[Hammarlund] Old Hammarlunds

[Kenneth G. Gordon]

On 12 Apr 2011 at 14:15, Richard Knoppow wrote:

>     I used a BC-779 as my station receiver for some years. I 
> used several experimental LO and RF circuits in it at one 
> time or another.

Could you describe those for us, in general?

> The main improvement to stability was 
> adding a VR tube regulator to the oscillator.

I did that to a National RBL and it made a significant difference. It became 
almost as stable as my RAL-7.

>     The extended range version of the RX, which trades the 
> 540khz to 1250khz range for 20 to 40 mhz uses a different RF 
> circuit with the amplifiers shunt fed rather than series 
> fed. This probably increases the effective Q of the RF 
> stages and reduces image response somewhat.

Interesting information, thanks.

>     Somewhere I have a military communications manual c.WW-2 
> which has charts showing performance characteristics of 
> various receivers available to the signal corps at that 
> time. The Super-Pro is head and shoulders better than any 
> other in terms of lack of image or spurious responses and 
> some other characteristics.

I would LOVE to see that!

> The SX-28 looks awful in 
> comparison. These were probably the best receivers available 
> at the time and were also the most expensive. I think its 
> likely the RCA AR-88A would probably have bettered it in 
> some ways but does not seem to have been used by the signal 
> corps.

For some strange (to me) reason, as I understand it, almost all of those went 
to the UK. There are very few here in the U.S. 

I was also told some time ago that an entire freighter-load of those was sunk 
just off Seattle during WWII, not by enemy action, but by some accident.

> I am not sure when the AR-88 design originated, it 
> may have been too late.

No. Hundreds of those were used in UK listening stations during WWII.

>      The Super-Pro also had Hammarlund's exclusive variable 
> IF, done with a mechanical arrangement to change the mutual 
> inductance so that the curves remained farily symmetrical 
> and did not change center frequency, plus Hammarlund's 
> patented crystal filter, the best of the bunch.

Yes. Absolutely!

>      Another note, someone asked about the Pro-310, it was 
> from all reports, a dog. I remember when they came out 
> lusting after one but they had a lot of problems including a 
> low frequency IF causing serious image problems on the lower 
> bands where it was single conversion.

I think it was 52 Khz...at least one of the IFs was...

> It was also a 
> mechanical nightmare. Not many were built before they were 
> discontinued and I suspect H lost a lot of money on them. 
> They look sexy but were not very good receivers.

Hmmm...I have heard that before from others. Well...at least it WAS really 
sexy looking...

Ken W7EKB