<html><body><div style="color:#000; background-color:#fff; font-family:arial, helvetica, sans-serif;font-size:12pt"><div><span>Not to ask a stupid question, but have you checked the value of the meter shunt resistor? It is a 1.5 ohm resistor, R-15 on the schematic. Also check C-19 which is a 2 mfd @ 150 volt electrolytic. If the shunt resistor has gone low the meter reading will definitely be low.</span></div><div> </div><div>Glen, K9STH<br><br></div><div>Website: http://k9sth.com<br><div style="font-size: 12pt; font-family: arial, helvetica, sans-serif; "><div style="font-size: 12pt; font-family: 'times new roman', 'new york', times, serif; "><font size="2" face="Arial"><hr size="1"><b><span style="font-weight:bold;">From:</span></b> Kenneth G. Gordon <kgordon2006@frontier.com><br><b><span style="font-weight: bold;">To:</span></b> Heath@puck.nether.net<br><b><span style="font-weight: bold;">Sent:</span></b> Sunday,
September 18, 2011 9:47 PM<br><b><span style="font-weight: bold;">Subject:</span></b> [Heath] SB-200 problems...again...<br></font><br>OK. This time I'll try to get it finished before I hit "Send".<br><br>My SB-200 has been odd in that since I have had it, the plate idle <br>current has NEVER been 90-100 mA as the manual states it should be.<br><br>And, for that matter, grid bias voltage has never been exactly -2.0 <br>VDC either...<br><br>I finally got fed up with this state of things, and decided to <br>carefully examine every component in that grid-bias string, or in the <br>plate metering circuitry, to see if I could find <br>something....ANYTHING....that was out of spec.<br><br>I have been through practically every component, and have, so far, <br>found nothing out of spec.<br><br>Yet, at best, the plate idle current never rises much about about 20 <br>mA (which is ONE "hash-mark" above the lower meter stop, BTW).<br><br>Checking the bias voltage
at the RF-cold end of the grid RF choke, I <br>find that when I use one of those Harbach soft-switch units (the one <br>specially made for the SB-200), the bias voltage is -11.99VDC, which <br>indicates to me excessive resistance in the switching device.<br><br>If I bypass that Harbach unit by jumpering the relay switching point <br>to ground with a clip-lead, the bias voltage is then -1.8 VDC which <br>at least is in the ballpark, and SHOULD make the plate current read <br>90-100 mA....at least with the old Cetron 572Bs...but it still reads <br>very low, 20 mA at the highest.<br><br>As far as I have been able to determine, everything is within spec, <br>and wired correctly, yet I still have this problem.<br><br>Power output, with new tubes, into a dummy-load is 650 - 750 watts, <br>depending on band.<br><br>So, I guess what I am concerned about is linearity.<br><br>Before I continue here, I must ask: has anyone else here experienced <br>such ?<br><br>I
think the next step is to carefully examine the signlal output with <br>a scope.<br><br>The way things are, I may be trying to fix something that isn't <br>really broken.<br><br>Ken W7EKB<br>_______________________________________________<br>Heath mailing list<br><a ymailto="mailto:Heath@puck.nether.net" href="mailto:Heath@puck.nether.net">Heath@puck.nether.net</a><br><a href="https://puck.nether.net/mailman/listinfo/heath" target="_blank">https://puck.nether.net/mailman/listinfo/heath</a><br><br><br></div></div></div></div></body></html>