[AMPS] TL-922 Filament Transformer Protection

[Radiodan W7RF]

Tom Wrote:

> Rich gave good advice, except for the parasitic stuff. He has a
> fixation and pet theory that almost any failure is do to a "parasitic".
> Sorta like ethnic cleansing applied to PA's, where those nasty
> conventional suppressors have to go.
> The bulk of arcing failures in the 922 (and other PA's) are caused
> by improper relay sequencing,  improper loading, driver transients,
> or load faults.............
> While I can't say for certain an amp could never oscillate and
> cause arcing, it is probably one of the least likely causes of
> failures. I've never been able to get one to oscillate and arc,
> however, even when I intentionally introduced VHF oscillations.

Hey, I thought parasitic oscillations were the root of all evil?
Wow, it's a good thing we didn't try to recall all those 3CX1200A7
amplifiers that work just fine.

Whew! Tnx Tom!

73, Dan Magro W7RF, (President WARC 1999, member SCDXC, SCCC)
Manufacturers Rep & Distributor for HENRY RF Power Amplifiers.
www.radiodan.com <http://www.radiodan.com>     RFpower@radiodan.com
<mailto:RFpower@radiodan.com> A trip to our web site is worth the click!




> -----Original Message-----
> From: owner-amps@contesting.com [mailto:owner-amps@contesting.com]On
> Behalf Of Tom Rauch
> Sent: Saturday, June 05, 1999 9:41 AM
> To: Court; amps@contesting.com
> Subject: Re: [AMPS] TL-922 Filament Transformer Protection
>
>
>
> > CT.  .  .  The Kenwood 922 has a tendency to intermittently oscillate at
> > its anode-resonance freq. of c. 130MHz.  Such oscillations may cause
> > intermittent spitting at the Tune-C and or bandswith, large
> changes in the
> > R of the vhf suppressor resistors, and bursts of high grid current which
> > place lateral electromagnetic force on the hot filament-helices.  With
> > repeated oscillations, the filament may eventually be bent far enough to
> > touch the grid cage.  When the filament touches the grounded-grid, the
> > +110v power supply shorts to ground.  If the amplifier is not switched
> > off, the filament transformer will melt down.  One fix is to
> cut the wire
> > on the bias relay that connects from the coil to the bias contacts.  For
> > purists, the existing 100k resistor can be connected across the NO bias
> > contacts on the relay.  .  - later, Court
>
>
>
>
> Anytime you  drive a PA without proper loading, the tank voltage
> soars and can reach several times the normal operating voltage.
> That's an effect we are all familiar with in SB-220's, Viking Valiants,
> Rangers, DX-100's and other tube equipment. In MOSFET PA's, it
> just wipes out the FET's from drain to gate punch-through.
>
> A common problem in the 922 is they never bent the relay contacts
> slightly, to be sure the antenna connected before the drive could be
> applied. Another problem is rigs like the TS950, or IC775, that slam
> the PA with a few hundred watts of drive. That extra drive switches
> the tube hard, and tank voltages momentarily build up to many kV
> because the tube is misloaded for that drive level.
>
> Another common cause is operator error, where the operator tunes
> the amp at lower power and never loads the amp at full drive.
>
> Also, lightning arrestor sometimes arc, and that disconnects the
> load allowing the tank to build up high voltages.
>
>
>
> 73, Tom W8JI
> w8ji@contesting.com
>
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>


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