[AMRadio] Re: 1930's Old Buzzard Open Rack Transmitter Finally


Larry Szendrei ne1s at neandertech.com
Sat Feb 25 14:19:59 EST 2006


Makes sense, Brett. I was trying to work it through using diodes at the 
"bottom" of the grid-leak resistor, and there didn't seem to be a simple 
solution that way. But since I'm using the grid-leak resistor also as 
the RF choke (typical old-buzzard practice), so I'd have to add an RF 
choke. May play with that at some point...

73,
-Larry/NE1S

Brett gazdzinski wrote:
> The grid gets its bias the normal grid leak way.
> At the grid side of the resistor, a diode is installed between the
> bias supply and the grid, in the direction that allows it to pass
> bias, but if the grid leak exceeds the fixed bias, it is reverse
> biased.
> 
> That's cathode towards the bias supply I think.
> 
> I like using big panel mount pots for grid leak, I have some BIG ones
> I got at fests for a buck each, 75 watt jobs of different resistances.
> 
> Brett
> N2DTS
>  
> 
> 
>>-----Original Message-----
>>From: amradio-bounces at mailman.qth.net 
>>[mailto:amradio-bounces at mailman.qth.net] On Behalf Of ne1s
>>Sent: Thursday, February 23, 2006 4:42 PM
>>To: Discussion of AM Radio
>>Subject: [AMRadio] Re: 1930's Old Buzzard Open Rack 
>>Transmitter Finally SeestheAirwaves! (Long)
>>
>>Sorry!!! 
>>
>>That was supposed to read "Could you or DON describe the 
>>protective bias 
>>circuit you refer to? " 
>>
>> -'1S 
>>
>>ne1s writes: 
>>
>>
>>>Thanks for the kudos, John!  
>>>
>>>Could you or done describe the protective bias circuit you 
>>
>>refer to? 
>>
>>>Probably could figure it out, but the group may be 
>>
>>interested as well...  
>>
>>>73,
>>>-Larry/NE1S  
>>>
>>>John E. Coleman (ARS WA5BXO) writes:
>>>
>>>>CONGRADULATIONS A JOB WELL DONE!
>>>>	I really like the choice of tubes.  I don't know what a 
>>
>>T55 is but
>>
>>>>probably one of the special Taylor triodes with 55 watts plate 
>>>>dissipation.
>>>>Probably not a lot different than the 812s but I know that 
>>
>>the 812s are 
>>
>>>>very
>>>>good tubes to use in a class C plate modulated rig 
>>
>>especially if used 
>>
>>>>with
>>>>100% grid leak bias or the configuration that Don, K4KYV, 
>>
>>uses where 
>>
>>>>there
>>>>is a safety bias supplied thru a diode and the diode 
>>
>>becomes reversed 
>>
>>>>biased
>>>>when RF drive causes grid leak bias.  The 100% Grid leak 
>>
>>bias DOES make a
>>
>>>>difference in the modulation characteristics of the rig.
>>>>John, WA5BXO 



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