How to re-cap Collins 75A-4 Ham tube receiver Deadly capacitor replacement
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- Опубліковано 15 вер 2024
- This video features installation of capacitors which can cause many performance issues. Also the main filter cap is replaced. If you own one of these fine receivers, I would highly recommend purchasing this all encompassing kit from Mark Olson, KE9PQ.com. Plan on about 4 hours for the complete task. There are a few micas that are a bit tricky to install. This kit will improve sensitivity, hum level and overall life of your radio. There are many improvements, service bulletins, etc, that I will cover in future videos.
As you noticed all 75A4s have hum. I was very annoyed at this so one day I decided once and for all to track it down. After an hour with the scope I found this hum was from the two low voltage chokes resonating. You can actually feel the chokes vibrating. I experimented with a resonating cap at the input. DC pins of the 5y3 to ground. Pin 2 or 8 works. One cap is needed. A single .047 orange drop or disk completely silences the hum. Voltage is only increased by 2 volts DC. Make sure to use at least a 600 or even a 1000 volt cap as peak to peak here is up pretty high on DC here. I typically do not like mods on my radios... But in this case it cures ALL of that hum and it drove me nuts.
I did this to mine tonight and I gotta say it works GREAT! My 75A-4 now gives my FT-DX3000D a run for the money.
My Collins is now my go-to radio for everything. Thanks for the tip!!!
Glad that worked! I had had lots of feedback from hams thatbhave tried my solution. No more hum.
It works great, turn the volume down and dead silence. This should be in the 75A-4 handbook!
Clark- I just got my 75A-4 Back from Howard Mills and he re-capped it for me and peaked the receiver. It's gorgeous. He restopred it for another owner 20 years ago to the month. However, like you, I still hear 60 cycle hum from the speaker with the RF and AF gain at zero. Otherwise, the radio is dead quiet. I pulled the bottom cover and attempted a .047 Orange drop on both pin 2 and pin 8 of the 5Y3 to ground with zero effect on the hum. I was very excited to eradicate that hum once and for all. Any ideas? Do I need to drag the Osco probe around in there? I'd rather not.
Great to watch your 75A-4 re-cap adventure. Just finished my second 75A-4 rebuild, previous event was in 2012
Chuck
This is the first project I've seen where you systematically replace all the mica caps.
Expertise extraordinaire
What a fine job Terry !!! Well done. I think I have said this before but it is so cool that you are keeping these radios alive... I wonder if the same will be true in 30 years.. Perhaps Emi will have a UA-cam Channel and carry on the tradition !!! Kudos to you my friend.
Sadly in 30 yrs there might be little point outside of being a museum piece or occasional listening to regular AM radio. Shortwave radio itself may be history!
Very helpful video, thanks! I'm replacing the caps in mine with the same kit you used and for the life of me I can't tell which cap is C101. Maybe its my eyes vs' the available schematics, but I had no problems finding and changing the rest of them out
Beautiful Collins! Looks almost brand new inside.
I did this many years ago. Generally focused on National, Hallicraftors, and Collins. I would call it my annual boat anchor. It was fun compared to my most recent stuff involving networks.
I have a Collins 75A-3 and have never recapped it but it will need it seeing as how it is older than a 75A-4 but on mine I also need to restring the dial cord. Another fun job on a Collins. Thanks for the video.
I really didn't hear the hum go away, too include in your final testing of the A-4 as you tuned around and i could still hear it in the quieter band portions. Normally, after I replace the multi-can, which I always do first like you, I will notice significantly less hum. So I was very surprised when I could not tell any difference in your hum after you changed the multi-can. Very odd. I just moved my QTH from Florida back to Maine and when I get my test bench up and running I'm looking forward to trying Clark Turner's mod on a couple of beautiful A-4's I've had since the 1960's. Now, if I can only figure out how to replace those pesky tub style caps in my lovely A-1 without ruining the aesthetics... 73's and keep up the good work!
Have two of these and will be starting recap of one soon that are fantastic receivers . I also have all the other A series recievers I love collecting them.
Hello Terry!! I have a 75A4 too serial 892 I think but I may be wrong, that may be my KWS-1, but at any rate recap for this is on my to do list shortly !! it is in operation at the moment and it too has had that small amount of hum. I plan on installing that .047 cap as Mr Clark Turner talks about here. Have a good day 73's KC2UVN John Bellas.
Excellent job, Terry! Wow, that A4 is in beautiful condition. Your videos inspire us to fix our vintage ham gear - and guitar amps.
My A4 had a plug-in solid-state rectifier replacement. That was the first thing I got rid of. I wonder why people thought that was a good idea?
A very nice looking piece of equipment.
I have an R388 51J3 (1953) that I haven't used in quite a while. It has distorted audio, receive was fantastic and no hum out of the speaker, I have a complete service manual (copy of the original military version TM 11-854/TO16-35R-388-5) for it but don't really know where to start. It has had at least one major change, the 5v4 is now a solid state replacement of some type, it was put in there by the previous owner before it was given to me.
Great piece of kit Terry!!
There is a shop in Bangkok Thailand that sells only capacitors. The Thai girl to work there know values and where the capacitor is stored In drawer or hanging somewhere. I was able to buy a dozen that are super small by old standards. The girl clerk sold me exactly the right item.
I went next door to the all resistor shop and bought a couple of correctly valued resistors also clerked by expert lady. Next door to that a shop sells Cinch-Jones varying pin plugs
There is a two or three blocked area in Bangkok that sells parts, including coaxial plugs and sockets. In one shop I was offered 75 ohm RG59 coax with three types of jackets and four types of center insulators. The little lady who worked there knew exactly what I asked for and supplied it.
Because it is very expensive, Amphenol RG8 top of the line is sold and only one grade in one shop and the sales distributor visits the shop to confirm what is being offered. Recently a shop started selling iCOM ham radios off the shelf but in another shop if you can spell the ham rig you want to buy, the shop will get it for you at standard American prices.
Just got a collins 75a-4 from my father in law, was his father's. I would like to recap, cant find the kit you mentioned from Mark. Great video, keep them coming
Thanks for this video Terry, I just bought a 75A-4 and a recap kit, going to tackle this when it all comes in next week.
....how did it all work out?
It worked out so well I did another one after it.
@@AmishSpecialForces ...I LIKE HAPPY ENDINGS-(!)
Me too, even went so far as to do the mixer mods to them. Well worth the trouble.
i found a can cap and the phenolic insulator for very reasonable from antique electronic supply. good stuff!
Man, you got a high noise level!
I did not see you go back and listen for the hum? did you forget to do that? Or did I miss it? nice video in any event. gud tips on a lot of things Thank you for doing it and better yet for sharing.
Congratulations Mar del Plata Argentina!!!
It works .. AM is great I clearly heard Massa AB9MQ!
That’s a beauty!⚡️⚡️
Hows the Sansui holding up?
D-lab Electronics Hey Terry sounds awesome! Can’t find anything that sounds as good these days unless you want to spend Booko denero!😁Thanks Again!
Great video. Thank you.
Great video....wonderful radio!!!
Something I am curious about...I know that when you start changing certain Silver Mica capacitors, you have the potential (depending on where in the circuit they are) of messing with the accuracy of the dial. Wondering if you checked that on this one?
I love Collins gear! I have a Collins S-Line set...still don't have it on the air....have to do some things first that require money that I don't have, but eager to get them up and running.
Say Hi to Marsha!!!
Thanks for sharing the videos with us!
Beautiful
Nice Job
Any thoughts on the capacitor outer foil (being a hum screen) connection & needing to be terminated to ground or equivalent potential in this circuit?
Rock salt instead of solder... Must have done the work during a blizzard!
VERY INTERESTING
Hello Terry, I've been looking through your IMPRESSIVE Video Collection. Do you have any interest in doing a repair video on a Zenith TransOceanic? Just curious.
Collins is in Cedar Rapids, Iowa.
How about a 51S-1? Those are the receivers everyone seems to want...the only vintage receiver I know of which will consistently sell for more than a Sparton Bluebird...
Never had one in the shop
In the process of restoring a 75A4 I have run into a problem that the crystal oscillator V4 will not work on the two 10M and 11M bands. I have replaced crystals, caps, tubes and adjusting tuning without results. Have you run into this or do you have any suggestions?
6:00 -Is that a bare wire connected to the case of the filter cap (lower-right)?
Wouldn’t the radio need re-alignment after replacing the capacitors? Charlie KM4ZZ
Only if the capacitor(s) are part of a tuned circuit.
None of there are
No tower at your qth?
6:20...BATTLE OF THE BULGE-(?)
11m OMG you'll have to sterilize your ears lol