Hi Don I did a check on the voltage divider resisters as you suggested & found that R75 read 82 ohms rather than the expected 680 ohms! I had accidentally put in an 82 ohm resister (R94! From the buffer circuit) and put the R75 680 ohm resister in the R94 position - they are consecutively fitted on page 59 on the bottom of the board and whilst I check the resistance before fitting I must have mixed them up!
I switched them round and the PreAmp now works as it should. The dc volts are now E 1.51vdc, B 2.22vdc & C 12.89vdc. Thank you so much for your help Don, and I feel I've really learnt something as well! 73 Ray G3XLG -----Original Message----- From: Don Wilhelm [mailto:d...@w3fpr.com] Sent: 25 December 2012 16:48 To: Ray Spreadbury Subject: Re: [Elecraft] K2 #7340 PreAmp Problem Ray, I would say that Q21 does not have adequate base voltage for it to conduct. The base voltage should be about 2.3 volts. Check R72 and R73 and C143 for good soldering and correct values. Check R75 on the bottom as well. The base voltage is set by the voltage divider consisting of R72 and R73 and R75. 73, Don W3FPR On 12/25/2012 11:28 AM, Ray Spreadbury wrote: > Hi Don > > Thank you for your reply. > I visually checked the components in the preamp circuit & reflowed the > solder of them all including the relay, T6 & Q21, but still got the > same results as before. The coil T6 wires have been put in the correct > holes but I can't check the wires were tinned correctly without > removing it but I think they were. > > However, I did a dc voltage check on the transistor Q21 & found some > anomalies- the E,B & C should be 1.6vdc, 2.3vdc & 13.3vdc but with the > PreAmp OFF they are E 0.00vdc, B 0.00vdc & C 13.36vdc. With the PreAmp > switched on, they are E 0.00vdc, B 0.33vdc & C 13.17vdc. (For > completeness I checked them with the Attenuator switched on & they > were the same as with the PreAmp switched off.) > > Does it look to you as though the transistor Q21, a 2N5109 is faulty? > > Regards > Ray > > -----Original Message----- > From: Don Wilhelm [mailto:w3...@embarqmail.com] > Sent: 24 December 2012 21:38 > To: Ray Spreadbury > Cc: elecraft@mailman.qth.net > Subject: Re: [Elecraft] K2 #7340 PreAmp Problem > > Ray, > > Check every component in the Pre-Amp circuit, including the relay. > > Do you have the leads of T6 well stripped and tinned? If so, check to > see that the leads are in the correct holes. > After that look critically at the solder pads for those components > around the preamp circuit - look at the schematic sheet 2 to identify > those components. You should see the solder flow out to an almost > invisible edge on both the solder pad and the component lead. It has > been said that the esolder connection should look like a mountain, but > not a volcano - if there is a ring around the lead or you do not have > concave solder fillets, not enough heat was applied to the connection. > > 73, > Don W3FPR > > ______________________________________________________________ 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
