[AMPS] Blown TL922A... What to do?

[Tom Rauch]

> >You must be using a new definition of resonance. Can you tell me 
> >what you mean?
> >
> zzzzz

Sounds like you have outgassed. You need to take more nichrome.
 
> >This is a series-resonance, not L-network, and it is shunting the 
> >path the tube must drive on VHF.
> >
> L-networks transform Z.  They shunt not.  

Nice diversion, but it is not an L network at work. It is a series 
resonance.
 
> >If the tank could freely pass harmonics, or step up the voltage at 
> >VHF to high levels, the amplifier would be a TVI nightmare. 
> > 
> If the tank were a high-pass Pi, VHF parasitic oscillation would be 
> unlikely.  

So you are saying an amplifying device driving a high load 
impedance, all other things equal, is more stable than an 
amplifying device driving a low impedance?

You can do better than that Rich, you are arguing against your own 
sales pitch!

If the network looked like a high impedance as you "propose" 
above, instead of a short circuit, the amount of ESR used to 
dampen the anode would have to be greatly increased. Any series 
resistance would be a smaller part of the overall system 
impedance, and for a given resistance Q would be reduced less.

The tank is typically a virtual short for VHF and UHF energy, 
because it has a capacitor shunting the input. All your claims 
about VHF parasitics damaging components are just "arm-waving" 
to sell kits and slam manufacturers. 

> >The impedance of the capacitor is highest at dc, and is reduced as 
> >frequency is increased. That's why the tank is a low-pass network.
> >
> >If the parasitic is NEAR the fundamental frequency, or lower than 
> >the fundamental frequency, it could indeed arc the tank 
> >components over...maybe. 
> >
> At the HF/MF fundamental freq. there is not enough feedback C to sustain
> oscillation.  

That isn't always true, especially with tubes like 811A's and 572's 
or tubes that don't have the grids correctly grounded.
 
> >Nice try. Now we have single frequency parasitics exactly on 120 
> >MHz, where the tuning capacitor has about ten ohms of reactance, 
> >driving the tank capacitor with thousands of volts.
> >
> Mr. Rauch conveniently disappears the series-resonance in the Tune C to
> support his agenda.

Mr. Measures fails to understand series resonances have lowest  
impedance, and less impedance than either "component" alone, to 
support his nichrome sales. 
 
> >What happen to your claim about grid resonance at 80 MHz, did it 
> >move in this application to fit your needs?
> 
> no.  The tubes can oscillate above grid resonance. 

Interesting. First they do, then they don't. Nice arm waving.


73, Tom W8JI
w8ji@contesting.com

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