Astron R-35A replacement parts

Discussion in 'Radio Circuits, Repair & Performance' started by KB2QQM, Jun 10, 2021.

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  1. KB2QQM

    KB2QQM Premium Subscriber QRZ Page

    Last week I purchased a replacement voltage board, New Rectifiers and a new C5 Filter Capacitor. The original Big Filter is a 64K @25V capacitor. Astron sent me a 100K @25v replacement. I called them and explained they sent the wrong part. They told me that they don’t have any 64K filters and that the 100K at 25V will work better in the circuit. I thought that values had to stay the same but I could boost the voltage capability.

    The tolerance on the cap says:
    100,000 uF 25V DC
    -10% to +75%

    Is this bull or just them explaining away their supply problem ? Or is it legit ?
  2. WB5THT

    WB5THT Premium Subscriber QRZ Page

    You're good to go, more is better in this case.
    AG6QR, KB2QQM, N0TZU and 3 others like this.
  3. KB2QQM

    KB2QQM Premium Subscriber QRZ Page

    Thanks :) !!
  4. AA3EE

    AA3EE Ham Member QRZ Page

    The only disadvantage of the larger value for a filter cap is higher inrush current when you turn the supply on. It's possible (but unlikely) that you'll exceed the peak current rating of the rectifier diodes. For a huge value like that, I'd put an inrush limiter on the mains side of the transformer.
  5. W9WQA

    W9WQA Ham Member QRZ Page

    64k might be 100k . big range of tolerance
    WA9SVD, WB5THT and KB2QQM like this.
  6. KB2QQM

    KB2QQM Premium Subscriber QRZ Page

    I changed out the Voltage Board, the filter cap and the rectifiers.. and a capacitor that goes to the exit leads can't remember what they call it. $60 in parts and it's running again. It was having Voltage issues. Took the time and re-greased the rectifiers and the Pass Transistors. Was very careful with the Mica. Now it's running great. I have had this thing running pretty much non stop for the last 20 years. So much cheaper than buying a new one (Linear Supply)
    WB5THT likes this.
  7. G4COE

    G4COE Ham Member QRZ Page

    Regarding 'leccy lytics' as I call them many a power supply uses a bank of smaller ones, maybe as many as 10 or more 4,700uF and can easily beat the larger one on ripple current rating... the larger 47,000uF can cost a arm and a leg to get one with identical current handling of a bank of smaller capacitors. Soooo when they pop, it's either a big bang or a 10 or 12 gun salute!

    KB2QQM likes this.
  8. W9GB

    W9GB Ham Member QRZ Page

    My “rule of thumb” for Linear Power Supplies (DIY Builds) is to Size the Filter capacitor, after Rectification (bridge rectifier or diodes), at least 2,000 uFd per Ampere (output).
    For the Astron 35 amp supply …. my range would be 70,000 to 87,000 uFd
    You adjust based on the “standard values” by the Aluminum Electrolytic manufacturers.
    Astron’s replacement would be good for a 40 to 50 Amp supply, by my sizing methods.
    G4COE likes this.
  9. G4COE

    G4COE Ham Member QRZ Page

    I gotta agree with W9GB, I always use 2,200uF per Amp output because it's a more common value, a 47,000uF would be good for about 21 Amps (47,000 total C. divided by 2,200 = useful amperage) or in W9GB case..... 47,000uF total C. divided by 2000uF = 23.5 Amps.

    You'll never see these values in switchers (switch-mode power supplies).

  10. WA9SVD

    WA9SVD Ham Member QRZ Page

    Considering the wide tolerance of such large (in capacity) capacitors, it may not be significant.
    G4COE likes this.

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