[Boatanchors] AM Amplifier

[Rodger Singley]

The overall efficiency for the apparent amplifier output will be less than the actual tube efficiency since output tank losses come into play and these can be very significant with the typical tapped or roller inductor pi net output circuit.  The older single band plug in coil setups can do better but there will be losses in all types of output networks.



The only amplifier I own that will safely do legal limit AM is a contest duty amp I built back in the early 1990s using three 4CX800 tubes in AB1 with a large blower and a Dahl transformer rated for 3KW CCS.  I am impressed with the overall design of my Heathkit KL-1 “Chippewa” outside of the exposed plate meter that is directly in the HV feed.  I had some fun using it to greatly increase the AM power of a Yaesu FT-817.



For high power AM I prefer my Desk KW and Viking 500.  A Johnson Valiant can produce about the same level of AM output as the typical twin 3-500Z amp designed primarily for SSB.  For those willing to run controlled carrier AM (as found in many popular 60s and early 70s rigs including the Drake 4 line transmitters and transceivers, Heathkit DX-60, Knight T-60, etc.) then any of the  SSB rated amps will work well.  Otherwise I would find an amp rated for RTTY use, load it to rated RTTY input, and then run it at no more than ¼ of this input at carrier level.



The cooling of typical amps like the SB-220 is marginal and it was common for contesters in the 1970s to run them with the outer case removed and just the protective shielding in place which helped them live under contest conditions.  Drake did a better job with the blower plus chimneys L4 series (cheapened when the nice looking L7 was released).



Rodger WQ9E



Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10



________________________________
From: boatanchors-bounces at mailman.qth.net <boatanchors-bounces at mailman.qth.net> on behalf of Rob Atkinson <ranchorobbo at gmail.com>
Sent: Sunday, July 8, 2018 5:24:17 AM
To: WA5VGO
Cc: Boat Anchors List
Subject: Re: [Boatanchors] AM Amplifier

He said his amp was class B.  Actually Class B is usually a little
better than 50%.

73
Rob
K5UJ

On Sat, Jul 7, 2018 at 9:23 PM, WA5VGO <hbrnut at suddenlink.net> wrote:
> The problem isn't voice peaks. At 100% modulation the amplifier should be
> about 60% efficient. However, as the modulation level drops, so does the
> amplifier efficiency. With no audio, it's down to 25-30%. I suppose if
> someone talks fast and loud, they can push things.
>
> Darrell
______________________________________________________________
Boatanchors mailing list
Home: https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmailman.qth.net%2Fmailman%2Flistinfo%2Fboatanchors&data=02%7C01%7C%7C1fac380314414374433b08d5e4bcfb96%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636666422675414296&sdata=T%2FWSTlXLWTGglkIX%2FEzYLHAQRTpCnzUP4A9%2FQM9fU%2B0%3D&reserved=0
Help: https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmailman.qth.net%2Fmmfaq.htm&data=02%7C01%7C%7C1fac380314414374433b08d5e4bcfb96%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636666422675414296&sdata=sMi2sk3GgDo%2BqHWGgZ7Ey3DXg6mH3ck%2BvYbCNqNwwTQ%3D&reserved=0
Post: mailto:Boatanchors at mailman.qth.net

List Administrator: Gary Harmon, K5JWK
** For Assistance: gharmon at idworld.net **


This list hosted by: https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.qsl.net&data=02%7C01%7C%7C1fac380314414374433b08d5e4bcfb96%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636666422675414296&sdata=JOduZYpDC07yGHPpDHorhd8KBA0C%2FJXqqMFvC1Wu6hk%3D&reserved=0
Please help support this email list: https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.qsl.net%2Fdonate.html&data=02%7C01%7C%7C1fac380314414374433b08d5e4bcfb96%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636666422675414296&sdata=Wln5oqGY8j9a8NaGpzJba6HxGgHWZtmvivtXRD7zG%2BU%3D&reserved=0