[Boatanchors] Embarrassing Rookie Question

[Richard Knoppow]

      The open box speakers used for most communications receivers are 
pretty bad having poor low frequency response and usually a resonance in 
the lower mid-range.  Almost any of the speakers in them will sound a 
lot better is a plain sealed box  of reasonable size.  The walls should 
be well braced and it helps to fill the cabinet with glass wool.  Three 
cubic feet is enough for anything up to 12" an smaller for smaller 
speakers.  A bass reflex will bring up the lows but must be tuned 
correctly or it will be tubby and make things worse.   Don't worry about 
the highs, most single cone speakers are good to at least 8Khz and often 
higher plus this receiver is pretty selective and probably does not have 
much output beyond about 4 or 5 khz from the radio.
       Most of these small speakers will also do well on a large flat 
baffle. About four feet on a side is enough but the larger the better.  
Actually, the closed box is more compact for the amount of bass it will 
produce.  It is amazing how good some of those cheap speakers sound when 
in any sort of decent enclosure.

On 3/14/2015 4:22 PM, Rob Atkinson wrote:
> I am not sure what your goal is, but if it is to have nice booming
> audio from that p.p. output stage, then it is hard to beat an old bass
> reflex wood cabinet with a 12 inch full range speaker.  You can find
> old speakers such as that at hamfests.  Look for Jensen, CTS (the made
> them for a number of manufacturers such as Zenith) RCA or GE.  The
> "bass" speakers in old stereo consoles were these with a simple cross
> over network that sent the high frequencies on to other elements.
> But, with nothing on them but the secondary of an output transformer
> they work fine up to 12 kc and are perfect for ham and SWL radio use.
> They can be had at hamfests for $3 each.  Bring an ohm meter to test
> the coil resistance.  With a good coil and visible cone inspection you
> are good to buy.
> A speaker like that in an old Electrovoice Aristocrat cabinet with a
> baffle port opened will sound fantastic compared to the matching metal
> box speaker most manufacturers sold.  Then you can leave the
> transformer in the NC200 cabinet.   You can find cabinets at hamfests
> or on craigslist.   A liittle work with murphy oil soap and Old
> English polish and you'll have that distressed old buzzard look that
> goes great with a vintage set (in my opinion).
>
> 73
>
> Rob
> K5UJ
>
>
>> I just picked up a beat-up NC-200 today as my latest project. I don't have the speaker, so is it OK if I work on this radio with headphones, no speaker, and the 6V6s removed?
>> Once I get this set working well, I plan to fabricate a new speaker by taking a traditional speaker in a metal box, installing a push-pull output transformer in the box, and making a cable ending in a five-prong plug. I recently did that with a Patterson PR-12 and it worked out very nicely. I doubt that I'll get lucky enough to find the proper National speaker at any hamfests this year.
>> As always, thank you for your help.
>>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL