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Author Topic: R-390A Advice  (Read 28135 times)
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W2PFY
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« Reply #25 on: August 01, 2011, 03:40:05 PM »

Looks very clean. What are those small trimmers caps about on the chassis to the left?

Looks to have a vernier drive in there too. Never seen anything like it.
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« Reply #26 on: August 01, 2011, 04:19:13 PM »

Here in the old continent the 390 is a myth. Every boatanchorer have to own one, and so i did. I decided for a collins 390 sn 51. It is in very good shape and aligned, but for me it is not the best of mine vintage receivers. Without the diode output to amp trick the audio is mediocre. The 8khz filter is too wide sometimes and the 4 khz too narrow for Am. it is not a bancruising receiver, and without the tmc-590 the ssb reception is ugly. I am sure that is a great receiver for point to point applications, but my recently restored RCA ar-88 receives the same stations but with a really better out of the box audio.
And you have to ear the R&S ek07d. Anyway the 390 is a very nice receiver
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« Reply #27 on: August 01, 2011, 04:47:09 PM »

The new/different potentiometer upper bracket: The original one turn pot was too course! The carrier level meter would not hold zero. So a 10 turn wirewound 2 watt pot is the answer.

Those trimmer caps, don't have a clue.

Craig,
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« Reply #28 on: August 01, 2011, 07:18:36 PM »

I never saw the extra stuff on the Left Side like that. (trimmer caps, and  trim pot?)
The BFO "counter?" on the front panel is new to me.

nice clean condition !!!! Any documentation on the mods??
Looks like a nice receiver to me
Fred
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« Reply #29 on: August 01, 2011, 11:40:56 PM »

An easy cure for the "carrier meter won't zero" problem is a 100 ohm or so resistor in parallel with the outer legs of the pot.  It carries part of the current so the pot doesn't heat up and drift, and puts your zero on a new place in case you have a dead spot in the pot right where you need it.
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« Reply #30 on: August 02, 2011, 01:12:11 AM »

The best way to use an R390A is with a Rycom R-1307 at the IF output to receive the station you want, after finding it with an SX-28 or whatever fast-tuning set you like. If that sounds like a lot of trouble, it is said that nothing worthwhile is easy.
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« Reply #31 on: August 02, 2011, 03:28:57 AM »

The turns counter on the BFO knob is rather common,  it's an RTTY depot mod.  The other items are ham creations.  The trimmer thing might be described in Hollow State Newsletter but I don't recall it.
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« Reply #32 on: August 02, 2011, 07:06:56 AM »

An easy cure for the "carrier meter won't zero" problem is a 100 ohm or so resistor in parallel with the outer legs of the pot.  It carries part of the current so the pot doesn't heat up and drift, and puts your zero on a new place in case you have a dead spot in the pot right where you need it.

Thanks John..........solved a LONG problem here. DONE!!
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Fred KC4MOP
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« Reply #33 on: August 02, 2011, 07:42:00 AM »

Here in the old continent the 390 is a myth. Every boatanchorer have to own one, and so i did. I decided for a collins 390 sn 51. It is in very good shape and aligned, but for me it is not the best of mine vintage receivers. Without the diode output to amp trick the audio is mediocre. The 8khz filter is too wide sometimes and the 4 khz too narrow for Am. it is not a bancruising receiver, and without the tmc-590 the ssb reception is ugly. I am sure that is a great receiver for point to point applications, but my recently restored RCA ar-88 receives the same stations but with a really better out of the box audio.
And you have to ear the R&S ek07d. Anyway the 390 is a very nice receiver

A couple of simple mods and they (390As) receive SSB like they were made for it. Just reduce the size of the plate dropping resistor for the BFO, and increase the size of the BFO injection coupling cap and they will receive sideband like a pro without installing a product detector. Mine has been that way for over 20+ years. 2 components to change is not a lot of work to do for what you get back.
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« Reply #34 on: August 02, 2011, 08:31:10 AM »

Quote
A couple of simple mods and they (390As) receive SSB like they were made for it. Just reduce the size of the plate dropping resistor for the BFO, and increase the size of the BFO injection coupling cap and they will receive sideband like a pro without installing a product detector. Mine has been that way for over 20+ years. 2 components to change is not a lot of work to do for what you get back.

Tell us more please. Is there a spot on the WWW where I can find this mod?

And where do you purchase a Rycom R1307?
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« Reply #35 on: August 02, 2011, 08:50:06 AM »

Terry,
        I'm at work, so I dont have the skizmatic here. Without looking at the skiz for the IF deck I dont remember what the the resistor and cap numbers or values were. I'm sure someone has it posted on one of the R390 reflectors somewhere. It used to be a pretty common mod. But it is very simple to do and mine receives SSB like it is made for it. You rarely ever have to back down the RF gain, if you do, it is only on the strongest needle-pinning signals. Just set the BFO +1kc for lower sideband and -1kc for uppa sideband and the tuning dial stays the same.

IIRC, the BFO only runs with 12 or 20 volts on the plate. So dramatically reducing the resistor and doubling the size of the coupling cap should get you somewhere in the ballpark. JN might remember what the values of the parts were.

IIRC, the old "rule of thumb" was that you needed to have BFO injection = to 10X the IF signal to the detector for "distortion free" SSB reception.
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The Slab Bacon
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« Reply #36 on: August 02, 2011, 09:11:37 AM »

An easy cure for the "carrier meter won't zero" problem is a 100 ohm or so resistor in parallel with the outer legs of the pot.  It carries part of the current so the pot doesn't heat up and drift, and puts your zero on a new place in case you have a dead spot in the pot right where you need it.

I have seen that on some of the ones I have worked on over the years. Hmmmmmmm.........

I always wondered what the full scale meter rating and was. They are something wierd, and a standard 1mA meter movement or universal "S" meter wont work right in them.
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« Reply #37 on: August 02, 2011, 12:50:10 PM »

A good working R390A s meter is pretty accurate. Full scale is .1 volts, 100dBuv.
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w3jn
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« Reply #38 on: August 02, 2011, 01:21:27 PM »

An easy cure for the "carrier meter won't zero" problem is a 100 ohm or so resistor in parallel with the outer legs of the pot.  It carries part of the current so the pot doesn't heat up and drift, and puts your zero on a new place in case you have a dead spot in the pot right where you need it.

Thanks John..........solved a LONG problem here. DONE!!

Cool!  Glad it worked for you Fred.
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« Reply #39 on: August 02, 2011, 01:31:38 PM »

The best way to use an R390A is with a Rycom R-1307 at the IF output to receive the station you want, after finding it with an SX-28 or whatever fast-tuning set you like. If that sounds like a lot of trouble, it is said that nothing worthwhile is easy.

Or just use a HRO-500 to start with; it will hear stations with a 30' wire that is buried in the 390 mixer noise.

IMO a slightly improved 51J4 is a better cruiser than either the 390 or 390A
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flintstone mop
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« Reply #40 on: August 08, 2011, 07:20:31 AM »

An easy cure for the "carrier meter won't zero" problem is a 100 ohm or so resistor in parallel with the outer legs of the pot.  It carries part of the current so the pot doesn't heat up and drift, and puts your zero on a new place in case you have a dead spot in the pot right where you need it.
Peeked inside my 390A for some maintenance needs and see a 22 ohm across the pot...is that good enough or 100 ohm better?? I might find a 10 turn pot also. Possibly my carrier pot has bad spots. Meter never settles. One day on zero next two hours on 20.
Thanks
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Fred KC4MOP
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« Reply #41 on: August 08, 2011, 11:19:19 AM »

That should be fine, Fred.  The problem is that there's a fair amount of power dissipated in that pot and it drifts, gets bad spots, etc.
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« Reply #42 on: August 08, 2011, 01:05:48 PM »

That pot has been a source of problems forever, as Johnny sez. There's a precision ten-turn pot available that addresses it pretty well along with the other suggestions.

A couple of simple mods and they (390As) receive SSB like they were made for it. Just reduce the size of the plate dropping resistor for the BFO, and increase the size of the BFO injection coupling cap and they will receive sideband like a pro without installing a product detector. Mine has been that way for over 20+ years. 2 components to change is not a lot of work to do for what you get back.

Sounds a lot like the Dallas Lankford AGC mod, Slab:

- one diode in parallel with R547, cathode as follows

  ---]<--- pin 2 V506A

- one diode in parallel with R546, cathode as follows

  --->[--- pin 1 V509A

- one 47 pf cap in parallel with C535

Quick and easy, easily reversible, and gives excellent results. Assuming that SSB reception without riding the RF gain is important, of course.

Phil, you got an excellent receiver. Looks pretty clean and complete. Should give you many hours of enjoyment and utility. Still the best receiver buy out there IMO. The microdial on the BFO is a mod for RTTY/RATT use as someone mentioned. ASA and a couple other groups used this. Wonder if you have a sticker on the back apron from one of them? Could be someone just added it for the coolness factor. They do make fine tuning of the BFO quite smooth along with adding a measure of logging.




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« Reply #43 on: August 08, 2011, 02:35:24 PM »

R390As are for people who actually get on the air.
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flintstone mop
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« Reply #44 on: August 08, 2011, 04:26:49 PM »

R390As are for people who actually get on the air.

I better get my ARSE in gear........thanks Dave
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Fred KC4MOP
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« Reply #45 on: August 08, 2011, 04:44:12 PM »

Not meant for you Phred. It's just anyone who operates at night on the lower bands knows how useful those wrist twisters really are.
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« Reply #46 on: August 08, 2011, 07:22:00 PM »

True story, though the passband tuning on the 75A-4 sure comes in handy, along with the mechanical filters, in such conditions. They've come down a lot in price, a decent one just sold for $660 on epay t'udder day. If you're not a collector, it's a $500 radio.

The 390s aren't as easy to tune, but then - they were never meant to be band cruisers. I seldom tune around when in conversation with others anyway.  Grin
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