Re: [AMRadio] Heathkit DX-60 grid current drops (Larry Szendrei)
-- Message: 1 Date: Thu, 27 May 2010 12:36:24 -0400 (EDT) From: "Larry Szendrei" Subject: Re: [AMRadio] Heathkit DX-60 grid current drops To: "Discussion of AM Radio in the Amateur Service" Message-ID: <[email protected]> Content-Type: text/plain;charset=iso-8859-1 As Jim says, you may be losing drive to the final grid because the drive signal is going away. But that's not all that can go wrong. Make sure the final grid bias resistor hasn't drifted off-tolerance or changing value as it heats up. If it is, replace it. I have also had bad final tubes (pair of 6146s in a DX-100) create the symptoms you describe. Originally I thought for sure the problem was with the drive signal, but that wasn't what it turned out to be. 73 es GL, -Larry/NE1S Reply by Jim, WD5JKO: Adding to what Larry says, it could be that the 6146 is running too hot. By hot I mean the filament voltage is too high, and a fragment of the cathode oxide has detached and landed on the control grid. If this is the case, with RF excitation, the fragment gets hot and becomes an electron emitter which will cause the grid current to gradually drop, and then reverse. This happens frequently with the 4D32. With the 4D32, lowering the filament voltage from 7'ish to around 6 volts usually makes the tube behave better. I've not seen this with the 6146, but it could happen, especially when running a vintage BA at today's higher AC line voltage. Jim WD5JKO __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: [email protected] To unsubscribe, send an email to [email protected] with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [AMRadio] Heathkit DX-60 grid current drops
As Jim says, you may be losing drive to the final grid because the drive signal is going away. But that's not all that can go wrong. Make sure the final grid bias resistor hasn't drifted off-tolerance or changing value as it heats up. If it is, replace it. I have also had bad final tubes (pair of 6146s in a DX-100) create the symptoms you describe. Originally I thought for sure the problem was with the drive signal, but that wasn't what it turned out to be. 73 es GL, -Larry/NE1S > Brian the final is losing drive from the driver/buffer/VFO. Check all > tubes first then if that doesn't fix it you will be troubleshooting > under the chassis to find out what components may be changing value. > > Jim/W5JO > >> My Heathkit DX-60 grid current drops after a couple of minutes and >> will keep dropping more rapidly as I increase drive level. Eventually >> the tube plates glow red. I am tuning by the book. >> Any ideas? >> >> 73 >> Brian > -- Pay a visit to my amateur radio web page at: ne1s.rfburn.org __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: [email protected] To unsubscribe, send an email to [email protected] with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [AMRadio] Heathkit DX-60 grid current drops
Brian the final is losing drive from the driver/buffer/VFO. Check all tubes first then if that doesn't fix it you will be troubleshooting under the chassis to find out what components may be changing value. Jim/W5JO - Original Message - > My Heathkit DX-60 grid current drops after a couple of minutes and > will keep dropping more rapidly as I increase drive level. Eventually > the tube plates glow red. I am tuning by the book. > Any ideas? > > 73 > Brian __ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: [email protected] To unsubscribe, send an email to [email protected] with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
