[AMRadio] Can you have Class D and Class E tube amps?


Chris Wilson chris at chriswilson.tv
Fri Dec 30 06:45:23 EST 2016


Hello Larry,

Tuesday, December 27, 2016


> On 12/27/16 6:36 AM, Rob Atkinson wrote:
>> Unless I am mistaken the Continental 314 was a class D tube rig.
>>
> I think the original person making the inquiry (Chris) was asking about
> using tubes in Class D or E service in the *RFPA* at 137 KHz. The "class
> D" (PDM, PWM) tube-type broadcast transmitters employ a class D 
> *modulator* operating at, I believe, the 60 - 100 KHz range. The RFPA in
> these transmitters is conventional class C. My homebrew "big rig" also
> uses a class D modulator (an 833A) at about 80 KHz, but the RFPA is just
> a tube-type class C final with the negative lead floating, because the
> modulator is in series with the final from a DC and AF perspective. 
> Because its a series modulation scheme, the DC supply needs to provide
> more than double the quiescent voltage required for the RFPA, but there
> is almost no extra energy wasted in the modulator. The HV supply needs
> to provide more voltage, but much less current, that a power supply that
> supplies both the RFPA and a "conventional" analog modulator (for 
> example, class AB1, AB2, or Class B).

> If a tube-type class D modulator can operate at 80 KHz, which it can, it
> is not a big stretch to expect it to be able to operate at 137 KHz in an
> RFPA. But this is the pulse repetition frequency, so there is 
> significant odd harmonic content, and therefore significant energy that
> must be amplified, at much higher frequencies.

> I have much less experience with/knowledge about class E amplifiers, so
> I cannot say much about that part of the question.

> 73,
> -Larry/NE1S
> ______________________________________________________________



Thanks  to  all  who have replied, some very helpful information here,
and  much  appreciated.  if anyone has anything to add plese go ahead.
Larry,  you have the right handle on what I was asking, sorry I wasn't
too  clear.  A  very  happy  and healthy New Year to all, have a great
2017!


-- 
Best regards,
 Chris                            mailto:chris at chriswilson.tv



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