[R-390] Cost reduction Ect Ect

[eldim at att.net]

Hello Bernie and crew,
I'd sure love to hear more info on ZENITH'S invention of the mechanical filter.
i.e. History, Dates, etc.
73,
Glen Galati, KA7BOJ
Tacoma, WA

-------------- Original message from "bernie nicholson" <vk2abn at bigpond.net.au>: -------------- 


> Hi guys I have three 390a rx s and a 391 and I also have one of the last racal 
> Ra17 rx s made the Aust. army date code for manufacture is 9th month 1974 , its 
> a nice reciever and it is very slightly more sensitive than a 390A, when 
> evaluated with a signal generator {The American RA17 RX s Had A FRAME grid tube 
> in the RF section and the rest of the world got a Cascade Double triode } BUT in 
> practical terms the the 390A outperforms it due to a FAR better signal to noise 
> ratio which is a function of the 2khz mechanical filter, [ I am Talking SSB 
> reception here ] if I wanted to listen to a broadcast station the racal RA17 has 
> nicer audio , the dynamic range of the 390A is Much better than Ra 17 around 
> 20Db in fact , the 100Khz I F in the Ra17 Just cant compete with the mechanical 
> filter for ssb and neither can the I F stage in the 390 rx ,I know that the 
> 390A project was to save money and it achieved that end BUT between the time of 
> the original concept and the 390A project Mechanical filters were invented By Mr 
> Adler at Zenith radio Corp and it became possible to exceed the original 
> performance specsof the 390 with less stages and also to take advantage of more 
> modern tube design , overall I see many advantages for owners of 390A receivers, 
> The tubes are Plentiful and easy to source, here in Australia 6AJ5 /6BJ6 /6082 
> ,are in the same supply status as rocking horse droppings and from what I hear 
> in the states people who have these tubes want an arm and a leg for them , on 
> the minus side with the 390A there is an ongoing problem whith the mechanical 
> filters, the foam rubber packing inside the filter with the passing of the years 
> has De -materialised and also become corrosive , especially the 4khz filter,I 
> have replaced a couple myself in the last few years but I bought a few spare IF 
> modules many years ago , summing up I would say that there is no BEST receiver 
> it all depends on what ones interests are, BUT if you want to work DX on forty 
> meters at night in amongst the broadcasters on SSB or CW the 390A is the way to 
> go !!!!!!!!!!!!!!!!! PS I wonder how much Collins Paid Zenith for the 
> Mechanical filter production licence??????????? Best Regards to everyone BERNIE 
> N 
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