Hallicrafters R-274/FRR/SX-732

[WB4AM]

Hello,

I picked up a Hallicrafters R-274/FRR/SX-73.

It seem to hear well from 75 meter down to the AM broadcast frequencies 55khz.

It uses a Turret device that has all the coils and such for all the bands.  As the Turret is turned there are finger stock contacts that meet up with the Metal Contact Tips on the Turret for each band.

From what I can see, the Finger Stocks are in tact.  I have sprayed Detox on these contacts and rotated the turret several time with no prevail.

Has anyone had this issue with their Hallicrafters of the same model?  Is there a quick fix or any suggestions on what might be going on or not going on in this case?

Thank you,
Ken

[w1vtp]

Ken

You're luckier than I am.  My SX-73 works on some bands - sort of.  I think you should be prepared to remove the various boards from the turrent and check for obvious problems.  While working on mine the plastic covers of a silvered mica cap fell out of the bottom.  That's when I stopped working - mostly turning the unit on until I at least check as I suggested.

Nice receiver -- too bad Hallicrafters had to use what appears to be sub military standard components

Gl, Al

[WB4AM]

Hello Al,

I have taken one of the boards off just to see what they are all about.  There's not much to them.

Do you know if the Turret is difficult to remove to inspect the underside of the chassie where the finger stocks are?

Here are two pictures of the one I picked up.

Thank you Al. 

[w1vtp]

Never got that far.  Too busy being retired     Maybe you will inspire me to pick up the project again

Al

[MikeKE0ZUinkcmo]

You might consider picking up print copies of TM11-897 and SX73 manuals.

[WB4AM]

Hello Mike,

Thank you so much for the link.  I have read on page 25 the mentioning of a "K1" which is a relay that connects the IF to 6MC which in turn has something to do with the upper bands 7MC / 54MC.  This made be a good place to start.  That is, if I read it correctly.


Page 31 states the "IF" gets 24 volts to the relay to activate it.  I guess I should find the relay and check for 24 volts on the coil when the band selector is in the upper portion where I am having an issue.

Imagine that, reading the manual to find some answers!  Who would of thought?  Yes I am kidding, well maybe a little!

Okay Al, lets get the manual out and place our R-274/SX-73 on the bench and see what we can find!

Again Mike, thanks for the link and the encouragement!

Ken

[w1vtp]

On 40 meters ( and certain other bands) the IF circuit becomes part of a double conversion circuit.  If 40 meters works OK then that circuit is working OK.

Yeah, if you do not have a manual that's your next task.  I got mine from eBay and it's a high quality manual.  There are really good sections in it on how the beast works.

Al

[Pete, WA2CWA]

I also have the military R-274/FRR complete manual.

[w1vtp]

I also have the military R-274/FRR complete manual.

As the Duke would say "Well, there ya go."

That's your next assigmnent.  Honest!  It's a good read.

Al

[WB4AM]

On 40 meters ( and certain other bands) the IF circuit becomes part of a double conversion circuit.  If 40 meters works OK then that circuit is working OK.

Yeah, if you do not have a manual that's your next task.  I got mine from eBay and it's a high quality manual.  There are really good sections in it on how the beast works.

Al

Hello Al,

My R-274/FRR/SX-73 is only working from 75 meter down to the Broadcast Band.  All bands from 40 meter on up are dead and act as if the receiver isn't even on. 

I have a copy of the manual from the seller who said he down loaded it from Bama. 

But it would be nice to have the original manual.

I down loaded the manual from the link Mike had given earlier.  Its a great manual indeed.

I have not had a chance to locate the relay mentioned in the Manual, but I will let you know what I find when I do.

Al when you say yours work...sort of, what do you mean?  Is it intermittent or is it maybe just low in receive?

Ken
 

 

[WB4AM]

Hello,

Well I found "K1" which the manual says its a relay for the bands 40 meter and above when turning the Turrent band Selector to 40 or above.  It is under the chassie in the back left hand corner as if the transmitter was not flipped over.

I was able to get two small modified wooden wedges in there and pulled the contacts together.

Well low and behold the receiver came a live!  So apparently the relay is not connecting the contact together.

***********CORRECTION***********EDIT 12-08-2015***********************************
After looking at the relay again to double check voltages, I found the RELAY to to be a Double Pole Double Throw Relay.
********************************************************************************

It is a double pole single throw relay that looks to have rg58 coax coming to it.  ALL 4 runs of coax go to a pin of a tube socket from underneath.  In other words there are 4 tubes that are involved and two tube pins come together on one set of contacts and the two pins of another set of tubes come together on the other set of contacts on the relay when energized.  Hope that's clearer!

When rotating the band switch the relay does not engage.  So, is it a bad relay or is it not getting voltage to the relay?  If no voltage to the relay, is it due to the Turrent Band selector contacts or is there something between the band selector contacts and the relay that is not completing the circuit?

Sorry, I haven't gotten any farther!  I thought I would just report what I have found so far.

I am wondering if anyone else has come across this and what have they found?

Thank you,
Ken

[W3GMS]

Hi Ken,

I don't have the schematic for your receiver, but I would measure the voltage on the relay coil and that will tell you if the relay is trying to be activated.  If you measure voltage at the coil and the switching is not occurring, you can assume a problem with the relay

Sounds like you are making progress and that's good!

Joe-GMS  

[w1vtp]

You really need that schematic.  you can get it from Pete or eBay.  Yes, the relay is needed as the sx-73 mixes to 6 MHz.  Be interested in what you find out

My 73 works on some bands.  I think I have some problems with the turrent and probably some components on it.

[MikeKE0ZUinkcmo]

I am wondering if anyone else has come across this and what have they found?

Why yes I did, it works.

[WB4AM]

Hi Ken,

I don't have the schematic for your receiver, but I would measure the voltage on the relay coil and that will tell you if the relay is trying to be activated.  If you measure voltage at the coil and the switching is not occurring, you can assume a problem with the relay

Sounds like you are making progress and that's good!

Joe-GMS  

Hello Joe,

Well you hit the nail on the head!  I was hoping for the best and expecting the worst.
I thought there would be an issue with the Turrent not making the contact before an issue with a relay.
I am glad its not the Turrent.

I was getting 31.2 volts up to 32 volts depending where the band selector was positioned on the terminals of the relay coil.  I think the manual said 28 volts, but this must be with a load on the circuit.

I also place the band selector back on 75 meter and checked for voltage, which there were none as expected.  Then move the band selector again above 75 meter and checked the voltage again and there were voltage as expected.  I did this a couple of times to be sure I was seeing what I was seeing!!!

So, now that I discovered its a relay, where do I find a relay that is the same as the original?  The original relay mounts with two screws to the chassie above the relay.  Having another type of relay might cause an issue when mounting.  

I can see its going to be a pain to unsolder and resolder the relay, but I guess this is what its all about when it comes to repairing these rigs.

Now to find a relay!  Thank you Joe.

Ken

[WB4AM]

You really need that schematic.  you can get it from Pete or eBay.  Yes, the relay is needed as the sx-73 mixes to 6 MHz.  Be interested in what you find out

My 73 works on some bands.  I think I have some problems with the turrent and probably some components on it.

Sorry to hear that Al.  The manual says use two guys when removing the the Turrent.  One to hold the Turrent in place, while the other guy removes the axle so not to mess up any of those Turrent contacts.

Ken

[WB4AM]

I am wondering if anyone else has come across this and what have they found?

Why yes I did, it works.

Gee, thanks Mike your a big help!!!!

Well it looks like I am making some leeway.  Mike, was it you who placed a link for the manual?  Its now gone?

Ken

[kg7bz]

Years ago (early 1990's) I scanned the manuals for the R-274/FRR and R-274A/FRR, they're on bama, been there for years. I did many other military manuals that are there too.

http://bama.edebris.com/manuals/military/r274/

http://bama.edebris.com/manuals/military/r274a/

August KG7BZ

[WZ5Q]

Hello Joe,

Well you hit the nail on the head!  I was hoping for the best and expecting the worst.
I thought there would be an issue with the Turrent not making the contact before an issue with a relay.
I am glad its not the Turrent.

I was getting 31.2 volts up to 32 volts depending where the band selector was positioned on the terminals of the relay coil.  I think the manual said 28 volts, but this must be with a load on the circuit.

I also place the band selector back on 75 meter and checked for voltage, which there were none as expected.  Then move the band selector again above 75 meter and checked the voltage again and there were voltage as expected.  I did this a couple of times to be sure I was seeing what I was seeing!!!

So, now that I discovered its a relay, where do I find a relay that is the same as the original?  The original relay mounts with two screws to the chassie above the relay.  Having another type of relay might cause an issue when mounting.  

I can see its going to be a pain to unsolder and resolder the relay, but I guess this is what its all about when it comes to repairing these rigs.

Now to find a relay!  Thank you Joe.

Ken

Hello Ken,
I have several of these as it is my preferred AM Receiver above all others.

Your measurements seem odd to me. I would suggest some more research and troubleshooting.

Please realize that Relay K1 is energized by GROUNDING the relay via contacts located at the RF Section of the "TURRET" (there is no "N" in turret)  . This relay is energized by switching the ground lead, not the power lead.

The voltage should be around -24V (yes negative as it uses the Bias Voltage Power Rail) at both terminals of the relay when the turret is in Band I, II, or III as it is feeding this -24V as bias to bring the 6.455Mc Oscillator (V8) into cutoff. When the turret is placed in Band IV, V, or VI then K1 is energized by giving it a path to ground which also grounds out the Cutoff Bias from V8 allowing it to Oscillate.

There is a resistor (R35) that is replaced with K1 when it energizes to maintain the correct parallel resistance on the -24V Bias Circuit. This is timed with another set of contacts in the Mixer Section of the turret. These contacts are not visible to the eye as they are buried on the other side of the turret next to the side panel. I remove the side panel to gain access to these contacts.

If you don't have to remove the turret, don't. If you must, you can take the turret out by yourself by making sure to remove all of the modules from the turret. This way it will not destroy the precious beryllium contacts from any unexpected mishaps like when the preload spring slams the turret to one side upon the shaft removal.

73

[WB4AM]

Hello Mike,

I am glad you chimed in.  I was only going by memory when I mentioned 28 volts.  So its 24 volts...-24 that is.

I did notice and fail to mentioned that when I saw the voltage on the volt meter, it was a -31.2.  This I remember because I looked at my leads thinking I had them backward on the meter, which they weren't.

I thought maybe the color wires were mistakenly wired from there after.  I really didn't give it anymore thought.

I measured the voltage by placing the leads right on the coil wires.  I had to flip the receiver on its back to get in there and to be able to see the connections of the coil.  The Black wire was the hardest to make the connection.  I actually had to bend my lead a bit to angle the probe onto the coil terminal.  One reason is my leads have this small umbrella like hat around and above the probe and it was hard to move it in the mist of the other components and wires.

Anyway, if I am hearing you correctly, I better go back and check the voltages again.  Maybe there's something else that is burned out causing more voltages on the coil terminal.

I didn't want to take the side panel off, but it sounds like I should, just to look things over better.

back to the drawing board...

Thank you Mike,
Ken

[MikeKE0ZUinkcmo]

Mike, was it you who placed a link for the manual?  Its now gone?

No but August gave you the links in his posting. 

Sorry for the pun, I just couldn't resist.

Mike

[WB4AM]

Mike, was it you who placed a link for the manual?  Its now gone?

No but August gave you the links in his posting. 

Sorry for the pun, I just couldn't resist.

Mike

Its All Good! 

Does anyone know where to find a relay (K1) for this receiver?

Thank you,
Ken

[WB4AM]

Hello,

I want to thank everyone who chimed in to help with this R-274 Receiver.

I have replaced the "K1" Relay with one I had on hand.  It is a 24 volt Dc 4PDT.  It is a crude install due to it not being the original Relay.  Looking back I should had used just a DPDT Relay.  It would had been easier to solder in the wires.  But I would had to buy one at 24 volts, verses the one I had on hand.  I had to use cut down a piece of wood and place it between the relay and the chassie wall.  Then I had to use a tie wrap to secure it tight to keep it from moving and possibly short out.

Also I had to use (Red on outer and white inner) heat shrink over the coax leads.  When just adding a little heat to solder the center conductor onto the relay, the center conductor would pierce through its insulation due to the bend in the coax which causes the center conductor wire to have pressure against the insulation.  These coax ends are old coax with very soft dielectric.  They don't take to heat like the coax we see today.

The heat shrink prevented this from happening during soldering.

I am hoping this is all temporary thinking I will find a relay that matches the original.  We shall see!

Anyway I have the receiver under test, and so far so good.  I switched through all the bands and all bands seem to be switching into play.  What I believe I should do is leave the receiver on and  set it on the higher bands that will activate the relay.  If the relay holds up and if any of the other sections of the circuit don't burn up, I would have to say this was the problem that needed to be fixed!

I am also including a "Pic" of the original Relay hoping someone may know where to purchase one or may have an idea where to search for one.

Again thank you for your help and support.

Ken
  

[W3GMS]

Hi Ken,

Congratulations on getting the rcvr up and running! 

When it warms up a bit, I have a couple rubber maid containers full of relays and your welcome to sort through them to see if I have anything that would work better for you. 

Happy New Year!

73,
Joe-GMS

[WB4AM]

Thank you Joe.

I am hoping this is all that had broke!

Thanks for the offering of looking through your container of Relays.  I might take you up on it!

I want to use it as is for now and make sure there is nothing else that is wrong with it.  Since the other relay was bad, I was thinking maybe there was to much voltage on the relay causing it to burn out.  Of course the relay could be original and it might just have to many hours on it.

Funny thing is, I have applied voltage to it and the mechanical metal flapper pulls in but not enough to engage the contacts.  I have tried to manually push on the metal flapper and it seems there is something holding it back mechanically.  I haven't studied it to see it that's the case but later I will.

Thank you Joe, and Happy New Year to you as well.  And Happy New year to all.

Ken