[Hallicrafters] DD-1 Audio amplifier


Duane Fischer, W8DBF dfischer at usol.com
Fri Feb 24 16:21:13 EST 2012


Richard,

Per my prior post of the specifications of the DD-1 by Chuck Dachis, Radios 
By Hallicrafters 2nd Edition, the frequency response was 200 Hz to 6000 HZ. 
More than adequate for speech communications and not too shabby for general 
listening either!

Because Bill Halligan, Sr., and his partner Toby, traveled the world, 
literally, to purchase the best transformers, resistors, capacitors etc. it 
is most likely that the DD-1 contained the best quality components they 
could procure.

Now let me state without prejudice, that a very brilliant Engineer designed 
the DD-1, and it did have its share of proponents and opponents among the 
Hallicrafters powers that were. This same Engineer designed two other 
receivers that I am aware of. One was a brilliant success, the other was a 
total flop. Primarily because the Engineer refused to make several changes 
in the RX that other Engineers told him were needed. Ego got in his way, the 
SX- failed badly and he lost his job.

Yes I know his name, but most of you probably know of whom I am speaking of 
already.

While I was performing around our country I used a HME Dual Diversity 
receiver with a wireless lapel microphone. It performed nothing short of 
fantastic! I suspect the Engineer who designed the DD-1 might have been too 
many years ahead of the engineering mentality of the time.

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: "Duane Fischer, W8DBF" <dfischer at usol.com>; "Waldo Magnuson" 
<magnuson at mac.com>; <Hallicrafters at mailman.qth.net>
Cc: "Waldo Magnuson" <magnuson at mac.com>
Sent: Friday, February 24, 2012 2:08 PM
Subject: Re: [Hallicrafters] DD-1 Audio amplifier


>
> ----- Original Message ----- 
> From: "Duane Fischer, W8DBF" <dfischer at usol.com>
> To: "Waldo Magnuson" <magnuson at mac.com>;
> <Hallicrafters at mailman.qth.net>
> Cc: "Waldo Magnuson" <magnuson at mac.com>
> Sent: Friday, February 24, 2012 9:37 AM
> Subject: Re: [Hallicrafters] DD-1 Audio amplifier
>
>
>> Was it a "Hi Fi" amplifier or a Dual Diversity RX?
>>
>    The DD-1 was an elaborate dual-diversity receiver. It
> was an amazing product for a company which seems to have
> been dedicated to building equipment of good value rather
> than exotic, high-end stuff. If I ever had a handbook for it
> its lost due to my archive hard disc dying. I don't know if
> it had a variable IF; Hallicrafters knew how to make them
> and used a variable IF in the SX-28 and other receivers. The
> fidelity would depend on the IF bandwidth. However, the
> amplifier was intended to drive a large loudspeaker with a
> good quality signal. I am suspicious that the performance
> might seem poor by hi-fi standards because it had too many
> transformers in it and no feedback. Most pre-1945 audio
> transformers were not very good, the best of the bunch was
> the Linear Standard series made by UTC but they were also
> about the most expensive. Western Electric also knew how to
> make decent transformers but they were found mostly in WE
> equipment. Probably this amplifier had a frequency response
> of no more than perhaps 50hz to 10Khz, perhaps less, and THD
> of perhaps a few percent. Similar amplifier stages can be
> found in a number of "deluxe" radio sets of the time.
>     The main advantage of diversity is to reduce the
> effects of fading. This includes selective fading which can
> cause severe distortion. A more modern approach would be to
> use a synchronous detector which does not rely on the
> carrier being present and combines the sidebands in the
> detected output. The result being a substantial reduction in
> the effects of selective fading. A diversity receiver with a
> synchronous detector would deliver good audio from quite
> poor signals.
>    The effectiveness of a space diversity system depends on
> the antennas. In commercial applications the antennas were
> spaced a few wavelengths apart. Dual and triple diversity
> systems were common in commercial long-haul radio circuits.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
>
>
> -- 
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