As a general rule I find that disk ceramic capacitors, regardless of voltage
rating, aren't the best choices in high circulating RF current conditions.
Component tolerance is typically 20% and often worse with heating by RF.
Thus a 1000pf cap can easily change to 1200 pf or drop to 800 pf. This will
certainly change any critical tuning in an amplifier. On the other hand,
I've found that disk ceramic caps work quite well as bypass caps as the
inductance is quite low compared to other designs. (All capacitors aren't
created equal.)
In the door knob series:
HT-57 series is 1.187" D x 1.89" L 10-32 UNF thread Depending on value
price is $32 - $39 ea
HT-58 series is 0.813" D x 0.89" L 6-323 UNF thread Depending on value
price is $11 - $18 ea
The Sprague series:
500pF @15 KVDC 10A RF Price is $25 ea
1.375" D x 1.250" L 8-32 UNF thread
The Hi-Q series:
1000pf @ 10KVDC 7A RF Price $18 ea
1.125" D x 0.625" H body, 1.625" overall w/ studs
Surplus Sales of Nebraska
1-800-244-4567
(I have nothing to do with this company except I that send them
money.........they send me parts.)
73
Bob, K4TAX
----- Original Message -----
From: "Tom K2TA" <tom@k2ta.com>
To: <tentec@contesting.com>
Sent: Monday, March 17, 2003 7:46 AM
Subject: Re: [TenTec] Omni VI & Titan tuning repeatability
> I've gone to Surplus Sales' website. I don't see physical dimensions for
> the various mica/ceramic caps posted there.
>
> 1) Are there archives of old Ten-Tec newsgroup postings that I can search
> through for details on what components others have ordered.
> 2) Is there anyone who can privately e-mail me the list of caps that they
> ordered from Surplus Sales for their Titan..ie. part #'s etc.
> 3) Any "gotchas" I need to look out for when I'm ripping out the loading
> caps? Any suggestions?
>
> Thanks
>
> Tom K2TA
> tom@k2ta.com
>
> ----- Original Message -----
> From: "Tom A" <althofft@concentric.net>
> To: <tentec@contesting.com>
> Sent: Monday, March 17, 2003 8:28 AM
> Subject: Re: [TenTec] Omni VI & Titan tuning repeatability
>
>
> > Without a doubt tuning drift is caused by the fixed caps in the loading
> > circuit and not by the .001 blocking caps.
> >
> > Was this a bad brand of caps? Bad design (too low current / voltage
> > ratings)? Aging of components?
> >
> > If I have to get into cutting out a bad cap I'm going to go through the
> > trouble of replacing all the fixed caps with higher ratings..including
the
> > DC blocking caps. I'm beginning to not trust any of the components in
my
> > Titan. It's turning into a ground up re-build. But it will be a
> > better-than-new amp once I'm finished.
> >
> > Anyone taking odds that now that I've replaced every cap in the PS, new
> > meter bulbs, tightened and lubricated band switch wafers, replaced all
the
> > loading caps....
> >
> > That the first time I hit the key the tubes will head off into the
sunset?
> >
> > Tom K2TA
> > tom@k2ta.com
> >
> >
> > ----- Original Message -----
> > From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@isunet.net>
> > To: <tentec@contesting.com>
> > Sent: Sunday, March 16, 2003 8:30 PM
> > Subject: Re: [TenTec] Omni VI & Titan tuning repeatability
> >
> >
> > > The plate blocking capacitors should be the least effect at 160 meters
> > > because the tube plate C is far less than the tuning C. At 10 meters
the
> > > tube plate C is a large fraction of the circuit tuning C so changes in
> > > the blocking capacitors may have a greater effect. On the other hand
the
> > > tube C is maybe 20 or 30 PF and the 1000 pf series C of the blocking
> > > capacitors can change a lot without changing the effective tuning C.
But
> > > the posted complaint was loss of output at 160 meters, not 10 meters.
> > >
> > > On the other hand, loading padding capacitors are only in the circuit
on
> > > the low bands and drift in their value will change the output of the
> > > amplifier.
> > >
> > > Only changing 45% seems small for the Z5U dielectric. I've seen some
> > > loose 80% from room to soldering temperature. Suitable only for
> > > uncritical bypass applications when the bypass capacitor has been
> > > selected to have several times the value needed for stability. NOT
> > > suitable for any kind of tuned circuit.
> > >
> > > 858s are good, expensive, and hard to find, but good for RF circuits.
> > >
> > > 73, Jerry, K0CQ
> > >
> > > --
> > > Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
> > > Reproduction by permission only.
> > > _______________________________________________
> > > TenTec mailing list
> > > TenTec@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/tentec
> > >
> >
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
>
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