Herbert, Regarding your points 5 through 7, it has been my experience that if any section of a multi-section cap becomes defective it is only a matter of time before the remainder of the sections fail, either open or short. The latter condition, of course, is the worst case.
I only parallel a cap section for testing to determine if it corrects the problem. If it does the entire cap is replaced. I normally leave the original can in place for aesthetics and place the new, smaller caps under the chassis as you suggest. 73, Ken, WA2LBI [EMAIL PROTECTED] Quoting Herbert Schulz <[EMAIL PROTECTED]>: > Peter, > > i do not own a R-4A, but i may have some practical comments: > > 1.) A large ripple voltage combined with excessive trans- > former heating may also point to an overload condition, > not necessarly may it only be one or more failed cap's. > So, before doing any repair, i would suggest to look for > that first. The voltage chart usually stated in Drake's > manuals could be of some help here. > > 2.) It may also be, that one of the two rectifying diodes > has failed. This could also lead to transformer heating > (dependent on the type of diode failure). Anyhow, in > that case the ripple should be asymmetric in the appearance > of the waveshape with respect to the positive and negative > portion of the mains-sine-waveshape. In that case i would > suggest to replace both diodes against 1N4007's. > > 3.) A ripple voltage in the range of several [Vpp] seems > to be normal direct at the rectifier and the first cap. > The ripple voltage of more interest would be the one on > the final HV-DC-supply line. In my R-4C, this ripple vol- > tage on the +150[V] line is very significantly below 1[Vpp]. > I do not know, how the power-supply of the R-4A is made up, > but i assume, that there are not too much differences. > > 4.) As long as one of the cap's has no short circuit (which > is usually not the case, they simply dry out), the cap's > should not be the reason for your power-transformer to > heat more than normal. Maybe this "more than normal" > heating has another reason? > > 5.) If the cap's only have low capacity and no shorts, i > would recommend to parallel them on the bottom of the > chassis with the approbriate capacity values. 100[uf] > 250[V]DC are really small capacitors today compared > to the time the R-4A was built. And a 22[uF]/25[V] > cap may be so small nowadays, that it may be hard > to see. In this way you do not tamper with the origi- > nal state of the receiver in a irreversible way. I > did exactly this type of repair with my SPR-4. > > 6.) As dried-out electrolytics also may exhibit contact pro- > blems between the foil and its associated electrode > connection to the outside world, i would suggest to > parallel each paralleled electrolytic named under topic > 2.) with an 0.1[uF] ceramic capacitor with approbriate > voltage rating. The reason for this is to supress any > possible contact noise of this dried-out-electrolytics > at the source by shorting it to ground. The new, paral- > lelled electrolytics can not do this job because they > exhibit significant ESR (equivalent series resistance) > at higher frequencies which they have not been made for. > > 7.) In case of space problems, i would not see it as a pro- > blem, to place the new, paralleled electrolytics at a > place under the chassis, where it is approbriate and > where the corresponding DC-wiring is runing to. At least > in my R-4C the +150[V] DC wiring is distributed nearly all > over the bottom of the chassis, so that it should be possible > to find an comfortable mounting place. Due to the small > currents, that are drawn from the HV-DC-supplies, i would > not expect the wiring resistances to generate any serious > problem. > > Much success in repairing your R-4A, kind regards and 73 > > > Herbert, DG7MCC > > > > > Peter Hoon schrieb: > > > R4A: It appears that one or more sections of the Sangamo power supply > filter > > cap are defective, since I measure 5.2 volts p - p with a scope at the > > junction of diodes D4 and D5 (156 VDC). And my power transformer gets very > > hot. > > > > The cap is in a single aluminum Sangamo chassis mount with: > > 100 MFD 200 VDC > > 100 MFD 200 VDC > > 100 MFD 200 VDC > > 20 MFD 20 VDC > > > > 1) Anyone have a spare from an R4A they are parting out? > > > > 2) Suggestions for a source for this filter cap from others who have gone > > before me. > > > > 3) Have improvisors found discrete caps from a source (pse recommend one), > > left the chassis mount unit alone, and mounted these discrete caps under > the > > chassis? > > > > 4) Has anyone actually drilled out this filter cap shell, and mounted > > discrete components inside? > > > > Any other ideas or comments appreciated. > > > > Peter, VE1CHS > > > > ---------------------------------------------------------------------- > > Submissions: [EMAIL PROTECTED] > > Subscribe: [EMAIL PROTECTED] - subscribe drakelist in > body > > Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in > body > > Hopelessly Lost: [EMAIL PROTECTED] - help in body of message > > Brought to you courtesy of TLCHost.net http://www.tlchost.net/ > > ---------------------------------------------------------------------- > ---------------------------------------------------------------------- Submissions: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] - subscribe drakelist in body Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Brought to you courtesy of TLCHost.net http://www.tlchost.net/ ----------------------------------------------------------------------
