[Amps] Source of Mica Caps?

[Carl]

>> IMO, you gotta be nuts to use grid caps + chokes on any 3-500Z amp.
>
> ** OH? So you and a few other glorified techs want to argue with 
> experienced
> engineers that designed the amps? I give them the benefit of the doubt
> considering the number of Heath, Drake, KW, and other amps out there that
> far exceed the very little minority that believe "if it aint broke dont 
> fix
> it"
>
> ## engineers that designed the amps ?    Surely you are joking right ? 
> They are not engineered,
> more like ill conceived.  The heath needs a real bandswitch, with a real 
> detent.  And 6:1 verniers
> for both tune + load.............+ step start ..+ a standby-operate switch 
> etc, etc.

** The Heath were cost reduced but the switch was used in other 1000W INPUT 
amps as was the law when it was designed in the 60's.
OTOH, some other companies never had a real engineer and one still doesnt.

>
> ## On a side note, a buddy in W7 land with a SB-221 tells me he has severe 
> TVI  into his neighbours
> satellite setup.... but only on 17M.  I get him to grnd the grids.   He 
> did so but with using just ONE piece of
> solder wick, and ground one grid pin per tube only.  He left the caps + 
> choke in place.  Presto, TVI gone.
> But that may have been one of the caps  acting up on 17M, dunno.   he was 
> using a F-12 20-17-15-12-10m
> yagi.  Drive power dropped at least 20w, and amp is stable with stock 
> suppressors.

** Those caps can get troublesome if whacked by an arc/short. So can the 
chokes, especially when the pi's slam together or turns shorted internally.

>
> ##  Another friend has a very unstable TL-922.  He installs  richs 
> nichrome and all is well.   he tries bonding the
> grids to chassis, and drive requirements drop 20-25 w.  Amp still stable. 
> Then he removes the nichrome and installs
> the oem suppressors..and amp is rock stable.   Removes grid bonding 
> straps, so grid caps and chokes are back in the
> circuit.  Amp is now unstable !  CC  resistors in the oem suppressor’s are 
> fine.


** Then he didnt find the problem which is usually a grounding one between 
the output section and tube chassis.


> ##  This time all 6 grid caps are tossed, + both chokes.   been like that 
> for several years now.   I must have got email from
> at least 30-40 folks now who have bonded the grids to chassis  on sb-220’s, 
> and also 221, and tl-922.

** And the 1000's of others sold just chug away happily. Im always getting 
emails from those that took advice from myself and others and have been very 
satisfied. I dont count or save them as boasting material.

>
> ##  adding a glitch r is no big deal.  25 ohm 25 watt wire wounds, 2 of em 
> in series,will allow  one to get them in there. They can be
> far apart if you want.   Adding a 50 ohm, 50w  ww to any drake amp is 
> easy.  I have done the drakes  by installing in either the
> outboard drake hv supply  or the rf deck itself.
>
> ##  since most folks will add a glitch R  of some type to these older 
> amps.....adding a simple HV fuse,  just prior to the glitch assy
> is pretty easy.   A single fine strand of the correct gauge, is all that 
> is needed.   Then cover the strand with heat shrink, or 88 tape,
> teflon spaggeti tubing etc.  Any anode to grid flashover, and hv fuse 
> opens up..event over...no follow on current either.
> Drake uses a  .82 ohm @ 1/2 watt  resistor for a  B+ fuse.   Blows  clean 
> in half.  Works just as good as a hv fuse.

** Dentron used a pair of 1 Ohm 1/2W in parallel. National used 1/4 W grid 
and screen resistors.
Lots of things  from 40-50 years ago still work when a tube fails to keep 
other parts from blowing up.Its when the power level gets above 3KW or so 
that things get touchy.
I know a guy who blew a 4X 8877 amp by not providing even basic fault 
tolerance into it

Carl


> A hv fuse will open up a lot faster than any 240 vac mains relay 
> /contactor.   2 msecs  vs 35 mecs/.
>
> Jim   VE7RF
>
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