[Amps] TL922A and AL80A

[rlm]

>> The TL922 manual says "DO NOT under any circumstance OPERATE your exciter
>in
>> CW mode when the linear is in the SSB mode. Failure to head this warning
>may
>> cause immediate, extensive damage to the amplifier""
>>
>> "REPEAT: DO NOT OPERATE CW IN THE SSB MODE"
>
>The TL922, like the SB220, was designed when the power limit was 1kw CW DC
>plate input power.
>
>Power supplies and cooling systems were designed for power level, plus a
>safety factor.
>
>> As long as I am asking questions, the AL80A manual says to tune up to 550
>mA
>> of Ip and then back off to 400.  I think the 3-500Z max Ip is 400 mA.  Is
>it
>> really OK to drive it at 550 mA?
>
>Sure. Thoriated tungsten tubes are not damaged even when operated at
>emission saturation, 

**  True

>which is several amperes peak plate current in a
>3-500Z. 

>Tuning it slightly beyond the operating current of 400mA sets tank Q
>at designed operating values, 

**  So the amplifier was designed beyond the tube's ratings?

>and also makes sure the amplifier can handle
>any exciter transients or overshoot with arcing.
>
**  ... and remember, there is such thing as a VHF oscillation in a HF 
amplifier.  

>In IVS modes you can reach the peak current with damage to the tube, and
>linearity is still good.

**  Not according to the characteristic curves.
>
>All that was approved by Eimac.
>
**  Welcome to Fantasyland, boys and girls.  

>> this level?  Is 400 mA the destructive limit or is it the point at which
>> tube aging  will accelerate?  Also, in a grounded grid configuration like
>
>Emission demands do not shorten the life of a 3-500Z. The primary cause of
>shortened life is sitting idle for long periods (the seals leak and the
>elements inside the tube can outgas), and material and manufacturing defects
>in the tube. 

**  it's always the other guy's fault.

>You can see more at:
>
>http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm
>
>> the AL80, at what current would linearity be lost?
>
>Linearity is really lost very quickly when the anode is underloaded, 

**  ... or overloaded.

>by tuning or "peaking" output at low anode currents and drive power. That is
>the worse possible operating error, since even with just a few dozen mA grid
>current and a 100mA anode current a 3-500Z can be very non-linear when the
>tank is misadjusted and presents a high load impedance to the tube. It also
>increases chances of tank circuit component failures quite drastically when
>an amplifier is underloaded, or only loaded at the steady output power you
>expect to run.
>
>On the other hand the tube is linear up to and beyond 150mA of grid current,

**  True

>and 600mA of anode current or more, 

**  The 3-500Z's characteristic curves indicate that this is not true.

>when the tank is adjusted properly.
>
>It is best to follow the manuals.
>
**  Yes, even when the manual is serving thick-sliced bologna sandwiches.

>73 Tom

-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K, 
www.vcnet.com/measures.  
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