[EMAIL PROTECTED] made an utterance to the drakelist gang ---------------------------------------------------------------------- On Mon, 5 Dec 2005, Mike Williams wrote:
> I am seeking a set of 3-500Z's and chimneys for a L4B I am in the > process of renovating; they need not be factory fresh by any means; just > have enough transconductance left to pump a few hundred watts! If you > have any sitting around, let me know how much you want for them! Try to find some chimneys with the tapered tops to push air across the anode seal and plate heat dissipator. If you use glass cylinders that are not tapered at the top (Coleman lantern glass) you might as well not use any at all. This depends on your operating style, however. If you rarely run the tubes beyond dull gray with a tint of red you can get by without a proper chimney. If you run the tubes red to almost orange (pretty easy to do with 3-400Z) you will want chimneys with the tapered rim. The glass envelope can take more heat than the anode seal where the pin comes through the glass. As for the tubes, my recommendation would be to buy from someone who has used tubes in good working condition (sometimes Tom's Tubes has some nice ones that are used). I've blown a lot of money on crap sold at the auction sites - I have a shelf of dead 3-400Z and 3-500Z tubes that were "sold as is" - $300 worth of junk that would have bought a NEW matched pair of 3-500ZG. Late model 3-500Z Eimac tubes are prone to leaks and usually fail immediate on turn-on if they haven't been used for 10+ years. Last but not least, if you see about 2500V in SSB position and 160mA or more idle plate current you might want to consider good chimneys because the tubes will get awfully hot. My L4 will deliver 650W with 65W drive in the CW position with 3-400Z and it will run forever on any band - do this in SSB mode for another 2dB (1100W) without good chimneys and you'll melt the solder in the tube pins and ruin your tank coil or bandswitch on WARC (17m operation for example). Sorry if i'm sounding preachy. Hope this helps. -- 73 Jason N1SU http://n1su.com/ ---------------------------------------------------------------------- Submissions: drakelist@www.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 ----------------------------------------------------------------------