Post by thetragichero on Jul 20, 2019 11:40:40 GMT -5
it's baseball season so i had an idea to try to capitalize the time i spend sitting in front of the tv. i stumbled across some good deals on craigslist/online so i decided that maybe I'd try my hand at restoring/repairing some amps (with a concentration on old solid state) to sell. took almost two weeks around the fourth to drive from Florida to the northeast for a wedding/family time, so i was able to scour Craigslist for great deals (miffed i wasn't able to pickup an acoustic 140 for a hundred bucks in Nashua, NH but that was way further north than i wanted to go)
so this is the first of 3 acoustic 140s I've handled that started my love affair with them. purchased online from a tube amp tech who had recapped it but was at his wit's end because it still didn't work. after bringing it up on a lightbulb limiter (learned my lesson continually replacing power/driver transistors on the kustom!) and nothing sitting to ground. hooked it up and it sounded like tube amp sag times 1000 ie zero attack and the note would ' bloom' in. so i take it apart and he missed a small electrolytic, which i replaced. then i noticed one of the big horkin power resistors had lifted its solder joint from the board. so i fixed that and it worked great!
cosmetically, this thing absolutely Sino when i received it, as if it had spent the past 40 years not in a smoky bar but inside a smoker's lungs. cleaned and febreezed and eventually got the smell out, polished up the chrome bits b and replaced the rusted screws and finish washers with new stainless ones from home depot and it looked almost new
took it to a friend's gig and left with $150 and acoustic 140 #2 (even more of a mess than the first!)...
Post by thetragichero on Jul 20, 2019 12:07:39 GMT -5
acoustic 140 #2 looked like it had been dropped or kicked or something. a couple of pots were broken, still had all of the original filter caps.... no wonder it didn't work!
bent out the front, performed surgery on the pots (for some ungodly reason acoustic used pots with two flat sides, so i had to figure out how to attach the shaft of the broken pots to a working pot, and then attach resistors to the outer lugs to achieve the 50k pot the schematic called for... with some patience and some bad words i was successful)
these amps must be hard on the 5w resistors on the power board because this is what came pout of 140 #s 2 and 3:
they still worked perfectly well, but far be it from me to leave a burnt out part in there
once again washed and polished and now she's listed on reverb
Post by thetragichero on Jul 20, 2019 12:17:35 GMT -5
acoustic 140 #3 is an odd one...
somebody chopped off one of the preamps (ave the chassis along with it) and made a smaller box for it! they did a pretty good job too. had to sacrifice the knobs for #2 along with the pots, so this one got big mxr-style knobs. replaced the electrolytics. this one actually got the preamp board from #2 (that way I'm keeping the one that's the least stock). ended up replacing all of the preamp transistors to modern jellybeans. sounds great and i dig the uniqueness!
Post by thetragichero on Jul 20, 2019 12:21:20 GMT -5
1972 sunn concert bass. picked this up on montclair, nj. power cord was toast sci i replaced it with an iec socket, replaced the electrolytics. cleaned up the metal bits and tolex (spray foam tire shine works WONDERS on old tolex). this thing friggin HOWLS on the boost setting
Post by thetragichero on Jul 20, 2019 12:30:23 GMT -5
1990s ampeg svt3-pro i picked up in raleigh, nc. tube gain pot was broken and the knob was missing. spent more on shipping than i did on the parts (so i bought a second set for the bin). 5 minute repair and paid an obscenely low price for the unit. this totally cops the 90s punk rock bass tones i chased after as a kid
I've got an acoustic 370 that is now working but still have to finish the cosmetic stuff. will post that once it's completed. bought two broken pedals at a swap meet for $20. repaired the boutique klon clone and put a better buffer in the buffered volume pedal. volume pedal/wah enclosure itself was worth the 20 bucks
Seriously, good work. Nice to see someone get a double-benefit out of his/her TV time. (i.e. input of Officer Training Materials, and a positive cash flow. Only thing better would be hot-and-cold running Bier Garten maidens!)
Keep up the postings!
An optimist is one who believes that we're living in the best world possible.
Post by thetragichero on Jul 22, 2019 21:20:23 GMT -5
1973 (by my guess from pot/capacitor date codes) acoustic 370
this thing was a bit of a disaster when i received it. somebody replaced the bass pot but tried to make the smooth round shaft have two flat sides using a grinder so that it would fit the stock knob
guy i bought it from said a tech attempted repair but said that it would be too expensive. said low output. for a capacitor-coupled output, that was my first guess. replaced ALL of the electrolytics (including about a billion 1 and 2uf tantalum coupling capacitors). super low output, attached the line out to another amps input and got nothing but noise.
so the problem was in the preamp. my next thought was to test for any open resistors, but before than i just went through all of the resistors on my meter's continuity setting (not sure why, but i did). one of the resistors tested as shorted. so i took it out and it tested fine. head scratch. tested the solder pads where the resistor belonged and sure enough it was shorted. i guess the tech went over all of the solder joints and basically sorted two legs of a transistor together. little to no output makes sense now! cleaned up that mess and tested 'er out...
MUCH louder output, sounded like a cocked wah with the guitar i was testing with. only the mid tone control and volume worked. took a look at the schematic and saw that it could be one of two transistors, one of which had already been replaced with a metal can 2n2222. i have a glut of bc547, so seeing that it was relatively similar to the 2n2484 the schematic called for (relatively small signal stuff, what isn't similar? pinout worked without any weird contorting). and then it worked! i replaced all of the preamp board transistors just for the halibut. had to replace one of the eq sliders (totally busted) with one i got from an organ.
so the original filter caps in all these 70s amps are HUGE. like coke can huge. modern capacitors are tiny in comparison. so how to secure to the chassis if i can't reuse the mounts? like most things, i look for my answer at the hardware store
conduit straps from the electrical section. works for me!
this thing is so growly and wonderful! i planned to keep just the half 140 but this thing SMOKES with guitar or bass!
just need to find another knob since the chrome part fell off
Post by thetragichero on Sept 26, 2019 2:08:45 GMT -5
responded to a Craigslist ad for two celestion vintage 30s ave what i did not know is that they came inside an amp...
95 trace elliot super tramp twin. previous owner stated there were issues using the footswitch. came with a crate footswitch with leds. turns out the switching circuit in the amp doesn't like leds (or diodes in general, I'm guessing) being placed on the contacts. plugged in the vox two button switch i purchased years ago (because it was the cheapest guitar center had) and switching between channel 1 (clean but can get a little overdrive with the gain up), and channel 2 (no clean only distortion) and boost on channel 2 works as expected other issues i found: hum even with guitar volume off, scratchy mastery volume pot, reverb not working as expected (with either channel volume up. it almost seemed as if there were a hard limiter on the reverb... play staccato note with no reverb until the guitar was silent and then it would splash back a little... weird) tone wise i dog the distortion as long as the treble knob isn't too high. seems to only control fizz lol clean channel i felt was too trebley and too bassy. couldn't use a distortion pedal on the clean channel unless the pedal's tone knob was turned all the way down
okay so time to open er up.... (i actually did it twice to troubleshoot some stuff)
hum turned out to be the big 4700uf filter caps. thankfully the ones i had on hand from my last Ali express order fit perfectly, and that the caps i didn't (several 47uf 63v) weren't causing my hum
clean channel: changed 180pf bright cap (c4) to 1nf to allow more than just the highest of fizzy highs through at lower levels of the gain pot attempted lowering the two caps on the bass pot (c11 and c12) from 22nf to 10nf... ended up killing TOO MUCH bass. settled on 15nf
cleaned all the pots, replaced the master volume pot (somebody had already replaced the stock pot and it was a DISASTER)
reverb took some tinkering. at first i thought it was r68 (mix resistor) being too large so i dropped it from 100k to 22k. not that simple there were two tantalum caps in the send and recovery circuitry. both tested at what they should, but i replaced with electro caps just to rule the tants out. r76 measured 100k so i replaced it with the proper value of 47k r73 measured 1k5 and now I'm guessing that was a revision (brown green red, so not a drifted value). i replaced with the schematic value 3k3 tr17 (j112) measured as a short from drain to source so i replaced with 2sk117bl i had (had to reorient but i made it work). apparently my meter registers 30ohms as a short, so it's possible that i replaced a jfet that wasn't dead. all i know is that now the reverb works as it's supposed to. slight volume increase when the reverb is active but I'm okay with that
replaced the speakers (i always intended the v30s for a 2x12 to match my Hammond amp) with Fisher brand musical instrument speakers from a lowery organ. this is the second pair I've gotten and I've had to replace the foam surrounds on all four. there is absolutely zero information online about musical instrument speakers made by Fisher (i spent a few hours and learned way more about the history of Fisher stereo speakers than i ever cared to know).... these roll off more highs than the v30s and i think a little less flubby bass as well... plus all i got in em is about 20 bucks for the foam surround kit
Post by thetragichero on Oct 9, 2019 21:31:24 GMT -5
moog/gibson lab series l3. overpaid for this one but i wanted it. couple things added to this not working: one leg of an electro cap had come unsoldered - easy fix. one of the 2n3055s had both of the mica insulators so the other's collector was connected directly to ground. the output transistors tested okay but i replaced them anyway tracking down why the output was so low. turned out to be a bad speaker Jack. replaced that. this is an interesting preamp. among two dual op amps (lm358 but i socketed and found tl062 to sound much better). also uses the mosfets from a pair of unbuffered cd4007 chips (usually used for bypass switching in effects) as gain and reverb/tone control recovery stages. neat! and you could tell the pcbs were designed by engineers
unseen in this photo is the top two box joints had popped undone. somebody tried a halfassed repair with wood glue and some small common nails. as a whole-assed kinda guy, i removed the tolex and cleaned up the shoddy repair attempt. glued and clamped
buddy i refinished the sg for in green wants me to make his new orange head match his guitar so i ended up ordering two yards of "British emerald green" tolex. won't need that much so i took a little over two feet of it and recovered it. were this for a customer i would've cut it longways for better seam placement, but that's much too wasteful for this project
cts gets great pr from your average guitarist but i find their post 60s speakers (after Bob Gault left to start eminence) terrible. the mid-to-late 70s stock ceramic 12" was no different. had a 10" pyle speaker from an organ pull that sounded just as great as the jensen c10n i pulled and sold for $$$, but it was 8ohms and this is a 4ohm capable power amp so i paired it with a 6x9 also pulled from an organ in a new baffle board, used some grill cloth i purchased for a 2x12 I've been building
I've learned some stuff i would not do again with the tolex and that's important. I'm still not sure if the 3m spray contact cement is the best adhesive. will have to research more
donated the amp to a little church I've been playing guitar at the Sundays I'm not playing bass at the big church. the Trace Elliot 2x12 i ended up with was way too powerful for such a small space
Post by thetragichero on Jan 11, 2020 8:39:01 GMT -5
95 or 96 Marshall jtm60 (same guts as jcm600) mini stack in a lot of ways i think this was the predecessor to the jcm2000 series, not so much in gain and options but in construction methods. 8000 ribbon cables (which if you put back wrong the amp doesn't amplify, just oscillate.... ask me how i know). questionable board placement (close enough to the tubes to suffer heat damage). same runaway bias issue (that's what you get for trying to get cute with zeners and stuff, Marshall!). underspeced bridge rectifier for the heater tap (which was replaced before this one came to me. board is discolored from when the old one bit the dust). besides gobbling through my stash of old and probably already bad el34s, this one sounds pretty good. i like the independent reverb controls (never been a fan of verb with high gain). parallel fx loop volume, when the loop is jumpered, acts like a fatness control. definitely more ac/dc gain than thrash metal the friggin replacement logo (it's creme instead of white) was a months-long ordeal (originally ordered in October, finally received a week ago) I've had it up on reverb 6 hours and already have 8 watchers so hopefully it moves quickly
received this in a trade for the acoustic 370 head and a hartke 4x10 i needed to get rid of. i didn't do much on this besides touch up a solder joint (the crackling sound when the tremolo was on was due to a coupling capacitor that was making intermittent contact to where it was supposed to) be and give it a good cleaning you can definitely see from some of these old sano amps where fender got the ideas for their wonderful pawnshop excelsior (my personal all is in about its fifth iteration, running 6L6s but next time i get the tickets I'm gonna try to run a NFB wire for more headroom.... anyway) anybody else love jumping the channels on a 4 hole input amp? YUM
Post by thetragichero on Jun 18, 2020 0:31:29 GMT -5
never posted this here but i got this jet city 50w combo a few weeks back. it's basically a soldano super lead overdrive with only a couple of component changes and relay switching. came to me cheap because it would oscillate on the overdrive channel and guy didn't know where to go next. turned out to be a bad filter cap. while in there i also cleaned up some previous work that had been done on the amp: guy mentioned that the heaters had been "raised" which to me means the center tap is connected to somewhere with a greater than 0v potential to possibly prevent noise. what actually was done was cutting the traces for pins 4 5 9 on the first three preamp tubes and connecting wires between them and to preamp tube number 4. a lot of work for little to no benefit in my opinion, especially when it's sloppy and you've got heater wires touching other components.... so got it working but wasn't quite satisfied with the "crunch" channel (seemed a bit too lifeless). messed around with that part of the preamp (taking some inspiration from jmp/jcm800 schematics) and now it's in hot rod Plexi territory. ballsy and bright but not ice pick. then the "overdrive" channel sounded blah in comparison so i tweaked that a bit. it's nice cranked but man that 39k cathode resistor on the cold clipper stage definitely compresses the signal a whole heck of a lot. it sounds nice and saturated and i dig it for heavy rhythm but man that crunch channel screams!
Post by thetragichero on Jul 12, 2020 16:55:17 GMT -5
1971 (was sold as a 1967) sunn sceptre that came to me in bad electrical shape (besides all original power supply caps the receipt/vibrato board was trashed, two conductor mains wiring, death cap, etc), missing the back panel, listed as reverb not working. ended up having no tank so of course it wasn't working come to find out there transistors on the reverb/vibrato board were oriented incorrectly, the dropping resistors on the low voltage supply rail had caught fire because as usual, the zener failed short (don't know if I've run into a old amp with a functional zener diode... be it's almost as if it's not the greatest idea to use them to drop voltage). so i removed any traces that were near the scorch marks (carbon being conductive and all) and rerouted where i needed to. put some newer low noise transistors in the right way. added a new accutronics tank. revert worked but not the vibrato. since my oscillator was oscillating i checked the ldr and that was working. then i noticed that whoever mucked about in here before must've gotten tired of the amp not working and jumpered the two leads together. works fantastic! i like the sound of vibrato (TREMOLO) into reverb! recovered in hiwatt/vox panama tolex, made the back panel out of scrap ply (traced the one from the 200s I'm working on now)
all metal bits scrubbed with chrome polish and a toothbrush (wire brush used where really bad)
so now I've got this 1968 sunn 200s. transformers were covered with rust so i decided to remove the bells and paint them. that's when i came across this
glad my vanity decided to paint those end bells! can you imagine 500v+ from the ot plate supply on the chassis? picked up some grommets to reinstall properly