DX100 HI-VOLTAGE PROBLEM

[ve6pg]

...hi from tim..i've received a few ideas as to why i'm having problems with my dx100, but thought some different views may be warranted.
  my dx 100 is blowing fuses, and was arching from the rivets in the sockets of the 5r4s, to ground. ok..i looked for, but couldnt find carbon tracks. i cleaned the chassis in this area, removed the sockets, and lowered them down further, with nylon spacers.  ok, no more rivets arcing to ground, but still blowing fuses, and the 5r4s will crackle fer a second, before the fuses go. i've checked, and replaced all toobs, and she still blows. the plate cap from the 6146s has been replaced with a higher value, and even with the 6146s removed, plate switch on, (in cw), fuses are still blowing....ideas?...tim...sk...

[WQ9E]

Tim,

Is your .092 metering resistor to ground intact? (check resistance from centertap to ground).  Any chance one of your 5R4 sockets has an internal crack with carbon track to mounting area?  Check the bottom of the 5R4's themselves to see if there are carbon tracks on the base of the tube, these often happen after arc-overs on the socket.  Other than that I don't have any ideas-I guess some shorted turns on the transformer primary would cause some really high voltage on the secondary/rectifiers but this is probably not the case.

Rodger WQ9E

[N3DRB The Derb]

check yer 5R4's. drop in another pair. My Derb 100 had a internal carbon track inside of a 5R4 socket when I got it. Only way I saw it was to sub out both sockets and break both of them in half, then all was revealed.  The outside glazing of the porcelain had hidden the track. Inside was black.

Pull all HV connections to the other tubes. See if you still blow fuses. Isolate the HV Xmfr. Measure (with the HV dead and shorted out) YOU ARE USING A BANGSTICK, RIGHT? the ohmage of the xfmr from CT to each side, then from each side to case..you are looking for a BIG difference in static resistance from each side to CT. There will be a small difference becuase of teh dc inside to outside winding length of teh wire.

You DID replace both of the 100 uf filter caps, right? Isolated them above ground? those cap cases are not at ground. After 50 years they have undergone teh gay sexors change and become resistors, don't expect em to work. They wont. Make sure the replacements are rated for 500 vdc each, NOT 450.

check out dis rap and come awn back. I would actually do the last thing first. Check he main HV caps. Unless you changed em, they are toast.

now, go and get down.

[w5rkl]

Wonder if the .001ufd 2KV final B+ bypass cap is going bad?
Just a thought.

73
Mike W5RKL

[ve6pg]

...bypass cap, replaced with a 6kv doorknob, gonna order some 100mfd 500volt caps...sk..

[Ed-VA3ES]

Tim,  where are you ordering your 100mf/500V caps from?  I have a few DX-100's  to recap.

[ve6pg]

...hey ed...gud to hear u the other nite...i'm going to SAYAL today, but there is a guy in scarboro that sells the stuff via mail, etc...   www.justradios.com   
  it seems he has gud prices... i gotta go to toronto this morning, and will stop at sayal.  they have them as well...check their website, as they have tons of stuff.....
   cant make markham, late changes in my weekend plans....see ya...tim...sk...

[WA1HZK]

While you have those DX-100's opened up, replace the .001 blocking cap on the output of the 5763 driver going into the 6146 grids. When this sucker shorts it puts the Lo B+ on the final grids.... For about a micro second.
Just saying.
Keith
WA1HZK

[ve6pg]

...KEITH...WHAT IS THE VOLTAGE RATING FER THIS CAP, AND DO U KNOW HOW IT IS IDENTIFIED...(c5, etc)...TIM....sk...

[ve6pg]

...JUST LOOKED AT THE MANUAL...THAT .001 IS A MICA CAP..WHAT ARE THE CHANCES OF THIS THING CRAPPING OUT?...tim...sk...