Progress on the 813 amp; not vaporware anymore

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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?  ;D

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