xpyttl wrote:


"Max" wrote in message
...
Hello,
The panel meter (plate voltage 0-3Kv) of my Linear amplifier fl-2100Z is
broken.

We often see requests for analog meters, which are fragile and hard to
come
by, to say nothing of expensive. If the objective is to refurbish a
vintage amplifier, then probably the best bet is to find a junk amp to
cannabalize for parts.

But if the objective is to actually -use- the amp, then a micro and an
LCD, along with a little design work, can lead to a meter that is more
accurate, more robust, and cheaper than the original.

==============================
However in the RF environment of an power amplifier it might be very
difficult to suppress RF in a micro/LCD equipped device.

I would go for a replacement moving coil meter by checking the voltage
metering circuit resistors and after finding a suitable low mA meter (size
wise) ,determine its resistance and initially replacing the defective meter
with a resistor of that value. You then can measure the mA current through
that resistance . If that current is higher than the replacement meter
can handle ,replace a series resistor in the voltage metering circuit by a
(preferably ten-turn) trim potmeter and adjust the current through the
resistor to the corresponding current through the future replacement
meter.

You then either change the replacement meter's scale or accept the existing
one . Then install the replacement meter ,removing its temporary
replacement resistor in the circuit and finally with a suitable HV meter
adjust the reading of the new meter with the trimpot .

If the above HV meter can't handle 3000 V but say only 1000 Volts ,use a
variac at the AC supply input to the amp and temporarily reduce the HV-DC
voltage to the amp to 1000 V Then adjust the meter reading (with the
trimpot ) to 1/3 of the meter scale.

After all ,this is a homebrew NG.


Frank KN6WH/ GM0CSZ