Hammarlund SP-400 Restoration - how to remove shaft to oscillator assembly T5?

[w6nrd]

Jason here (W6NRD) -

This is my first post to the forum, thank you for reading. 

I've been working on a SP-400 for about  1 1/2 years and it's finally close to finished.  I've learned a ton as this was my first boat anchor restoration project, and probably more than I should have started with - hi, hi.  I'm down to a few last items and one thing I've put off is removing the Oscillator can to verify/replace/change any parts in this can.  The reason I've put it off is there is a Shaft coupler that feeds into the can and though I can remove the coupler the remaining shaft is still too long to get the can off.  There is, what appears to be, a tiny little pin running through the shaft going into the can.  I've tried using a punch to get the pin out and pull the wood shaft off but no luck.  I'm afraid of hitting the pin too hard for fear of breaking it.  Thus, my question is, has anyone figured out an easy way to get this Shaft off so I can pull the can off the oscillator T5 and get into it? 

Any and all suggestions or answers are very much appreciated.

Respectfully,
Jason (W6NRD) 

[KA2DZT]

Jason,

Welcome to the Forum.  I read your post earlier today, surprised to see you haven't yet gotten any help with this.  I have a SP-200 but I'm not sure what exact shaft you're referring to.  Those little pins through the shaft can be a PITA and very often very difficult to remove.  Some may be split pins which can be removed.  Some may be taper pins which only come out one way.  The straight solid pins are the hard ones to remove.  If you hit them too much the end gets a little mushroomed and then they won't come out.

Maybe you can post a picture of the shaft.  I'm sure you'll get some more helpful replies.  Slow day on the Forum, must be a hamfest somewhere.

Fred

[WBear2GCR]

Talking the BFO shaft?? It's phenolic, the shaft.

Which part of it are you trying to get off??

                     _-_-

[W7TFO]

Oh boy, be careful with the phenolic shafts...there are two, one as mentioned on the BFO, the other is on the crystal phasing unit.

The BFO metal shaft ought to just pull out after loosening the setscrew.  If not, check that the panel bushing is not stuck, or perhaps has a snap ring preventing withdrawal.

PM me if you need any parts, I have many SP parts widows.

73DG

[KA2DZT]

Yes, DG (W7TFO) is the resident expert on Super Pros.  Subtracting however many SPs are in the hands of hams around the world, Dennis has the entire remaining number of Super Pros ever built.  This includes all the military versions.  Dennis even has the Super Pros the aliens were using in their rocket ship when it crashed in Roswell NM in 1947.  The US gov. knew he collected SPs so they gave the aliens' SPs to Dennis.

Fred

[w6nrd]

Thanks for all the input.  It is the oscillator shaft.

I've attached two photos, showing each side of the shaft with the pin I'm trying to remove. 

Again - thanks for the input and help!

Jason - w6nrd (nerd)

[WBear2GCR]

That's the Beat Frequency Oscillator?

Best question yet, why do you want to remove the shaft??

The one on the SP-200 has a side panel that is put on with screws...

                   _-_-


I did not look at the ones on my SP-200/BC-779 units (yet), but from your pix, I suspect
that you can not just knock them out. It looks like it may be a soft tapered pin with
one side peaned over... it might require some precision work, flattening the rounded side,
pricking the center and gently drilling/countersinking that side to release the pin. Then it could
be pushed through... but I am guessing. They could have done this job more simply, since there
is no need to have much clearance, but also guessing, they put the cap into the can with the
shaft in place.

[w1vtp]

That's the Beat Frequency Oscillator?

Best question yet, why do you want to remove the shaft??

<snip>

Yes, why do you want to touch that assembly at all?  Is the Beat Frequency Oscillator not working?

Al

[KA2DZT]

I agree with Bear,  the cap was put in the can with the shaft.  Might be better to remove the entire can and file the end of the pin flush with shaft, then, using a small vise to hold the metal part of the shaft, gently try tapping it out with a thin pin punch.

I think the cap has threaded spacer nuts affix to the cap,  try unscrewing the cap once the can is removed.  Probably the whole assembly can be removed once the screws are removed.

Before you do anything, make sure you need to do any of this.

Fred

[w6nrd]

My reason for doing this is it appears there is a capacitor in the can from the schematic, so I've replaced all the old capacitors and want to replace this one. 

[KA0HCP]

That is a fabric/phenolic shaft.  You can see the weave pattern of the cloth (typically either cotton or linen).

I recommend using a small file to file off the head of the pin. Then either pull or push out the pin.  You might apply heavy tape on either side of the pin and on the side of the can to prevent stray file marks.

[Pete, WA2CWA]

If you haven't determined the capacitor inside the assembly is bad, I wouldn't touch it. But, if I had to do it, I would disconnect all the wires coming out of BFO assembly that are attached to chassis hardware points and then remove the hardware holding the assembly in place. Then remove the entire assembly. Working with the BFO assembly on the bench is a lot easier then screwing with it mounted on the chassis.

[w1vtp]

If you haven't determined the capacitor inside the assembly is bad, I wouldn't touch it. But, if I had to do it, I would disconnect all the wires coming out of BFO assembly that are attached to chassis hardware points and then remove the hardware holding the assembly in place. Then remove the entire assembly. Working with the BFO assembly on the bench is a lot easier then screwing with it mounted on the chassis.

Yes.  Have you established that the BFO circuit NEEDS to be recapped?

[WU2D]

BFO circuits are very prone to failure pretty much on all old military designs including the command sets and TCS receivers. That is because they are normally compromise designs done late in the design and many of them are reflexed circuits. Another issue is the low voltage that they are run on and the series feed resistors climb in value and especially as the bypass caps get leaky, the problem of voltage starvation becomes worse. Eventually the ARC-5 command sets stop working with around 20V on the plate. Another common cap that goes is the grid leak cap. This one fails for the problem of not much voltage on it and it oxidizes.

[Steve - K4HX]

I'm pretty sure the 400 is not an old military design.

[w1vtp]

This thread is interesting to me as I have a SP-400 in the back room that I should put on the work bench.

That said, I'd work around the BFO (being an avid AMer not a CW type) and then worry about it if it doesn't work.  I looked for my SP-400 manual(s) and wouldn't you know it, I can't find it - ARGHH!

[w1vtp]

OK.  Found my SP400 manual.  The only catastrophic potential I can see is C71.  Otherwise, I'd do everything else and leave that last after I try the BFO.  If it works then I'd be inclined to leave it alone

Here's the partial and complete schematic

[w6nrd]

For my first post, this is sure fantastic!  What a very thoughtful and helpful group of folks, Thank you all for the answers. 

I like the idea of pulling the entire assembly out but removing the wires from the chassis so I can work on it on the bench. The small file approach also sounds like a good idea.  Thanks for looking up your schematic and posting.  It is the C71 I'd like to replace.  When I replaced all the others most were pretty bad.  As for why there are two reasons.  The main reason is to ensure this cap is good for the rest of the time once this project is done as I don't want to have to pull it off the shelf once I have everything all done.  The other reason is I have done voltage and resistance checks on all points referenced in the manual tables and as I've worked through them these are the last of the issues I see in my tables.  So, I'm pretty sure that cap is bad.

If I take the entire can out I can then put the shaft in a small vice and drill it out with a drill press.  Then on replacement I just need to pin it with something more easy to remove ;-).   

[WBear2GCR]

I'd not touch the pin at all.

IF I had to dork with that, I'd replace the whole assembly with a purpose made one, made by myself.

Yesterday I looked at the pin on my BC-779 (SP-200), same shaft assy.
Using an eye loupe it looks to me like the end of the pin has solder on it!
Not a lot, but it looked like solder.
I used a dental pick on it to poke around...
The other end has a slight "head" in as much as the edge looks like it has a ring.

The phenolic shaft is brittle.
Drilling it is not likely to be an option.
Heat on the end of the pin, may work, that would be the tip of a hot soldering iron.
The one on my parts unit was broken in half and spliced with a brass panel bushing (not very well done).
Although I did not look, I think I could discern the shape of the pin's shaft with a closeup look at what is
now a cross section.

You can likely pull the can, and remove the guts, including the shaft and replace the cap.

I'd skip that unless the BFO fails to work - it's likely to keep working for another 50 years anyhow.

[KA2DZT]

Remove the entire can and you probably can remove the assembly with the shaft on the cap.  Think about it,  Hammarlund didn't hammer a pin into the shaft with the cap in the can because of possibly breaking the cap.  Those caps were made with that short shaft on it.  I have some here with those short fiber shafts on them.

You may even be able to replace the cap without removing the assembly from the can.

Next step, remove the can from the chassis and let us know what you find.

Don't try to drill out the pin as you may damage the shaft and you'll never drill it straight through.  File off the pin to the edge off the shaft and use a thin pin punch to tap it out, if you need to.

Fred

[W7TFO]

Time to ring in again...

Fact 1:  The can be removed from the chassis after loosening the 4 screws on the varicaps and the 2 under the chassis.  One can wriggle the thing off without too much effort after pushing the top cap back into the can.

Fact 2:  There are NO paper caps in there, only micas.

SO....quit futzing with the thing and move on.

If you do pull the can, it will be an exercise in getting the top cap(the one with the phenolic shaft) back in place...a pipe cleaner wrapped around the shaft can be useful.

Just a bit of experience/advice from a guy that has taken these RX down to rivets and back again.

73DG   

[KA2DZT]

Thanks DG,  if anyone knows about that can it would be you.  Just what I thought, the whole assembly can be removed with the shaft on the cap.

Fred

[w1vtp]

All

I'm pretty sure I can produce a higher resolution schematic of the SP400.  That scan was taken off a 5 x 7" print.  I have larger original prints available.  I may even have the PS schem...

[K7MCG]

Schematic attached

73
Chuck K7MCG

[w1vtp]

I'm going to resist the urge to hijack this thread.  Chuck I'd like to PM you on a question. Those schematics are top notch.

Thanks, Al