Collins R-390A/URR help?

[prcguy]

Forgive me for chiming in again but the BC-610 transmitter is a WWII item (1942) and several radio generations before the R-390A which first appeared around 1955. The companion receiver to the BC-610 would usually be the BC-312 or the BC-342. The only time you would see a BC-610 paired with an R-390A would be by pure accident, or in a ham station.

There is no 24v power socket on the R-390A that I can find unless your describing the internal wiring harness that plugs into the power supply strip on the underside of the radio. This does not have any connections to the outside of the radio and is simply the main route between the power supply and all other modules. There are no external connections to the various B+ voltages either.

The rectifier tubes in the R-390A have 26v filaments, otherwise the 12v and 6v tubes are in groups wired in series so the filaments add up to 24v. Maybe there is a really special version of the R-390 that has these external filament and B+ connections but we can't find it yet. It would certainly be worth a lot of money if it turns up.

For the last 2 months I've been slowly bringing an R-390A back to life by replacing tubes, rebuilding filter caps and doing upgrades for AGC, SSB reception, extended audio response and general alignment. Maybe its a coincidence that I've been researching all the manuals and R-390 forums recently and that's where most of my limited knowledge of this radio stems from.

Working on this beautiful piece of mechanical and electrical art also brings back good memories of an R-390 and 390A I had in High School about almost 40yrs ago. I think the going rate was about $75 back then for a working unit.
prcguy

"The R-390A Frequently Asked Questions Page is a link with information about the R390A, and clearly showing it a 115/230 VAC item."
Yes, but why then does the power socket have a 24VDC input to the heater strings? I'm still waiting to hear if there is a B+ connection on one of the rear panel strips but that should come in time. Oh and BTW I just remembered its mate was the BC610 transmitter.

 

[a29zuk]

I have a R390 (no A) at home in my garage. It's dated July 20, 1955. I remember replacing the rectifier tubes on the power supply with solid state diodes. I also seem to remember a smaller voltage tap off of the transformer in the power supply for the heaters but can't remember the exact voltage. When I get a chance I'll pull out the schematics and take a look and also see if there is B+ connection on the rear.

 

[kb2vxa]

Not to start a squabble with you PRC but you seem a bit confused. Please note the bit of my post you quoted, I never said there was a 24VDC power socket, I said there is such a pin on the power socket.

"There are no external connections to the various B+ voltages either."
Multiple connections wouldn't make sense, I'm thinking of one connection having voltages broken down internally. Still I could be wrong, it's been a long time and without the full original manual tracing it all out is a royal pain.

"The only time you would see a BC-610 paired with an R-390A would be by pure accident, or in a ham station."
You've got me there, that's exactly where I've seen them paired. Not knowing the history and not being a military radio enthusiast it looks like I'm wrong again. Thanks for setting the record straight, there's enough misinformation around here as it is.

"Maybe there is a really special version of the R-390 that has these external filament and B+ connections but we can't find it yet. It would certainly be worth a lot of money if it turns up."
So why not turn one up? You know, build one! (;->)

"I think the going rate was about $75 back then (40 years ago) for a working unit."
Yeah, I remember... WWW WWW WWWWWAAAAaaaaaaaa!

Last but not least; have fun working on your beast as I had but remember, never irreversibly modify a boat anchor unless you want to ruin it's collector value. In other words, if you drill holes in one prepare to have holes drilled in YOU! (;->)

For zuk:
"I remember replacing the rectifier tubes on the power supply with solid state diodes."
Be careful with that, they deliver more output voltage that in some cases exceeds the limits of power supply components and critical circuits. This is especially true of old electrolytics that have become used to their operating voltage and lost their headroom. In other words the rated operating voltage no longer applies. If you got away with it good for you, smoke being essential for operation cannot be replaced once it escapes.

"I also seem to remember a smaller voltage tap off of the transformer in the power supply for the heaters but can't remember the exact voltage."
You haven't been paying attention, does 24VAC sound familiar? (;->) There are more in the power supply module to operate the relays, note what I said earlier about the selenium stack going sour.

"When I get a chance I'll pull out the schematics and take a look and also see if there is B+ connection on the rear."
Never mind the schematics, they'll drive you buggy. This could be why PRC said there is none and it seems to me he's working with something other than the original manual that has all the terminals on the rear strips clearly marked in the pictorial diagrams. Since the manual I worked from stayed with the 390 owner I have no way of checking it. BTW it's in the words of Jethro Tull, "thick as a brick" and really should be titled (to borrow another book title) Everything You Ever Wanted To Know About The R390 But Were Afraid To Ask. (;->)

 

[jim202]

"The R-390A Frequently Asked Questions Page is a link with information about the R390A, and clearly showing it a 115/230 VAC item."
Yes, but why then does the power socket have a 24VDC input to the heater strings? I'm still waiting to hear if there is a B+ connection on one of the rear panel strips but that should come in time. Oh and BTW I just remembered its mate was the BC610 transmitter.

There were several versions of the BC610. Been a number of years since I played with those, so can't
remember the different models and versions. There also should be a box of coils to go with the BC610
that would be changed out in the PA tuning section. The coils were determined by the range of
frequencies that you were operating the transmitter on.

Both the R390 and the BC610 were best in a cold climate as they tended to heat up the room they
were used in. Would also be best if the light company has cheap rates when you use either of
them.

 

[a29zuk]

For zuk:
"I remember replacing the rectifier tubes on the power supply with solid state diodes."
Be careful with that, they deliver more output voltage that in some cases exceeds the limits of power supply components and critical circuits. This is especially true of old electrolytics that have become used to their operating voltage and lost their headroom. In other words the rated operating voltage no longer applies. If you got away with it good for you, smoke being essential for operation cannot be replaced once it escapes.

(;->)

Thanks for the heads up. Been using the solid state diodes for almost two years...so my luck has been good so far.

I haven't met an electronic tech or an electrician yet that has ever been able to put the smoke back into a component.

 

[jackj]

I used to replace rectifier tubes with solid state diodes from time to time, mostly when the tube was unavailable or too costly. I added a resister in series with the output of the diodes. The value of the resister was determined by the current the power supply delivered but was usually around 100 to 470 ohm, 2, 5 or 10 watt. The resister actually performed 2 jobs, it limited the current in-rush to the filter caps on startup which protected both the diodes and filter caps and helped to lower the B+ voltage to equal that of the tube type rectifier.

 

[kb2vxa]

"Both the R390 and the BC610 were best in a cold climate as they tended to heat up the room they
were used in. Would also be best if the light company has cheap rates when you use either of
them."

If you think that's something try teaming the 390 with a 1KW AM broadcast transmitter re-tuned for 160M. Not only do they keep the shack warm but the electric meter looks like it is about to take off into the stratosphere. From the sublime to the ridiculous, this ham shack near Scranton, PA houses a 10KW Collins 21E powered by 480V 3 phase.