Progress on the 813 amp; not vaporware anymore

[N3DRB The Derb]

there's a complete input cap/coil assembly from a SB200 on ebay. go git it.

[W3RSW]

Thanks men.

Mack, yeah the gridded stuff was meant for layout; I just used it to protect the finish while drilling, especially making the meter holes - jig saw scuffs, etc.

It looked cool in earlier pix but in real life, view was pretty trashy, scuffed up and just enough out of square to annoy.  Not to mention the peeling edges.  I guess if put on very carefully, after holes are drilled and with some sort of framing to hide the edges, it might look ok.  I even thought about using the u shaped binding that you make notebooks out of but couldn't find any 19" long.

[N3DRB The Derb]

Ya done good. I love good homebrew and de-hamboning stuff. It shows a tiny part of ham radio is still alive.

I'll be building a 160 meter monoband amp later this year health allowing. I hope I can find a good example during the course of hamfest season with all the hard metal work done....thinking about tubes.....

It's super bad how some of the personality of the builder shows through in the final results. I've always marveled at that fact.

[W1RKW]

Nice work Rick!!

[W3RSW]

OK boys, done !
(except for a few niggling details..)
like :
have to finish mounting in 32 in.rack, pwr. supply mods., installing breakers properly, etc.

Need to find a couple of coil clips for #12 B&W stock, 6 t.p.i. clearance.  (Temporarily using alleg. clip to find best match. May just solder it up using 5% Ag alloy.)  Anyone have a couple?

And after all the safety issues outlined on site;probably need to get proper Millen HV connectors.  I'll have interlock switch on rear cab. door but you know how it is.....

The front panel's been shown previously so here's other pix's.

Oh and BTW, here's a view through the peep hole.  The negative image is slightly out of focus unless you move your head back 5 or 6 inches. - -  Don't burn your eyes out.  The rear aperture (inside case) of the lens is 11/16 in.  The apertures in the fan's hardware cloth are 3/8 " for that matter.

Thanks for bearing with me on this project and all your thoughtful comments and help.  Probably you can spot some of your improvements.

[W3GMS]

Rick,
Excellent craftsmanship!  Can't wait to work you on 160 with it!
Joe W3GMS

[W3RSW]

Yep, thanks Joe; It'll be fun to work 160 again.  I miss the ol' single 813 "shoebox."

And here we are; ready for first light.
-gotta do the coil tap stuff after trying out the first formula guesses though, and drill the cab. rail to accept the 813 deck's non-standard height front panel.  -the holes didn't line up, heh, heh.  Well every rug's gotta have a flaw.

I see several 813 rigs in construction lately.  Might be a run on the bottles.

[WD4TC]

  Rick, I've been  looking at you 813 transmitter and the progress and got to say Nice Job.I just hope the one I'm building turns out OK....Tim..WD4TC

[W3RSW]

Tim, you'll be done before you know it.
Here's some interior views.

Paralleled a couple of 5mh rf chokes for the screen, 150ma each didn't look too hefty; just one 5mh in the grid bias circuit.

Series wired two audio chokes in the screen, one 8H from Hammond with a 5H on hand. I don't really need to have low f. cutoff at 30hz, -50 or 60 ought to be plenty.
Liberal use of .01/3kv bypasses just about everwhere on power leads, etc. Screen bypasses are .001  - Don't want to0 much or it'll suck down audio highs.
Anything else you need a pix of?

[W2XR]

Rick,

Very nice construction practices and technique! Looks like she'll be a real beauty.

I'll bet she'll sound every bit as good as she looks.

Congratulations and good luck with the new rig!

73,

Bruce

[Opcom]

So, very nice work indeed! Now, with this peep-hole thing going, you must add a small interior lamp for accent lighting, perhaps a 12V automotive lamp (or LEDs) running off the 813 fil. xfmr, so that you can see the innards better. A spectrally narrow deep blue light source like an LED (array) or an incandescent lamp with a dichroic filter would not interfere with the glow of the tubes.

[WA1GFZ]

Rick,
I think the metal around the base of the 813 likes to be grounded. Somebody correct me if I am wrong.  Nice tight layout to the plate tuning cap.
BTW. Keep an eye on the TR7A Mine the carrier drifts up as it warms up. maybe 5 watts won't be an issue but at 60 watts it is when I drive my class e final.

[W3RSW]

Francie,?)
I used a brass clip and grounded the 813 in the ol' shoebox xmitter.  None used so far in this twin 813 rig.
Found no difference in stability. Recall that an 813 has an internal bottom shield disk made of nickle.  Interesting that in some bottles the external shield is wired to a pin. Not so in the 813.

Also I notice in the RCA literature 813-4-55, 7 pages (1955) that all interelectrode capacitances are referenced with, "with no external shield and with base shell floating." Cgp 0.25pf, Cg1 to fil&g2&g3 16.3pf, and Cout 14pf.

It certainly wouldn't hurt to ground the base shell but would call for re-neutralization if I were to do it. Glad I wasn't shooting for 10 meters, Cout might be close to unobtanium using the traditional pi. net and base shielding.

I'd be interested in any literature recommending or definitely requiring grounding of the base shield in an 813.

Also I see in many designs that the base shell is sunk in the chassis which is a design requirement for some tubes, (Eimac's "Care & Feeding..." )but not the 813. If Screen caps., grid caps, etc. are grounded to common point, socket above, at or below chassis are fine. In my design, sockets are above a large hole allowing for a % of air flow to come up around the pins, fan blowing out the rear of the cab. In the 1962 ARRL h'book for example, two 813 rigs are photo'd, neither with base shell grounded.  One design shows raised socket, other at deck level.

Regarding shielding, many forget that a large ceramic socket might as well be a large hole anyway. - as well as the ceramic base of the 813 itself.  That's why it has an internal shield.

The maiden voyage was Feb. 24 on 3733kcs. Also loads up fine on 40 and 160. Po's range from 350 to 370 output, no instabilities.

I like the illum. peep hole idea; also thought about a neon pulsing in time with the audio. ...   But then might be too CBisih?