[Kenwood] TL-922A question

[Kenneth G. Gordon]

Ah! Zero Signal Anode Current.

Well, if it really IS zero at ZSAC, then there is something wrong.

I think at this point we need to step back and reexamine the entire situation.

According to the TL-922 operators manual, the ZSAC for CW should be 100 mA: for SSB it 
should be 200 mA.

If yours REALLY IS zero, there is definitely something wrong.

Either your metering circuits have failed, the biasing circuitry has gone bad on you, or there is 
another problem, like a bad tube or tubes, like a grid to cathode short.

To check this, you might pull one of the tubes, check ZSAC, then (CAREFULLY) reinsert that 
tube, and yank the other one, then recheck ZSAC.

All this with POWER OFF, PLUG PULLED and HV allowed to drop to ZERO before doing 
any of the above.

Furthermore, according to the Kenwood manual, the absolute maximum drive power should 
be 120 watts, and you should be able to get full power output with 80 watts drive.

Grid current under full drive and with the amp loaded up properly should not exceed 110 mA.

One common problem with 3-500Zs is that one or more of the tube PINS become unsoldered 
internally. This can often be fixed by the judicious application of a 260 watt soldering iron to 
the tube pins, one at a time, and a little added solder if needed.

Let's do a little visual checking here:

First, fire up the amp, preferrably into a good dummy load, and load it up to full output. 

With the exciter in TUNE, what does your plate current and plate voltages read? You said 
earlier that was 2100 VDC at 210 mA. That is only 440 watts INPUT. If your ZD is really 
putting out almost 100 watts, this is a clear indication of something seriously wrong.

What does the TL-922 GRID current read? If this is above 110 mA (exciter in TUNE), this is 
"a bad thing". Don't hold it this way for very long.

Now, with the exciter in TUNE (full carrier output), hold full-carrier for a while (grid current 110 
mA or less), then look at the 3-500Zs: does either one "show color" i.e., is either plate red or 
orange? Are both plates red or orange? Is NEITHER one red or orange?

If only ONE tube shows color, the one that DOES NOT show color is bad, has a bad socket, 
connection at the socket, or some thing else associated with that tube is not right.

Please report back at your earliest convenience.

Good luck.

Ken W7EKB