[AMRadio] 813s push pull Triode Connected Bias question.


Paul Baldock paul at paulbaldock.com
Wed Apr 22 22:12:48 EDT 2015


I think this is class B, so no significant control grid current. The 
screen grid is connected to the control grid in this triode 
configuration so there will be screen current, but I would assume 
only a few tens of mA as the peak voltage is only a couple hundred volts.

It is a step down transformer designed to modulate a pair 813's 
(about 12K Ohms).

Unfortunately I don't believe any data sheet exists for the 813 
configured as a triode.

- Paul


At 06:43 PM 4/22/2015, you wrote:
>if that is correct, you are running an input of about 1 KW and even 
>accounting for transformers losses etc, (10%) you are dissipating 
>over 500 watts in the plates. Hope you have plenty of 813s. even in 
>AB1  a pair is shown at about 67% eff. Of course the control grid 
>and screen currents  also appear in the cathode current, so the 
>actual power input may be significiently less if you are not 
>deducting that.  the 10k load may be too low unless the mod 
>transformer is a step down. The plate to plate Z for a pair is above 
>19,000 Ohms.  Bernie----- Original Message ----- From: "Paul 
>Baldock" <paul at paulbaldock.com>
>To: <amradio at mailman.qth.net>; <boatanchors at mailman.qth.net>
>Sent: Wednesday, April 22, 2015 7:59 PM
>Subject: Re: [AMRadio] 813s push pull Triode Connected Bias question.
>
>
>>I just fired up my new  Modulator, driving a 10K resistor instead 
>>of the PA. It works well except the efficiency is low. The HV is 
>>about 2500V. Idle current is about 60mA (150W). Efficiency at 400W 
>>RMS output is 42% as calculated by plate voltage times cathode current.
>>
>>Does this seem typical for this configuration?
>>
>>Thanks
>>
>>- Paul  KW7Y
>>
>>
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