[AMPS] SB-220: Operate/Standby Switch

[measures]

>
>Hi Peter,
>
>My "spam" filter made me miss most of this, but I should add a few 
>comments. 
>
Spam -- that which questions pontifications.  

>> Rich says:
>> 
>> >Consider that the price of a 25w rheostat is under $6.  
>
>Of course Rich always leaves a few things out.
>
>1.) There would have to be some reasonable assurance lack of a 
>rheostat actually is causing a problem with tube life. That doesn't 
>seem to be the case since almost 80% of tube failures are G/K 
>shorts and the remaining percentage mostly due to loss of vacuum 
>or voltage breakdown failures.
>
>2.) If the rheostat was added, provisions would have to be made for 
>monitoring voltage accurately. Most expensive panel meters are 
>only 2% of FS anywhere on the scale, and to make that worse it 
>would be driven by a rectifier and true-RMS filtering system that 
>would be full of components with tolerances. By the time all is said 
>and done, the $6 rheostat would add $100 of cost to the PA 

[chortle]

>if you 
>bought new parts (which commercially you have to do, unless you 
>are someone who foolishly mixes in surplus parts) and would have 
>to be hand calibrated.
>
>3.) If you get past the above you have given someone, who's skill at 
>reading meters, eyesight, and common sense are unknown, ability 
>at the mere tweek of a knob to RUIN a tube quickly. You can bet 
>that person, even if he did something wrong, would demand a free 
>tube...or it could be a V31BB who actually rewired his transformers 
>for 200 volts (on a 240 volt main ) so he could run more power!
>
>
>4.) Even if you stopped some life reduction by allowing filament 
>adjustment, the end result would be to add a certain number of 
>hours to the tube life. It would not make the tube live forever, and 
>very likely would not improve it a measurable amount in Amateur 
>service.  
>
>5.) Factually the easier you make it for someone to screw up or 
>abuse the equipment, the more likely it will happen. There would be 
>a reasonably large percentage of additional failure from component 
>failures and customer abuse or errors.
>
The DTR2000 runs 5.9v on the 8877 heater.  The max fil. V is 5.25.  

>> Yes. Which is why in a home brew amp, you'd fit one, 
>> without argument.
>
>Not me. None of my amps have rheostats for filaments. The reason 
>is simple. My line voltage varies from 241 volts to 252 volts from the 
>highest demand periods of summer to the lowest demand times in 
>winter, and I am in a rural area many miles from generating plants 
>and even HV transmission lines. 


I know folks who have wider fluctuations.  

.....
>Most tube failures are due to manufacturing defects 

NIH syndrome.  

>in the tubes, or 
>abuse. Virtually none are controllable and correctable failures.
>
gold-sputtering is a correctable problem.  Use a parasitic suppressor 
with less Rp.  Use a glitch resistor. 
>......

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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