[BC] FM10K

[Tom Taggart]

1. The tube that was in there replaced with a brand new Eimac 4CX300A. No change in symptoms.

2. The plate voltage...though not listed in the manual proper--should be around 2 kv, according to the tube specs.  It's not metered, and I don't have anything that will handle that high a voltage.  However, it comes directly off the 6 kv line through a 200 ohm resistor & small coil; PAPV measures normal.  Resistor measures 185 ohms out of circuit, coil measures reasonable resistance (that is, it's not open).

3. No metering on screen voltage--believe it is listed in the manual--have to see if it is something I can measure.

4. Same with bias voltage

5. Cathode current normally 180 mils--now around 20 mils or so.

6. There are only 2 top hat style caps on the tube socket, they bypass the filament & look OK.

7. The small wattage resistors on the grid circuit show no sign of stress & as noted reflected back to the exciter is a 1/2 watt on 10~15 watt in.  Never ran at 7 watts, even when we had the original MX15 exciter normally took about 12 watts or better drive to make output power.

>
> Bias voltage ?
> The four top-hat bypass capacitors mounted to the tube socket ? These are
> sometimes self-indicating by blowing apart.
> Check every resistor you can access, especially on the side wall. Replace
> any defectives with some of higher wattage, as many of these are
> marginally
> rated..
> Seven watts of drive should saturate the IPA grid. If more is required,
> there is something wrong ( keep in mind that earlier versions of this xmtr
> came with 10 watt exciters).
> Pls report what you find........
> M