beeker Posted August 29, 2013 Share Posted August 29, 2013 I have noticed him on here. I hope to see him with more product for sale. Im looking to pulling some solid state amps off the shelf and use tube. Seeing him on the forum as i asked the question nosvalves was on my mind. I will get in touch with him in december and i'll be ready to spend. thank you. hopefully there are more suggestions around here. vacuum tubes are simply amazing is all i can say Quote Link to comment Share on other sites More sharing options...
mustang guy Posted August 29, 2013 Author Share Posted August 29, 2013 Great advice guys, thanks. Fortunately I didn't burn down the shop. Trust me, I would have thrown that thing through a plate glass window before I would let it burn up shop! I didn't even give it a second thought, since this amp looked like new. Live and learn... After checking out the transformer, I'm gonna look for a 40/40 500/500 cap. Not as easy as one would think. I know how to properly discharge the caps using a resistor, and will make sure to use the one arm rule when tinkering inside. I will de-solder and remove the culprit, replace the questionable caps, test the resistors and replace bad ones, check out the potentiometers. The power tubes are matched, and since I don't have access to bias equipment, I'm gonna let that go for now. I will probably go ahead and replace the cord with a 3wg. I think I have a few old computer cords in a box somewhere. Is there anything I have missed or have out of order? Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted August 29, 2013 Share Posted August 29, 2013 I'll restate what I said before- don't just replace the electrolytics! If the coupling caps feeding the grids of the output tubes are leaky (and they probably are!), you're risking frying the tubes and stressing the output xfmr with excessive current draw. There is usually a bypass cap between one or both legs of the power cord and the chassis. Those are often found to be extremely leaky. Be sure to replace them with class Y2 caps- that should be done before you even think about powering the amp. When you do apply power, use a variac and monitor the voltage at the either the cathode or filament (depending on what tube is used- I don't recall at the moment) of the rectifier, as well as the plate/screen voltage of the output tubes. If you want more help, send me an email and I'll dig out the schematic so I can be specific. Maynard Quote Link to comment Share on other sites More sharing options...
mustang guy Posted August 29, 2013 Author Share Posted August 29, 2013 More great advice! Thanks Maynard. I just purchased a1957 FISHER 80-AZ amplifier SERVICE MANUAL photofact schematic 30W tube DIAGRAM. I also have this manual for my Fisher 80-T. I don't have a variac, so I am also buying one of them. There are many on Ebay to choose from, so that won't be a problem. I love projects like this! I will take pictures of everything I do as I do it. I don't want to create a how-to, as this is no speaker recone. Nobody ever had their heart stopped reconing a speaker. I do; however, want to share with the community my learning experience, my successes and my failures. For what it's worth, there is an as-is Fisher setup on Ebay for $4,999 which includes two of these 80-AZ's. I have a hard time believing they are worth anywhere close to that if they haven't been professionally restored and certified by a tube technician. I sure wouldn't pay that much! Here's the link: Fisher Tube Stereo System Pair 80AZ 80-AZ Pair 80C 80-C Series 80 Tuner in Cabs Quote Link to comment Share on other sites More sharing options...
mustang guy Posted August 30, 2013 Author Share Posted August 30, 2013 I am adding a major thing to this rebuild. All new resistors. I just read this article on CF resistor drifting: http://www.ppinyot.com/links/resistors.htm As near as I can tell from the pictures, every resistor in this thing is carbon comp. One thing is for sure, before I solder a new resistor or capacitor in, it gets tested. I am still waiting for the service manual to arrive. Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted August 31, 2013 Share Posted August 31, 2013 I am adding a major thing to this rebuild. All new resistors. I just read this article on CF resistor drifting: http://www.ppinyot.com/links/resistors.htm As near as I can tell from the pictures, every resistor in this thing is carbon comp. One thing is for sure, before I solder a new resistor or capacitor in, it gets tested. I am still waiting for the service manual to arrive. There's no need to complicate matters more than is necessary, and replacing every resistor is making unnecesary work for yourself and increasing the potential for a screw-up. A 60 year old carbon based resistor which measures within 5% of it's specified value does not need replacement! And, depending on its function in the circuit, values of 10-15% out of spec may be of no consequence whatsoever. Also, depending on where in the circuit the resistor is located, measuring its value without desoldering one end may give you a totally erroneous result leading to replacement of a perfectly good resistor. Some will argue that carbon based resistors don't sound "as good" as metal film, or some other kind of material. It would be very difficult to prove that one way or the other! Maynard Quote Link to comment Share on other sites More sharing options...
mustang guy Posted August 31, 2013 Author Share Posted August 31, 2013 Good advice once again! Desolder one end of each resistor and test it. Replace as necessary. I found the datasheets on the EL37 and KT66. I am posting those links here for future reference. EL37 KT66 Quote Link to comment Share on other sites More sharing options...
mark1101 Posted August 31, 2013 Share Posted August 31, 2013 The vintage sound of the amp is going to be gone with all new modern components. The rebuilds are an art. NosValves has mastered retaining the vintage sound. It would be worth consulting Craig on what resistors and caps to use. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted November 10, 2013 Author Share Posted November 10, 2013 (edited) I may not be a competent tech, but I am persistent. I joined the DIYAudio tube forum, bought a couple books, watched videos, read articles, acquired a bias tester, turned a fan controller autotransformer into a bench variac, opened an account at Mouser, ordered new caps, cautiously installed them, installed a ground cord, installed bleeder resistors on the caps, tested all resistors, tested voltages, and have used the amp successfully. Here it is: Edited November 10, 2013 by mustang guy 1 Quote Link to comment Share on other sites More sharing options...
Greg Oshiro Posted November 10, 2013 Share Posted November 10, 2013 Mustang-- Excellent! I think we all can appreciate a DIY kinda guy. If you're still interested in finding a metal can capacitor, I found this: http://www.technicalaudio.com/pdf/Electronics_Catalog_Extracts/Mallory_FP-WP_Series_capacitors_1985.pdf I think you want a Mallory FP288. If you can find one NOS, read up on "re-forming" electrolytics before installing. I also heard a rumor that CE Manufacturing is making brand spanking new metal can caps, primarily for restoring vintage guitar amplifiers. Quote Link to comment Share on other sites More sharing options...
The Dude Posted November 10, 2013 Share Posted November 10, 2013 Looks like you have done your homework, I think the key thing is to check all your voltages and have good components. Someone said you loose the vintage sound in these units, and they are right. That is one thing I learned about caps, but it from the looks of it at least you used some orange drops which should help. Good luck on your rebuild, its all ways nice when a plan comes together. Quote Link to comment Share on other sites More sharing options...
SonicSeeker Posted November 10, 2013 Share Posted November 10, 2013 The man to speak to about this would be Craig at "NOSValves" who is pretty knowledgeable about these things................. just don't bother him too much, as he's rebuilding a Scott amp for me now! I second this. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted November 10, 2013 Author Share Posted November 10, 2013 Honestly, I can't tell any difference in the sound. As far as I'm concerned, this amp is done. If I had another one with original caps I could do an A/B comparison. If there were any noise, or it was in any way unpleasant sounding my LaScala would tell me. Here are the caps used... Quote Link to comment Share on other sites More sharing options...
mustang guy Posted December 17, 2013 Author Share Posted December 17, 2013 OK, I got two of them done. They both operate and sound identical. The only problem I can see is the neon indicator on the last one I did is lighting at a presumably lower voltage. I will troubleshoot this later. I bought the second amp and it came with a very nice pair of EL-37 Mullards. I am using KT-66's, so I will be selling these. I connected the monoblocks to a set of AL-3 LaScalas. The sound is very different, and seems to be a bit midrange heavy. Not sure what is going on with that, so if anybody has any ideas what it might be, I will troubleshoot that later. Here is the picture of the matching Fisher 80-AZ's: Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted December 17, 2013 Share Posted December 17, 2013 Great job Craig! Glad the amp didn't let the magic smoke out of YOU. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted December 17, 2013 Author Share Posted December 17, 2013 Thanks Carl. I have an electronic crossover I am going to use to connect one of the THT's. I'll report back... Quote Link to comment Share on other sites More sharing options...
mustang guy Posted December 20, 2013 Author Share Posted December 20, 2013 (edited) My report is this. It sounds fantastic! I admit that using an electronic crossover in this system is somewhat diminishing the whole point of going for the heritage sound. Today I received an exquisite Fisher Model 90-T. I am going to y-split this into the two monoblocks. Before I do anything, I am going to install a ground plug and check the caps etc. Should be nice... More pics here Edited December 20, 2013 by mustang guy Quote Link to comment Share on other sites More sharing options...
Tarheel Posted December 20, 2013 Share Posted December 20, 2013 Wow.....now that is a handsome Fisher! Quote Link to comment Share on other sites More sharing options...
minermark Posted January 26, 2014 Share Posted January 26, 2014 When I got into tube amps pretty much yours reminded me of my early days. Best advice that I paid for , for years, scrap the amp, Ebay search, "Class A tube" and shop. Imported stuff is kickazz these days, and they back them up. 70 watts in my Mancave and the neighbors are at my door if I crank 10 watts from the LaScallas. Trust me, you time and your ears will thank you in the long run, out with the old in with the new. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted January 30, 2014 Share Posted January 30, 2014 late to the party..did you check the bias after doing the re-caps? Quote Link to comment Share on other sites More sharing options...
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