r-388A (51J-4) Alignment

[W7SOE]

Hi All,
   I am aligning (or trying to) my R-388A using the 51J-4 manual.  I am to step (c) in 5.3.10 of the RF alignment.  This aligns band three.  In step (b) the inductor in the tank(?) circuit is peaked with the dial set at 2.6 mc, which seemed fine.  The frequency is then set to 3.4 mc and the trimmer capped is adjusted for peak voltage at r151.  Here I get no response at all. 

Bad trimmer? 

Thanks

Rich

[WBear2GCR]

Gotta pull out the schematic, and it seems absent from my computer!?!?!

Two quick thoughts.

First, make sure that ur on the correct peak for the inductor - I've seen it where sometimes on some receivers there can be two positions for the slug, one is good
one is not so good. (I'd expect that the position was very very close to where it was when you found it, unless the rcvr was hammy hamboned?)

Second, assuming that's not the issue, detune the slug and see if the trimmer has any effect.

Third, (I can't count) try the same adjustment on another band to make sure of how it works...

Now to find the schematic and download it to a folder where I can find it again.

                              _-_-

[nq5t]

Hi All,
   I am aligning (or trying to) my R-388A using the 51J-4 manual.  I am to step (c) in 5.3.10 of the RF alignment.  This aligns band three.  In step (b) the inductor in the tank(?) circuit is peaked with the dial set at 2.6 mc, which seemed fine.  The frequency is then set to 3.4 mc and the trimmer capped is adjusted for peak voltage at r151.  Here I get no response at all. 

Bad trimmer? 

There are multiple tuned circuits (3 inductors and 3 trimmers) to be adjusted here.  Do any of the 3 trimmers have an effect?

Grant

[W7SOE]

Tonight I will try de-tuning the inductor and see if that helps.  I haven't tried the other trimmers on that band, I just stopped when I got not response.

Thanks Guys

Rich
 

[Jim, W5JO]

I don't have a factory manual for that receiver but do have a SAMS Photofact.  Are you sure you are tuning the correct trimmers?  My memory is hazy but think they are marked with the proper frequency they affect.  If they are  not, you may be on the wrong trimmers.

[W7SOE]

I don't have a factory manual for that receiver but do have a SAMS Photofact.  Are you sure you are tuning the correct trimmers?  My memory is hazy but think they are marked with the proper frequency they affect.  If they are  not, you may be on the wrong trimmers.

yes, they are clearly marked.......

Thanks

Rich

[Jim, W5JO]

Do any of them have an effect on the signal strength?

[nq5t]

Tonight I will try de-tuning the inductor and see if that helps.  I haven't tried the other trimmers on that band, I just stopped when I got not response
 

Maybe.  It's a lot more likely that one (or maybe more) of those three trimmers needs to be cleaned or is simply broken.

Did you have any similar trouble with the 2.5-1.5 range?

Grant

[W7SOE]

Did you have any similar trouble with the 2.5-1.5 range?

Grant

No, that band peaked nicely.

Rich

[WBear2GCR]

fyi, bama/edebris has the R-388 military manual in the "military" section.
100+ pages of it...

which trimmer designation(s) are you trimming here? "C-xxx"?

                 _-_-

[ka4koe]

Good luck on your alignment. Let's hope your heterodyne crystals have not drifted too much.

I basically stopped fooling with mine, figuring it was "good enough". It appears to be pretty sensitive on 10m AM.

Philip

[W7SOE]

An update. It looks like it is not the trimmer. I have a signal generator and I verify the frequency with a digital counter.
I have been setting the dial to exactly 3.4 mc, for example. This morning I noticed that the output at the diode load peaks at 3.4 mc minus 18 kHz. At that point all the trimmers peak nicely. So it appears I have been aligning while off-frequency.

I don't see the same amount of error at the other end of the dial.  PTO out of whack?  If I don't see the same PTO error on each band would that indicate that the crystals have drifted?


Rich

[nq5t]

An update. It looks like it is not the trimmer. I have a signal generator and I verify the frequency with a digital counter.
I have been setting the dial to exactly 3.4 mc, for example. This morning I noticed that the output at the diode load peaks at 3.4 mc minus 18 kHz. At that point all the trimmers peak nicely. So it appears I have been aligning while off-frequency.

I don't see the same amount of error at the other end of the dial.  PTO out of whack?  If I don't see the same PTO error on each band would that indicate that the crystals have drifted?

The 2.5-1.5 and 3.5-2.5 ranges act as 1st IF's for all of the other tuning ranges.  There is no crystal used for either of these ranges.  PTO endpoints are the usual suspect.

It's fixable, but will take some work, and if it really is out 18 kHz end-to-end, will probably require some surgery on the compensating adjustment inductor inside the PTO can.  Can only be done in any case by removing the PTO from the radio.  I've probably done a dozen of them over the years.  PITA, but doable and well worth the effort.  The correct adjustment tools are unobtainium, but there's an easy way to make usable ones with brass tubing and a file.

Some material:

http://www.qsl.net/k9ly/New_Life_for_51J_PTO.pdf
http://members.storm.ca/~nshepherd/VE3OWV/R388PTO.htm

Grant

[N8ETQ]

   Cams and Clamps ?

/Dan

[nq5t]

   Cams and Clamps ?

/Dan

The PTO itself is the only frequency determining element for these two bands.  It's mixed either + or - with the signal direct from the input tuned circuits.  So to get a frequency error across these two ranges (1.5-2.5 and 2.5-3.5), it's only the PTO that can be blamed.

it could be that the kHz dial isn't on the shaft properly, but if it zero beats at 2.5 MHz at one end (for example), and is off 18 kHz at the other, then it's the PTO that's out.

Grant

Grant

[W7SOE]

Thank you all for the ideas and expertise.   I will continue with this RX as time allows.  I find all the "center frequencies" on each band, eg 3.0, 4.0.., to be spot on.  So it looks like the PTO is off.  I am going to leave it for now. 

I went forward with more of the RF alignment, peaking the output before the adjusting inductors/trimmers to make sure the PTO was tuned to the signal generator frequency. 

I have to use strong signals to get the output between 1-5V.  Like -20 dBm to -10 dBm.

I tried listening to the aligned bands like 4.0 but they are dead, the receiver is quite deaf.  When I touch the antenna lead to the connector there is no increase in background noise, no hiss, pop, nothing.  So although I can get output and align bands there is zero reception.  I can hear broadcast stations on the lower bands but their reception does not change with or without an antenna.

I re-tested the tubes and they are OK.  (Hickok 600A)  I did discover that V112, the limiter tube, is a 12AT7 instead of the specified 12AX7.  I don't have a 12AX7 to replace it with so I left it.

I am now going through the tube voltage chart.  I will then do the resistance chart.


Rich

[nq5t]

I tried listening to the aligned bands like 4.0 but they are dead, the receiver is quite deaf.  When I touch the antenna lead to the connector there is no increase in background noise, no hiss, pop, nothing.  So although I can get output and align bands there is zero reception.  I can hear broadcast stations on the lower bands but their reception does not change with or without an antenna.

It could be any number of things.  Some quick things to check -- make sure the antenna terminals are not shorted -- it could be a problem with the high level protection bulb across the antenna terminals (I-104) or the relay contacts on the muting relay (K-101).  Also, if you have all the filters in the radio, try the other filters.  On my current 51J4, the 3.1 filter was dead, and a second one I bought as a replacement was also dead.  Took 3 tries, although that's a somewhat unusual experience.

Good luck with the thing ... a working J4 is a great radio.

Grant

[W7SOE]

It could be any number of things.  Some quick things to check -- make sure the antenna terminals are not shorted -- it could be a problem with the high level protection bulb across the antenna terminals (I-104) or the relay contacts on the muting relay (K-101).  Also, if you have all the filters in the radio, try the other filters.  On my current 51J4, the 3.1 filter was dead, and a second one I bought as a replacement was also dead.  Took 3 tries, although that's a somewhat unusual experience.

Good luck with the thing ... a working J4 is a great radio.

Grant

Those are good suggestions, I will add them to my list....

Rich

[W7SOE]

While cleaning the wafer switches (again) I noticed that I could get the receiver to come alive if I tuned the BAND switch off it's detent.  (progress!!)  The reception comes on smoothly, not quick with a click or pop so it seems like it is the movement of the ferrite slugs bringing it alive not a switch contact.  Could be wrong, often am.

I am not sure yet what this means.  I have double checked the position of the switches and I think they are ok.  I have also checked the cams but maybe I am wrong (see above).

I only get ~30 minutes at a time to work on this thing so please excuse my stream-of-conciousness postings.

Rich

[W7SOE]

Thanks all