Does anyone have recent experience with the old HA-201 walkie talkie
amplifiers? They use electronic transmit/receive switching. They are
rated for 8 Watts out for 1 Watt in, and 10 Watts out for 1 1/2 Watts
in, using a 13.6 Volt power supply. Maximum drive is 3 Watts. The
amplifier uses a single 2N5590 transistor.

Back in the 70s, I built an HA-201 and worked on at least one other. I
can not remember much about them, except it was impossible to stabilize
them per Heath's instructions and technical notes. I found a "fix", but
don't recall from where.

At a recent Hamfest, I obtained a couple more of these amplifiers. They
both tuned up per instructions, but at a slightly low output power and
with the instability as noted on an AM radio. Adding the stability
"fix", the power output was still the same.

Since both units seem to perform the same, I wonder if the design is
just not able to put out rated power from rated input? I used a Kenwood
Handheld as a source with 20 feet of RG-58 to knock the power down to 3
Watts. For 3 Watts input, they both put out 11 Watts. Using a
different Handheld with 2 Watts output, they put out about 8 Watts.

If anyone is interested in the stability "fix", it involves using a
tantalum electrolytic capacitor (low ESR) in parallel with the 100 UF,
and a 330 Ohm 1 Watt resistor in parallel with the RF Choke.

Fred
K4DII

In article ,
Fred McKenzie wrote:

If anyone is interested in the stability "fix", it involves using a
tantalum electrolytic capacitor (low ESR) in parallel with the 100 UF,
and a 330 Ohm 1 Watt resistor in parallel with the RF Choke.

That was Saturday. Today the "fix" is not working! The only difference
in my setup was the power supply.

I wanted to see if tuning an amplifier with less drive, might result in
more power when drive was increased. I tried 2 Watts, and then 0.3
Watts drive. In all cases, the instability shows up as garbage on the
nearby AM radio. The garbage comes and goes as tuning is adjusted.
When tuned with 0.3 Watts, output was the same when changing to the 2
Watt source. I think the amplifier is acting as an oscillator being
excited by the drive.

One difference between this "fix" and the one from the 70s, was before
the 100 UF capacitor had been replaced by three 22UF tantalum capacitors
in parallel. The current version only has one 22 UF tantalum capacitor
in parallel with the 100 UF. This may explain the motor-boating sound
of the interference.

My amplifiers oscillate but my oscillators don't!

Fred
K4DII

In article ,
Fred McKenzie wrote:

If anyone is interested in the stability "fix", it involves using a
tantalum electrolytic capacitor (low ESR) in parallel with the 100 UF,
and a 330 Ohm 1 Watt resistor in parallel with the RF Choke.

I found the source of my "fix". It was in a QST "Hints and Kinks"
article by Ron Baxley, N4GB, probably from the early 80s.

I've tried everything I can think of. It appears that a resistor in
parallel with the RF Choke makes NO difference, except the resistor gets
hot! A resistor across the input, suggested by Heath bulletin HA-201-2,
also makes no difference except for a slight reduction in power. These
two resistors may make a difference for a different transistor. The two
I'm working on use a 2N5590, while some kits came with a CTC B12-12.

I removed the C9 100 uF capacitor, and replaced it with a couple more
Tantalum capacitors to agree with the QST article. As far as I can
tell, this makes an improvement but not a cure.

The closest thing to a cure seems to be a revised procedure for tuning
the compression capacitors. Initial settings for capacitors involves
snugging them down and backing each off a specific fraction of a turn.
Tuning then involves adjusting C1 through C5 in sequence, for maximum
output. From the initial settings, peaking C1 involves opening the
capacitor another half turn or so, and gives rise to the oscillation.

My revision was to NOT adjust C1 until after C2 through C5 have been
adjusted. Going through the sequence a second time starting with C1, I
found that all were close to their peak, and the oscillation was not
present.

Listening on a nearby AM radio, the "garbage" previously noted is not
there. But wait! I let the HA-201 cool down, and now there is a "rip"
sound in the AM radio when the handheld is keyed. After a few seconds,
there is no longer a "rip" when the handheld is keyed, after something
has heated up. The only thing I can think of that would cool off and
heat up so quickly, are the 1N4149 diodes used for electronic switching.

Heath discontinued the HA-201 and brought out the HA-201A in the late
70s. It was a major revision that uses PIN diodes for switching.

Fred
K4DII

The best thing you can do with that amplifier is throw it away.

Why waste your time and money on junk.

BUY yourself a transceiver and forget about walkie talkies...

Walkie talkies has a couple of purposes.

If you are at a hamfest, you can use it to communicate between club members

If you are working a civic event, you can use it to communicate

If you get a flat tire, you can stick it under another tire to keep your vehicle from rolling away.

Walkie talkies are the last radio you should buy, not the first...

People confuse amateur radio with cell phones..

They want something where it is small and doesn't cost much and they can squawk on the one or two local repeaters with no investment of time, money or knowledge.. You don't need to know anything about antenna's, feed lines or sWR, all you have to do is squawk....