75A-4 mods: 1s that work well

Discussion in '"Boat Anchor" & Classic Equipment' started by W5INC, Jan 25, 2015.

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  1. W5INC

    W5INC XML Subscriber QRZ Page

    Putting together a list of caps that need to be changed out and this is the list so far. All are Digi Key part numbers.

    1 uf @ 600V 338-1138-ND 1 needed

    .1 uf @ 800V 338-3432-ND 12 needed

    470 pf @ 500V 338-3446-ND 4 needed

    100 pf @ 500V 338-2622-ND 1 needed

    1000 pf @ 500V 338-2622-ND 1 needed

    Still need 50 uf @ 160V (2) and 50 uf @ 160V (2) as I haven't found these caps as of yet. The 40/40/40 @ 350V big aluminum cap is available from a few sources on the big auction site. I'm waiting on the 75A-4 manual and don't have the actual values of the Black Beauty caps that needed to be replaced also. Does anyone have the actual values of these caps? TNX agn to the BA folks in this Forum for their help in this project. :)
     
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    I am sure Glen has that info.

    The manual should be available online.

    I can look in my manual if needed. It sounds like you have it under control.

    I never did recap all of mine, I just replaced the bad ones.


    Enjoy.
     
  3. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    You don't need any 800 volt capacitors!

    All of the "black beauty" 0.01 mfd capacitors and the other capacitors in the receiver were rated at 500-volts because those were readily available. The highest voltage in the receiver is under 250 VDC and 400-volt capacitors are going to be well within the specifications. I use 400-volt capacitors in all of the receivers that I repair, restore, etc.

    You are not going to find values like 50 mfd these days. Capacitors are now rated in the same tolerance values as resistors. Therefore, a 47 or 56 will replace a 50. A 47 will replace a 40, etc. The tolerances of modern electrolytic capacitors are much closer with +/- 10-percent or +/- 20-percent being the most common. The old capacitors routinely had a tolerance of - 50-percent to + 80-percent. Just go with the +/- 20-percent capacitors and all will be well.

    As for the "can" electrolytic: Just cut it loose and install new single 47 mfd capacitors at 350-volts or 450-volts under the chassis. there is PLENTY of room to do this. Leave the original in place for "looks" if you wish.

    I get virtually all my parts from Mouser ( http://www.mouser.com ). They are overnight delivery to Richardson and probably 2nd day to Houston. Mouser is located on the south side of Fort Worth.

    You don't need "orange drop" capacitors! The brown encapsulated capacitors are just as good and, usually, a lot cheaper.

    Glen, K9STH
     
  4. KM1H

    KM1H Ham Member QRZ Page

    The only benefit you get from Orange Drop overprices is helping maintain the Chinese economy.

    I use disc caps in the RF stages and often in the IF's and the ubiquitous yellow tubular film caps for higher values. All radio manufacturers switched to discs during the 50's and the result is measurable performance improvement on the higher frequencies.

    Electrolytics are only bought thru Mouser or other large distributor and only well known name brands. Never buy them from basement and garage bargain shops or vendors at hamfests as fraud is rampant at the Chinese end. many have had them fail in use and sometimes causing considerable damage.

    Carl
     
  5. W5INC

    W5INC XML Subscriber QRZ Page


    TNX Mr. Glenn and Mr. Carl for their answers in this posting. Sure don't want to re-invent the wheel so I will be using the brown encapsulated capacitors instead of the orange drop guys. I will put the money saved towards the 75A-4s matching counter part, if I can get lucky enough to find a good Xmtr out there. :) Easy to see parts, lots of room to work with inside the big box radios, it's almost like working on a small block engine inside of a 1957 Chevy Belair engine compartment. A few of my friends have seen the 75A-4 just sitting there on a table and they were impressed with the looks of the rig, without it even being turned on. Maybe the old A lines could be considered a piece of industrial American Art. They sure are in my perception and also maybe to a few other AR OPs, still out there today. Time to move a couple of the Rice boxes on to new homes and make some room for some true pieces of American "Iron". :)
     
  6. KM1H

    KM1H Ham Member QRZ Page

    I had several 57 Chebbies over the decades from a 6 cyl Bel Air 4dr with PG to a Nomad and convertible with the optional power packs and a 150 2dr with a Corvette LT-1. Always enjoyed wrenching on them.

    My summer toy for the past 15 years is a 68 Impala SS 396 convertible and that engine looks lost in that massive compartment.

    Collins and National most always made servicability straightforward....except Collins didnt envision PTO problems decades later and well past expected scrap dates. Even so they can be overhauled with a bit of patience.

    OTOH several Hallicrafters appeared to be built to scrap instead of repair.

    Carl
     
  7. W5INC

    W5INC XML Subscriber QRZ Page


    I'm guessing here Carl, you possibly have an SS car that came with the 396/402 package. With a rag top that makes for a very nice rare car and if you do happen to have a 4 speed setup you are talking big bucks for your car. Even with an automatic transmission you are still in good shape with that BB/convertible package that is your play toy these days. MeCum just had an auction in Fla last week. 1969 Charger Daytona with the big rear wing, custom nose piece, plus 426 Hemi / 4 speed car with 6K original miles went for 900K dollars. The BA rigs from most US manufacturers, just like the cars from the 60s to 70s weren't designed with planned obsolescence built in from day 1. That is why they are still out there in use, even till this day. Finding some parts for Dodge SRT engines that are only 10 years old is a chore and more then 1of these parts has become unobtanium in today's World. Enjoy the Impala, it was 1 of Chevy's biggest sellers throughout their history and for good reasons why it was such a big seller. :)


    https://www.mecum.com/results.cfm
     
  8. KD2AZI

    KD2AZI XML Subscriber QRZ Page

    I held off for months on attempting the PTO rebuild after reading bunches of threads and doom-saying articles about linearity. The hardest part was figuring out how to get that lock nut off for the end-point adjustment. The rest was relatively easy. Linearity wasn't hard...the tedium of tweak-replace can-check counter-retweak was overcome by the challenge of it. Dive in!
     
  9. W5INC

    W5INC XML Subscriber QRZ Page


    Heeding your advice there Mr. Glenn, this is what I have come up with so far with Mouser numbers.

    C-20, C-54, C-62, C-70, C-97, C-98, C-108, C-111, C-112, C-115, C-116, C-146 .1 uf @ 400V #667 ECW F4104JL A .98 cents when buying 10 or more.

    C-113,C-137 50mf @ 150v # 75-TVA1414E3 $5.35 a piece

    C-124 .5uf @ 200v # 598-225P474924D3 $1.60

    C-08, C-75, C-81, C-104 470pf @ 500V Mica # 598-CM06FD47492YD3 $1.60 a piece

    C-34 100pf @ 500V Mica # 598-CD15FD101J03F $1.25 a piece

    C-71 1000pf @ 500 Mica # 5982-19-500V1000 $2.50 a piece

    C-95, C-96,C-101 .01 uf @ 600V ceramic # 810-FK22C0G2J1103J $1.26 a piece

    The search for the C-102 guy which is a paper cap rated @ 1uf @ 200V doesn't seem right to me in looking up these parts. I come up with a # 75-V735P105X9200L, don't know if this is the right unit for the job. I will be checking the tubes today and will see what condition they are in and be ordering any dud replacements as necessary. Will check to see if the Collins updates are installed already when checking the tubes. TNX agn to the Forum here for the help. :)
     
  10. W5INC

    W5INC XML Subscriber QRZ Page

    After checking the tubes on the TV-7 it looks like 7 of the 22 tubes are bad in the rig. Not surprising since I am sure it was a donor rig for it's tubes 1 time or another in it's Life. It does have the 12AT7 tube in V7 so it doesn't have #1 of the Collins service bulletins done as of yet. One of the mods in service bulletin #1, changed V7 @ 12AT7 to a 12AX7 tube and by adding a couple of resistors in the circuit. I will get 10 6BA6s as they have a large presence in this rig. I only try to buy JAN tubes if possible and will get a hold of the tube vendors out there to get these tubes gathered up. Will get some 0A2 tubes also as someone told me they are getting scarce out there for some reason, but I sure can't figure out why. More tubes to add to the ever growing stockpile of glass, which is a good thing, I reckon. :)
     
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