Bob Good wrote:
> Gentlemen, I learn daily from all the interesting posts. I now have a
> question. I am in the process of restoring a DX-100 and am ready to apply
> high voltage. I have only run filaments so far. I am aware that the
> rectifier filaments have to be hot before they will conduct to the capacitors
> and the same transformer supplies the filament as well as the low voltage
> stages. I have a Variac in line. Since it is a common transformer supplying
> both filament and LV, I do not know how I am going to slowly bring up the
> voltage to the electrolytic since I have to have full filament
> voltage.......The same goes for the HV to the finals and modulator. In my
> old age I have perhaps forgotten some of what I am supposed to know. Just
> trying to do it correctly. Any suggestions would greatly appreciated.
> thanks and "73, Bob K4BG
In several months I shall be doing the very same thing.
The procedure I have used in the past is to put a VOM on the high Voltage line
and watch the 5R4s
and the meter as you increase the AC Voltage, (on the 100 or 200 Volt scale)
when you see the meter
start to move stop and wait until the DC plate voltage Voltage quits raising,
like 1/2 an hour.
Slow bring the AC up until you get about 30 Volts wait a few hours, you are
drying out the
transformers also. Slowly bring the AC up until you get about 60 Volts wait a
few hours.
Slowly bring the AC up until you get about 100 Volts wait a while.
Slowly bring the AC up until you get about 200 Volts wait a while.
(100 Volts at a time Etc.)
You must monitor the inside of the 5R4s for any sign of spark no matter how
feeble.
That is a sign of way to much electrolytic (S) leakage current.
This will be my second time for this unit.
I have several comments about this fine unit.
1. The 5R4s are just fine for this transmitter there is no reason short of a
fetish to replace them
with solid state replacements.
2. The 5R4 sockets should be lowered two nut thicknesses * below the chassis
with longer bolts, as
the rivets on the sockets tops arc to the chassis.
3. The 6146 sockets should be lowered two nut thicknesses * below the chassis
with longer bolts, to
allow some air flow up through the bottom of the cabinet to cool the tubes
better. (hard to do)
4. The shield between the two 6146's and the 12BY7 (I think) should be soldered
to the chassis at
4-6 places on each side of the shield to provide a good electrical connection.
I used a Weller GT-7.
* 1/4" spacers would be perfect
There is an AM net in the Tampa area I want to check into, and the DX-100
will put out almost 1/2
of the maximum power allowed in addition to the fine cw the rig does. Enjoy es
73
--
Ron KA4INM - I'm proud to be Chuck's pop!
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