.  I plan on using the exciter only for 75m and having a switch on the back to select and external exciter (rice box) for other bands.

Rich

The iron is as follows??  On right is the mod xfmr, back is fil, left looks like UTC iron - mod reactor(s)??

I'm going to be running into the same weight issue. My RCA mod trans weighs ~ 80 lbs, the 48 hy reactor ~ 100 lbs fil tans weighs about 15 lbs (Thanks Richeroni K1ETP) So 80 + 100 + 15 = 195 lbs.  Guess I'll be getting one of those lifts too. I'd weigh the stuff to make sure but I'd throw my back out -

Al

GORT, the 813 rig here, I put all the heavy iron on the bottom of the rack, PS transformers and chokes, etc..  The mod transformer is on a separate chassis which has SS audio amp to drive it.  All are connected by HV wire. Didn't want the rack to be top heavy and tippy. I'm figuring the whole rack weighs about 350 to 400lbs. If top heavy, it's an accident waiting to happen.

Built a drawer with similar stuff. Almost 300 lbs. Easiest way to rack it was to place empty drawer on platform made with old hardwood doors atop concrete block. Filled drawer with iron using engine crane. Saves on fingers.

The filament xfmr is underneath, the black one is another choke in series with the two UTCs to form the reactor.  The cap is the blocking cap.

Rich

Wow Rick, nice progress!

You must have gone to Army Transportation School.

That's where you learn how to load 16 tons of canaries on a 8 ton truck. The secret to managing this is to beat on the side of the truck to keep half of them flying ;D ;D ;D

It's always great to see how people arrange their rigs.

Why put the mod iron on the deck?  I always put all the iron in the bottom of the rack and run high voltage wire up to the mod tubes and rf deck.  The hv neon wire is alot cheaper than a ruptured disk or hernia.  The long leads to the plates don't seem to affect the modulation.  Just my two cents worth.

Looks great Rich!

I have found as time has moved along that something seems to have happened with the gravity on this planet. Things I could easily lift 25 years ago now seem more difficult. I may soon search for a planet with a sun less like Krypton's.

Rob W1AEX

Absolutely awesome pilot lamp jewels!
ka7woc  ;)

Plexiglass....Why?

Whats the matter with about 3/4 or 1" of plywood and just letting the heavy stuff sit on it so it can be moved if necessary for changes or repairs? It insulates, cuts and drills easier.. Downside? What am I missing?

Carl

Termites  :D :D :D Sorry, couldn't help myself ::) ::) ::)

Very nice looking set. Next time the weight is an issue, try something like this to help with part of it. I think there are vents near the top of that rack? It is easier to hold the weight with a strap:

http://www.bunkerofdoom.com/kd5oei/psurack1/index.html

I love working with the plexiglass.  It cuts and drills easily and glues super fast, dries in a minute.  I like the way it looks too.

Plus, plexiglass rigs get all the cool names.  ;-)

Tom,
  I have attached a couple pics of the bottom, you can see the GFZ MOSFET audio board in the enclosure.  The toroid is its power supply tranny.

Rich

Yeah but you cant cut plexi with a chain saw and create holes with a .44 Magnum ;D   Im very handy with both ::)

Plywood absorbs moisture. I had a breakdown once in the summer humidity with HV components sitting on wood. I switched over to plastic.

Wow, vely pretty work underneath, Rich. Professional looking.

Too bad you couldn't have a Plexiglas view of that as you operate the rig. Pity such nice work must be sealed and hidden from view... ;)

T

What we need here is some transparent wood!!! :P

Rich,
I don't know about that power transformer driving the audio board. Looks like it would handle six of them. Just kidding, looks great.

Remember my rev A moving the fuses to the positive side of the output FETs. As it is now if a fuse opens the 813 becomes a diode and hauls a lot of current. One thing you could do is add a couple high value resistors between the output of the fuse and negative supply. This way if a fuse pops the grid will pull down to tube cutoff.
Also if the 813s oscillate you might want to put a small cap grid1 to chassis.
The G3 leads look kind of long. I would mount a lug on one of the socket screws and make it a lot shorter. A double nut either side of the lug so you don't stress the ceramic.

Thank you Frank.  That is good advice.  I will leave the fuses on the grid and add resistors (~50k?) from the grids to a negative supply.  I don't have a negative voltage on the mod deck but I can run the finals negative bias to it.

Rich

Rich,
100K at 3 watts should be fine. Just connect it between the output side of the fuse to the negative supply of the audio driver supply. This way everything is in the driver shielded chassis.

A couple of coats of urethane or marine varnish would take care of that. You could even rig up a little NE-2 leakage detector.  Or just put a piece of scrap plexi, Formica, etc on top. The plywood is for strength. My 2M 1500W amp PS has been on 3/4" plywood for over 25 years and none of the heavy stuff is bolted down. The diodes are on G-10 bracketed to the plate transformr, caps are a pair of 12uF @ 4KV oil filled which run on 3800V no load.

Plexi sure looks nice but its not a local commodity plus it doesnt like me anyway ::)

Ahhh ha, Carl, now we know the REST of the story!!!  ;D