[HomeBrew] She's a "whooper". . .

[Dick Foster]

Run the xtal oscillator from an OD3 or OB2 voltage regulator (octal and 7
pin miniature versions, respectively).  That is the least painful solution.
The voltage regulation would be greatly improved through the use of silicon
diodes rather than the 6X4, but the rig wouldn't be pure hollow state then.
You said you don't have room for a choke....  I am kind of fond of using
dual section choke input filtering with silicon diodes in power supplies for
tube rigs.  You have to have enough transformer voltage to tolerate the
voltage drop across the chokes, but the regulation is much better.

Very 73,
Dick W5TA

----- Original Message ----- 
From: "Philip Atchley" <beaconeer at sbcglobal.net>
To: <homebrew at mailman.qth.net>
Sent: Friday, August 05, 2005 6:28 PM
Subject: [HomeBrew] She's a "whooper". . .


> ** Please do NOT cross-post messages when posting to HOMEBREW **
>
> Hello all,
>
> Today I did the first preliminary tests on my "Rockin' '50s MOPA"
> transmitter (6X4, 12AU7 and 6AQ5).  Not having any "proper" rocks, I
> used a 3579.5 KC colorburst Xtal for testing.
>
> I got about 3 Watts out on 80M (80M Loading capacitor needs tweaking)
> and 5 Watts out on 40M.  So that's good.
>
> HOWEVER, Every time I key the transmitter, the B+ takes a "dive" from
> about 360 Volts static to 250 Volts (loaded to 40mA 6AQ5 Plate current).
>   Since the same B+ point is used for both Oscillator and final, the
> frequency takes a bit of a "dive" along with the B+.
>
> Not as bad as a few Homebrewed transmitters that I've heard out there,
> but unacceptable to me!  At least it's "somewhat" stable.  At normal
> keying speeds the chirp isn't too obnoxious, it's that initial "swoop".
>   To be honest, I didn't expect the B+ to drop that much under keying
> (88uF of filtering.  NO room for a filter choke etc).
>
> I'm not sure if it's the high transformer secondary resistance, (340
> Ohms in each leg) or the plate resistance of the 6X4 rectifier (which
> tests good).  Perhaps going to silicon rectifiers will reduce this
> effect, but I REALLY wanted to keep the set entirely '50s vintage!
>
> Anyway, troubleshooting and further work will have to be put aside for
> the moment as I have a friends Collins R-388 receiver here that needs to
> be recapped and overhauled.  That'll give me time to think the whole
> thing through. . .
>
> 73 de Phil  KO6BB
> RECEIVERS:
>     Hammarlund SP-600 (Circa 1952)
>     Heathkit Mohican (Circa 1962)
>     Icom IC-751  (Circa 1982)
>     Grundig S350 (Circa 2004)
>
> Beaconeer's Lair: http://www.geocities.com/ko6bb/
> QSL GALLERY: http://photobucket.com/albums/y123/KO6BB/
> Merced, Central California,
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