The AM Forum

In searching for some projects with 807's I came across the RCC 230L from Feb '63 QST.   Usually, if it was a notable design I would expect to get more hits when searching for it but very few came up.  A few things that stuck out was the HV supply being above the max plate voltage of the 807.  Another item was the L matching on the input to eliminate neutralization.  Is this worthy of pursuing or are there far better versions of this?  Im just fact finding right now looking for some older designs to put my pair of 807s to use or possibly a pair of 6DQ5's. 

http://www.qro.it/amp/schemi/pdf/6302029.pdf

Lot of things happened back in sixty-three that look weird today, don?t think they cared about flogging tubes back then like the 807 although that amplifier uses 807W tubes that are a little harder to come by. I like how they have the plate current meter directly in the HV feed to the amplifier. Let?s put one thousand volts DC right behind a thin plastic shield on the front panel. They also used four 6DA4 tubes for the HV bridge. That was a tube used as a damper tube in old B&W TV sets back in the fifties. Keeping that in mind maybe they should have used 6DQ6 horizontal output tubes and called it new use for old TV Tubes amplifier?

It definitely seems to be a one hit wonder.  The article did mention about getting 4 years of life out of the tubes which makes sense if they exceed the ratings at 50 cent 1963 prices.

There are plenty of articles using sweep tubes which Ill probably consider anyway. 

In the days that the dinosaurs ruled the earth, or maybe at the end of their reign and long before modern power transistors or power fets evolved the 807, 6146 and later 6LQ6 and 6JE6 sweep output tubes were the bomb. Least if you did not have the money for 811 or modern power tubes.
How many of us who were there ran five or six hundred volts on a 6V6? If its not glowing its not going.

The max plate voltage for tubes is more than meets the eye, for example, they are rated for max plate voltage and current at some altitude far above the surface of the earth.  The last I saw was 20,000 ft.  There are other factors but escape me right now.

Hi Jim,

I built the exact affair x 2 and made a few mods. Running 4 parallel old RCA 807's at 1100 V on the plates, 300 V on the screens. No neutralization with heavy grid swamping. I did run simulation of the design in spice and did more pencil scratching then usual, but it was fun.
Run this on CW only.
 

I found an early picture while constructing and testing.
A restored AT1 as exciter and homemade VFO and a couple of supplies.
You can see the 4 || 807's in the center. The amplifier is compact.

1250 volts resting, 1100 volts key down on 6LX6 tubes was my white plate moment.

--Shane
WP2ASS  / ex KD6VXI

What power does that 4 tube affair produce with a given input?  It looks like a nice setup. 

Hi Jim.

Just north of 10 dB power gain, 10 W in 125 W out on 40 meters.
I started out also concerned about the higher than spec plate V, however, the transformer on hand I wanted to press into service. Caution to the wind. Started out at 850 V and with full line service, 1100 V. The plate current is monitored via cathode returns and the grids are heavily resistive loaded. So more grid drive than usual. I made other mods to his paper, but for the most part followed his guidelines. I also collected a large notebook of 807 designs. Must be a 3 inch thick binder from the early 40's to the late 60's. 

This amp was my first RF tube project in 2015. I had an experimental license for 630m before it became a ham band. I needed some extra power for my very inefficient 33' vertical so it could put out a watt or two EIRP. I built the amp on a pine board, driven by a WSPR transmitter. I got a solid 100W out on 630m with a B+ of about 900V. I didn't build the T-R switch circuit since I didn't need it.

The 807s are definitely tough - I had them glowing cherry red a number of times when there was a poor match to my antenna. Never seemed to bother them.

Richard

I've been running a pair of 1625s at 600 volts for a while now, getting about 90 watts out.  One day while tuning up, I noticed a lot of extra power on the power meter.  "Where's that coming from, I wondered ?" By that time, the tubes died and output dropped to zip.  The capacitor across my tuned input choke had shorted, and now the power supply had a capacitor input filter.  The plate voltage rose to over 900 volts.  Lesson learned, conservatively rate your tuned input capacitor.

I wouldn't run 807s over the published ratings, cause I want them to last.  Good luck.

"I wouldn't run 807s over the published ratings, cause I want them to last.  Good luck."

Where's the fun in that? :)

What, and howzabout a gaggle of 1625's (5 for a buck from the surplus guys back then), with kamikaze voltages and lots of oomph out?

That was one of my long-lost builds back in the 60's.

73DG