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Alignment of Vintage Shortwave Receiver - Pilot T-511

Aug 3rd 2011, 13:43

W1MG

Joined: Apr 4th 1998, 00:00
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I am in the process of restoring a 1947 vintage Pilot T-511 receiver. Convention for the AM broadcast band is to set the local oscilator to be 455 kHz higher than the intended receive frequncy. Is there a similar convention for the shortwave band for a receiver of this type and vintage? I checked both Ryders and SAMS. Neither specifies if the LO frequency should be above or blow the intended receive frequency. I can also align the oscillator and RF to work either way, but would like to have it the way it should be. Does anyone have experience or thoughts on this?

Thanks,
Mike, W1MG
Aug 4th 2011, 00:51

w1rfi

Super Moderator

Joined: Apr 4th 1998, 00:00
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In the AM BC band, almost every tuning capacitor is a dual-ganged type, with the LO capacitor of smaller value than the main RF tuning capacitor. If the same thing is true in the receiver you are aligning, clearly the LO belongs above the IF by 455 kHz.

A few thoughts came to mind, Mike. First, I bet the frequency range over which the LO tunes is greater when it is above the IF than below. This would mean that when you adjust the LO to be on the right frequency for the low-end of the band, corresponding to the tuning dial, the frequency on the upper part of the band would be too high and the frequency you are hearing would be too high. You'd have the opposite problem if the design were for the LO to be below the IF by 455 kHz. So one way to tell which is right is to pick one, see what the tuning accuracy error is, then try the other and go with the choice that put the frequency closer to the dial on the upper end.

Now, on the lower frequency ranges of the receiver, I'm surprised you can get that much tuning range variation out of the LO. I'd bet that on the lower range, the tuning error for the "wrong" setting will be somewhat noticeable.

The wrong choice will also probably throw off the tracking of the tuning cap and the LO oscillator cap, so you would see the sensitivity be off on the upper end.

Now, this will be complicated by the fact that there are padder caps on most variable capacitors used in receivers that will let you compensate for the tracking errors.

The way to adjust the tracking is to adjust coils at the low end of the tuning range, then use the trimmers to bring it into tracking at the upper end. There will, of course, be some interaction between the two.

First, set the capacitor trimmers to the middle of their range (as best you can guess). Then, tune the receiver to the low end of the frequency range and adjust the LO coil to be spot on. Now, go to the high end and adjust the trimmer capacitor to have the LO be spot on there. A frequency counter is best, but you can also set a signal generator to the correct frequency and adjust to have the receiver tune it correctly. Go back and forth between the LO coil and the trimmer cap. You may have to do some compromise to get the trimmer set correctly on the high end for mutiple bands.

After you get the LOs correct, the RF tracking is adjusted the same way. Set the receiver to the low end of the dial and peak the RF inductor for maximum sensitivity. (You can peak by ear on band noise.) Then, go to the high end and peak the trimmer on the tuning capacitor. If necessary to compromise, adjust that trimmer for maximum sensitivity on the highest band, as a slight reduction in sensitivity on the low end will not be noticed because the limiting factor on low HF is almost always external noise.

If you are really lucky on the design, there is a separate trimmer cap for the LO and RF on each tuning range, but if not, once the LO is right, everything else should fall into place, at least within the bounds of reasonable compromise.

The LO frequency will usually be adjusted with some form of slug-tuned coil. It is likely that when the LO is set to the correct frequency, the coil slug will be somewhere near the center of the coil, while the "wrong" setting will place the tuning slug near one end or the other of the coil's ajustment range.

Now, to the rest of the folks reading this forum, note that the ARRL Lab guys are using the forum, too, not only to answer questions, but to ask them! :-)

73, Ed Hare, W1RFI
ARRL Lab
Technical forums moderator
Aug 9th 2011, 14:48

WB1GCM

Joined: Apr 4th 1998, 00:00
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Dear Mike,

It depends somewhat on the radio. In about 90% of the receivers of this type, the image on shortwave is usually *below* the intended receive frequency. In this case, the local oscillator is 455 kHz higher than the intended receive frequency. The image, however, should also be noticeably weaker.

For the remaining 10% of these radios, the image on shortwave is actually above the intended receive frequency. The local oscillator frequency in these cases is 455 kHz lower than the intended receive frequency.

Trimmer adjustments can often provide an important clue as to which setting is correct. Try setting the local oscillator 455 kHz higher than the intended receive frequency first.

You may be able to attain a copy of the alignment instructions from the Vintage Radio and Communications Museum in Windsor, CT. They have all of the Ryder's manuals in that time era.

Bob Allison
WB1GCM
ARRL Test Engineer
Oct 13th 2011, 00:20

K3PID

Joined: Apr 4th 1998, 00:00
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Mike, A quick look at eBay showed several sources for the Sam's data for the T-510 from a couple of bucks to 20..

Good luck
Ron H. K3PID
Dec 28th 2011, 18:34

W1MG

Joined: Apr 4th 1998, 00:00
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Thanks Ron. Unfortunately, the Sam's data does not provide this information. Neither does the Ryder info. That is why I wondered if there was a standard or convention for this.
Dec 29th 2011, 01:29

AA6E

Joined: Apr 4th 1998, 00:00
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The world should know that W1RFI and W1MG work in adjacent offices. It's just that they inhabit different time zones. :-)
Feb 5th 2013, 14:38

westmountain

Joined: Feb 1st 2013, 14:54
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It is all about the tracking of the First Tuned Stages and the LO that deternines the size of each tuning cap. Putting your finger on the cap will tell you if you are moving the LO or the front end.

W9TSQ

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