The AM Forum

I was loading up the T3 on 15 Meter AM yesterday and when I went to turn the Loading crank, I heard a pop and now the crank turns free. 

I found the Bellows coupler from the turns counter to the vac cap is broken.  This coupler looks like 1/4 on one side and 3/8ths on the other.  Its made of brass.

Called around and cant seem to find this part.  Anyone have a solution?   Gary at Fair radio said he would dig for me but did not have one handy.

I cant use a straight coupler as there is an offset.  If anyone has a solution or the coupler, Raise a hand!

I got the deck out, bushings so the assembly turns easier in prep for some kind of part replacement.  Might as well check the tubes in the rig while I have the decks out and clean the filter.  The rig was going to make it to 15. I had a strong signal from the Exciter on the receiver.  I found a dip on the plate. But when I tried to increase loading, the coupler snapped.

Thanks!

Clark,

   Can you post a picture of it? So what length span and horizontal offset does it provide?

What about a piece of 3/8 rubber fuel hose and some clamps? :-)

Jim
WD5JKO

I feel like an idiot. That sounds like a great solution. I have a Garage full of fuel line and Goodridge hose.  I am going to try that Jim!

C

The simple answers help the most sometimes.  ;D

My Friend stopped by and helped me get the deck out while he was here.  I will start the work soon.

C

Ok. What a PITA.  There is only a 1/4 inch space between the shafts.  I had to take all the screws out of the large vac cap and side it out.  My hands are cut up :(

The cap is 1/2 inch and the turns counter is 1/4 inch.   The difference is to great for hose.  Its possible I can get some 1/4 hose inside of a half hose and glue it, then clamp it three times.


- vac cap- 1/2 inch hose with clamp-1/4 inch hose inside 1/2 inch hose with clamp, then 1/4 hose and clamp- turns counter.

What a rig job.   I wish I could get a new coupler.

C

Can you post a picture?  I, or someone else, might have the exact piece in our junk box, or at least a usable substitute, but I'm not exactly sure what to look for.

Here ya go Don.  TFO Dennis stopped by today.  We are brainstorming on how to make this work.  I emailed a company that stocks bellows.  Lets see if they email me back tomorrow.  I have to be on the dynomometer all day so I wont have time to call them.

https://sdp-si.com/eStore/


Pictured is the end of the vac cap which is 1/2 inch.  The turns counter is 1/4 inch. The space is 1 and 1/4 overall.  The offset is almost nothing.  Maybe 1/16th. 

Also pictured is the broken coupler and the tuning cap bellows which is intact still.

C

Anyone?  Out of ideas here.

C

Try this company:

https://sdp-si.com/eStore/

WA8DRZ

Take a big 1/4" Johnson coupler such as this:


http://www.ebay.com/itm/E-F-Johnson-104-262-1-4-Ceramic-Insulated-Shaft-Coupling-Coupler-/320834004172

And then take one side apart, and then attach the brass collar from the big end to it by brazing, soldering, etc.

Jim
WD5JKO

Not enough flex Jim.  It binds.  I rigged up something like that before. Over my lunch hour, I found some 1/4 ID hose and some 1/2 inch ID hose.  I washed them in soapy watter, then pounded the small line inside the larger line.  I also got some clamps from the junk bin.  I am going to try to slide the vac cap out, Trim this assembly down and clamp it in place. 

I really hate rigging things like this up. 

C

I think I have some couplers like that, but don't know if they will fit.  I believe one side of yours needs to take a 1/4" shaft and the other a half-inch.  I think mine take 1/4" shaft on one side, and the other takes something larger, but I don't think they go to 1/2" size.  I'll look and see what I have.

Hi ;
 try this  is what i used from (surplus center .com )
 hope this helps.
                           73 John kc2fxe

I think the type of coupler John FXE is using is a LoveJoy coupler. I couldn't remember the type when I visited John but that is the one he is using. Google them.

The collars are too long for the t3.

Can they be machined down? One nice thing about Lovejoy couplings is that you can mix and match the ends to get whatever sizes you need. (and they're cheap)

Then machine a little off of each end to shorten it up a bit. You can also machine a little off of the center spider and the prongs to make the whole assembly shorter. It's a piece of cake to do. They are made of sintered iron and machine very easily.

I might try that frank. A good friend has a machine shop in town. Thanks

Clark,
        ANYONE who has a lathe can do it, it shouldn't take them more that 10 minutes to do it, it's a simple job.

Also, if you cant get one with a 1/4" hole, see if you can get a blank, unfinished one. The 1/2" side is a common electric motor shaft size

Clark

I had the same problem before here's what i did..I took the shaft out of the cap an put about 3 nuts on it so i would not bother the threads an stuck it in the drill press...I thought i would take a flat file an bring it down to a 1/4 inch.....Well when it got to almost 1/4 i noticed the meltal was changing colors an a big chunk of the end came off.....well i didn't get as long of a shaft as i thought but their was still enough for a normal 1/4 to 1/4 coupler to fit..Oh also i left a little amount of the 1/2 inch their so it would still ride in the cap on the bearing ok....Don't know if this helps but that was my fix....

That might be the real solution here. Thanks for posting man.  I am going to unscrew the front of the cap.  I am told the 1/2 inch shaft just unscrews.  Then I can have my buddy mill it down to 1/4

C

Before milling all the way down to 1/4",  see if you  can come up with a coupling that will accommodate a 3/8" shaft.  1/4 to 3/8" couplings are very commonly used in a lot of equipment.  I'll look and see what I have here, particularly at the ones that appear identical to what broke on yours. A bushing with set screws will grip a 3/8" shaft much more positively than it will a 1/4" shaft, and milling down only to 3/8" is less likely to cause this sort of damage:   

Don i've also seen them with a bolt of the same threads with two nuts locked together an a washer then cut the the head of the bolt off.....an make sure that it's not longer than the original that goes into the cap...A little grease on the washer an nuts never hurts...an that will also give you 1/4 to 1/4 coupling...

Dont forget that the 1/4" threaded internal "shaft" on a vacuuuuum variable doesn't turn. The threaded "overshaft" screws down on it and pulls the inner shaft out as you turn the outer shaft. The cap changes value by pulling in and out on the bellows and internal plates. You dont want to turn the inner 1/4" screw or you'll break the seal.

It is better to try to leave the 1/2" outer shaft intact if possible. If you are going to turn it down, I wouldn't go much below 3/8".

I noticed you still have the brass end bells from the existing coupling... you might be able to clean them up enough to solder some copper tubing of a close diameter and length between them and... with a number of cuts from a hack saw, partially relieve the tubing every 90 degrees across its diameter weakening it enough to allow it to flex... if successful you would have a part that fits the existing shafts more or less as B&W intended while waiting for Fair to find you the correct part...

Thats a great idea also!

C

Google: McMaster Carr

Complete catalog on-line

See   High-Precision Bellows Shaft Couplings

BINGO!!

They accept small orders from small people

To get their catalog is impossible as you need a machine shop and a salesman might come to drop it off
other possibility is Ebay  but online catalog is very good

AC0TX

And they ship the same business day or the next.  I can place an order on-line over the weekend, and if they have the merchandise in stock, it usually arrives here by the following Tuesday.  They are not cheap, but they have stuff I haven't been able to find elsewhere locally or on line, and they don't require a minimum order. Their on-line catalogue is great. I wouldn't want the paper catalogue (didn't even know they had one); to contain all the info you can get on  line, it would have to be about  8" thick and would likely go out of date very quickly.

Thanks for the tip but not a single part they list will work.  The coupler is 1.25 inchs over all length,  1/4 on one side and 1/2 on the other.   They do make a 2 inch version but there simply is not 2 inches in the T3 without making or machining a ring mount to space the big capacitor back 3/4 of an inch.  I suppose, I could rig something up with standoffs as a last resort.  The problem there is you get the HOT side of that cap closer and closer to the chassis wall.  It would be just my luck to have that arc out.

I have not had good luck with rubber hose. 1.25 and that large diam diference is too great.  I messed with it for hours. 

The Fair radio part came in the mail today.  Woops.. one side is 1/4 and the other 1/4.  No room to bore it out.  Guess it goes into parts stock.

My rescue this time around was w0vmc.  He was nice enough to take this part out of his personal unrestored T368 and send it to me.  What a hell of a guy.  I am still looking for replacements. THe website which stocks the part I need will not email me back and nobody returns calls.  I am sure this part exists and when I find it, I will order spares for Roberts rig and mine. I am sure other T3 owners might want one each as a spare.

For now, I think I will have the rig up and running next week!  I cleaned up the deck, Put in some new 4-125 eimacs, got some SS plug in for the screen voltage supply for the Modulators (hoping for a tad more audio power) and checked all the speach amp tubes.  Cant wait to get the ole Girl back on the air. I was enjoying myself kicking back in the big high back chair, Feet up and a D104 in my hand.

C

I broke mine last weekend.  Problem solved within an hour:
Loosen the good coupling (loading or tuning) so that it can also slip free.
Unfasten the 4 screws holding the tune/load counters in place and back the panel out slightly.  Do not loose the backing plate that secures the 2 inboard screws.
Remove the halves of broken copper bellows from the counter and cap.
Go to kitchen and find vinegar - put enough in a dish to cover immersed broken copper ends.
You need this step to help clean the copper in prep for soldering.
Soak the coupling for at least 10 minutes in vinegar.  Then thoroughly rinse the bellows and finally dry with compressed air. Other cleaning methods are encouraged.
On the bench match up the broken bits and secure them lightly by pinching the broken copper sections.  Secure the assembly in a small clamp.
Using a big soldering iron flow solder between the broken bellows.  Use plenty of heat.  Keep solder away from all other sections of the bellows.
You should now have a cleanly soldered, repaired, squeaky clean bellows assembly.
Re-assemble via reverse of removal procedure.
Calibrate both by backing the counters to zero and turning the caps to match (this step will assure you that the tuning graphs in the book are in agreement).
This repair method has lasted 10+ years on the loading cap.  Hopefully the tuning cap coupling repaired last week will last as long.
73
Tom

Mine was torn apart and twisted. Not repairable.  Someone had hammy ham boned both couplers already over the years by doing just what you said.  Solder.  The loading one had four seperate slober jobs.  The right one had two spots.

This job for me is complicated because I cant pull the Plate with the turns counters out like you did.  Boy would that make life easy..  My T3 was restored and repainted the painter did not remove the two sections so the joint is smooth with paint. i would have to try to cut it wout a blade and then you would be able to see it. I had to remove the cap and slide it back instead.

I realy like fixing things the proper way and it really bothers me to rig things. Its just my nature I guess.
C

WOW, I didnt realize I was such a hammy hambone!  I almost feel bad I posted such a horrid repair suggestion.
I hope the community can find some correct replacements to keep these rigs going.
73

no Tom
Do not worry about that. IF you can flow solder correctly, it would not be Hammy Hambone. I'm sure Clark's repair was not a good solder job OR someone went past the stop and twisted the living hell out of the tuning knob. That would fold up the entire bellows.
Fred

I looked again at the ones in my T-3 and they do appear flimsy...

I'm just guessing but... perhaps they were built mechanically weak so as to be sacrificed during that very event you mention rather than possibly damaging the vacuum variables?  That is, they are a consumable by design?

Tom. I did not mean to insult you. That came out wrong.  I am sorry. 

I just do not like to rig things back together.  When you use Solder, that bellow can no longer flex.  The factory parts lasted for years but it seems this is a sore spot for T3s

C

Me too. I was thinking about solder. I better stop doing that.

Here is a thought :o  ???

I usually look for a mechanical solution that is better than the original (stronger in this case) Beings that I am a half-assed machinist I won't hesitate to machine something up to do the job.

How about taking a universal joint from a 1/4" drive socket set, bore the female end to take a 1/4" (or whatever) shaft and then drilling and tapping it for a setscrew. Then take a 12 point socket close in size to the larger shaft then bore (or drill) it out to fit the larger shaft and drill and tap it for a setscrew as well. Snap the 2 together and fit it in place of the original bellows coupler. It would be many times stronger than the original, and none of us would live long enough to wear it out and it would allow for the slight misalignment of the shafts.

If overall length is an issue, maybe try it with a swivel socket instead.

I have used socket set universal joints in the past for other similar applications where speed is not an issue. They are reasonably cheap and readily available.

Just another $.02 worth...........

Clark:

Well I guess I got to chime in also.

Seems like this is somewhat common in the T-368. I have a couple vac variables with a 1/2” collar and “leftover” copper material.

A bellows coupling is intended to couple two shafts together without adding backlash that’s it’s advantage over a “Love-joy” type coupler.  However you may not be concerned about the backlash from a spider type coupling in this application.

My concern; if I am looking at your pictures correctly the two shafts are way out of alignment.  If you look over a spec-sheet for a bellows type coupling you will notice that they do not tolerate shaft misalignment like a spider type coupling will. The “why it broke in the first place”.  Also the lateral force on the vacuum variables lead screw is not the best thing for longevity either. The aluminum “cup” on the capacitor floats, so lateral force is taken by the plug or “nut” in the capacitor causing premature wear.

Look around for a replacement and if at all possible try to correct the misalignment as much as you can or you may be through this again. :(

JMHO.

Best regards
Ted / KC9LKE

Thanks for the tip on the alignment. I have the replacement on the desk here from robert. I am going to install it tomorrow.  I will try my best to align everything.  I am eager to get the ole girl back up and running on 15 meters.  I have been using the yaecomwood with about 25 watts and I am currently having "transmittter envy" when I hear a big signal come on :)

F, I dont think a Universal would work here. We only have 1.25 inches.  Thats a great idea though.

C

Update,

I got the bellows coupling in from w0vmc.  It was in great shape. No slobber jobs on it.  I ended up using a blade and tracing around the panel through the paint. Then loosening the turns counter unit and sliding it out. If you remember to loosen the tuning bellows this is an easy job. 

I had some trouble getting the turns counter lined up with the correct capactance for full load. I just kept sliding the drawer out and then loosening the bellows, cranking the crank, then tightening the bellows.  With in a few minutes, I had it back in line at 250 MA on the plate and readings that where very close to my old chart. 

While I was there, I replaced the 5R4's with Solid state plug ins from Ebay.  These are $5 each. The T3 finaly reaches 100 % mod now. The old readings on the power master NIST meter where 1280 before flat topping (watching O scope) with 5R4s.  Now, I get 1480 with SS plug ins. This is great as I dont want to run over legal limit. Carrier is about 405 loaded down and about 500 loading by the book.  The peak output modulated power stays the same at 1480 either way.  Can you tell on the air?  Maybe not.  But having all those 5R4s out makes the room that much cooler and we are going into summer here in AZ. 

I am glad to have the T3 back up and running and will put the rig on the air tonight on 75 meters.  I tried and tried and the T3 just will not make it to 15 meters.  The books limit says 20mhz and I think that is right.  The Exciter will go right to 15 but the transmitter will not.  I have heard of people running T3s up there but they must have moved the High band tap over a bit on the coil. 

C

Mine tunes up fine on 15m with no changes needed. Power out is not as good as on the lower bands but I think it was around 400 watts. I use a HP function generator as a signal source. 

Only on 15m it seems there isn't much T/R isolation in the antenna vacuum relay though... my Harris RF 590 receiver shows a RF overload warning and has a fit.

Interesting.  I think it might be the range of the tuning cap.  I ran out of range.  I guess I could unscrew the bellows and turn the crank a bit to get me more range. I bet then it might go. 

C

I'm glad you got the T-3 back on the air Clark.  Interesting discussion.  I'm hoping my A model keeps plugging along, as it sure seems to be bullet proof since I've put it on the air years ago.  It's a wonderful transmitter.

Hi Fred.  Hey!  I'm Reddy Kilowatt :)

Good luck Clark and I'll look for you on 80M soon, T-3 to T-3.

Dave KA2J