Robert, If you can get 10 watts or more out, the base K2 PA transistors are likely OK.
The power discrepancy between your RF probe and the K2 display could be caused by a dummy load that is not right on 50 ohms or has some reactance. In using RF voltage to measure the power, the value of the dummy load is critical. Once you get the KPA100 wattmeter going again, you can calibrate it using any external wattmeter that you trust. I would advise calibration at 80 to 100 watts - there is some non-linearity in any wattmeter, so you want to calibrate it near full scale. 73, Don W3FPR On 4/22/2011 5:22 PM, Robert G. Strickland wrote: > > -------- Original Message -------- > Subject: Re: [Elecraft] K2/100 pwr out control problem > Date: Fri, 22 Apr 2011 21:22:17 +0000 > From: Robert G. Strickland<rc...@verizon.net> > To: d...@w3fpr.com > > Don... > > The base K2's power is continuously adjustable from low to over 10w as > measured by the RF probe. However, the Vrms readings don't jibe w/ the > power out as indicated on the K2 lcd. I did run the bare K2 through my > antenna tuner that has a cross needle forward/reflected meter [yes, > they're barely accurate at best] and that showed continuously variable > power from nil to quite a bit over 10w indicated. > > The exact power reading at this point is indeterminate, but I'm pretty > sure that it's up there. When this problem started, I noticed it by not > being able to control the power out from the amp; it was being driven to > around 700w out [too much]. To do this would require a drive level of > around 50w from the K100 which would, in turn, require "something" from > the base K2. I'll get some diodes and report back. > > Thanks. > > ...robert > > > On 4/22/2011 20:55, Don Wilhelm wrote: >> Robert, >> >> Yes, that is the first step. >> >> The K2s attempt to drive the power higher (the microprocessor thinks the >> power output is low) may have damaged one of the base K2 PA transistors, >> but replace the diodes first and then that check can be made. >> >> If you have to order the diodes from Elecraft, you may want to check on >> the health of the base PA first. >> To do that, remove the KPA100 and check the maximum power output >> available from the base K2. If you cannot get at least 10 watts out of >> it on most bands (all exxcept for possibly 10 meters), then it is likely >> the PA transistors must be replaced - order K2PAKIT from Elecraft. >> >> 73, >> Don W3FPR >> >> On 4/22/2011 4:33 PM, Robert G. Strickland wrote: >>> Hello, Don and others.. >>> >>> Thanks for everyone's suggestions. Much appeciated. The problem >>> persists regardless of using an antenna or a dummy load. I carried out >>> Don's suggestions as described below. >>> >>> I don't have a watt meter, so I used the RF probe on a 50ohm resistive >>> load and calculated the Vrms for the various power levels. Calculated >>> and observed readings are as follows: >>> >>> Power Vrms [cal] Vrms [observed] >>> 10w 22.36v 18.0v >>> 5w 15.8v 18.0v >>> 2w 10.0v 18.0v >>> >>> Computed power out at 18.0Vrms is 6.48w >>> >>> In addition, I notice the following LCD readings at all three power >>> levels: the moment the TUNE button is pressed a HI CUR reading appears >>> that immediately changes to a power out reading is 2.1w and an SWR >>> reading 9.9:1. Again these reading occur at all three power settings. >>> >>> Don, I'm going to assume that your first suggestion to change D16 and >>> D17 still holds. Yes? >>> >>> ...robert >>> >>> On 4/22/2011 15:47, Don Wilhelm wrote: >>>> Robert, >>>> >>>> Make the following setup and check into a dummy load with an external >>>> wattmeter between the K2 and the dummy load. Please follow the testing >>>> method given, there is a reason for that test methodology. >>>> 1) Remove the APP power cord from the KPA100 and power the K2 only from >>>> the coaxial power jack on the lower rear panel. Set the K2 to 40 meters. >>>> 2) Set the power requested knob to 5 watts and press TUNE - what is the >>>> power on the external meter? >>>> 3) Set the power to 2 watts and again press TUNE - what is the power on >>>> the external meter? >>>> >>>> If the actual power was 10 watts or more in both cases above, change >>>> diodes D16 and D17 in the KPA100. >>>> If the actual power tracked the requested power, then you have a >>>> different problem - power the KPA100 from the APP power cable and try >>>> again into a dummy load (not an antenna). Set the power requested to 50 >>>> watts and do a TUNE - the actual power should be near 20 watts. If it >>>> goes to a large value, then we need to investigate your KPA100 - remove >>>> it from the base K2 and take the shield off, and let us know the status >>>> of your results. >>>> >>>> 73, >>>> Don W3FPR >>>> >>>> On 4/22/2011 10:46 AM, Robert G. Strickland wrote: >>>>> I'm running a K2/100 Ser# 5957, operational for about three years. Just >>>>> now, control of pwr out has become intermittant. I can control pwr out >>>>> in the basic K2 thru the range 0 -13w. Anything over that and the K2 >>>>> meter sticks at about 13w, but the amp output jumps immediately and >>>>> somewhat randomly to between 50-100w with no "smooth" control. >>>>> Decreasing the K2 pwr out below 10w or so, and the overall pwr out >>>>> drops >>>>> accordingly, the K2 meter reads "correctly," and the total unit pwr out >>>>> (external meter) agrees with the K2 meter. I've tried cycling on/off, >>>>> different bands, different modes. All the same. Any suggestions most >>>>> welcome. >>>>> >>>>> ...robert >>>>> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
