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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