[Boatanchors] Hammarlund Pro 310 Rcvr on eBay

[Robert Nickels]

On 12/29/2011 4:53 PM, Richard Knoppow wrote:
> I am under the
> impression that the Pro-310 is single conversion on the two
> lowest bands using a 50khz IF. If so it would have pretty
> bad image response in this range despite the -50db spec.
> Does anyone know if this is indeed the case.

You are correct Richard.  The PRO-310 is double conversion above 2.2 mc, 
single conversion below that.  A separate 1.75 mc oscillator is enabled 
for the lower two bands to convert directly to the 52 kc IF.

Like the SX-88, the PRO-310 was obviously designed with a certain set of 
customers in mind (I doubt even back then the bean counters allowed 
phrases like "cost is not a factor" to be used!)     I don't know how 
disappointed the companies were with sales figures, as they knew the 
market well and perhaps saw these receivers more as a "statement" about 
the level of design and performance they were capable of, similar to 
some high-end automobiles.      In 1955, single sideband was still just 
a novelty so there's no surprise it did not play a greater role in 
defining the feature set, but clearly things like mechanical stability 
and bandspread repeatability were considered important.    Having 
completely rebuilt the double gearbox of the SX-88, I can say that the 
mechanical complexity of the PRO-310 is vastly greater, and also the 
weakest point in the design.    I know the drive cord system in mine 
needs attention, fortunately there is a very detailed Electric Radio 
article that shows how it's done.   You can get some idea of the 
mechanical construction at W8ZRs website:  
http://www.w8zr.net/vintage/receivers/pro310.htm

Back in the day, the performance differences would have been more 
apparent, perhaps.  I can't imagine Hammarlund ever made any money on 
them,  so maybe low sales were a blessing in disguise.  Maybe there were 
PR benefits from using the PRO-310 as a showcase for their 
capabilities.   But today it's just another interesting boatanchor radio 
with a combination of good and bad points,  although it certainly is unique.

I have a little 12 page booklet that was published by Hammarlund called 
"The PRO-310 Story".   It's advertizing fluff, but also provides insight 
into what the company was thinking:  "The PRO 310 the the culmination of 
a carefully planned intensive engineering development program of more 
than two years duration, based upon studies and investigations prompted 
by our customers".

"This superb receiver is by no means an accident - it is certainly not 
the result of a pressured effort to get a piece of merchandise out onto 
the market by a specified date with the usual number of compromises 
which must result from "Engineering by Crisis".

Signed by Lloyd A.Hammarlund, President

73, Bob W9RAN