Mandate from the Tron

[N2DTS]

One 813 does 300 watts carrier out easy.
2000 volts at 200 ma.
10 K ohms.

[KA2DZT]

One 813 does 300 watts carrier out easy.
2000 volts at 200 ma.
10 K ohms.

I have a single 813 with about 1900 volts at 200ma but only get about 220 watts out.

Fred

[N2DTS]

380 watts in.
220 watts out, 160 plate dissipation more then you should have on an 813 that is rated at 100 watts ccs or 125 watts icas.
Very inefficient.

2000 volts and 200 ma is 400 watts in, 300 out, 100 watts plate dissipation.
That is about 75% efficiency.

One 813 does 300 watts carrier out easy.
2000 volts at 200 ma.
10 K ohms.

I have a single 813 with about 1900 volts at 200ma but only get about 220 watts out.

Fred

[KC2ZFA]

Thanks guys, I'm hoping within a year I'll be on the air.

I want to thank Brett, Phred, 'INR, Ron, Dennis G, and others who have sold me stuff over the last couple of years I've been tinkering.

Peter

[KA2DZT]

380 watts in.
220 watts out, 160 plate dissipation more then you should have on an 813 that is rated at 100 watts ccs or 125 watts icas.
Very inefficient.

2000 volts and 200 ma is 400 watts in, 300 out, 100 watts plate dissipation.
That is about 75% efficiency.

One 813 does 300 watts carrier out easy.
2000 volts at 200 ma.
10 K ohms.

I have a single 813 with about 1900 volts at 200ma but only get about 220 watts out.

Fred

I was thinking the same, should be more output.  I think the plate voltage is not 1900.  I have to take an accurate measurement.  Also, I have a mod reactor in line that is 280 ohms, at 200ma that's a drop of almost 60 volts. The screen current is from a dropping resistor, so it runs through the mod reactor also. Then the current runs through two plate chokes that have some resistance where the plate voltages drops more.  Another thing is that I'm measuring the cathode current which includes the screen and grid drive currents.

I just reworked the plate supplies so I need to do some measuring.  Could be the plate voltage is around 1825 and plate current alone is only about 180ma.

1825 volts at 180ma is about 325 watts input with 220 watts output leaves about 105 watts dissipation.  This could be about right.

Fred

[K1JJ]

Class C 813s really come to life when the plate voltage is above 2000V and screen / grid currents are adjusted accordingly to match specs.  Even 2500V is not too much.  

I have run 3KV on my pair. If plate modulated, run deeply into class C, almost class D - and plate loaded to maximum, gives an 800W to 1KW carrier, modulated at 130%.   I usually run spec screen current - and a little over spec for the grid drive. A little more grid current helps the positive peaks.   This assumes your mod iron can handle the extra voltage and power.  Back everything off and you have plenty of headroom and safety factor.

I think 813s, even though officially rated at 125W dissipation, are more of a 175 watt amateur class tube - and can do even more with lantern chimneys and air.  I always add some air to them. The tubes last forever. I've never lost an 813. (Run the carbon plate 813s with NO plate glow.)  Air helps to increase this glow threshold level. The filament is overrated and emission is robust for a "125 watt" tube.

Build well and tweak the tank circuit and operating parameters for maximum efficiency. 813s are incredible tubes in the proper class C environment, just like the 4-1000A.

The 813s X 813s (with modulators triode-connected) are one of the cleanest THD/IMD plate modulated rigs I've tested, even at 3KV.  Be sure to run a clean audio driver or all bets are off.  I prefer the solid state MOSFET design by WA1GFZ.  This way, audio is totally transformerless except for the mod transformer. Add at least 6dB of audio negative feedback and it doesn't get much better than that for tube rigs.

Phil - Sorry, but I have no additional documentation for the 813 AM rig schematic  posted on  the AM Window.  Continue reading the old handbooks and you will eventually learn enough to build this or any project from a schematic. Axe lots of questions here and on the air.

T

[N2DTS]

Very interesting about the 813 intermod.
I have never run them as modulators, but know they loaf along at 700 watts carrier output for a pair.
I have had the same two 813's in my rig since it was built 35 years ago, and about six good tested spares.
I bet I got most of them at fests for under $10.00 each.

[KA2DZT]

I took some accurate measurements,  plate voltage at the B+ end of the mod reactor is 1800 volts.  Voltage drop through the mod reactor and plate chokes (about 300 ohms x 225ma) is about 70 volts.  So, I have 1730 volts on the 813 plate and loaded to 190ma plate current is about 329 watts input.  I'm getting about 220 watts output (Bird watts).  This leaves 109 watts of dissipation, looks about right.

Fred

[ka4koe]

Good numbers; thanks. What is the current state of availability of 813's??

Philip

[N6YW]

Good numbers; thanks. What is the current state of availability of 813's??

Philip

813 are still available but do not buy online unless the person is a known seller of good tubes. I would never buy tubes on Ebay. If you need a good supply of 813's then inquire here and PM from there. You will find them. If I may, here are my words on the subject:

The ART-13 is perhaps one of the greatest transmitters ever designed, and for it's size and weight is unbeatable with the proper power supplies. The 813 tube is one of the reasons, and with that in mind, you cannot go wrong with building a TX with the 2X2 813 format. The iron is out there. Do your homework, decide on your design and parts needs and go from there.
Concentrate on one element at a time, such as power supply, speech amp, modulator, rf deck etc. Keep a log of your project and photograph everything. Ask for advice and help and always work with one hand behind your back when HV is present. The most rewarding aspect of this hobby is rolling your own... and it can also be your biggest supply of disappointment if you don't plan your work, and do so carefully. Triple check everything before you commit, and this is especially true for parts placement, lead dress and building practices. If it's worth doing once, it's worth doing right. Make it a legacy project as it will likely become one of your greatest triumphs that brings you years of enjoyment. Big or small, make the effort worthwhile.
I own 4 major transmitters and a couple of nimble band cruisers. ART-13, GK-500C, BC-610-E, and a Harris BC-1H. I have repaired and or restored all of them with my own hands and nothing has brought me better joy in this hobby (BC-1H is currently being modified) than doing this.
And, like was mentioned earlier, recycling and/or reusing, updating previously built transmitters as built by SK is a great way of gaining useful experience not to mention bringing something back on the air. That is fun unto itself. Whatever it is you decide to do, do it right and make it fun. Be yourself and blaze your own trails.
 
Billy N6YW

[Steve - K4HX]

Yep. Both a power transformer and mod tranny have been available in the For Sale section within the past few days.

[ka4koe]

Need to get my Bushmaster out of layaway and then we will start collecting parts. I think I will roll my own 813 rig. Lots of good inflammation here!

FEELEEP

[ka4koe]

Latest shack configuration video....

https://www.youtube.com/watch?v=TI3hOq8TlOk

[KD0HUX]

Latest shack configuration video....

https://www.youtube.com/watch?v=TI3hOq8TlOk

Nice station