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Re: [Amps] Source of Mica Caps?

To: "Jim Thomson" <jim.thom@telus.net>, <amps@contesting.com>
Subject: Re: [Amps] Source of Mica Caps?
From: "Carl" <km1h@jeremy.mv.com>
Date: Thu, 6 Jun 2013 13:14:37 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>


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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