2 x813 Linear Amplifier

[KC4VWU]

I made good on the promise of photos by the weekend; just a little slow uploading by about 2 hrs.

I've been doing a little cleaning and had to dig back a ways to get it. These are some pics of the RF deck. It looks pretty nicely built using good parts. If anyone recognizes it, please pass along the info.

I'm going to add some Millen HV connectors and try to reposition the blower first thing tomorrow morning. After that, I believe this part will fly. Power supply is a totally different story and I'll have some pics of that also.

Phil 

[KC4VWU]

Some inside shots...

[KC4VWU]

Here's where it gets scary ... the power supply ...

[KC4VWU]

You think; a little ugly, but workable. Check this out...

[KC4VWU]

That's an ARC-5 transmitter antenna post for the B+ hookup with ground stud right beside it.  And the B- return they were using is braided cable! 2500 v. @ 270mA  waiting to shake your hand! Party on!

[Ed/KB1HYS]

What's the matter? it's clearly marked "Danger HIGH VOLTAGE" in nice red sharpie.

[N2DTS]

I punched the 4 holes for the 813's last nite, and received my 10v 20 amp filiment transformer in the mail.
I found 16 matching spacers to sub mount the tube sockets, and drilled holes and test mounted a socket and put a tube in it.
The home despot greenlee punch set made the perfect size hole, air can pass up and around the tubes, so I might pressurize the lower chassis with something quiet.

I am going to try untuned input as the antenna tuna in the flex might work fine.
I dug up some spacers for the plate tuning cap to get it the same height as the loading cap, but need to order some vernier drives, I like them as they have scales on them allowing things to be set per band without guesswork.

I am still in the 'round up parts and design stage', with this sort of amp, I suppose its best to leave the HV on and put a relay in to bias the tubes off on RX.
The design I like has two 813's with a 7.5 volt 10 watt zener diode in the filiment center tap, so I might make a string of diodes with the voltage drop adding up to about 8 volts, with a relay that puts a high value resistor in place of the zener on RX.
http://www.raibeam.com/zl1axb/813_amp.html

Power output is high, distortion is supposed to be low, although I dont know how much the unusual tuned input has to do with that.
I just plan on boosing it up with 4 tubes, and plan on getting 100 or 150 watts carrier out.
I have been surprised how well the flex gets out (at times) at 25 watts carrier...

I also notice the flex does not wipe out the TV (at 25 watts) but the 32V3 at 100 watts does, and wonder what power level out of the flex+amp will allow the TV to work....

Brett




 
 

[KM1H]

You might consider the Ameritron drives for their better amps along with the scales and knobs. Pretty reasonable and look nice also.

Ameritron sells any individual part you want for any of their products.

Carl
KM1H

[N3DRB The Derb]

guy dont believe in chokes?

[KC4VWU]

Nope. Two different builders of the RF deck and P/S. The guy who built the P/S is one of those "just make it look good on the wattmeter" types. Supply is bare bones, but I figured I'd have to build another one heavier for AM use anyway.

BTW, has anyone ever used metallic core spark plug wire for HV lines? Looks to be about 18ga.

Phil

[The Slab Bacon]

BTW, has anyone ever used metallic core spark plug wire for HV lines? Looks to be about 18ga.
Phil

If you use the old style (non resistor) type stranded wire like the good old Packard 440 stuff, it will be fine. Dont use the resistor stuff!!

(hot Frank tip of the day)  - - - use the sparkplug and / or distributor cap boots for end insulator covers on porcelain feed through insulators if you cant get any suitable high voltage connectors.  

[N3DRB The Derb]

here is the hot lick. old reproduction magneto wire. copper, cloth and cool kolors.

the red with black tracers is cool as hell, I've seen it in person.


http://www.magnetoparts.com/wire.htm

[KM1H]

The hotrodders/streetrods use copper core plug wires in various colors with red and clear being popular.  Check out Speedway Motors for starters and also JC Whitney.

Carl
KM1H

[W3SLK]

I just use boiler ignition wire. Its just as good and just as flexible.

[Steve - WB3HUZ]

Frank, how much resistance does the resistance wire have? Many HV supplies have a low value resistor on the output for glitches. Maybe the wire could do double duty?

BTW, has anyone ever used metallic core spark plug wire for HV lines? Looks to be about 18ga.
Phil

If you use the old style (non resistor) type stranded wire like the good old Packard 440 stuff, it will be fine. Dont use the resistor stuff!!

(hot Frank tip of the day)  - - - use the sparkplug and / or distributor cap boots for end insulator covers on porcelain feed through insulators if you cant get any suitable high voltage connectors.    

[w1vtp]

I just use boiler ignition wire. Its just as good and just as flexible.

I like that idea.  Wonder where one would get such wire.  Like Bear's suggestion about the boot.  I'll be using HV porcelain in the 813 xmtr.  Nice combination of ideas.  It should manage 2.5 KV plus mod voltage peaks.

Al

[KM1H]

The glitch resistor is sized to survive the arc or short circuit load until the fuse/breaker blows.
A wire will potentially burn apart, possibly catch fire or have a live HV wire dangling into something.

Carl
KM1H

[Steve - WB3HUZ]

Good point. I was thinking out loud, so to speak. That will teach me to go off thinking.   

The glitch resistor is sized to survive the arc or short circuit load until the fuse/breaker blows.
A wire will potentially burn apart, possibly catch fire or have a live HV wire dangling into something.

Carl
KM1H

[W2XR]

Nope. Two different builders of the RF deck and P/S. The guy who built the P/S is one of those "just make it look good on the wattmeter" types. Supply is bare bones, but I figured I'd have to build another one heavier for AM use anyway.

BTW, has anyone ever used metallic core spark plug wire for HV lines? Looks to be about 18ga.

Phil

Phil,

The entire high voltage section of my homebrew transmitter is wired with that stuff; it is known as Packard 440 high voltage ignition wire. I picked up (2) 100 foot rolls of that stuff at a classic car show/swapmeet a number of years ago for $10.00/roll. Your mileage my vary; $10.00/roll was a great price and I should have purchased more of it at the time, even if I've used <100 feet after all of these years! I think the current retail price at your local auto parts store for the Packard 440 cable is now around $70.00/100'.

I use the Panduit crimp-on ring terminals with this wire, to get a nice, clean, professional looking termination. This is what the broadcast transmitter manufacturers did when they wired the old tube rigs with high voltage wire. The O.D. of the Packard wire is about 8 mm as I recall, so the I.D. of the nylon crimp sleeve on the Panduit terminal must be large enough to accomodate the O.D. of the wire jacket.

73,

Bruce

[W2VW]

Automotive resistive spark plug wire has way too much resistance to use in a ham rig.

The other stuff works great and the jacket is designed to survive in a harsh environment

[KC4VWU]

I have a couple pics of the wire. It is made by Belden, so I know it's good stuff. I wouldn't consider it resistance wire; I think that is the surpressor wire that is more commonly used today and is carbon impregnated fiber.

Speaking of plug wires, did you know you could use a vacuum line for a spark plug wire in a pinch? Just keep it from arcing to ground and don't touch it!

Phil

[kg8lb]

 Automotive resistance type wire uses a carbon coated thread conductor. The resistance is around 2.5 to 5K per foot.  There is another type known as magnetic supression wire that uses a monel wire core that is wound like a closewound spring to achieve RFI supression .

  The solid core wire in bulk used to be pretty easy to find on the shelf at the auto parts store. Not so common today. A cooperative clerk can look it up in the catalogs. The last roll I bought was Belden and 100 ft cost $28.00.

 
 

[The Slab Bacon]

Frank, how much resistance does the resistance wire have? Many HV supplies have a low value resistor on the output for glitches. Maybe the wire could do double duty?

Like Dave and KG8LB said, it is not suitable. I dont know for sure what the resistance per foot is supposed to be. But checking plug wires from a car with an ohm meter they usually measure 100-200K.

They also couldnt take the current of a plate supply, they would burn to a crisp!! They are designed for very high voltages (20kV or higher) but very low current. With the high resistance, all of your HV would be dissipated in the wire

[KM1H]

Good point. I was thinking out loud, so to speak. That will teach me to go off thinking

Chalk it off to the AM Dinner and the ride home   You need a few more days to recover.

Carl
KM1H