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 Post subject: R-274 Alignment
PostPosted: Feb Fri 16, 2018 5:53 pm 
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Location: Warminster, PA
Working on bringing an R-274 back to life. When running through the alignment, I get the upper and lower frequencies dialed in fine, but the mid scale frequency is not close. On band 1 for instance with the end points on, the mid reading is off by more then 10khz.

I know enough to not expect to get 0.1hZ accuracy but is there anything that can be done to get the dial reading closer?

Tom


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 Post subject: Re: R-274 Alignment
PostPosted: Feb Fri 16, 2018 7:14 pm 
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Does the tuning cap turn freely on it's own (disconnected from dial assembly)? This tuning cap has ball-bearings on both ends so it should turn with almost no resistance.
The tuning cap arm is spring connected to the dial assembly; so if the cap has stiff rotation, it may lag behind the dial.
I had much trouble with mine, and it took hours to clean and lubricate so it was free of bumpiness, which resulted in dial error.

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 Post subject: Re: R-274 Alignment
PostPosted: Feb Fri 16, 2018 7:28 pm 
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Location: Warminster, PA
Yes. The bearings were full of crud. I removed the tuning cap assy cleaned and lubricated the bearings. Nice an smooth now with no hang ups.

I will confirm tonight whether I have this issue across all bands or specific bands.


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 Post subject: Re: R-274 Alignment
PostPosted: Feb Fri 16, 2018 7:43 pm 
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Tom,

Just to clarify are you talking about the Hallicrafters version (aka the SX-73)? Although the Hammarlund units are typically referred to as SP-600 or "Super Pro" they are also under the R-274 general contract.

Make sure that the dial is properly aligned to the capacitor following the instructions on page 8 of the manual.

Check that the bendable outer plates of the oscillator section of the tuning capacitor haven't been severely bent. Sometimes people get these way out of reason and it will throw everything off.

In their ad Hallicrafters claims two tenths of one percent or less (sounds nice for ad copy) which would mean up to around a 5 Khz. error on the first band according to my quick calculations.

Rodger WQ9E


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 Post subject: Re: R-274 Alignment
PostPosted: Feb Fri 16, 2018 8:34 pm 
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Interesting ad - the guy has a microphone, so this makes me wonder how good it is on HF; hmmm I wonder how good it would be on SSB. I'll do some reading on that.

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Last edited by SmoothOscillator on Feb Sat 17, 2018 2:24 am, edited 1 time in total.

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 Post subject: Re: R-274 Alignment
PostPosted: Feb Fri 16, 2018 9:04 pm 
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SmoothOscillator wrote:
Interesting ad - the guy has a microphone, so he's not just DXing.
I wasn't aware that one could not DX using a microphone.

Perhaps I should cancel my 277 DXCC contacts, all voice.

- Leigh

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 Post subject: Re: R-274 Alignment
PostPosted: Feb Fri 16, 2018 11:38 pm 
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Location: Warminster, PA
Sorry - Hallicrafters R-274 (no D) Serial Number 757. Come pics can be seen here: http://www.thdesignsinc.com/R-274.html

Just got home and checked the tuning cap, sure enough C2 has a couple bent fins which are at the upper end of the dial. Interesting that when I started the alignment process I noticed that the upper end needed more adjustment then the lower end to fall in place.

Later tonight I'll run some tests on each band and see if the same tuning accuracy trend follows each band. If so then I may start looking into those bent fins...

Tom
W3TA


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 Post subject: Re: R-274 Alignment
PostPosted: Feb Fri 16, 2018 11:44 pm 
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Tom,

Hopefully it is something simple and it is always a good idea to check the other bands to see whether it is a trend.

I did a quick check with the SX-73 I currently have set up and operating and on band 1 it is off a couple of Khz. at each endpoint and it reads 3 Khz. low when tuned to 1,000 Khz. so there is a reference point for you. It has been six years since I aligned this one so I don't recall how close it was originally but it certainly holds its alignment well.

I was pretty sure you had the Hallicrafters version (which I really like) but I wanted to be sure because I was involved in another thread several years ago that made it to page 3 before it became apparent that we were all assuming a different receiver under the same general contract number. It probably caused a lot of confusion to the original poster who was relatively new to vintage gear and some of the suggestions made definitely didn't apply.

Rodger WQ9E


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 Post subject: Re: R-274 Alignment
PostPosted: Feb Sat 17, 2018 2:30 am 
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post updated for Leigh. I hope your 277 DX contacts were more worthwhile than some of your 31,000+ ARF comments; you may wish to consider cancelling some of those instead.
:mrgreen:

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 Post subject: Re: R-274 Alignment
PostPosted: Feb Sun 18, 2018 3:18 am 
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Location: Warminster, PA
Completed the alignment on 5 of the 6 bands. Band 6 is dead - seems to be the VFO in the band 6 position, it stops oscillating. Need to look into that a bit more.....

The plates on the main tuning cap section C2A were bent out a bit at the low frequency end. I experimented a bit and found that I had calibration results when they were bent back to their "like new" position. I still had issues with the dial being off in the mid range of the band though.

I did some more tinkering. After several hours I found a good way to get the full range pretty darn close.

First calibrate the low end, then the high end per the manual. I then picked a frequency in the approx middle of the two end points. If that point was off I used the low freq adjustment to bring it back in line. Then I went back to the low freq and used the padder(?) capacitor to adjust the low freq again. After doing this a couple times everything started to line up across the dial. The manual says that this padder is factory set but after 60 years it is probably time to reset it. I don't know how they adjusted it at the factory, but using this method I was able to get the dial readout pretty close across each band.

Now onto band 6......

Tom
W3TA


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 Post subject: Re: R-274 Alignment
PostPosted: Feb Tue 20, 2018 7:10 pm 
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Location: Warminster, PA
Band VI update:

Issues with band 6 not functioning - swapped the OSC turret section with the one from band 5 and I now had VFO operation in band 6 - not correct freq, but operation. This narrowed my issue specifically to the band 6 OSC module.

I carefully removed and measured all of the caps and each was well within the tolerance for the value. Reassembled the module and retested, same issue. Tried to think of a good way to test the module out of the radio - pulled out the trusty old B&W dip meter. Tacked a cap across the terminals where the VFO cap would connect that would represent the approx mid point of VFO travel. Tested with the dip meter and it seemed to resonate around 36mhz - about 10mhz too low. For a sanity check I removed the band 5 module and ran the same test, results were good, dip freq was approx mid band plus 6mhz for band 5.

I started changing the cap values in the band 6 module and ended up substituting in a 20pf cap in place of the combined 55pf cap to get a resonance around 45mhz which is where I wanted it. Got a little too late to try it in the radio so tonight I'll run a couple tests. I'm a bit surprised at the drastic value change to get the module to resonate. Leads me to think something else is amiss...

Tom
W3TA


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 Post subject: Re: R-274 Alignment
PostPosted: Feb Tue 20, 2018 7:44 pm 
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Location: Canyon Lake, TX
Remember that the second harmonic of the local oscillator is used for band 6.

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 Post subject: Re: R-274 Alignment
PostPosted: Feb Tue 20, 2018 8:47 pm 
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Joined: Jan Fri 20, 2012 10:25 pm
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Location: Warminster, PA
Ed Engelken wrote:
Remember that the second harmonic of the local oscillator is used for band 6.



Hmmm, I went back and read the theory of operation and the second harmonic only comes into play when using the fixed crystal positions. When using the VFO the first mixer should be the receive freq plus 6mhz.

At least that is my understanding. I've been known to misunderstand a lot of things...........

Tom
W3TA


Last edited by thoyer on Feb Wed 21, 2018 1:23 am, edited 1 time in total.

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 Post subject: Re: R-274 Alignment
PostPosted: Feb Tue 20, 2018 9:18 pm 
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Here is a scan of the top of page 75 in TM 11-897 "Radio Receiver R-274/FRR."


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SX-73 LO.jpg
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 Post subject: Re: R-274 Alignment
PostPosted: Feb Wed 21, 2018 1:22 am 
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Joined: Jan Fri 20, 2012 10:25 pm
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Location: Warminster, PA
Ed Engelken wrote:
Here is a scan of the top of page 75 in TM 11-897 "Radio Receiver R-274/FRR."



Figures - right in front of my eyes............ AND whats even worse is that I just walked over to the bench and the manual is open to that exact page!! :oops:

Thank you for pointing this out, don't know why they didn't mention that little tid bit of info in the theory section........

Now things are making sense. I couldn't figure out why the coil for band VI didn't have more turns then band V. Since they both resonate near the same freq it now makes sense.....

So mid range of band 6 is approx 41.5mc. Half of that plus 6mc is 26.7mc. I'll go work with these numbers and see where things fall....

Thanks!

Tom


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 Post subject: Re: R-274 Alignment
PostPosted: Feb Wed 21, 2018 2:56 am 
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Joined: Jan Fri 20, 2012 10:25 pm
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Location: Warminster, PA
Went back to the "as built" configuration and took some measurements at V3-1 the input of the VFO to the first mixer.

Using a Fluke Scopemeter set to read Vpp and freq. I took two readings on each band - main tuning fully CW(high end of band) and main tuning fully CCW (low end of band). Results:

Band 1 CCW = .983mhz, 30vpp
Band 1 CW = 1.744mhz, 62vpp

Band 2 CCW = 1.7mhz, 23.3vpp
Band 2 CW = 3.485mhz, 54vpp

Band 3 CCW = 3.4mhz, 20vpp
Band 3 CW = 7.5mhz 58vpp

Band 4 CCW = 12.82mhz, 8.5vpp
Band 4 CW = 19.86mhz, 18vpp

Band 5 CCW = 19.2mhz, 2.2vpp
Band 5 CW = 32mhz, 4.5vpp

Band 6 CCW = NADA
Band 6 CW = 27.34, 6.7vpp

Watching the scope while tuning through band 6 the oscillator stops working around 20mhz on the scope, 36mhz on the dial which may or may not be close...

I also noted that while tuning through the bands and monitoring the voltage on V3 pin1, it increases and decrease several times on the higher bands. At some points it gets so low that I wonder if any signal would be heard.

I don't have much time tonight to "play" tonight so until tomorrow........

I'm open for suggestions....

Tom
W3TA


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 Post subject: Re: R-274 Alignment
PostPosted: Feb Wed 21, 2018 3:27 am 
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Tom,

Start by trying a different 6C4 HFO tube and trying more than one substitute is a good idea. Hammarlund receivers are well known to be extremely picky about 6C4 HFO tubes and I guess this Hallicrafters Super Pro competitive design is close enough that it may have the "Hammarlund disease."

Tube testers are useless in choosing a tube for this position because they don't test the tube at RF which is where it normally falls flat. I have had a little better luck with the industrial/rugged versions of the 6C4 in Hammarlund receivers but it is still a matter of choosing the "best" tube. Common tube related issues with this type of oscillator circuit is a tube that goes dead above a certain frequency, has dead spots as you approach it upper frequency, or shows rapid small frequency jumps (which is likely from the tube operating on the verge of dropping out of oscillation).

Rodger WQ9E


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