Darrell Bellerive <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- Garey,
Thanks for the tip on the 6EA8 at V-2. From what I read on the web it looks like a direct replacement. Just plug it in. Am I correct? I have four good 6EA8's. Testing them on my Mercury Model 990 tube tester show the following emission levels: ProComm (Gt Britain) Triode 81 Pentode 81 HitRay (Japan) Triode 80 Pentode 78 Phillips Triode 79 Pentode 77 RCA Triode 76 Pentode 70 The tube tester good range is from 50 to 100. From your message it looks like the oscillator triode is the problem with the 6U8 and not the pentode (1st mixer) section. Which of the above tubes would you use and why? 73, Darrell VA7TO On Wednesday 23 July 2008 20:07, Garey Barrell wrote: > The 2-B came with Sylvania or RCA tubes when new. By the way, Zenith > didn't make tubes, and all Zenith branded tubes were made by Sylvania. > > V2 can be problematic. The 6U8(A) is marginal on gain, and as it ages > the 18.0 MHz crystal will sometimes fail to oscillate. The oscillator > circuit is a little different in that it operates with fundamental > crystals below 18 MHz, and 3rd overtone crystals from 18 MHz and up, > with no switching. Anyway, the 18.0 MHz crystal is a 3rd overtone, and > seems to be "on the edge" in more ways than one. Changing tube to a > 6EA8, with its higher gain, will make this circuit more reliable. Quite > a few 18.0 MHz crystals have been replaced over the years, when a simple > tube change would usually "fix" the old one. > > The 8BN8 is correct also. The very first 2-A's had a 6BN8 here, but at > s/n 1000, it was changed to an 8BN8 for hum reduction. There is an > article at www.wb4hfn.com explaining the mechanism involved. > > You're off to a good start! > > 73, Garey - K4OAH > Glen Allen, VA > > Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs > <www.k4oah.com> -- Darrell Bellerive Amateur Radio Stations VA7TO and VE7CLA Grand Forks, British Columbia, Canada ---------------------------------------------------------------------- Submissions: drakelist@zerobeat.net Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net ----------------------------------------------------------------------
