[Hammarlund] Old Hammarlunds - audio output power

[Richard Knoppow]

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: <Hammarlund at mailman.qth.net>
Sent: Sunday, May 15, 2011 12:52 PM
Subject: Re: [Hammarlund] Old Hammarlunds - audio output 
power


> On 14 Apr 2011 at 17:37, Carl wrote:
>
>> The military and commercial enviroment some of those sets 
>> were
>> initially used in might have needed that much power.
>>
>> We are listening to AM, not a symphony or some wailing 
>> opera
>> screecher.
>
> Actually, those receivers came with a phono input, so 
> maybe some of them,
> at least, were used for listening to a symphony. :-)
>
> What was that very rare Hammurlund in the wooden cabinet? 
> The SP-155,
> or something?
>
> Maybe Hammarlund just figured that once that 14 watt audio 
> stage was in
> their receivers, they might as well leave it there.
>
> Ken W7EKB

    At the time the Super-Pro was first put on the market 
many "deluxe" radio receivers had fairly high power, 
push-pull audio. It was sort of a horsepower race, plus the 
Super-Pro was a very high performance receiver for broadcast 
use and quite high fidelity. Remember, this was before TV or 
FM and the main source of entertainment broadcasting was AM 
radio. Also, many listened to short wave station which could 
sometimes deliver good quality audio. The push-pull stage in 
the Super-Pro and in other receivers of the time also had 
the advantage of lower distortion and much better low 
frequency responce than the usual single-ended output stage. 
Actually, despite its being overkill for communications use 
I found the low distortion of the Super-Pro reduced the 
effects of noise and QRM due probably to its lower IM and 
harmonic distortion. This can make a surprizing difference 
even for CW.
     BTW, I strongly disagree with Carl about "headroom" or 
the ability of an amplifier, or whole system to deal with 
peaks. While this is of little relevance when the sources 
are highly processed to eliminate peaks it cerainly makes a 
difference for high fidelity reproduction. I mis-spent a 
large part of my life in professional audio and know how 
much difference good peak handling can make to the sound 
even though the peaks may be short. Certainly even one watt 
on a high efficiency loudspeaker can make a very loud sound 
but many high quality systems trade efficiency for bandwidth 
and are far from efficient plus the peak to average ratio of 
unprocessed music, or even speech is surprizingly large. 
Even if only twenty db the peaks for a 1 watt average will 
be 100 watts (db power ratio).
     Typical medium high efficiency speakers will be around 
94db SPL at one meter from 1 watt. 94db is _very_ loud. If a 
speaker system does not need to reproduce low frequencies 
(say below 250 hz) it can be made to have very high 
efficiency especially if using horn loaded compression 
drivers of the sort used for public address applications. 
Because these have high conversion efficiency and are also 
quite directional they will produce ear-splitting levels 
from a watt at a few feet.
     On an old-fashioned horn loaded movie theater speaker a 
couple of watts will be quite sufficient. Typically old 
style theater amplifiers were around 10 watts for smaller 
theaters but then the dynamic range of old photographic 
sound traces was rather limited.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com