R-388 PTO overhaul

[KM1H]

What is considered an average time to rebuild one of these from start to buttoning up the front panel ? Replace some caps and get end points back on again.

Carl

[KL7OF]

took me a week

[W4NEQ]

I did not have to mess with the washer stack on mine.  Took about a day and a half.

Chris

[Ralph W3GL]

Carl, check with John, W3JN,.  He's rebuilt and calibrated several as I recall..
Should be able to give you a close estimate..

Check on here in technical as well, he might have done a write-up on the subject...

[WQ9E]

Carl,

There have been a few useful articles in Electric Radio.  Set up a simple holder for the PTO to make it easy to work with the corrector stack and hook up a frequency counter and it will go quickly.  It took most of one Saturday to do mine several years ago and the receiver (51J-3) was already out of its cabinet but it was also the first Collins radio I had gone through. 

If the PTO isn't tuning smoothly AND you are estimating a repair for someone keep in mind that the PTO could have serious mechanical damage through a combination of degraded/dirty lube and heavy usage.  There are a few that show up this way so cover your butt if this is a "contract job"

[Todd, KA1KAQ]

I was gonna suggest exactly what Ralphie said - drop Johnny a PM if he doesn't pop in here and get his tips. Ask him too if the mental welts have healed that he received from some members of the CCA for DARING to permanently alter the PTO to adjust the end points. I still laugh about it every time I see or hear 'R-388'. 

I should qualify this statement by adding that, in my experience, at least 90% of the CCA members and Collins folk in general are great, friendly, helpful people. It's the 10% or whatever the average is for narcissists, elitists, arm chair experts and whatever else any active hobby attracts that come across as the idiots they are. Unfortunately they tend to be the ones people remember.

[KA8WTK]

Looks like I am going to go through the same thing myself.
JN's insights would be most helpfull.

Bill

[KM1H]

Yeah, this is for a quote to do one, its 10KHz end to end out and supposedly very smooth and no frequency jumping. But Im also highly fussy so my interpetation may be different

Ive done several over the years taking my sweet ass time while also doing other work and never put a clock on it.

My WAG was $200-250 but dont want to wind up stepping on my crank
Too bad JN wasnt closer, Id send the guy to him.

[RolandSWL]

What are the symptoms of a PTO in distress? I've got a '388 with some issues. Things like wide variations in sensitivity depending on band, difficult to tune upper side band. Dirty pots. Etc.

Roland

[KM1H]

Frequency jumping due to one or all 3 of the known trouble tubular  caps in the PTO and end point problems such as mine.
http://www.boatanchors.org/R388sn2256pix/PTO3.JPG

Your problems could be as simple as tubes, coil rack alignment or a wrong antenna. Zerobeat the BFO slug. Pots are sealed so drill a tiny hole and inject some good spray cleaner. Dont expect good sensitivity above about 14MHz, you have a piddly little 6AK5 feeding three 6BE6 noise generators and the front end coils are designed for short endfed whips or similar; the manual goes into that area requirement. Variable sensitivity from band to band could be low crystal injection signal or a bad 6BE6. Look at the manual block diagram which includes the conversion scheme and see if there is a pattern.

The last one I did was a 3/53 build, all three 6BE6's barely moved the Hickok 752A meter, both 12AX7's were toast as well, plus several 6BA6's were well  below minimum. The 5V4 was also soft. All tubes had 1953 date codes. Inside showed the PTO seal had been broken but everything else looked as built. Serial 6146  with a USN stamp but Id guess the Navy didnt use it long as their PM schedules are demanding. The tag was missing.

The stock R-390/390A isnt much better but dont tell the CCA crowd that

Carl

[w3jn]

It's not too hateful a job, but you gotta remove the PTO entirely from the radio.  It's been a long time since I've had to do one but I think you gotta pull the front panel, which isn't too bad actually.  Before you do, check and see.  As I recall there are some screws holding the front of the PTO to the radio that are impossible to get to unless the front panel goes.

You'll need to unslobber the wires.  Pull the can of the PTO and remove a turn from the endpoint adjuster.  It's MUCH easieer to set the endpoint with the PTO out of the radio.  Just set the PTO for exactly one end of the band, using a knob with a pointer, and a piece of wire affixed to the PTO as a fiduciary.  Should be exactly 1 MHZ for ten turns of the knob.  Adjust the PTO endpoint until you get it right.  Set the PTO for one end of the band or the other, and make sure the dial assembly is correct (the KHz dial should be at zero when you install the PTO, and haven't turned the PTO shaft).

Beware of the stupid little locking nut on the PTO endpoint adjust screw, on the exterior of the PTO housing.  Removing that makes it REALLY hard to do the endpoint adjust with the PTO in the radio.

You can probably do it in < 4 hours once you get your strategy together.  Take into account the time you'll need to adjust the endpoint, it takes several attempts and is best done with a freq counter.

[KM1H]

Thanks Johnny. Where you been hiding, folks have been asking for you?

Brian never did get to Athens while you were there, he is back in Germany until coming here late this month and then off to Tiblisi for embassy duty in some military capacity.

Carl

[w3jn]

I've just been busy with a bunch of RL stuff combined with a slight case of RBS. 

[WQ9E]

I've just been busy with a bunch of RL stuff combined with a slight case of RBS. 

John,

Don't dis the RBS, those are my initials

I picked one up last year at a hamfest but it hasn't made it to the bench yet.  The RCA finally got off the bench but now a Patterson PR-16 is stuck there.