Been trying to get a Heath DX-60 going. Here's what she does: It loads fine
to the proper grid and plate current however when the key is up the current
jumps to 200 or more ma. Then when I key it, it drops back down to the
nominal 120 ma. Ive checked everything but am missing something. In the grid
position it shows no current except when the key is down and peaking the
grids is normal. But when I switch to TRANSMIT the plate current goes to
over 200 ma and stays there until I press the key to transmit; then it comes
back down to normal values. I've swapped with new 6146 and checked the
6CL6s...all good. Any ideas? Tnx Carl

Hi Carl,
The 60B uses grid block keying. As I recall there is a halfwave rectifier
ckt that provides something on the order of -80VDC to cut off the final
during key up. You might want to start there as it sounds like that supply
is not working.

Bob
"Carl" wrote in message
m...
Been trying to get a Heath DX-60 going. Here's what she does: It loads
fine to the proper grid and plate current however when the key is up the
current jumps to 200 or more ma. Then when I key it, it drops back down to
the nominal 120 ma. Ive checked everything but am missing something. In
the grid position it shows no current except when the key is down and
peaking the grids is normal. But when I switch to TRANSMIT the plate
current goes to over 200 ma and stays there until I press the key to
transmit; then it comes back down to normal values. I've swapped with new
6146 and checked the 6CL6s...all good. Any ideas? Tnx Carl

Hi,

Did you check the neutralization? If the 6146 is taking off
on some frequency way out of band, the plate current will
be high. When key down, the excitation at the normal frequency
captures the 6146's operation, back to normal plate current.

Have you tried keying the rig while in a.m. position?
That will reduce the screen voltage of the 6146,
reducing the input, and reducing the output to around 10W.
That won't solve your neutralization problem,
but it should keep the 6146
from being ruined with excessive plate dissipation.
If you try this, don't forget to first unplug the mic.

I had several 6146's which had fairly high key-up plate current,
about 40mA, just due to variations of the 6146 production lines.
They all tested good in a TV-7 tube tester,
but some 6146's required quite a bit more
negative grid voltage to reach cut off than the DX-60 provided.
I just couldn't use those particular tubes in the DX-60.

If you use a DMM to check the negative supply in the DX-60
(which feeds the neon PWR light), you should also check the negative
supply voltage with the DMM set to a.c. volts. If the negative
supply electrolytics are dried out, you will get a big ripple,
and a lower average d.c. voltage output.
(This could explain why the 6146 isn't cut off in key up,
since the negative supply is the source of the grid-block keying).

Many DMM's will fool you
on d.c. volts when checking a d.c. supply with bad hum, and read as if
the d.c. voltage is unchanged from what it should be.
The a.c. volt DMM reading (should be only a few volts) will prove
that the negative supply electrolytics are OK.

73,
Ed Knobloch



Carl wrote:
Been trying to get a Heath DX-60 going. Here's what she does: It loads
fine to the proper grid and plate current however when the key is up the
current jumps to 200 or more ma. Then when I key it, it drops back down
to the nominal 120 ma. Ive checked everything but am missing something.
In the grid position it shows no current except when the key is down and
peaking the grids is normal. But when I switch to TRANSMIT the plate
current goes to over 200 ma and stays there until I press the key to
transmit; then it comes back down to normal values. I've swapped with
new 6146 and checked the 6CL6s...all good. Any ideas? Tnx Carl