The AM Forum

The Lew McCoy amp mentioned in another thread has me thinking about building my own.  Mainly for use on SSB.  I have a lot of parts already but not a suitable plate transformer.  I ma thinking a single 813.  I would like to have the unit be complete, the power supply built in.

The article mentions a voltage doubler giving 2300 VDC from 800VAC. 

Anyone have a source for a suitable transformer?

How about the Antek toroidal transformers with secondaries wired in series?

Microwave transformer?

Thanks

Rich

Hi Rich, If you do build the McCoy 813 amp. be sure to leave enough
room for a BIG plate tranny say a 350/400W. That was the mistake I made
my cabinet is going to have to be redesigned.
Good luck.
Gary
KB3WYZ

Good advice Gary, thanks.  What transformer are you using?

Rich

Hello Rich, The transformer I am using for the plate is from a tube TV set.
It has a 5v,6.5, and a 425-425/CT. I'm using the 850vac going to the rectifier
board giving me about 2300vdc.The transformer is only about 90W...To small.
Big 300/400W TV transformers are hard to find anymore, if not impossible.
Did you read my thread, Lew McCoy's 813 linear amplifier?
I was going to wind a heaver plate tranny, but my coil winding machine went
bad :'( I am thinking very serious about cashing in on the project...
I have been having some health issues.
The cabinet I had made by a tin smith, and is very nice. If your interested in the
whole set, I will sell it all at a very reasonable price. Or start parting it out.
If interested let me know and maybe we can work something out.
Gary

Gary,
   I am sorry to hear of your health problems, I hope they are short lived.  It seems that the plate transformer is the missing link in these projects.  I think you should hang on to your project and just keep an eye out for a transformer.

I have a lot of parts left over from an 813 based transmitter project that I did not have the bandwidth for, so I have most of the parts for this linear.

On of the left over parts is a homemade RF deck with two 813's mounted in it.  I plan on using this for the amp.  I have a an (real old!) Hammond transformer purchased from some one here.  It has 880V - CT 880V outputs and is rated for 220 V.A.  Perhaps it is worth trying?  It is for 25 Hz but I understand that is not a problem.  Alternatively I could hold my nose and try a microwave transformer.

Since my R.f. Deck is already setup for two 813's is it possible to use two instead of one?  What modifications would be necessary to the "Junker Amp" design?  Perhaps in anticipation of finding a plate transformer with more strap?

Rich

http://www.ohio.edu/people/postr/bapix/813amp.htm

Here is something using 2 813's Maybe you read this before.
Looks like your well on your way parts wise.
I have thought about micro wave transformers. There are some good youtube
videos on MOT's.
Keep me posted on your progress, if I can be of any help just ask.
Good luck and be careful, that HV..
Gary

Thank Gary,
    I am going to try this transformer first then, when I find that it doesn't have the poop, I will explore other options.  ;-)

I am struggling to find the best rectifier/doubler circuit, given the output of this transformer.  It  has two sets of outputs, two terminals marked 880V and two marked 620.  There is a middle terminal marked 0, can I assume this is the CT?

There are four more terminals marked 0, 1, 2, and 3.  Anyone know what these are?  I have attached a picture.

Given that I want to supply one or two 813's what is the best way to rectify or double these voltages?  The voltage doubler in the article is about 2.8x.

Thanks

Rich 

There, almost done. ;-)

Basic question, The "Junker Amp" does not include any input tuning circuitry.  Why is that the case when I see other designs that include it?

Thanks

Rich

Rich, Looks GREAT!!! That plate Xfmr should pull the mail with ease!
Did you read the link about the McCoy amp?
You have Loading and tuning capacitors. You just run your transmitter's output
to the Amplifiers input. What are you going to drive the amp with? Should be at least 50W
output.

Gary

Because it's either a bad design or was designed when the drivers were tube based and had output tuning networks. Even then, some would claim that having no input tuning is a bad design.

Well luckily I will be driving it with a Drake TR-4CW.  Lot's of room to add input tuning later I suppose.  I wish I had hung on to my B&W coil turret.....  Anyone have one?

Rich

Thank Gary,
     I have been following your transformer woes.  I hope you find some good iron.

The transformer in that pic looks ok but it is only rated for 220VA.  I plan on building the amp but not mounting any transformer until it has been verified to hold up.  It seems there are a lot of variables in power supply design!  Doubler or not, type of rectifiers, impossible to find iron....

Rich

don't overlook control power transformers .... and I don't understand bias against voltage multipliers .... no pun intended

Tank coil assembly complete.

R,

Very perty.... You do good work, especially on the drill holes in the plexie  method.

The ONLY suggestion I'd have is to go to the local Homely Despot or Rude Value and buy so copper fasteners. Then it would look marvelous.


klc

Antek's work very well! They are some of the best trans. for the money.

I renew my concern for method of manufacturing .... a high voltage secondary bifilar wound with only the enameled wire insulation between the windings is inadequate insulation for series.... no problem with the secondaries in parallel 

Some progress.  I have gathered most of the components.  I tested the voltage doubler circuit, at least with no load.  It was ~3150VDC.  I need to add a bleeder as it took 3-4 minutes to bleed down with just the equalization resistors.

I am having some trouble laying out the components, it is hard with the tubes in the front.  The load cap will be under the chassis....

Rich

PS  Looks like attached pictures are not working so you can see them here:

http://s1227.photobucket.com/user/rsoennichsen/library/813%20Linear