[Amps] TL-922 question

[Joe Subich, W4TV]

Tom, 

> 1. Replacing the blocking cap may have necessitated increasing the
> padder caps on 80 and 160.  It seems like all the load positions are a
> bit less than the manual would indicate.  The other bands are still in
> range.

Not likely ... 

> 2. The 80 meter padder cap, which is also used on 160, is actually 
> 2 ganged sections of the 5 section Load variable cap.  It is 
> possible that this cap has become disconnected somewhere in the 
> path from the bandswitch to ground.  The 160 padders are discrete 
> components

If the amp loads even at maximum capacitance on 80, the second section 
of the loading capacitor I getting switched in.  You could not "get 
there" with the 40 meter values. 

when you use the amplifier at powers above the design parameters, 
the plate load impedance decreases.  Lower plate load impedance, 
will necessitate larger capacitors ... if you are pushing and amp 
designed for 1200 W PEP output to 1500 W PEP, you have decreased 
the plate load impedance by 20%.  A 20% decrease in plate load 
impedance will require a 15 to 20% increase in the values of the 
tune and load capacitor (and similar decrease in the coil).  I 
haven't calculated new capacitor values if the coil is kept 
constant but I would bet the big issue is lack of capacitance 
to handle the new operating point. 
 
> 
> When I get to work on the amp again I will,
> 
> 1. Check the mechanical integrity of the 80 meter padder cap 
> connections
> 2. Up the blocking cap to 2000pf since this seems to be a better 
> value for this purpose.

Don't bother ... 

> 3. IF these do not work, add some more padder capacitance to the 
> 80 meter Padder.

Adding another 500 pF across the 80 meter capacitor MAY get you 
close enough.  Take a set of three or four replacements for 
C69/C70 with you just in case they are bad and use one on 80. 

73, 

   ... Joe, W4TV 
 



> 
> Does this sound right?
> 
> 73, Tom
> 
> 
> 
> -----Original Message-----
> From: Georgens, Tom 
> Sent: Monday, August 28, 2006 8:39 PM
> To: amps at contesting.com
> Subject: [Amps] TL-922 question
> 
> Hello -
> 
> I have a question about my TL922.
> 
> When I tune on 80 and 160, the LOAD control bottoms out before I can
> peak the power.  The output power is about what I would expect so the
> peak must be close but I am uncomfortable that the tubes are 
> not seeing
> as good of a match as they could.
> 
> The amp has always been real close to the 0 position but I don't
> remember it being quite like this.  To be complete, I have made the
> following mods to the amp.
> 
> 1. Inserted a HV fuse resistor
> 2. Directly grounded the 3-500Z grids
> 3. Replaced a blown blocking cap (1000pf).  The service manual says to
> use 2000pf but the operating manual says 1000pf 4. Replaced the tubes
> (unmatched)
> 
> The seems to work otherwise and has seen extended operating 
> on the high
> bands.
> 
> I would like to get the tuning back in range.  Could any mods have had
> this effect?  Is it worth trying to add to the padder caps?
> 
> 
> Thanks and 73
> 
> Tom W2SC
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> 
>