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Drake Ps7 Service Manual
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OK, I got three service manuals. At this point I can draw the entire mannual blindfolded.In this test I disconnectd and bypassed the TR-7 final low pass filter estage and this stage includes also the internal meter of the transceiver and also the ALC detectors and controls so the PA is working without control deppending only on the position of the driver potenciometer,I am checking the final PA alone, and I still get the same problem the readings on both meters are the same value. In this check the final PA is working at low power without the control of the transceiver, so is like checking the PA (driver included) using the transceiver as a generator and checking the output on to a dummy load.I have not a RF generator at hand so I could not test the Pa module alone. Of course I suppose the transceiver was designed for a 50 ohms output, if not my test is nonsense.The result is that using the PA and driver module alone gives the same problem as inside the transceiver. It looks the power amplifier has a problem.I wonder if my problem is one of the pair final transistors damaged making a mismatch of impedance?biass of all transistors is right all the time.I know there were problems with predriver transistor but this predriver is cold and looks fine. I suppose also that a leak or thermal problem could reduce the power but not the impedance.I ordered a MFJ antena analyzer to check the path of all the low pass filters, SWRmeter and dummy load but that does not help with final stage and toroid transformers of the amplifier.Any Idea?Logged.
Bird dummy load thermaline 8141 reads 51.5 Ohms, and a home made using few resistors in oil 51.8 Ohms., so the load is correct. I changed the coaxial pach cables and also testd tree different SWR meters. At this point I sodered a bnc connector directly to the PA output to assure a good conection.The problem with this transceiver was that suddenly the needles of the SWR meter whent full final scale, and sometimes worked fine. Lately worked fine the first second and after that full scale.I do not trust on pl and So connectors and I check always the conection to asure is right.This is not the problem, Thanks for your help.Logged. Sorry for a shot gun approach.hOWEVER I suspect the 8 volt bias.1)Check with the DRAKE MUSEUM HELP PAGE.2)DRAKE MADE 2 VERSIONS OF The predriver.You say you get the same foward as reverse.How much power is that?
Service Manual Ford
Try another good rig with your test set up, so you know nothing outside the drake is faulty.If your PA BRICK IS HEALTHY, you should get over 200W out when you remove the ALC WIRE. This test is in the service manual.Put an ammeter in series with the Ps and amp. When in transmit, the draw on the final buss is 25A MAX.I hope you are using only a Ps-7 to power the TR-7.The TR-7 will not turn on if there is a serous fault or short.keep us postedHope any of this helpsLogged. I checked the power output using the dummy load an a DAIWA CN-101L SWR meter. It reads 90Wats at max of the carrier knob.as the pot in the predriver was set at max resistance (minimun power) I decrease this pot to get more power and let the PA power free, the power increased a bit up to 100 wats, after that increasing more on this potenciometer makes the power supply to trip. (I think it trips at 110-120 watts.)The DAIWA is not a BIRD and is not checked aginst any other Watt meter, but I trust more or less on it.Forwad and Reflected show the same reading more or less as if the impedance is not matched.An Amp meter of this range is not at hand so I do not kmow how many amps it takes.Remember that the output of the PA brick is passing directly to the dummy and meter, so there is not control of the ALC,this test was made at 40 meters band.I do not know if this power is enough. Specs say CW 250 watts input,I do not know if my about 100 watts are input or what?Thanks,Logged.
Just a hunch. Try all new cables and an SWR/PWR meterthat DOES NOT HAVE a foward set pot.You do not need anything like fancy like a Bird 43.(I have A digital bird,I just like it because I found I can use a 1000W slug and be able to measureright down to the watt on a 100W rig.)Borrow a cheap SWR/PWR meter.
Try to get one with no foward cal. Pot.Yes, the supply tripped exactly where it should.The TR-7 is a great radio. It is the internal power supply card that blows first. I never heard of anyone having Final problems on a TR-7.
It is extremely overbuilt.Logged. Something still doesn't make sense, simply because it doesn't matter what the source (PA) impedance is: When you measure SWR, you're measuring the line-to-load match. If there's no 'line,' you're measuring the SWR bridge reference resistor-to-load match, in which case you're still measuring a match relative to 50 Ohms. That remains the same whether the PA is 1 Ohm or 100 Ohms.Since you've altered the original grounding path around the PA by making the connnections you've made, possibly the PA is oscillating - that would be no big surprise; however, even then, the SWR should still be low as long as the dummy load looks good at the oscillation frequency.WB2WIK/6Logged.