Re: Hallicrafters SX-25 Rebuild: New Mains Transformer Questions.
 

Voltages were given for some of the pre-WW2 SX's eg: the SX17 which I used to have.

Lawrence.

Re: Hallicrafters SX-25 Rebuild: New Mains Transformer Questions.
 

I'm depending on the Rider's coverage on these sets. It seems that they didn't include all the information on some models. It either was an oversight or located in a different location or a different volume. I use the Nostalgia website even though I have most of the printed volumes.
Dave, USradcoll1 :soapbox:

Re: Hallicrafters SX-25 Rebuild: New Mains Transformer Questions.
 

With a 5v directly heated filament taking 2 amps, if you were less worried about originality than the cost of the rectifier, a socket swap could allow you more choice. Guitarists have been keeping rectifier prices high, but I'm not sure they've noticed the 5R4 yet. Overkill, but there's the heater current available. Hmm, second thoughts, it looks like the toob rolling fraternity have noticed them, I see listings with emphasis on the colour of the base, the colour of the anodes and the shapes of getters. Oh dear!

It depends on what you have available, but a swap to an octal socket may expand your opportunities.

David

Re: Hallicrafters SX-25 Rebuild: New Mains Transformer Questions.
 

The service info I had for my SX17 was a reprint, also had a couple of SX28's but the service info I had for those was the original.

Nice receivers.

Re: Hallicrafters SX-25 Rebuild: New Mains Transformer Questions.
 

I have Riders volumes 1-23, the special abridged volumes, and some other stuff they put out (all in library mint condition). I could find nothing on the SX-25 beyond what you can get from BAMA.

Re: Hallicrafters SX-25 Rebuild: New Mains Transformer Questions.
 

Round 1 of aligning my SX-25. Not sure how close until I try it out tonight, but I am sure I totally bolo'd the Hallicrafters instructions for IF/Phasing/Xtal/and BFO alignment. The rest of the set aligned well except for band 4: 30 MC was not reachable by my signal gen so I set it down to 28 and the set would not go past 26.5MC (trimmers).

The alignment seems to be pretty good, but I don't think its spot-on. This one seems harder than my SX-43 alignment (which was the first set I ever aligned).

I am sure I have many alignments in my future I'll be doing on this to get it right.

Anyone ever master the first part of the alignment procedure in the enclosed Hallicrafters document with some advice?

Re: Hallicrafters SX-25 Rebuild: New Mains Transformer Questions.
 

The IF alignment procedure given there is similar to that for the SX24. However the procedure for the SX24 makes no mention of the crystal phasing control.

What I did was to first determine the crystal frequency by connecting it in series with a signal generator's output and a 'scope's input. You need a fairly high output level, but the peak waveform is easily seen as you tune through the resonant frequency. In my case it was 455.42kHz.

I then lined up the set on 455.42kHz using an output meter to show the output level, much better than doing it by ear IMHO.

Next I stepped the SG's frequency up in 10Hz increments starting at 455kHz. I could see the peak all right, but not the twin peak called for. I then started experimenting with the setting of the crystal phasing control. I found a sweet spot where the twin peaks were visible either side of 455.32kHz and realigned the IF to that frequency. The dip between the two peaks isn't great, but it's clear to see. The setting of the phasing control and IFT trimmer are very critical, a few degrees either way and you'll lose the peak.

I intend to clean the crystal and repeat the test using a sweep generator, displaying the response curves on a 'scope.

Re: Hallicrafters SX-25 Rebuild: New Mains Transformer Questions.
 

That totally is the way that makes more sense to me. The procedure in the manual is looking at the symptoms of everything working rather than analytically. I used an even more indirect method to figure my crystal on one of my radios: I adjusted the SG to the crystal as per the instructions and then measured the SG result with a frequency counter right after it. It was just under 455.

My SX-25 needed a complete shift from where it was at before making my think the crystal might not be perfect around 455 - I initially attributed it to the poor and sloppy work, the attempt the previous owner had to retrofit a 700VCT transformer in the set, and the small fleet of Ohmite WW resistors to try to bleed off excessive voltage.

The alignment is not front and center. To aggravate the situation, the T1S trimmer looks like it have a shallow channel in the top of the trimmer which makes getting a good hold on a screwdriver (alignment type) AND it takes lots of effort to move it - like it is corroded in the threads.

Re: Hallicrafters SX-25 Rebuild: New Mains Transformer Questions.
 

The mystery is revealed (I believe).

453.06-453.07 Khz.

'Twas an impressive display of twiddle fingers to get the vintage signal generator I have to cooperate but I got a clear and distinct peak at 453 Khz and some change.

Re: Hallicrafters SX-25 Rebuild: New Mains Transformer Questions.
 

I think I figured out the alignment - after following the instructions 3 or 4 times in a row I was able to complete the alignment (by ear using speaker tone). What I found is when I did the first part of the procedure, the part that a 5000Hz tone is used I noticed the different the SG had to tune to across the zero beat (to get a 5000Hz tone) was not what I thought it was.

I started alignment at 455.06 and after the 5000Hz tone portion of the alignment procedure I noticed this difference to be a SG shift to 456.19Khz (difference of 1.13). Then the bands aligned well.

When I went with my measurement of 453.06Khz for the crystal as I measured it and used that as my IF frequency it was a total disaster. The low rumbling (motor boating) I heard before was evidently a major difference in working IF and my crystal. The crystal tuning seemed to intensify the low rumbling sound and adjustment of RF gain did little to help.

When I followed the procedure the crystal tuning works remarkably well. I did tune my TXS width to cover the crystal's working range and that seemed to dramatically improve the overall performance - not too sharp and just broad enough.

Listening for a tone is less than desirable - I would always prefer a response measurement. The problem is that loudest tone seems to imply not the loudest tone, but rather the cleanest, clearest, loudest tone without distortion. I tried the loudest noise I could generate during the entire process and I can tell you that's the incorrect way.