The AM Forum

I am the new owner of a DX-100B.  I have no history on the radio, so I am carefully trying to examine it by comparison with the manual before applying any power.  So far so good, no major items missing, but a couple items stand out.

First, someone has applied red tape under the entire outline of the modulation transformer (part 51-22).  It does not appear to be a good enough job to electrically isolate the transformer from the chassis.  Could this be to mechanically isolate the transformer from the chassis and limit audio-induced vibration?

Second, under the chassis near the modulation transformer, my rig has a big cylindrical component resembling a modern electrolytic.  It's about 1 3/4" in length by 1" diameter.  It has a "C-D" logo on it, with a part number CP28AIEH203K.  From the schematic, it should be an 0.02 uf @ 1600V, but the size of the component is huge, at least compared to a modern component with these ratings.  There is also an 0.001 uf at 3 KV disc ceramic tacked on in parallel with the big capacitor.  Is anyone familiar with this big capacitor ?

Thanks,

Bruce
WB8VCM

The modulation transformer is suppose to be mounted to the chassis using metal screws; not with tape between the
transformers case and the chassis.

With tape between the modulation transformer and the chassis, I would suspect there is a short between the case
and one of the windings. If so, this present a huge safety hazard as the high voltage, 750VDC, is applied to both
primary and secondary windings of the modulation transformer. With a short between one set of windings and the
case, puts the 750VDC potential on the transformers case, a big safety hazard. I highly recommend you fix that and replace
the .02ufd 1.6KVDC "electrolytic" to a disc cap and remove and discard the .001ufd 3KVDC cap all together before applying
power to the DX-100B. You want to get the DX-100B working as originally designed and eliminate any safety hazards before
doing any modifications.

The capacitor across the modulation transformer should be a .02ufd 1.6KVDC disc cap not an electrolytic. You are
correct, the original cap is a .02ufd 1.6KVDC but the .001ufd 3KVDC is not original.

73's
Mike
W5RKL

Thanks Mark and Mike.  The transformer is bolted down with metal hardware and there are no insulating washers, so hopefully it is not shorted to the case.  I'll watch for this when I get a further down the road.

General opinion seems to be that perhaps the big cap is an oil filled job.I'll remove it (and the disc ceramic) and replace it with a standard 0.02 uf.  I plan to get it running in "stock" configuration before looking at any mods.

Thanks,

Bruce