[AMRadio] HRO question for the day

k4kyv at charter.net k4kyv at charter.net
Thu Dec 17 14:43:08 EST 2009

> National decided in the HRO50 design to use a 4.3 Ohm resister in series 
> with the fil of both 6H6  dual diodes, ( noise blanker and detector) 
> dropping the fil to about 5 v.   In the Hro 50-1 the noise blanker 6h6 
> operates at normal Volts and the detector still at reduced voltage. I see no 
> reason for this and the tube data sheets do not address lower volt 
> operation. only effect I notice is that it takes several minutes for the 
> detector to warm up and produce audio. It can not be for life as when this 
> was designed and built 6h6s were cheap, still are.  certainly not to save 
> energy or battery operation.  perhaps it fools the detector into something 
> other that a square law detector due to low emission.  tube life would be 
> extended, but so what, this is not a transmitting valve and the only one I 
> have seen where reduced voltage is recommended for standby is the 813, data 
> recommends 8 volt when on standby and I have never done that or seen one 
> used that way.  So does anyone KNOW why national did this?    I have never 
> seen this in Collins so it must be wrong!!!! HI   Bernie W8RPW 

I vaguely recall having the same question years ago when I was helping Roger, N4IBF(SK) with his, and learning that the resistor was there for a good reason, but I don't have a clue what it was now.  Hopefully someone will have the info.


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