[Amps] Efficient amplifier design

[Carl]

The 833A will run fine to 20M and it was also THE TUBE for Class B 
modulators.

The Gates BC-1T BCB rig I stripped for "iron" parts ran 4.


----- Original Message ----- 
From: "Manfred Mornhinweg" <manfred at ludens.cl>
To: <amps at contesting.com>
Sent: Monday, May 01, 2017 3:38 PM
Subject: Re: [Amps] Efficient amplifier design


> Cathy,
>
>> How much easier does the design become if
>> we select an upper frequency bound of 15 MHz instead of 30 MHz?
>
> To give a simple-to-grasp figure, I would say it becomes roughly 3 times 
> easier. That's because a lower frequency limit opens the doors to use many 
> more devices, and also because all problems related to stray inductance, 
> device capacitance, etc, get smaller. In addition the bandwidth will 
> become smaller, given that we are still starting at 1.8MHz.
>
> Just one example: When I played with cheap switching MOSFETs in TO-220 
> cases for linear HF amp use, I ended up with pretty few really usable 
> devices that would cover up to 30MHz. There were a lot of cheaper and more 
> powerful devices, which I discarded simply because their practical 
> frequency limit was too low. With a 15MHz limit, many of them could have 
> been used.
>
> In fact my own use for an amp would be mostly confined to 40 and 80 
> meters. But then it's something like a given mindset, that an HF amp 
> should cover ALL of the HF spectrum. 160m, while outside HF, is easy to 
> add, so why not include it. But I leave 6m out. An amplifier covering 
> 160-6m has twice the bandwith of a 160-10m one, which significantly adds 
> to the complications, and 6m is VHF... so let's leave it out.
>
> Of course there are many hams who will want 6m too, but many others don't 
> need 6m coverage. Or like you, might be happy with 160-20m coverage.
>
> With homebrew amps, a practical thing to do is to base the upper frequency 
> limit on a "best effort" basis: Make sure it works on the bands you want 
> most, and try to extend coverage to the higher bands as much as is easy 
> enough to do, but don't despair if some of the highest bands are left out!
>
> Hams have been doing that from the beginnings. I remember having seen 
> circuits using the 833 tube that were usable only on the lower HF bands.
>
> Manfred
>
>
>
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