fini Posted December 1, 2004 Share Posted December 1, 2004 Yesterday I was presented with the opportunity to purchase a pair of these for $200 cash money, out the door, from a local shop. This is the pair I bugged Craig and Tony about (asked questions) a month ago. They're each modified (the amps, not Craig and Tony), but in a different way (don't ask me how, but they have different-looking parts under the hood). Both have had the rectification changed (tube eliminated). The shop took them in in trade, and never took the time to bring them up to snuff. They're basically tired of looking at them. Here's the problem: They both blow the fuse. I haven't seen them plugged-in, but this is what their tech says. Now, I had asked Craig if there was a way to test to see if the transformers were OK, and I seem to remember him saying to power them up without the tubes. I wanted to confirm this proceedure here before attempting it. Cosmetically, they look pretty nice. Original boards, no leaking or burn areas, Philips EL-34s, decent cages. They seem to be perfect candidates for stripping down to transformers, sockets and chassis. Opinions? This might be the start of a fun project, as long as I can confirm the iron's condition. Thanks! Quote Link to comment Share on other sites More sharing options...
sfogg Posted December 1, 2004 Share Posted December 1, 2004 Joe Curcio has a PDF on how to test Stereo 70 transformers. Should work for the Mark IV too. http://curcioaudio.com/Stereo%2070%20Restore%20Addendumsl-R0.pdf If the transformers are good and they are in decent physical condition they are a steal at $200. Shawn Quote Link to comment Share on other sites More sharing options...
sunnysal Posted December 1, 2004 Share Posted December 1, 2004 good url from mr. fogg...let craig ring in again on how to be sure the trannies are fine. I mentioned before that these are great amps, I am not sure why they would mod them for SS rectification but what the heck...at $200 + $X for restoration and mods they should still turn out be giant killers at munchkin prices. Best of luck, Tony BTW I, for one, have been modded, my wife says for the better...lol! Quote Link to comment Share on other sites More sharing options...
fini Posted December 1, 2004 Author Share Posted December 1, 2004 Yes, thanks for that page, Shawn! Do you have any idea how those instructions could be modified for amps not using tube rectification? Since I don't have these in front of me, are the fuses thole little short buggers (like, 1/2") or the longer pups (~ 1-1/8" or so, if memory serves)? I'd like to show up with the right stuff, if I can convince the tech to assist me in testing the transformers. I may end up going with my gut on these, crossing my fingers, and bring them home to test, where only the cat will see me looking like I know not what I am doing. Oh, Tony, I have been modded, too (at my wife's request). They didn't touch my rectifier, though. Quote Link to comment Share on other sites More sharing options...
sfogg Posted December 1, 2004 Share Posted December 1, 2004 " Since I don't have these in front of me, are the fuses thole little short buggers (like, 1/2") or the longer pups (~ 1-1/8" or so, if memory serves)?" They should be the longer (AGC?) fuses. Not sure on the rectification. Depending upon how they wired in the diodes for rectification you might be able to just clip them out to get back to the 5AR4. If they took out the socket and wired the diodes in across the connections that will take a little more work to go back to the 5AR4. As far as the rest of the transformers the power transformer was specific to that unit though I think aftermarket replacements are available again. The output transformer would be the A-470 of the Stereo 70 or perhaps the later model that Dynaco went to on the S70s. Double check to make sure the output and power transformers match between the two amps. " I may end up going with my gut on these, crossing my fingers, and bring them home to test, where only the cat will see me looking like I know not what I am doing." At that price that is a pretty safe bet.... I'd have bought them already if it was me. Since you need to strip them down to repair them anyway check out Curcio's mods for the MKIV. They look pretty tempting. (I have a St70 and one MKIV) Shawn Quote Link to comment Share on other sites More sharing options...
NOSValves Posted December 1, 2004 Share Posted December 1, 2004 Fini, Since the tube rectifiers are no longer in the amp DO NOT FIRE THEM UP WITHOUT TUBES !! To test the power transformer you will have to lift the SS rectification to see if the power transformer blows a fuse with no load if it blows a fuse without the rectifiers hooked up the power transformer is shorted. Why don't you just send me your number and we can talk about it craigostby@comcast.net my LD is included in my monthly bill so no big deal. Also get me some detailed pictures of what the hacks did to the amps. I have a set here that another forum member bought that were highly modified with SS rectifiers and both Power transformers are crispy burn't as is the output iron ! I refused to try and bring them back to life. If you fire them up without tubes and there SS rectified the Power supply cans will see a huge over voltage condition that will fry to PS cans. Do the amps instantly blow a fuse and I mean like instant ? If so the PT are most likely fried unless there some dead short in the wiring. Craig Quote Link to comment Share on other sites More sharing options...
Deang Posted December 1, 2004 Share Posted December 1, 2004 My opinion is that an amplifier is not completely broken in until it has caught on fire a couple of times. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted December 1, 2004 Share Posted December 1, 2004 Well in your case then it's still not broken ! Quote Link to comment Share on other sites More sharing options...
fini Posted December 1, 2004 Author Share Posted December 1, 2004 You've got mail, Craig! Good advice there, Dean... Quote Link to comment Share on other sites More sharing options...
NOSValves Posted December 1, 2004 Share Posted December 1, 2004 Get off the phone Quote Link to comment Share on other sites More sharing options...
fini Posted December 1, 2004 Author Share Posted December 1, 2004 Sorry! Off now! Quote Link to comment Share on other sites More sharing options...
fini Posted December 1, 2004 Author Share Posted December 1, 2004 Well, I picked them up this evening. I did a rudimentary test on both. One does not blow the 2 amp fuse (at least after a couple minutes), but the other does blow, IMMEDIATELY, even with the 2 red leads snipped (indicating a possible shorted trannie, according to Craig). The owner of the shop was kind enough to offer to give me my money back if indeed I determined the transformer was kaput (is that spelt corekly? Craig???). I will post photos tomorrow (when the little lady is out of the house, if you catch my drift...). Sheltie Dave, if you are reading this, I am still looking forward to that Pilot! BTW, has anyone seen hide and/or hair of Dave?? Quote Link to comment Share on other sites More sharing options...
NOSValves Posted December 1, 2004 Share Posted December 1, 2004 Fini, The amp blew a fuse with the HV leads removed from the SS doides and the tubes out of the amp ? If so and there are no bare shorted wires the PT is shot. No other option. Start shopping for a amp for parts. Craig Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 1, 2004 Share Posted December 1, 2004 I guess if it gets too ugly there is always Ebay..... Quote Link to comment Share on other sites More sharing options...
fini Posted December 1, 2004 Author Share Posted December 1, 2004 Craig, The tubes were still in at that point. I have not tried it without tubes. The tech wasn't in when I was there, and the salesman left me alone at the bench (!). I didn't want to blow something up, ya know. I thought snipping wires was bold enough.... I can test more tomorrow. So, possibly one good one, at least. I could ask for a partial refund I guess... Quote Link to comment Share on other sites More sharing options...
Klipschfoot Posted December 1, 2004 Share Posted December 1, 2004 Pack 'em up and send them to NOS. Don't waste your time with old stuff unless you are above the "what's that thing do?" level of electonics knowledge. I have wasted time and money monkeying with things I know little about. In retrospect, if I could have saved and bought things that were already up to snuff, I could have had more time with things that I really enjoy. Most of the vintage stuff I bought on eBay went right back up on eBay because I don't have patience for them. Shortcuts are rarely worth the risk. And when it comes to electronics, we are talking about potentially lethal risks. Don't screw around with electronics unless you are well "grounded" in, at least, the fundamentals. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted December 2, 2004 Share Posted December 2, 2004 I have to agree that troublshotting an amp is best done by those who know. It am sure craig can quickly get to the bottom of things and give ypu a quote to bring them back to life. regards, tony Quote Link to comment Share on other sites More sharing options...
fini Posted December 2, 2004 Author Share Posted December 2, 2004 Well, right now I'm just trying to determine if the iron is good, with reasonable assurity. The seller will give me my money back, within a reasonable amount of time. I wish Craig were close by! I'm pretty sure one MK IV has good iron (although the wiring looks pretty durn bad. Photos in a couple of hours ). Quote Link to comment Share on other sites More sharing options...
Marvel Posted December 2, 2004 Share Posted December 2, 2004 fini, Good ol' Ned at Triode Electronics has drop in replacement power trannies. I think they are about $100, but it would be the right size for it, it that model uses the same as an ST-70. Even if one is good, you could pull it and put two new ones in (so they would match) and sell the single back on ebay. I'm still waiting on parts from Mouser for my ST-70. UPS let them get as close as Atlanta and then sent them back to Houston! Package was supposed to be here on Tuesday, and now they say it will be at least next Monday. I am pretty irritated. Marvel Quote Link to comment Share on other sites More sharing options...
NOSValves Posted December 2, 2004 Share Posted December 2, 2004 The Mark IV uses a different power transfomer then any other Dynaco product. The only souce for them is from another Mark IV as far as I know. The model number of the power transformer is PA-135. Craig Quote Link to comment Share on other sites More sharing options...
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