212Mavguy Posted January 9, 2013 Posted January 9, 2013 Found myself in a bit of a time quandary so had the work done this time, by my fave tech Mike Christenson, House of Guitars, SLC, UT. The process is called amplifier blueprinting, in this case replacing most of the resistors in the amp with ones identical in type and vintage, at very precise adherence to original parts values. The old resistors with time drift upwards to way out of original tolerances in some positions. As part of the process, Mike was supplied with some military stock Russian Paper in Oil coupling caps to use where he thought fit. When it got back it had been all PIO'ed from the phase inverter back to just behind the first preamp tube's section, where the original blue molded caps were left in. In addition, a reversible modification was performed on getting reverb in both channels, a vibrato "tick" quieting mod, bias probe sockets were also supplied and they were installed, worked great. I found a very high quality of cap for the bias supply board. Had previously sourced from Mike at vintagefenderamprepair.com a set of power socket precision matched NOS Allen Bradley carbon comp resistors, also complete sets of preamp plate and screen resistors, again tight to original tolerances and to each other in respective values, a set of F&T filter caps and Sprague cathode bypass caps to blackface specs, native to this amp. I resocketed with all VOS tubes chosen for make and tone briefly for each position. The original 4/10 cab had a couple speakers that did not sound right, as if there was a cone rub. The amp was a 350 dollar buy/rescue in what was thought to be non working condition, the SS rec was yanked and a real rec tube socketed, it worked fine, but sounded like it needed a recap and retube, hence the all out blueprinting, because the amp's circuit deserved it. So now the chassis was done to a more "Liquid" sound but a couple of the original four ten's were rubbing, and I had some nice 15's around, ordered me up a 1/15 baffle off eBay, it arrived yesterday afternoon Got home from work and saw the package, got it unpacked, noticed that the new one was a bit thinner than the original, so was worried about original screws penetrating through. Went and got some black grabbers an eighth inch shorter. Time was running out, there was an open mic and I had a guest to meet there. Mounted the vintage JBL G135 speaker, then the chassis, connected reberb tank speaker and footswitch sockets. Fired her up and a very brief wow moment, less than 5 minutes to dial in tone settings, slapped the girl into the back of the ride and went to the Jam. Short story...spectacular right off the bat, other players were enjoying playing through, Great sustain, reverb and vibrato were lush and smooth, plenty of low end, great detail in entire range of instrument and tonal consistency from low to high notes, simply stellar, after the recap the bottom was tight, no flab, almost like a SS rec tight. I was running a Bendix Red Bank 5R4WGB, it has huge plates like a 5U4 but puts out slightly higher voltage while using less heater current. This morning I yanked the nice sounding Russian 6l6GC tubes and stuck in some socket adapted vintage Sylvania blackplate 6BG6GA, a repinned 7581a, sorta super 6l6 type. Harmonic detail and transient crispness were improved even more. Will try to get some clips jamming out later this week if possible.
smurph1 Posted January 9, 2013 Posted January 9, 2013 WOW..didn't understand the technical stuff, but sounds like a kickass amp!!
H Posted January 9, 2013 Posted January 9, 2013 Great write-up! Would be nice to hear some of your amps too:) Is the vibrato 'tick' cure you mentioned a VTL5C1?
212Mavguy Posted January 9, 2013 Author Posted January 9, 2013 The vibrato was just a new opto bug and possibly a bit of a circuit tweak, it's much quieter now. 6bg6ga's were not as nice as a 7581a pair. So they are in it now. Speaker is subbed out, a JBL MI-15 is in for a bit at least.
bolero Posted January 9, 2013 Posted January 9, 2013 man, that is quite the project!! looking forward to pics/clips I remember having vibrato tick probs with my SF twin as well, I think I still have a spare "roach" around here somewhere..might cone in handy when I get that SF super reverb if it needs one
212Mavguy Posted January 10, 2013 Author Posted January 10, 2013 Will shoot a few soon. Amp porn coming.
rockabilly69 Posted January 10, 2013 Posted January 10, 2013 Hey Mavguy, what jam do you go to in Salt Lake City? And yes Mike is a great tech at House Of Guitars. Very fair on prices and quick turnaround. My band The Legendary Porch Pounders are playing at Pat's BBQ this Friday night from 7 to 9, if you're in town drop by and say hello. The BBQ is pretty righteous there. Dan
yoslate Posted January 11, 2013 Posted January 11, 2013 rockabilly, Mavguy...not so hot a math, I'm assembling 2+2, and arriving at 4.... I'm assuming you're both in the Salt Lake City area? My son's in grad school there. I hope to be out there to visit, spring or early summer. Would love to get together, if we might. Care to pencil that one in...?
golferwave Posted January 11, 2013 Posted January 11, 2013 What a project! Seems to be quite a science matching the replacement components to the older broken in parts. I'll bet it sounds sweet!
rockabilly69 Posted January 11, 2013 Posted January 11, 2013 rockabilly, Mavguy...not so hot a math, I'm assembling 2+2, and arriving at 4.... I'm assuming you're both in the Salt Lake City area? My son's in grad school there. I hope to be out there to visit, spring or early summer. Would love to get together, if we might. Care to pencil that one in...? Yes I'm in the Salt Lake Area (Ogden), and would love to get together if I'm in town!
212Mavguy Posted January 11, 2013 Author Posted January 11, 2013 Ha! Dan, you used to play through a Frenzel, right? As in Dan W? We know each other! I will be sitting in for a few tonight (Friday) at Fat's grill with Chicago Mike Beck. @Yoslate, absolutely!
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