lwhaples Posted January 1, 2006 Share Posted January 1, 2006 While waiting for Craig to finish up a pair of Mk III's for me,I bought a second pair. They've been sittng till last night. One had all it's tube and looked real clean. I picked up a Powerstat variable transformer,and wired it so I could hook up the MkIII. I put my multi meter in line so I could see the voltage. I decide,why not? If I break it,it's off to Craig anyway.Well, so far it's still working and sounds good. The ones I had rebuilt are running KT88's. This one has 6550's and seems to run alot cooler.Is there any reason I shouldn't be running amps side by side with different tubes? Now I need to get the BOX for running the third amp. I still have a Dynaco ST70 that was rebuilt awhile ago,but has a burn't PA060 trans. I don't really need it and hate to spend the money fixing it. Sell for? trade for? Larry Quote Link to comment Share on other sites More sharing options...
intotubes Posted January 1, 2006 Share Posted January 1, 2006 "I put my multi meter in line so I could see the voltage." You mean current, right? Do you have an analog meter (one with a needle)? I think they work best for seeing little current spikes when reforming caps. What blew the tranny in your Dyno? I have an H.H.Scott FM tuner I might be willing to part with. Quote Link to comment Share on other sites More sharing options...
lwhaples Posted January 1, 2006 Author Share Posted January 1, 2006 With me not knowing,but trying to learn. I was reading voltage, so as to bring it up slow until I hit 120v. Not sure why the tranny went. After a few minutes,the last time I turned it on. I got a smoke show and alot of stink. What model Scott? Larry Quote Link to comment Share on other sites More sharing options...
intotubes Posted January 1, 2006 Share Posted January 1, 2006 When you bring vintage tube gear up on a variac, use an analog AC amp meter (not milliamp) connected in series with one leg of the 120vac. Use a seperate volt meter to watch line voltage if you want but you are keeping an eye on the amps. Watch for little spikes and jumps as the caps reform. The current should increase temporarily then slowly subside. A sudden or steady increase in current means a short is happening in one or more caps, shut the power off right away. Try again, if it happens again you need to replace the electrolytics and hope it wasn't a can that shorted. If you can get it to 120 volts with less than 2 amps or so (slowly, over a period of several hours IMO) then watch it for a while looking for spikes. I ran mine with a meter in series for hours before bringing it into the house. That's how I do it. ymmv H.H.Scott LT-10 Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 1, 2006 Share Posted January 1, 2006 A properly working Mark III should pull about 1 Amp AC from the wall. Reforming can buy you some time but with an all original Mark III sooner or later the PS can is going to fail. Chances are its bad already. They fail in many ways and will not always short to ground. Craig Quote Link to comment Share on other sites More sharing options...
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