Safety cap issue, Eico HF22 rebuild

Discussion in 'Tube Audio' started by buickguy62, Oct 11, 2017.

  1. buickguy62

    buickguy62 Active Member

    Messages:
    193
    I'm rebuilding an Eico HF22 power amp, and replaced (C13) the original standard paper-foil .033uf line-to-ground cap with a correct new Safety Cap. I used a Y2 (line to ground) .033uf (same uf as original) 250VAC Safety Cap. On varistat power up, at about 85 VAC, I felt a decent voltage tickle from amp chassis to building ground. My digital VOM indicated no voltage from the chassis to ground, either AC or DC. I prefer a two wire connection (no third wire ground) to prevent ground loops. Removed the 5U4 rectifier, issue remained, which eliminated most of the circuitry. Further troubleshooting indicated the issue to be the Safety Cap. Upon removal of the new Safety Cap, the tickle was eliminated, would have been a decent poke at 115 VAC. I tried a second identical Safety Cap, same issue, tickle, amp chassis to ground. Now, with no cap, the amp is silent as to hum, I plan on leaving it off.
    Issue for me is that the safety cap was passing sufficient current to cause a shock, which seems to be completely opposite of the design and operation of the safety cap. I did check the value on my Heathkit cap checker, cap not shorted and within specs, no leakage, tested up to 350V. See pics.
    Thoughts,
    Tom safety cap (3).JPG safety cap (2).JPG safety cap (1).JPG
     
  2. knockbill

    knockbill Addicted Member

    Messages:
    6,447
    Location:
    SE PA
    I'd use a polarized two prong cord/plug,,, no experience with XY caps...
     
  3. primosounds

    primosounds AK Subscriber Subscriber

    Messages:
    1,363
    I
    If there is no AC or DC on your chassis it could be your imagination. I mean the hairs on your arms are very sensitive and sometimes i thought i have been shocked by a "hot" chassis only to discover that it was just a bit of over reaction to a poke by a sharp edge or something like that.
    Proper layout and a star ground or ground bus, makes ground loops a non issue and using a polarized AC plug the safest thing to do. I only leave the 2 prong plug on my vintage equipment to keep them stock.
     
  4. buickguy62

    buickguy62 Active Member

    Messages:
    193
    I do use a polarized plug and as a test, inverted it (with a modified extension cord) but still had the tickle, and it was electrical, I was poked several times and could control the intensity with the setting on the varistat with the plug in either polarity. I suspect the no voltage VOM reading was due to the VOM loading the circuit. I thought about using the scope which presents a much lower load, but when I found the problem to be related to the Safety Cap didn't go that route.
    Tom
     
  5. thorpej

    thorpej AK Subscriber Subscriber

    Messages:
    1,412
    Location:
    San Francisco, CA
    If you have an exposed metal chassis, IMO it's completely irresponsible to use anything other than a 3-prong cord with a proper safety ground.
     
  6. thorpej

    thorpej AK Subscriber Subscriber

    Messages:
    1,412
    Location:
    San Francisco, CA
    What kind of VOM are you using?
     
  7. battradio

    battradio Electron trainer Subscriber

    Messages:
    5,513
    Location:
    Near ST. Louis MO
    I would put the safety cap across the line not to the chassis .

    It is best to have only one component in your system with a grounded plug to avoid ground and hum if your CD player or preamp is grounded .

    If you still get tingled by the amp after moving the cap your power transfomer is most likely leaky , and a 3 prong plug would be a must on the amp .
     
  8. buickguy62

    buickguy62 Active Member

    Messages:
    193
    With the cap removed from the circuit, and the amp in operation, there is no tingle at all and my understanding of the purpose of cap on the incoming line was to provide a 'filter' as such for the incoming power. Many (most?) amps, etc. did not have the cap. The amp is dead quiet, so why not eliminate the cap? I see that often they are removed and not replaced. The notation of a 'safety cap' is used to describe the failure mode of the cap, (not it's purpose in the circuit) so that a Y2 Safety Cap by design does not fail in a shorted mode and put voltage from the line onto the chassis.
    My VOM is a cheap generic one. I suppose I could put the cap back in and check it all with my 'scope.
    Tom
     
  9. Tom Bavis

    Tom Bavis Audiophool Subscriber

    Messages:
    9,082
    Location:
    Macedon NY
    .033 will pass about 1.5 mA at 125V - enough to feel, not enough to harm anyone. Modern safety standards allow about 0.7 mA, so a .015 would be the largest value allowed for a Y-cap these days. I usually eliminate them and use a 3-wire plug, so chassis is grounded (not "sorta grounded if you get the power plug right")
     
  10. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    32,922
    Location:
    Southern NJ
    0.033 uf with 120v at 60hz can produce about 1.5ma of current max. Thats plenty enough to feel. Not enough to kill you though. P

    ersonally I'd make it an 0.01uf and use a polarized cord at a minimum. Of course it would rely on your outlets being wired correctly but that will produce a maximum possible current of 0.5ma. Still might be enough to feel but it should be a lot less.
     
  11. Brice

    Brice AK Subscriber Subscriber

    Messages:
    1,220
    Location:
    Hoboken, NJ USA
    I have seen this in many amps. I removed them, period.
    IMO the line AC stays within the cord, fuse, switch and the transformer.
    No cap to chassis in my book, too dangerous in case of cap failure.
    I haven't seen hill effect of removing it also.
     
  12. buickguy62

    buickguy62 Active Member

    Messages:
    193
    Thanks for all the good advice, I appreciate it,
    Tom
     
  13. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    32,922
    Location:
    Southern NJ
    The possible effect is RF interference if there is no path to ground. The AC line does actually provide one. Of course so would a grounded cord.
     
  14. thorpej

    thorpej AK Subscriber Subscriber

    Messages:
    1,412
    Location:
    San Francisco, CA
    Grounded cord + an X1 cap across the line should pretty much take care of all of it.
     
  15. buickguy62

    buickguy62 Active Member

    Messages:
    193
    Sounds like a winner, thanks,
    Tom
     

Share This Page