Re: Early solid state power amps

On Mon, 30 Jan 2006 13:17:49 -0500, "Arny Krueger" <arnyk@xxxxxxxxxx>
wrote:

>"Steve Urbach" <dragonsclaw@xxxxxxxxxxxxxxxxx> wrote in
>message news:5cvqt1pfb0b2cshb31tj1bnufvkuf1tc19@xxxxxxx
>> On Mon, 30 Jan 2006 02:38:04 GMT, "JohnR66"
>> <nospam@xxxxxxx> wrote:
>>
>>> When did decent solid state power amps become available?
>>> Were they direct, capacitor or transformer coupled to
>>> the load. Back in the 60's when the first audio amp ICs
>>> became available for battery powered radios and such,
>>> the engineers coupled the output through a transformer!
>>> It seemed hard to wean them off the transformer. Finally
>>> in the 70s...
>
>> My 1963 Heathkit AA21 was a transformerless bridge output
>> (neither lead grounded nor common with the other channel)
>> 8 Ohms was the MINIMUL load (the included a 4 ohm
>> wirewound in series with the terminal labeled 4 ohms).
>
>
>
>My recollection is that there was an interstage driver transformer, and the
>output was *not* bridged.
>
>The output stage was a so-called "totem pole" configuration with 2 output
>transistors effectively in series per side, 4 OPTs per channel.
>
>This was a rather fragile amp. There was a lower-powered version the AA-22
>and it was fragile as well.
>
>IME running a 4 ohm speaker without the 4 ohm series resistor would fry this
>amp pretty quickly, as would shorts.
>
>
I could have misremembered the output configuration, and YES there was
a interstage transformer.

I drove a Pair of Altec 605A (16 ohm) so i did not worry.
Burnt out Dial lights (#47F) across the top and Noisy level controls
were the repairs that got done in the 6 years this amp was in service.
.

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