[Amps] TL-922 voltage / bias

[TexasRF at aol.com]

Tom, that makes sense and sounds like a must do modification. I can't  
contribute anything to this discussion so will humbly bow out.
 
73,
Gerald K5GW
 
 
 
In a message dated 2/12/2010 9:49:21 A.M. Central Standard Time,  
tomp at prohigh.com writes:

>From  Rick Measures:

Converting a SB-220 or TL-922 from V-cutoff bias to  R-cutoff bias: will
prevent this from happening. The conversion: •• 1.  Remove +110v from NC 
bias
contact on relay without disconnecting the +110v  lead to the coil. 2.
Unsolder the lead of the 100k R that connects to the  NC bias contact, move
it to the NO bias contact and solder it . When  finished, the 100k-ohm R
should connect between the arm and the NO  contact.  During Rx, the drop
across the 100k R is c. 25v.   During Tx, the 100k is shorted out by the
relay.

This prevents a  transformer meltdown in event of a cathode to grid short

On Fri, Feb  12, 2010 at 10:46 AM, <TexasRF at aol.com> wrote:

>  Tom, I  am not familiar with the terms "v bias" and "r bias". Are saying
> the  zener bias diodes have been replaced with resistors?
>
>  73,
> K5GW
>
>
>  In a message dated 2/12/2010  9:40:18 A.M. Central Standard Time,
> tomp at prohigh.com  writes:
>
> Only mod was V bias to R bias.  At key down,  there is 7.5V at the zener.
> Maybe I should do the diode bias or get a  5.1V zener, or maybe just the 
old
> tubes are a little  soft
>
> On Fri, Feb 12, 2010 at 10:38 AM, Carl  <km1h at jeremy.mv.com> wrote:
>
> >  Did you modify  the bias circuit or check the voltage?
> >
> > Carl
>  >
> >
> >
> >  ----- Original Message  -----
> > *From:* Tom Prohigh <tomp at prohigh.com>
>   >   *To:* Carl <km1h at jeremy.mv.com>
> > *Cc:*  amps at contesting.com
> > *Sent:* Friday, February 12, 2010 10:34  AM
> > *Subject:* Re: [Amps] TL-922 voltage / bias
>  >
> > There are 2 tubes in the TL-922.  The grids are  DIRECTLY connected to
> > ground, I removed the caps and chokes and  also put in a second ground
> wire
> > from VC1.  This  eliminated some arcing/parasitics I was having.  The
>  tubes
> > are original Eimac 3-500Z not 3-500ZG.  The color on  the plates is 
fine,
> no
> > color at idle and red/orange at  full drive.  I do get about 600-700W 
out
> on
> > CW, but  only about 1000 key down on SSB on 20M.  80M is somewhat higher
>  >
> > Tom - AB3FL
> >
> > On Fri, Feb 12, 2010  at 10:30 AM, Carl <km1h at jeremy.mv.com> wrote:
> >
>  >> That idle current is fine for 1 tube and the voltage drop is  
excessive.
> >> Start by measuring the grid chokes for an open or  looking for color on
> both
> >> plates.
>  >>
> >> Carl
> >> KM1H
> >>
>  >>
> >> ----- Original Message ----- From: "Tom Prohigh"  <tomp at prohigh.com>
> >> To:  <amps at contesting.com>
> >> Sent: Friday, February 12, 2010  9:47 AM
> >>
> >> Subject: [Amps] TL-922 voltage /  bias
> >>
> >>
> >>   I have  recently aquired a TL-922.  It is on a stiff 240V line which
>  >>> actually
> >>> measures 245V.  No load  voltage on CW is 2200 and on SSB is 3100.
> Under
> >>>  full load the CW drops to 1900V @ 600ma and the SSB drops to 2400V @
>  >>> 800ma.
> >>> Is there really suppose to be this  much drop?  It has the original
> 200uf
> >>> caps  in it and I was thinking about replacing them with 560uf units.
>  >>>  Also
> >>> the grid bias on CW is 60ma and  on SSB 120ma which seems a little 
low.
> >>>
>  >>>
> >>> thanks
> >>>
>  >>> Tom - AB3FL
> >>>  _______________________________________________
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> >>>
>  >>
> >>
> >
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