On 12/06/2013 10:22 AM, ZR wrote:
The last DX-100 I rebuilt for a customer (I use various Johnsons and
other makes) had the fairly common 5R4 sockets arcing from whatever
contanimation they are afflicted with. NOS replacements still wrapped
up in boxes worked fine; Ive heard of Chinese sockets having a lead
content, never tried them. Dont even think of going SS.
Change the LV to choke input, there is too much voltage on the tubes
for reliability, especially the 6146/1625 screens. Increase the filter
cap to 47uF and also the HV output cap to reduce ripple. Replace all
electrolytics, dont waste time even thinking about it.
I have a long list that I can get to you and not take up space
here...if this even gets thru censorship.
The fixed padders in the VFO go up in value and tracking cant be
achieved. New silver micas matced to 1-2% of the schematic worked
fine. I also used a 6AH6 VFO and zenered the plate and screens at
100V. With all good tubes drive was more than sufficient even on 10M
and drift was reduced. Keep the 6146 drive down to about 3-4 ma total,
more does nothing but cook them and AM is still well modulated with
some basic audio circuit changes.
Carl
KM1H
Hi Carl,
Thanks for your comments. Those caps are definitely on my agenda. I have
used the solid state swap for the rectifiers in other power supplies
with no detrimental effects but that always included making sure the
higher voltages wouldn't meet any under-rated parts. I did find the 5R4s
bad - one with a dead short. I just happened to have two more that were
good in the spares bin. No solid state repacements - this time. The
DX-100 is old and has been hacked several times in the past. Some of the
past workers (and maybe me too) left some "elephant tracks" under the
chassis. I'm cleaning up some sloppy connections as I go along, too.
Fortunately I have a hard copy of the manual with prints and all. When I
get it so it's safe to run I'll make the voltage checks to help find
resistors out of spec, etc.
I have several replies in private email and all of the comments say
similar things. So far nobody has mentioned that original power cord
with the fuses in the plug. I will make that go away, too.
73,
Bill KU8H
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