Single 813 Amp Build

[W9ZSL]

I guess it's time to dump or get off the pot.  I have an 813 and socket on the way for about the last pieces I'll need for the AM/CW amp project.  There are at least three schematics that I've found all from ARRL handbooks including the classic 1957 job, however a couple are complete transmitters and quite complex ones at that.  I could always just build the final from one and hope for the best, but I'm wondering if anyone has a simpler schematic to suggest?  The exciter isn't an issue.

Plate voltage will be between 1800 and 1900 at 300 MA.  I can use the Pi Output from the 1957 amp since I have both the loading and tuning caps along with the same rotary inductor.  I have a UTC S-22 mod iron so modulating a 350 watter with a pair of 811As is the plan.  I'm going to concentrate on 80 and 40 for starters but with the rotary, more bands are no problem.  Modulator will have a separate supply 1250 to 1500 volts also 300 MA.

I know, this has been off and on for several years as the mind switches off and on and changes channels.  I turned 69 last month and have to do my "dream" project sooner than later before going SK!

Mike

[N2DTS]

Sure you need more then 2 or 3 bands?
Making a 2 or 3 band amp is very easy, and I just use home made plug in coils for the tank circuit.
All it takes is some copper tubing and some banana jacks, no big switch and big switch placement issues.
Looks very nice also.

I wind grid coils on pvc pipe and a small switch will do for that.

The only difference in designs is the grid and screen methods.
The best way is fixed and adjustable grid leak bias and a seperate screen supply with a big wire wound pot and a variac.
That way you can set it up to do whatever you want.

A single 813 is good for 2000 volts at 200 ma in plate modulated service, 300 watts out.

If you were starting out with the homebrew stuff I would say build things modular.
Power supply, 0 to 3kv, 500 ma.
RF deck,
RF control deck (grid, screen, meters, keying, PTT,
Modulator deck,
Modulator power supply,
VFO/exciter.

I have 4 RF decks, 2 control decks, 6 modulator decks, 1 vfo/exciter deck, 3 power supply decks and can use any combo, mix and match. I can also run things as amplifiers, or plate or screen modulated rf decks.

Be sure to build in a screen current overload relay, easy to do, any DC relay, a pot and resistor to ground.
Screen current flows through the relay coil, shunted by the pot (sets trip point) when tripped, screen voltage gets connected to the resistor to ground to hold the relay closed.
Another relay contact can light a light.
A cap across the relay coil can prevent relay chatter.
If you never overload the screen, an 813 will last forever.

 

[W9ZSL]

That variable inductor on the output gives me all the leeway I need.  If I can come up with a relatively simple input circuit, that would be a step in the right direction.

[N2DTS]

The mb40sl does 80 to 10 meters, one knob plus the link input (drive level).
I have one, almost used it on an exciter I am building but its only good for about 20 watts.

Not fond of roller inductors unless its ganged to the plate tune to maintain a set Q, as otherwise you can have millions of places where you get a good match with the Q all over the place.

[w1vtp]

The mb40sl does 80 to 10 meters, one knob plus the link input (drive level).
I have one, almost used it on an exciter I am building but its only good for about 20 watts.

Not fond of roller inductors unless its ganged to the plate tune to maintain a set Q, as otherwise you can have millions of places where you get a good match with the Q all over the place.

RE: National MB40SL - Bob W2ICQ uses that tuner in his 4-250 design and it works very well.  I was so impressed with its performance that I got a couple for my 813 amp.  I also got the MB150 which is missing that little RF choke (hint hint)  Neat design

Al

[N2DTS]

Yes, slick device, good for push pull or single ended, and has a feedback tap for neutralization.
I almost used it as the output of the exciter I am building, 20 watts would be enough.
I always liked link coupling. Real swinging and groovy man...

[W4RFM]

as the mind switches off and on I think that's called PDM. Mike you are a true AM person!

[W9ZSL]

Hey Bob!  Have you found a use for that Hammond Mod Iron we swapped?  Talk about changing a mind!  I sold the one you sent me and invested in the S-22.  So much for planning on building a "scaled down" rig around the 4-65A!  I'm still going to use that tube somewhere.  As for George,  it's going to be an 813 and a pair of 811As.  Tube and socket are on the way.  So do you have a diagram for a basic 813 amp laying around?

[W9ZSL]

N2DTS, this ain't my first rodeo!  It will be modular particularly the PA on one chassis with the tuning/output module just above it along with metering.  I've built more than my share of gear just not recently.

If anyone has a link to a basic single 813 amp I can build, that's what I'm looking for.  Design is not my strong suit.

[N2DTS]

I am not sure why you need a diagram, its all your basic stuff.
813, plate choke, bypass and coupling caps, 300 pf 6000 volt plate tune, as big a loading cap as you can get, B+W tank coil or plug in coil, or home made coil and switch, or roller inductor,  tube socket, filament transformer, bypass caps, grid tune circuit, 813 does not really need neutralization.

There is a diagram for a pair of 813's modulated by a pair of 813's done by K1JJ I think, just replace the modulator 813's with 811's and use one 813 in the final.

The handbooks are full of 813 rigs, one or two tubes, just remove one tube if they have 2.
If you do not need the CW/SSB modes just delete anything to do with that.

[N2DTS]

http://www.amwindow.org/tech/htm/813/813.htm

[VE3AJM]

Mike, I found this one in the 1959 ARRL Handbook. Single 813 amplifier. I can scan the entire write up and email them to you. Let me know.

Al VE3AJM

[VE3AJM]

Another from the 1955 Handbook.

Al VE3AJM

[W9ZSL]

That would be great Al.  W9ZSL@yahoo.com.  Like I said, I have several schematics but all but 1 are for complete transmitters.  I just need a simple amp with a single 813.  I can build things just fine, but when it comes to design, I draw the line.  I'm better at poetry! lol

[VE3AJM]

Check your email Mike

Al VE3AJM

[W9ZSL]

Thanks Al!

[w1vtp]

What?  An 813 amplifier with a "Goose Tube?"