Members onelife Posted July 23, 2011 Members Share Posted July 23, 2011 I was lucky enough to have been given a 70 Watt "Ultra-linear" Super Reverb that looks like it had been dead for 30 years. It appears that one of the 6L6 output valves shorted out, toasted the screen resistor and took out the fuse. Someone replaced the fuse with a 30Amp one and when the transformer overheated the thermal protector inside the amp acted as a secondary fuse and prevented any further damage. So the amp sat there for a very long time because it appeared to be "dead". It was an easy fix once I determined the transformer was okay but I am having a weird issue with the reverb. With the control all the way down there is a small but noticeable amount of reverb still coming through. When I unplug the springs from the back of the amp it is, of course, gone but doing so allows for comparison with the actual dry sound of the amp. From the drawings for the amp I notice that the delayed signal is amplified before the reverb control and again after the control by two stages of the same valve. Both stages share the same cathode bias resistor and capacitor. Is it possible that there is come kind of crosstalk going on inside the 12AX7 ? (I've tried a couple of different ones). I also read somewhere that one way to fix a clicking tremolo circuit on a Fender amp is to lift some components of a conductive eyelet board. Has anyone reading this heard about that sort of thing? Any other suggestions? While I was writhing this, I thought that perhaps I should check the control itself to make sure that the wiper of the pot actually goes to ground when it is turned all the way down. These high powered SF amps use very high supply voltages, a different kind of output transformer and has a solid sate rectifier. It does,however, sound very good. It is clean and loud and I'm looking forward to putting a good set of valves in it and using it for my outdoor gigs this summer. It took some cleaning up but now it looks like a "closet classic" that has been aged by the Fender Custom Shop. Did I mention that it is big, awkward, heavy and top heavy. I's as if my old SF Princeton suddenly got very large and very powerful. Link to comment Share on other sites More sharing options...
Members Bro Blue Posted July 24, 2011 Members Share Posted July 24, 2011 pics, please. I would think the pot is probably the problem, btw. Link to comment Share on other sites More sharing options...
Members Kap'n Posted July 24, 2011 Members Share Posted July 24, 2011 I would think the pot is probably the problem, btw. For the reverb, yes - it's either dirty or bad. In either case, the wiper isn't going completely to ground. It should go away completely if you use a footswitch regardless of the pot. If it's an issue, fix it, otherwise I wouldn't sweat it. For the tremolo - from the Music Electronics Forum http://music-electronics-forum.com/t25905/ On neon/LDR Fenders, on the neon bulb side of the module there is a 10M to one side of bulb, 100K to the bulb; from the 10M straight across the board is the gnd point of the LDR. Put a 0.02 cap from 10M/bulb to the ground point; this works by filtering the output of the oscillator. Link to comment Share on other sites More sharing options...
Members onelife Posted July 24, 2011 Author Members Share Posted July 24, 2011 Thanks for the tip Kap'n and for the link to the other forum. Tomorrow I'll get a chance to open up the amp again and have a look at the pot. The amp sat for a very long time and some of the pots were quite stiff when I started so I sprayed them all with tuner cleaner. Maybe dirt in the reverb control got pushed to a point where it stops the wiper. It's a great sounding amp btw. I think these things have an undeserved bad reputation. The build quality is far superior to anything I have seen come from Fender in the last 20 years. It's built like a tank and I can see it lasting for another 35 years. Link to comment Share on other sites More sharing options...
Members Kap'n Posted July 25, 2011 Members Share Posted July 25, 2011 The build quality is far superior to anything I have seen come from Fender in the last 20 years. It's built like a tank and I can see it lasting for another 35 years. Uh, oh. You've just taken the first step down a very slippery slope. Link to comment Share on other sites More sharing options...
Members rog951 Posted July 25, 2011 Members Share Posted July 25, 2011 Uh, oh. You've just taken the first step down a very slippery slope. Tell me about it. This could end up being a very expensive gift! Oh yeah, I want pix too please! Congrats on the amp! Link to comment Share on other sites More sharing options...
Members shoeless Posted July 25, 2011 Members Share Posted July 25, 2011 I found this a while back when I was looking for a fix for my SF Twin. Don't remember where I found it, but I believe it was Fender's service bulletin on the issue. Link to comment Share on other sites More sharing options...
Members Kap'n Posted July 25, 2011 Members Share Posted July 25, 2011 That's the origin of the mod I posted. Part of a Fender service manual. Link to comment Share on other sites More sharing options...
Members wagdog Posted July 26, 2011 Members Share Posted July 26, 2011 Before I gutted it, I had a UL super twin reverb. 6x6L6's of super sterile fender tone. LOUD. I'm not familiar with the UL Super, but I suspect you will find that it gets VERY loud and never breaks up. If your reverb configuration is the same as most silverface (and blackface) fenders, it has a 12at7 wired in parallel to drive the reverb tank, and 1/2 a 12ax7 (one triode) for reverb recovery after the tank and then the reverb pot. Do you have a link to the schematic? Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.