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Author Topic: R390A vs Tentec VII  (Read 54217 times)

Posts: 1284

« Reply #30 on: September 25, 2013, 01:47:21 PM »

There  was an input by me to Technical Topics in RSGB RadCom, but I can't remember when: probably after about 1997. That was using a 6SH7 (octal)/6AU6 (miniature) as a BFO/product detector.

If you really need to know how to make a Hartley oscillator with a cathode tap on the coil, the SSB signal fed in on g3 and the output on the plate, I guess I can find time to make you a circuit diagram.

Posts: 18464

« Reply #31 on: September 25, 2013, 01:57:03 PM »

I was hoping you'd remember the article, Peter, and perhaps have a copy on hand, as all I have
are the Technical Topics Scrapbooks, and I'm not sure which box they got packed into.  It
did generate a lot of feedback on whether the old receivers actually needed a product detector
or not.  Many have marginal BFO drive for good demodulation at high signal levels, so backing off
the RF gain control was an important part of the process for CW.

I'm assuming that the R-390 has a BFO, but the injection level and detector linearity are not
optimum for clean SSB, which is why an external product detector is desirable.

Posts: 1742

« Reply #32 on: September 25, 2013, 06:48:42 PM »

If I did an external SSB adapter for the 390A, I'd tap off the 390A bfo with a jfet, boost it with a simple amp and use a diode ring mixer (homebrew or otherwise) mix it with the 455 out and feed the audio into LM380 or similar and then into what ever audio amp you like, if you even need another audio amp.

Actually the radio will work pretty good in SSB if you will deal with the RF control while listening to SSB instead of the audio control.  Just turn the audio up about 60-80% and control the audio with the RF gain.  Of course your filters and AGC needs to be up to spec, or just turn off the AGC.

Only trouble with the 390A is the choice of filters for SSB.

You can use HDSDR with the 390A if you care to convert the 455 to 12KHz and use your sound card.  The AM is real good with that option.  I even use the HDSDR with my TS-2000 and pulled out the 12 KHz output for that.  AM is real great that way, you can have any bandwidth you like, as long as the signal is good.

Posts: 55

« Reply #33 on: September 26, 2013, 08:05:41 AM »

I know for existence of this product, nice piece of electronics but unfortunately this is not what I am looking for. I want to built detector by myself, using my knowledge and patience for homebrew electronics...Beside of this detector, and one from Surrey will be possible to find some other somewhere on the net or in drawer?

Pozar, Bob from Treetop Circuits wanted me to advise you of the following, maybe this could still help you with your request.

The circuits used in our products are (as you know) fully described in our instruction books, which can be downloaded from our website. We have no objection to folks copying them for their own use. If he replicates some or all of the SB-390 circuitry, and adds a BFO and a 24-volt AC supply, he'll have a good "outboard" adapter that will perform as well as the SB-390. I'd recommend a BFO with some range of adjustment, because the best results are obtained when it's adjusted to the right frequency relative to the mechanical filter.

I really like the 4-diode detector because it has a soft clipping action when overloaded. You can get quite good results even with no AGC. You have to "ride" the RF gain, but it's much more forgiving than the detector in the R-390.

Good Luck,

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