RAN Technology

Hammarlund PRO-310 Restoration

Vintage Ham Radio 0 Comments 01/14/2022 

"mechanically, it's a nightmare..."

Posted By: Robert Nickels (ranickels)

Having grown tired of seeing this rare and somewhat incredible receiver sitting on the shelf, unusable due to slipping dial belts, I bit the bullet and tore it apart to begin restoration.  The quote above comes from Tom Rousseau K7PJT's article in Electric Radio on the PRO-310 and boy, is he spot on!

Since I will be depending heavily on what he and others have written about this receiver, this will be more of a collection of resources than anything original.

Most importantly, the write-up which was done by Grant Youngman NQ5T is avaialble for downloading in the "Attachements" section at the bottom of this page.   Grant's interests have moved on and this document has become somewhat difficult to find since it was never published but was provided to those in need in pdf form.   Thanks to Grant for making this information available and for coming up with a source of replacement dial belts.

The last known source for those belts was Mark Olson Nationwide Radio   Contact Mark for more information.

Bob Sullivan WØYVA's restoration page and photos are HERE

Here are a couple of tips from my own experience in putting the PRO-310 back together -- several times...

#1.  Maybe those who pay more careful attention to the photos referenced would not make this mistake, but I installed the middle flywheel backwards.   It worked fine on the bench and I was able to assemble the modules into the frame and was actually connecting the speaker for a check out before I realized that the middle knob was frozen solid.  There is an interference fit between the flywheel and middle chassis when installed wrong, and the only solution is to completely disassemble the receiver and turn the flywheel over.    The two flywheels face OPPOSITE directions.

#2 The chain used to drive the band indicator drum is easy to install BUT also can be caught in the wrong place, requiring disassembly.    To avoid this make sure the chain is looped over the drum sprocket and hanging down freely as shown.

#3  The "exoskeleton" or three-sided frame that holds all the modules together can be difficult to remove and install because when it is not in place the modules can all move in various directions.  Several ground and signal wire soldered connections must be removed to allow the frame to come off as well as all controls and shafts, creating an unwieldly mess!    But I found a method that makes it very easy and only requires two hands!

First, position the receiver on a flat surface with the controls dangling by their interconnecting wires over the edge.    Then you can slide the frame on the benchtop and it's easy to align the modules to fit.   When the frame is in the position in the bottom photo, it will be necessary to pull up on the tuning assembly so it can clear and as the frame is engaged the bandswitch shaft and slotted "hook" must be aligned as well as the tuning gear during the final fraction of an inch.  But having everything supported firmly on the bench makes it MUCH easier and everything will just slide into place.  Double check to make sure the chain is hanging down and not hung up.     Then the two screws can be installed that hold the tuning unit to the RF front-end chassis.   Then three screws in each side on back, three on one side, and the two long screws with tapered pin ends that secure the tuning unit in it's grommets.    The four longer screws fasten the smaller chassis to the frame.    There are a few others but at this point everything is fastened securely to the frame and the receiver can safely be turned over to engage the chain drive (depress the tensioning arm to get slack).       An awl is handy to have to quickly line up screw holes.

Disassembly is just the reverse but you'll have to remove the small chassis screws before turning the receiver right-side up on the bench to avoid having to try to flip it over without frame support.

Mistake #N:  when reassembling I managed to get the bead chain flipped on the double pulley which resulted in the drum rotating backward compared with the turret.    Hint: see the marked up pic from Grant's document to show the proper way the chain should be installed.

ALIGNMENT TOOL:    Truth is, it took less time to make than I spend fussing about why I had to make a special alignment tool!   The photo below will perhaps be a bit easier to understand than the small drawing in the manual.    I found a leftover piece of #8 threaded rod that measures .164" OD and cut a piece about 12" long.   A sleeve of heat-shrink tubing provided the necessary electrical insulation and brought the diameter up to about .178" which is a perfect fit (the manual says no more than 3/16" dia).   The slot in the end was cut with my Dremel tool using an abrasive wheel that happened to be .040" thick but a hacksaw kerf would probably be about right.   A scrap piece of wood dowel was drilled and screwed on as a handle.

I have to say, this worked really slick.   The tool aligned perfectly with the adjustable trimmers and coils inside the turret and alignment went like a breeze thanks to high quality components.     The mixer alignment was off quite a bit on a couple of bands and made a nice improvement.   The RF tracking seems pretty non critical and while the oscillator is just the opposite, it's nice to know the receiver has been tweaked up as it should be.


Here's some great news for PRO-310 restorers!   Bob Mattson W2AMI who recently dug into his PRO-310 found a source for belts that are readily available and he reports they work fine:

"The supplier of the belts added the part no. PRO310 for the two custom belts. Without removing any modules, the belts can be replaced with four hands and hooks to pull the belts  to where they need to be.

This is good because the original quantity of woven fabric belts was limited and ultimately would be exhausted, if they haven't been already and the fact that these belts are much less expensive is a plus.    Click the linke for SUPPLIER INFORMATION


Click on the image title or on the image itself to open the full-sized image in a separate window.

Description Comment  
PRO-310 dial string information
Hammarlund PRO-310 color brochure
Grant Youngman NQ5T PRO-310 Notes


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