[AMRadio] AM and power

[Todd, KA1KAQ]

On Thu, Jan 26, 2012 at 12:24 PM, Bernie Doran
<qedconsultants at embarqmail.com> wrote:
> Yep, it does need to be a quiet band, sometimes I have to go to the 4KC and
> tune off center to pick up the sideband with the least QRM.

That's pretty much how I do it with the 75A-4 using the 6KHz filter.
Really need to get the 8 or 9 in there.

> Regarding the change from TL to TH, I think I just found the answer!!  the
> 75TH requires 175 Volt grid swing and the TL requires 300 Volts. they both
> produce  about the same power 300 watt for the TH and 350 for the TL. But
> look at this!!the TH has a THD of only 2 % while the TL is clear up to 6%.
> That is the first time that I have seen Eimac publish distortion data.   I
> will have to go and check the 100T and 250T , but I sure do not remember
> ever seeing distortion data.  That 75TH and then the 304TH is a Hi Fi tube.
> If I could reduce distortion by 4% just by changing tubes. It would not take
> very long to make up my mind!!!  bet the same does apply to the others also
> but may not be published.

IIRC, the 304T is just 4 of the 75s together in one envelope. The
internal plate structure sure bears this out. I've got the Eimac data
sheets here for both versions of the 75T and never noticed the
distortion ratings before either. I need to get a couple more spare
75THs. They break too easily. (o:

> Further evidence that  the old goats really did know of what they did!!!

This is true, though lost on some folks today who are certain that
they know more/better.

~ Todd/KAQ