What a wide collection of replies--bucking transformers, variacs and trust to luck--you have your choice. My shack is a mixed bag. I have about 20 stations set up. Most of these are powered on variacs permanently set to deliver 105V. But some of the rigs are more recently constructed homebrew units or they have output voltage controls on their power supplies and so I run them straight off the line. The few solid state items here also run directly off the line. Everything is switched through a sub-panel so that you can't just walk up to a piece of gear and turn it on--you have to turn on the panel first. I did that because I have kids who "look with their hands". But I put EMI/RFI filtering and circuit breakers into each of the panels and variac boxes too. So the panels do more than just switching.
I think the only truth here is that you can't take line power for granted. It's worth the time to think through the power situation and take no chances. My 2 cents. 73, Don Merz, N3RHT -----Original Message----- From: Brett Gazdzinski [mailto:[EMAIL PROTECTED] Sent: Friday, January 17, 2003 8:15 AM To: [email protected] Subject: RE: [AMRadio] Today's AC Mains voltage too high for many BA Rigs I ignore it. Never had a problem. I have two 32v3 transmitters, that are all solid stated, and run on the high voltage tap, no problems for over 15 years, not a single tube has gone south. I have an R390 that has not needed a tube or anything else, for over 15 years. I have an sx17 that has not needed any tubes or had problems, I have a Scott SLRM that has the filaments in series, no power transformers at all, no tube problems. My line voltage fluctuates wildly at times, for some reason, loads dim the lights, they will even pulse to some loads like my compressor running, or the washing machine. Never burnt any tube out in 15 to 20 years of frequent use. If something was marginal enough to go because the line voltage is a bit high, I want it replaced anyway. I wonder just how long this equipment can go without any tube failures. I have blown out some old scruffy PA amp tubes like 4-400,s and 6146,s but they were broadcast pulls I think, or bad to start with. ...$5.00 ham fest specials. If you are running equipment you have to worry about because the line voltage is slightly high, its bad news, things are supposed to have some headroom... Brett N2DTS > > Follow-Up on 20A. > I have an observation that is perplexing me. Some of my > old AM Boat > Anchor gear was designed in the days when the AC mains power > was lower. For > example on one of my Central Electronics 20a 's, I measured the > filament voltage (non-RMS DVM), and it came out to 6.9 vac > with a AC line > voltage of 123 volts. I had to lower my ac mains with a > variac to 112 vac to > get the filaments down to the nominal 6.3 volts. > > This brings up a couple of issues: > > 1.) The filaments running ~ 10% high may have more emission, > but cathode > longevity may suffer along with more likely heater to cathode shorts. > > 2.) The AC power transformers may not have adequate flux BH > headroom, and > could start to saturate, leading to high AC input current, and hot > magnetics. > > 3.) The High voltage may be beyond the ratings of the > components (too much > voltage) which may lead to higher heat dissipation. For example, > electrolytic capacitors may see too much voltage. This is > especially true > when solid state power supplies are used with vacuum tube > circuits. The > voltage soars to the peak AC value until the tube heaters > warm up enough to > pull current. The higher tube element voltages may also (if > unregulated) > move the DC operation points to dangerously unstable levels. > For example, a > 10% rise in the G2 voltage (say 400 to 440) of a Beam Power tube can > increase the DC operating point such that the plate > dissipation is too high > leading to a thermal run away condition. > > My first thought of attack concerning my 20A was to add > resistance to the > filament wiring. This is doable so long as the ac mains voltage is > reasonably constant. The DC voltage issue can be solved in > other ways, such > as regulating the G1 fixed bias, and the G2 screen voltage to > my 7591 beam > power tubes. It seems that when the ac mains increases, the > G1 fixed bias > goes more negative, and the screen G2 goes more positive. The > sensitivity to > G2 is greater than G1, so the plate current varies quite a > bit with a small > change in ac mains voltage. Just thinking about this, I could > add some gain > to the G1 potential VS ac mains voltage change to cancel out > the G2 effect > on plate current. A little bit of cathode bias to the 7591's > might also help > with stabilizing the DC operating point as well as adding a little > degeneration (gain, and distortion reduction). This approach > might be an > option to regulating both element voltages. I have plenty of > headroom with > the electrolytics. > > Another option would be to add a multi-tap buck/boost > transformer so that I > can accommodate a variety of AC mains voltages, and still get > the nominal > 6.3 volts ac to the filaments. This need not be large, and could be > installed within the rig. A 12Vct 2A transformer could be > used to add 6, 12, > or subtract 6, 12 volts from the AC mains input. It would > require a fancy > switch (maybe 2), or network of jumpers to work however. > > What I have ended up doing was to install a 5 amp variac to a > 6 plug outlet > strip. I am currently running my RCA AR88 receiver, CE 20A, > BC-458 VFO, and > a rack mount Kepco 200 volt power supply all off the strip. I > set the variac > to 114 volts. The AC drops to 112 with my linear set to 200 > watts carrier > output. Now I need to find out about my Gonset GSB-201 linear > (4 X 572B), > and determine what filament voltage is on the 572B's. Hey at > $50 bucks each > (today's prices) I don't want the filaments burning at 7.0 volts (6.3 > nominal??). I will need a 15 amp solution to dropping the > voltage to the > Gonset should the filaments be too hot. > > Do any of you fine folk have this problem, and if so, how are > you dealing > with it? > > Jim, > WD5JKO > > > > --- StripMime Report -- processed MIME parts --- > multipart/alternative > text/plain (text body -- kept) > text/html > The reason this message is shown is because the post was in HTML > or had an attachment. Attachments are not allowed. To learn how > to post in Plain-Text go to: http://www.expita.com/nomime.html --- > _______________________________________________ > AMRadio mailing list > [email protected] > http://mailman.qth.net/mailman/listinfo/amradio _______________________________________________ AMRadio mailing list [email protected] http://mailman.qth.net/mailman/listinfo/amradio
