QRP 5W HF linear amp transistors and design
 

Dear all
I want to build a power amp for SSB HF 1.5-30 MHz
Specs
approx 5W out
Cheap/easy to source components
Surface Mount parts/small
Rugged/stable into any/most loads
Gain around 40 dB
Flat gain to 1 dB or so

Thought I would do something like

Class A MMBT2222 - 2X push pull MMBT2222 - finals push pull balanced

What to do for the finals?
I looked at the PD55003 RF MOSFETS - can you get these easily?
Will they work down to HF?

What other issues?
What about transformers?
Is this a practical proposition?
I havent seen any similar designs

I would be grateful for some pointers

Thanks
Richard

QRP 5W HF linear amp transistors and design
 

Richard Hosking wrote:
Dear all
I want to build a power amp for SSB HF 1.5-30 MHz
Specs
approx 5W out
Cheap/easy to source components
Surface Mount parts/small

Usually the largest parts will be the RF transformers for broadband
stuff.

Rugged/stable into any/most loads
Gain around 40 dB
Flat gain to 1 dB or so

Thought I would do something like

Class A MMBT2222 - 2X push pull MMBT2222 - finals push pull balanced

What to do for the finals?

Generically you are in the "CB final" transistor class.

They don't sell as many CB's as they used to :-).

Good starting point is RF Parts' webpage:

http://www.rfparts.com/transistorspecs.html

I havent seen any similar designs

Communication Concepts has many Motorola app notes online from the 70's
that cover this with bipolars. e.g. AN779 with MRF475/476. A lot of
these app notes ended up being repeated almost verbatim as QST
construction articles. In some cases they sell PCB's and component
kits:

http://www.communication-concepts.com/

Tim.

QRP 5W HF linear amp transistors and design
 

In article ,
wrote:

You need a stiffer driver than 2222.

Common CB finals 2sc1971, 1909, 799 and other are all good for that
power level and easily run to 30mhz (some to 6m!).

FWIW, the Elecraft K2 uses a single 2SC2166 as a driver, feeding a
push-pull pair of 2SC1969s.

--
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Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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boycott any company which has the gall to send me such ads!

QRP 5W HF linear amp transistors and design
 

On Mon, 03 Apr 2006 21:12:59 +0800, Richard Hosking wrote:

Dear all
I want to build a power amp for SSB HF 1.5-30 MHz Specs
approx 5W out
Cheap/easy to source components
Surface Mount parts/small
Rugged/stable into any/most loads
Gain around 40 dB
Flat gain to 1 dB or so

It is hard to beat CB PA and driver transistors for this job.
2SC2166 makes a great driver. If you only need 5W, you could
use them as the final stage. For slightly higher power levels,
the 2SC1969 or 2SC2312 are a good choice. The 2SC1945 is particularly
attractive because the HS tab is connected to the emitter rather
than the collector. Genuine Mitsubishi are usually better than
unbranded generic transistors. http://www.grandata.co.uk usually
have the best prices for Japanese transistors.

Thought I would do something like

Class A MMBT2222 - 2X push pull MMBT2222 - finals push pull balanced

What to do for the finals?
I looked at the PD55003 RF MOSFETS - can you get these easily? Will they
work down to HF?

My experience with modern devices is that you can easily
get them for free as samples but you can't buy them for
love nor money :-)

The Philips BFGxxx series of surface-mount transistors are readily
available on this side of the planet.
BFG235 12V 2W and BFG135A 15V 1W have multi-GHz ft and
are available from Maplin.

What other issues?

Don't let the smoke out.

What about transformers?

Broadband ferrite.

Is this a practical proposition?

Yes.

I havent seen any similar designs

Thats because we are all using CB transistors.

BTW, It is nice to see you back on r.r.a.h We all missed you.

73, Ed. EI9GQ.

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Yes, my username really is: nospam

QRP 5W HF linear amp transistors and design
 

Thanks all
I will investigate the CB transistors

R

Richard Hosking wrote:
Dear all
I want to build a power amp for SSB HF 1.5-30 MHz
Specs
approx 5W out
Cheap/easy to source components
Surface Mount parts/small
Rugged/stable into any/most loads
Gain around 40 dB
Flat gain to 1 dB or so

Thought I would do something like

Class A MMBT2222 - 2X push pull MMBT2222 - finals push pull balanced

What to do for the finals?
I looked at the PD55003 RF MOSFETS - can you get these easily?
Will they work down to HF?

What other issues?
What about transformers?
Is this a practical proposition?
I havent seen any similar designs

I would be grateful for some pointers

Thanks
Richard