Progress on the 813 amp; not vaporware anymore

[W3RSW]

Construction pix as of today.
Large parts placement complete and temporarily installed on plastic chassis overlay.  Most large holes and cutouts done, just the little stuff to go.  That'll be at least 50% of the work. Plus the wiring.  Still designing the input circuit. Probably will be separate coil/cap. for 160, 75 and 40; not like my single 813 rig, The  "Shoebox" which had one tapped coil and dual 365pf for tuning.  I need to get a decent plate choke; note the homebrew one wound on an oak broomstick handle.  Ho.ho. Well it worked ok on a single 813.

I'm leaving room in front left of deck behind the meter shield for a separate xtal osc. and buffer amp/driver  which may be installed after I play with the amp for awhile lashed to the Drake TR7 for carrier driver/receiver.  Mod drive is provided by a 25 watt PA amp into currently 811's soon to be triode connected 813's.

Iron from left to right is screen audio choke, bias fil./ Ry voltages(OA2 in front) and Raytheon fil. xfor for 813's.  The "Ray" is too big so will be buffered down with a 50 ohm, 50 watt r. in primary.  The bias will be OA2 for neg. 75 into grid resistor for next -75, a la K1JJ.  The 7kv tuning cap is under the quad loading cap (from some ancient TRF radio?)  Boy they sure don't make radios like they used to.

This deck will go into the top of the 32" rack that I picked up at Howard Co. fest a few years ago.  Power supply and modulator mostly done.

Can't wait to get this on 160 particularly in such a lousy 80 meter season. Shoebox is not working now since I "borrowed" a few components.

Rick

[John K5PRO]

Nice work, great looking layout there! Gud Luck with her, I think you got a decent project there.

[WA1GFZ]

Very nice but a suggestion. Swap plate tune cap with band switch to make distance between the tubes and plate cap short. Stability issue.

[W3RSW]

Thanks John, it's been fun so far. 
- And 'GFZ', good point. Your wish is my command.

Meters are now on right side; panel simply flipped around. Nothing like symmetrical layout and Ctr. line drilling to make this sort of thing easier. Also the Screen AF choke is simply placed under chassis, same holes looking up with sufficient clearance for plate tune cap (now on posts, rotor will be grounded of course.)

[Steve - WB3HUZ]

Hey, none of this homebrew talk is allowed on here. We need special section for it.

[W3RSW]

Steve,

Please, Pleeeeze, don't move me to Gary's boneyard.



And as an extra added attraction I now have room on the upper left front panel for a VIEWING window.
How cool.

 I'm now debating between rectangular or round with screen. Didn't they used to make screened hole fillers?  HEh, heh,

[Steve - WB3HUZ]

The round holes will give your audio a fuller sound, with a much more transparent sound stage.

Steve,

Please, Pleeeeze, don't move me to Gary's boneyard.



And as an extra added attraction I now have room on the upper left front panel for a VIEWING window.
How cool.

 I'm now debating between rectangular or round with screen. Didn't they used to make screened hole fillers?  HEh, heh,

[WD8BIL]

And be sure to use gold plated fuses in your modulator power supply !!

[WA1GFZ]

Very Good! You want the connection from the plate to the tuning cap as short as possible, you are there. I learned it the hard way when I tried to build a Quad 572B linear......Then I visited my high school buddy and his wife in S.F. I bought my first 4-1000A at Ham radio Outlet for $22.50 with socket and plate cap included. New tube.

[W3RSW]

$22.50; those were the days... sigh..  but then I wasn't making $, x20 "new" then either.

Yes, inflation.  ur generic silver dollar, one ounce's worth what now?   -Say, $14.50 now since they withdrew the priviledge of trading in paper for one in '63? 64?   And I don't want to even talk about gold. 'Fraid my fuseees will be plain ol' vanella.

Anyway the links from plates to C,neut. will be Cu strap. Links from 850pf coupling cap to C,tune will be strap too.   Then I can 'STRAP."

[WA1GFZ]

you gotta know your crap if you really wanna strap and it don't kum easy....

[W4EWH]

The round holes will give your audio a fuller sound, with a much more transparent sound stage.

Yuck! Jeesh! Have you no mercy?

[W3RSW]

Panel Progress:

Almost all the chassis work, drilling, and parts placement done now.  Panel location of controls and HV/Fil/Main switches done.  Even thought I have a variable timer module on hand, I'm electing to build this Class C amp. with three simple switches, a la 1950's.  First switch, Main 240VAC to fils. and bias/control xfor; Second for HV contactor and Screen voltage; Third for Amp bypass.  Plate HV/screen contactor in a lower panel  will have step start, however.

Unique feature is the optical peep hole shown in front in the pix (panel upper left).  It's a negative lens that shows a lot of the compartment when viewed a few inches away. Yeah, couldn't bring myself to chop a large cutout, add screening, but the first 2/3 of an old Cook lens looked like a nifty way to go.

Rick

[WA1GFZ]

RF will cook your eyes so don't look into it too much

[KB5MD]

What is the finish on the front panel?  It really catches the eye. 

[ka3zlr]

I spy, the RF in my eye...Not gud...

[ka3zlr]

i have another opinion to add to this,.  that by far is one of the biggest failings of this department..RF Safety..or lack of concern for...That picture should be pulled...This Forum is read by millions of people, and the chance of someone seeing something like that and sitting back and thinking Hey I could do that too, and Key the damn thing and put his or her eye against it...Lord forbid something like that happening...

I know we know the RF guidelines, "Us Here"...a board should be put forth on this forum to watch for such things...I can't stand by and watch this...I have to speak up...


jack KA3ZLR.

[W3RSW]

All too easy to jump on the sacrosanct safety Gods.  Not too worried; middle element of a Cook triplet is leaded flint glass.  Anyway, as I mentioned before, you don't put your eye right up to the lens; it won't focus.  Viewing distance is sort of like a rifle scope, several inches, shows a wide angle view of cage behind.   And the 'hole' is about 3/4" ; Don't think too much RF at 160 meters is going to radiate any more than some 4 x 5 viewing widows on 4x1 rigs I've seen, even those screened with 1/4" hardware cloth.  I guess the operative, scary word must have been "peep hole."   And how about all the 211 to 100T breadboard rigs so proudly displayed in QST, this page, ER, etc?   Just because a 'hole' appears at a panel doesn't mean that suddenly the whole 1kw is magically focused to and re-radiated from that point.  Jeeze, think about it even if you don't re-derive Maxwell's equations.

Reminds me of every PCB and Asbestos scare I've worked with over the years.  The original PCB regs. were written for workers in the friable PCB industry and exposed to dust all day; an act that's since blossomed into an entire Lawyers relief act for every sniffle an errant piece of siding around.
     PCB's have never been proven to cause cancer; some of the original, pre-political literature has posited that the Zylene carrier was actually the culpert... and at  doses that would kill the average mouse from the liquid quantity alone. . Don't get me started on alarmist safety regs.... some of which for the gas and oil industry I'm ashamed to say I helped originate. 

BTW if you all want calc's for a 1" aperture, essentially a hole in an infinite screen with an at most 1kw RF environment behind it, shouldn't be too hard.  We're not talking original point source here, not even inside the RF cage itself. ( Optics 101/  E&M 201, you name it.) BTW I have run the radiative equations for the antennae at 'this here' shack using the ARRL's very cursory graphs and formula but good enough for the log. Wonder how many of us have done that?

[WA1GFZ]

RF density of 10 mw per cm squared is considered a problem 1 KW - 50 dB are you feeling lucky
I remember when the motorola training movie when they cooked a rabbit's eyes with low power......Hopefully they cooked the whole animal so he didn't suffer blindness

[Steve - WB3HUZ]

1 kW radiating from an "antenna" with -50 dB gain doesn't generate much density. And it still must make it through the tiny (relative to the wavelength) hole in the front panel. Add in the leaded glass, the field at the front panel is about zilch. Much ado about nothing.

[W3RSW]

Hmmm, I must do a little more research.
Interestingly RF at 160 meters has a very low energy fraction compared to microwaves.  Yes, I know quite a few research grants have focused (pun intended) on radiation in the last several decades, so I must ask, how long was the rabbit exposed, at what wavelength, intensity, etc.? I am interested in research of much lower frequencie's biological damage.

... But & oth, light waves at a much, much higher energy fraction than microwaves do damage (e.g., cataracts) only over many decades, given at much lower intensity.  Yes, different waves for different effects; cooking protein at microwaves vs. enjoying a lifetime of sight with visible light waves including enjoying the sight of two filaments lit with an occasional glance..... (you won't see any plate glow in a graphite 813.  I suppose the casual SSB'er passing by the rig operating at a hamfest would be curious.)

   Ah yes, microwaves, quite a peak in the ol' biological damage vs. freq. chart, eh? Yes, dangers abound in this present world. HV I quite respect.  Immediate effects, of course.   Oh, I almost forgot, the lens cell is 1/8 in. thick, leaving a glass aperture of 3/4".  Now I know that some texts and manuals say that apertures should be no more than 1/4" for reasonable practice, usually rigs expected to be operated on 10 meters? How much 160 meter radiation escapes from a 10 x 14 x 17 enclosure through a 3/4 hole anyway? How many rigs have you seen with no meter shields?  How many bald headed hams can attribute their 'loss' to this?

Well, methinks me doth protest too much...   ya' must have hit me nerve.

[W3RSW]

Almost forgot to respond; Mack, your right. The panel material is exactly that, from a roll of gridded, plastic masking for laying out punch holes.  In the picture angle taken with back reflection of the camera flash it looks pretty good. Kinda like those wonderous shots on Epay.  But looked at head on, in real life with natural light, it's pretty crappy.  Looks just like cheap plastic. Not exactly square, at that.  Too bad; it really looks good in the pix.

Thinking a little more; most of the RF is going out the wire; E&M field from the coil is inside the case. Since it's pretty much a diameter from most metal and sidewalls the circulating currents are pretty much 'unmolested.'  Be interesting to see what the real RF field is inside the cage, given that most power is directed up the line, with remaining 30% dissapated as infrared (heat.)   

"Up and Out" -Yeah, we're all sitting in the near field on 160.  Might as well sit inside the cage

[W3RSW]

Getting ready for Heavy Metal Night.  Very close to being finished.

Here's the mod. deck and power supply getting ready for RF deck to be placed above.
Will try the 811a's first and if not enough strap will go with triode connected 813's. 

The 811a's are on a little sub chassis on posts that can be changed out with 813 sub-chassis extending into blank space between mod & pwr. supply section if required.

- As seen from the back of the 36" rack pix;
and In front of 811's are left to right:
 20w backwards AF xfor. from Fair Radio (driven by a PA amp w/3 section tone controls); 811's fil. xfor.:  BC610 mod iron behind the 811's.  Middle of pix shows screen xfor, screen filter choke below it; P. Dahl hypersill plate xfor in right rear. with filter choke(tan) in front of it.  HV contactor; step start relay and delay circuit in right front of pix.  All this stuff already proven on the single 813 'shoebox' rig shown some years ago and still on HUZ's website.  Pretty sure it will work fine on twin 813 rig up to a certain power point.

 Well I'll definitely have over 250 watts (already had that with the single 813 come to think of it,) and am working mightily, component by component to achieve the 250 lb. goal too

Looking forward to great Christmas and New Year's operating season.
Uh, ok, would you believe Dec 29?

[W3RSW]

Dual 813 rig's about finished. Here's a view of panel.

Finishing up input coil circuit. Found that a 3 turn link best matches 40, 4 turns on 80/75 and 5 to 6 turns on 160.  Simple method used in finding best match; temporarily wired in about 4k load representing grid of 813's, fed 5 watts or so from the TR7 and tapped/tuned for lowest SWR. Wrote down the 'drive' settings.

Will use same method to pre-set the PI-net output circuit; Temp. add 2k load non-inductive resistors from tube side of plate coupling caps to ground (no tubes in socket) and back feed a few watts from TR7 for lowest SWR on TR7.  Guess there's some advantages to having a very picky 50 ohm SWR foldback solid state final in the TR7.
"Let the 'foldback' do the walkin' "   

 Well, that will get the pi net preliminary settings so I can start neutralization.
Will isolate the output on the other side of the plate coupling cap, add the two k to ground at that point to represent the pi-net load, then feed a very low signal into the tubed circuit, (fil's. and bias on, no hV or screen voltage) and set neut. cap. for lowest feedthrough to a receiver (attenuated as necessary.)

Then I have to go back into supplies in base of rack and add breakers and finish wiring, and build a rack support with differernt clearances.

[Steve - WB3HUZ]

Very nice Rick! Can't wait to hear it on the air. You'll likely break my S-meter.