[R-390] Best ballast tube resistor

Mon, 12 May 2003 23:28:20 -0700

That sounds like a great idea, Jim.  There are lots of tubes around, and so
what if they don't quite operate at the right voltage as long as they
operate ok.  You can probably also eliminate drift by adjusting your
control.  I might try that on mine.  I don't have any space left on the
front panel, so think I'll use a screwdriver slot type and won't need a
knob.  It should fit just below the Line Meter switch.

I couldn't find a right meter for my set, so I used a larger meter.  It is
easier to read anyway.  I had to carve a little out of the washer underneath
one of the handles, because the meter bezel bumped into it and
unfortunately, the saw slipped when I was expanding the meter hole, so there
is a little "air" on that side of the meter, but I used larger sheet metal
screws and one of them holds it down real good.

I didn't like the on-off switch, so I drilled another hole right above the
frequency readout and put in a toggle switch.  Also, the calibrator isn't
very good, and my PTO isn't very linear anyway, so I drilled another hole
just below the function switch and mounted a rotary switch with 100kHz,
10Khz and 1Khz positions.   I put in a transistor crystal calibrator kit,
mounted it right on back of the front panel.  It only took one screw to
mount it.   A neat trick is to cut up a piece of innner-tube and put it
under the circuit card so the parts don't make contact with the panel.  I
tried using a flat-head screw to mount the card so it would look "original"
but I don't think it was worth the effort, cause it is real easy to make the
mounting hole too big.  Its hard get it just right anyway, but it holds ok.
It shouldn't be too tight, or the card stops working.  I don't know why.

The mechanical adjuster lets me tune to an exact zerobeat now on most of the
dial, but sometimes I have trouble telling which zerobeat is which.

Unfortunately, I can't turn off all of the calibrator, so some of the
signals I hear in the radio have a squeel to them now.  But the dial light I
put in the panel just below the bandwith switch looks great in the dark,
even if it makes the set hum a little.  I made real short wire connections
from the guts in the radio to the front panel, too.  They were a bear to
attach from underneath but they finally made good contact.

On the back, I didn't like the antinnna connectors, so I drilled holes and
mounted a SO-239 plug and connected it right to the antenna coils.
Something needs fine tuning, though, because the Antenna Trim adjstment
doesn't seem to work anymore.  I'll have to try taking turns off the coils
to see if that helps.

I also mounted a T/R relay on the back.  There is a lot of room to mount
whatever you want.  Be careful when you drill, though, because there are
wire harnesses and parts right on the other side of the back panel.  I
wonder why they made the set that way.  Gees, it is really easy to drill
into something when you are making a hole.

I've heard you can soup up the set with some more modern tubes, but I
haven't found step-by-step instructions yet that I can follow to let me make
the modifications.  I hope one of these days a good article will be
published on Internet or in a magazine.  The radio works pretty well except
on the higher frequencies and a preamp should help there.   Of course it
would be better to modify the front end instead.

Good luck with your radio.  What are you planning to do to it next?  I'm
just about out of bare spots on mine.

Bill

----- Original Message -----
From: Jim Miller
To: [email protected] ; [email protected]
Sent: Monday, May 12, 2003 6:53 PM
Subject: Re: [R-390] Best ballast tube resistor

I drilled a 1/4 inch hole in my front panel to the right of the VU meter and
installed a 15W wirewound pot.  I am able to adjust the pot for optimum
operation of the oscillator tubes.  Since the changing filament voltage does
cause a slight frequency shift, this can also double as a vernier tuning
capability.  I am now working on calibrating the dial in Hz offset.  You
must be very careful to avoid turning the pot to zero however, as it will
fry the oscillator tube filaments.  I am thinking of using a sheet metal
screw as a safety stop for this purpose.

----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Monday, May 12, 2003 9:29 PM
Subject: [R-390] Best ballast tube resistor

> Should I use a 39 or 40 ohm resistor to replace my bad ballast tube?
>
> 1%, 5% or 10% and what wattage?
>
> Someone told me that if I use a resistor, my R-390A would not work
properly.
>
> What should I do?
>
>
>
> The Firebottle
> The Original
> Accept No Substitutes
>
>
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