The AM Forum

This is more of a mechanical query of course, though the end effect is electronic.

Was finishing up my TX-1 this afternoon in anticipation of installing it with the RX-1. Noticed that the Final tuning knob was a bit stiff, so I cleaned and lubed up the bushing and shafts for the mechanism. Was working it to an fro when *SNAP*, it converted itself from closed to open circuit.

Closer investigation revealed at least two previous repairs, including a smaller piece added into the mix. This addition changed the length of the belt, so apparently the original owner opted to run it beneath one of the other control shafts to take up the slack, which added tension and assured early failure.

Does anyone make replacement straps? If not, has anyone made their own and if so, of what material? The original is copper, probably with beryllium, dunno. I was thinking if I have to make one, some of the newer plastics would be a better choice, along the lines of cable ties or plastic strapping, just thinner. The screw holes that hold it to the pulleys are the weakest points, though this one snapped elsewhere too.

Would prefer not to re-invent the wheel if possible. Was *this* close to having it back in the cabinet and online today. Instead it's still spread out taking up space for the next project.

Todd,

I remember reading somewhere (maybe Electric Radio) that the heavy and stiff plastic strapping used for shipping boxes was a good replacement.  After reading that I saved a couple of pieces just in case but I have never had to use them (the sound of knocking on wood).

Search for 75s-1 preselect repair,should work.Joe

Todd,
Many years ago mine on my long gone original Apache broke as well.  I did a solder fix, but it was marginal at best.  I do remember someone selling some replacements but that was years ago and the details are lost. 

I like Rodgers suggestion and it looks like Joe gave you a path to follow as well. 

I do have an Apache and a Mohawk rcvr, so let me know what you find. 

That's why I prefer my DX-100B since it does not use the crazy bands.

Joe, GMS 

Would try your local RC hobby shop, they sell copper and brass sheets.  Have used these to remake the straps in the cantenna when they broke. Available in different size and thickness. Been a while, was not too expensive.

73

James WS4JH  former KG4PBI

I have an Apache and while my straps are still ok, here is what I've thought about doing if they ever need to be replaced or repaired. 


Go to an R/C hobby shop and get some control line wire.  It comes in different dimensions, so likely I'd chose a medium diameter.  It is braided and very flexible and strong and doesn't have any appreciable stretch.  You can solder eyelets on the ends to use where the strap attaches to the drive drum.

73 - Gary - W5GW

Thanks for all the ideas, guys.

A fellow in 6 Land from the AMRadio reflector has offered to make me a couple replacements. The difficulty is in giving him accurate dimensions, since the original band has been patched and the holes are hogged out from use.

I like the idea of the toothed belt and cogs we discussed on 80m last night, Joe. Even better might be the hobby store gears & chain drive for long term reliability. At some point I'll be dropping the front panel and looking at this possibility.

The control line suggestion never entered my head, but seems like it would be simple to implement: just hook one end to the proper screw, run down and around the center screw on the control shaft, then back up to the starting point. Pull line taut, tighten screws. Using a fine wire cable would insure strength, and being able to pull the line tight would remove the flex that causes issues with the tuning. I like it!

Looks like I have plenty to work with. Will post the outcome once it's complete & functioning.

So here's the final update:

Posted a request here & to a couple of email groups. Got excellent replies from all. Mel/K6KBE on the AMRadio reflector corresponded with me about some material he had that would fit the bill, beryllium copper. He cut a strip a bit longer than what I needed, drilled the first hole, and shipped it to me Monday from California. Received it yesterday, measured/marked/drilled/trimmed it to fit. Much stiffer to work with that the original lightweight copper Heathkit used, a real PITA to get into place in fact. However, this works well once it's in place as the added stiffness (seems to be roughly twice as thick) makes for a firm yet conforming fit to the wheels/pulleys. Had it installed within an hour of opening the package, without removing the front panel.

A couple shots of the final result attached. Looking at the material, I first thought it was some type of band saw blade used to cut stone. Turns out it was from some fingerstock Mel had saved. He trimmed off the fingers and dressed the edge for me. Though there is still a slight saw-tooth edge to it, this area comes into contact with nothing, and the entire control travels only 1/2 revolution stop to stop. It might even ad a bit to the flexibility. The control feels solid now, far better than the flex in the original material which condemns it to failure if you use the control very much. As this one had been patched multiple times, it's clear that this has been an issue with the Apache. The replacement material will likely outlast me and whoever ends up with the transmitter next, assuming someone does.

Thanks again to everyone who offered suggestions, and especially to Mel Farrer who not only provided the material to me gratis, he prepped it well after saving it for however many years. Never met the man, yet he was willing to help out a stranger in the spirit of the amateur fraternity. Thanks Mel - I owe you!

Todd

Just be VERY VERY careful about how you handle this alloy. 

http://en.wikipedia.org/wiki/Beryllium_copper   (read section about toxicity)

Beryllium can be very toxic if it finds its way into your lungs.  Watch any formation of filings, or if it is heated be sure there is a negative ventilation away from you.

Al

Al,

Todd and I were in QSO last night when he mentioned the material he
received to fix the TX-1 and I attempted to seriously warn him about
that stuff however he never acknowledged my suggestion  so I assumed
he was aware of the high toxicity of the material, not something to be
ignored.

I was particularly concerned when he stated all he need do is trim to
fit and "drill a hole" in the strip. 

Sure hope he payed attention...
   

TNX guys - I did in fact heed your advice Ralph, and as Al said - was VERY careful. The strap was drilled outdoors with my trusty hand drill, at slow speed to both prevent tearing the material or creating any dust. Only a few small shavings resulted. Trimming the excess strap was easy as the material snapped clean with a good crimp and bend with a pair of Dykes. Washed my hands numerous times too.  ;)

I actually remember reading an article in QST or CQ magazine back in the 70s about beryllium oxide if I'm remembering it right. It was used in the ceramic insulating materials for RF tubes. A very scary read for a 15 yr old kid. As a result, as with high voltage, I've shown anything that could be even remotely connected to this nasty stuff a lot of respect.

The good news is, it's on and working great, so I shouldn't need to deal with it anything soon, if ever again. But I do appreciate the concern. You never can be too careful with such things. Just ask Steve, Johnny, or Joes/PJP/GMS what a coward I am when it comes to high voltage!

That should do it Todd.  The harm is if you breath in the dust from fine shavings or vapors from heat.  I'm real glad you got it fixed.  I was up tonight but looked at the screen while typing this and no sig at 3705, At least so far

Al