Commander 2500 Magnum

[W3TZ]

I'm looking for advice on repairing a Commander 2500 Magnum. Their is no ouput on 20 meters. The grid input circuit relay coil looks good, 500 ohms, and the bandswitch supplies a good ground. I would like to fire up just the LOW voltage in the xmtr and keep the HI"E" off and the filiments off. The schmatics have very poor labeling , the HI"E" is obvious but the rest of thevoltages are a toss up. Any help out there?
Art W3TZ

[W1QJ]

Ok, couple of- questions here.
1. What is a grid input relay?
2. What do you mean the bandswitch provides a good ground?

Aside from the above questions, Does the 2500 have relay switched input circuits or are they swithced with a typical rotary switch? When on 20 meters, when you apply drive and attempt to load the amp up, do you see any plate and grid current vary with drive level and rotations of the tune and load caps? What is the swr the radio sees when you attempt to load on 20 meters? We need to get these questions answered before we continue.

I smell an answer coming from KA5N

[W3TZ]

The Commander uses relay switching in the tuned grid ckt. The relays are activated from a switch on the bandswitch shaft. The plate 'I' goes to 700 ma with a few grid ma. The drive is at 30 watts and the load is a BIRD dummy load ( 500 watt).

Thanks for the reply, this circuit card realy isn't made to come apart to easy so when I remove it I want to be sure.

Art W3TZ

[W1QJ]

DON'T go taking anything apart just yet!! You did not answer all my questions. You answered a couple but not all. I am going to assume that the amp works as it should on the other bands. That said, here are the questions:
1. When on 20 meters with 30 watts drive and 700ma plate current and a few grid ma's, Do you see ANY output at all?
2. When you turn the load and tune knobs, does the plate current vary at all?
3. What is the input swr the radio sees when this is happening?

[KM1H]

That area is a bear to work on and relays do develop open coils.

While (If) you are tearing it apart you might as well pull the RF deck and replace the filter caps and metering resistors. That amp is pure insanity when it comes to ease of maintenance.

Carl

[W3TZ]

W1QJ: I did not look at the SWR of the xcvr, the power held at 30 watts so there must not have been much fold back. I have the transmitter on a bench, I need to make up a couple of cables to get it operating, To dam heavy to set back in it's normal position. Will leave you know about the tests on Monday.

KM1H: The RF deck has a removable plate to get to the bottom of the tube sockets and caps. This Magnum was made by PALSTAR/KI6SZ Don Kessler in 2009. Thanks for the input I'll take look at the inerds while it's apart.

Art

[W3TZ]

I did alsort of checks on the input circuit to no avail. The thing works works like it should with a 50 ohm dummy load in the out put of the grid ckt. Put the ampl back together and loaded up on 20 meters. I used CW for the input mode and the thing worked, in the past I used FM for the tune up mode, I tried it (FM) and the ampl faults out. By fault I mean that the power light stays solid but the is no grid current but show 700 ma on the plate. Went to CW mode and it tunes up like a champ, RTTY mode acts the smae as FM. All of the other bands will tune with what every you input.
I did notice that with the ALC hooked up and on 20 ALC action is at 1500 watts but on 15 it hits at 1200 watts.
There is no help or advice from former or future manufactures so good luck if the PIC process goes bottom up.

Art W3TZ