[Heathkit] Hot Water 101 Final Question

[Glen Zook]

The 6146A/8298 is definitely a direct replacement for
the 6146.  Now using a 6146B/8298A or a 6146W with a
code date of mid 1965 or later will generally cause
problems.  The primary difference between the 6146 and
the 6146A/8298 is the fact that the 6146A/8298 has a
"dark heater".  The "dark heater" was a production
change made to eliminate problems with heater
("filament") voltage when used in commercial two-way
FM mobile operation.

For the article which appeared in Electric Radio a
while back (and has been reprinted in other
publications since then) go to

http://k9sth.com/Page_2.html

and scroll down to the heading "Articles".  The 6146
article is the first link.

It sounds to me like one, or both, of the 6146A tubes
has an internal short.  There is a very slight chance
that the neutralization is "way off" but even if the
tubes were "taking off" you should still be able to
have some control.

Another possibility is that the plate meter "shunt"
resistors (actually the meter reads cathode current)
have gone bad.  The 6146 series actually has 3 pins
connected to the cathode and from each of those pins
to ground is a 10 ohm resistor.  These quite often go
"high" in value and that results in badly distorted
meter readings.  These 6 resistors (all in parallel)
have an effective resistance of 1.6667 ohms.

Although the original resistors were 1/2 watt I
definitely recommend replacing them with 1 watt 1%
resistors (available from Mouser among other sources).
 "Modern" 1 watt resistors are almost the same
physical size as the old 1/2 watt resistors and by
increasing the wattage of these "shunt" resistors they
are MUCH less likely of causing problems at a later
date.

Again, the 6146A/8298 is a direct replacement for the
6146.

Now you have tried to "set" the idling current.  This
is done by turning down the microphone gain control
all the way counter-clockwise and then keying the unit
in one of the SSB positions.  The bias adjust control
should then be set for the "plate" reading at the
little "triangle" on the meter (this represents 50
mA).  Actually, I recommend setting the control at
just a little bit lower (40 mA) for a little longer
tube life but 50 mA is fine.

Glen, K9STH


--- William Aycock <arkansasbill at sbcglobal.net> wrote:

I have a HW 101 and just replaced some bad 6146 finals
with some 6146As from Sylvania.  With the 6146As, the
plate current is all haywire.  When you place it in
Tune, the plate current is about 90 milliamps with no 
drive.  Key the mike and the plate current pegs the
needle. Has anyone experienced anything like this? 
The only thing that I can think of is that the 6146A
is not a direct replacement for the 6146 although the 
Heathkit manual for the HW 101 said that either may be
used.









Glen, K9STH

Website:  http://k9sth.com