[SEDXC] Homebrew Amps

[John Harden, D.M.D.]

JT,

I have built a lot of gear from scratch over the last 45 - 50 years. If
you do it's important to have a well stocked "junk box". If you buy the
parts new it can be prohibitively expensive. There are many sources of
surplus and used parts. 

Even the hardware can be expensive (screws, nuts, lockwashers,
insulators, rubber grommets, etc.). I keep a whole array of assorted
hardware.

One possibility is a one-band, solid state amplifier. It is easy to
build. I built a solid state 40 meter CW transceiver around 1975 with
assorted RTL, TTL circuits and individual transistors. It had a 2 watt
output. Then I built a 30 watt solid state amplifier using an MRF-449A
(Motorola). I still have it today. It works fine.

As a teenager I built a speech amplifier and 811A modulator from scratch
along with the HV power supply. That was the only way I could afford it.
I used a military surplus transformer for the plate modulation
transformer.

Look at QST December 2005 for the "Superpacker HF Amplifier", and at QST
December 1975 for "Slippers for the HW-7 transceiver". With an MRF-450A
you can get 50 watts out with 2 watts drive with the latter amplifier.

73,

John, W4NU



-----Original Message-----
From: sedxc-bounces at contesting.com [mailto:sedxc-bounces at contesting.com]
On Behalf Of Bill Coleman
Sent: Saturday, September 23, 2006 9:13 AM
To: JT Croteau
Cc: *SEDXC Group
Subject: Re: [SEDXC] Homebrew Amps


On Sep 22, 2006, at 8:34 AM, JT Croteau wrote:

> Anyone have any schematics/plans/ideas for getting ~200W from either
> 5W or 50W drive without breaking the bank?

There's not a huge difference between 50 watts and 200 watts. That's  
only a single S-unit.

>   I have acquired a nice
> Ten-Tec Argosy that I am cleaning up and it will have a really low
> noise floor and improved dynamic range when I am finished.  Some type
> of foot warmer would also be nice.

If 50 watts is not enough, consider finding a used older-generation  
tube amplifier. Something like an SB-200 can be had for less than $500.

Last year, I bought a used AL-80A from a ham's estate. I spent a bit  
more than $500, but what the heck. It uses a single 3-500Z and with  
50 watts drive will produce about 500 watts or so.

> I know Tokyo Hy-Power has some commercial pre-built options in this
> range but I, and my wallet, would much rather homebrew if possible.

Homebrewing an amplifier can be done, but it isn't cheap. Key  
components, like the HV transformer or tube(s), can easily run you  
over that $500 budget, if you buy them new.

Amplifier design and construction also requires a certain level of  
care and expertise. The voltages can easily kill you. The energy  
stored in the power supplies can be enough to explode components.  
Proper component choice is necessary to avoid catastrophic failures.

You're better off looking for a used amplifier. If you are totally  
focused on homebrew, you should consider buying used amplifiers for  
key parts.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901

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