38-15 Project - Printable Version
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RE: 38-15 Project - Ron Ramirez - 10-02-2012
...or, maybe, a previous owner ran the set with old electrolytics to the point that it began to seriously overload the transformer windings. A bad or marginal transformer does not always manifest itself with leaking wax.
Don't overlook that possibility, when/if all else fails.
RE: 38-15 Project - ipwizard - 10-02-2012
I powered the set off my variac last night on 110v and after about 20-30 minutes the PT was at 113 degrees. I didnt get a chance to check for carbon traces on the band switch or the tube sockets yet maybe tonight.
I hope it's not a PT issue. It ohmed out fine when I first started this project.
Would it be worth it to unhook the secondaries of the PT and see if it still gets hot with no load?
RE: 38-15 Project - Ron Ramirez - 10-02-2012
ipwizard Wrote:Would it be worth it to unhook the secondaries of the PT and see if it still gets hot with no load?
Yes!
RE: 38-15 Project - codefox1 - 10-02-2012
You can always pull all the tubes which will eliminate any load on the transformer. Should not get hot then.
But 113 F is not indicative of any major problem. You can insert a bucking transformer to get down to 110 volts, and that would be a good thing. Check the output stage once again to see if bias is correct and/or sub another output tube.
A good old fashioned DD C ma meter can be inserted anywhere along the voltage divider to measure current draw. I have several different ones, 50ma, 250 ma, 1 amp. Red dot goes to the more positive side.
RE: 38-15 Project - TA Forbes - 10-02-2012
I had a Marine radio tech tell me that the most dangerous thing out there was a Marine Grunt with a screwdriver.
RE: 38-15 Project - LASJayhawk - 10-02-2012
Dang ip, these guys think 113 is hot! Ambient here at my house was 103 today.
RE: 38-15 Project - ipwizard - 10-03-2012
lol It was 101 here in AZ today not too bad seems like it's cooling off now no more 115+ hopefully. Only 94 in my garage much more user friendly then the 107-110 it was a month ago.
Well I cleaned all the tube sockets again, and douched the bandswitch with deoxit. I ran it without any tubes or dial light and the PT never not hotter then 95 (it's 94 in the garage) so I think thats a good thing and it was plugged into the wall ~123-125vac. The amp meter I had in line showed .85mA being pulled.
I put the tubes and dial lamp back in and it is pulling 309mA (according to riders it should be pulling 40w, or 348mA) at 115vac running off my variac, and the PT is at 105 and its been running for about 15 minutes now. I'll leave it run awhile longer and see how it does.
I did notice that the 84 tube socket was pretty lose (tube pulled out real easy) so I tightened up the connectors. Also the DC from the cathode of the 84 (pin4) tube is low at 260vdc, schematic calls for 290vdc.