fender custom vibrolux reverb gut and rebuild

[thetragichero]

picked up this newer fender amp for a song because somebody decided they would pay 4x the price of the components for a mod kit and then attack their amp that cost over a grand. the results were not good, as one would usually expect, which is a shame because the general consensus is that these sound great even stock. the original owner sold it to the guy i bought it from as a fully functional amp. he got a quote to gut and rebuild and it was more than he was willing to sink into it so he sold it to me!

looks nice



ooh nice speakers



this will be the new cap board



not shown: the too-cramped main board i started yesterday, about 2/3 populated. didn't want the board to be too big but guess i could've given myself more room

so stock the normal and bright channels are pretty much the same, besides the bright cap on the bright volume and reverb only on the bright channel. tone controls similar to 6g11 vibrolux with a tapped treble pot, although 250k instead of 350k. bias trem which is pretty rare on 2x6l6 fender amps (vibroverb being the one i could find). cool!

so here's what I'm gonna do: normal channel will be the normal channel from the bassman 6g6b (with the proper 350k tapped treble pot). bright channel will be blackface vibrolux with a few changes to make it ever-so-slightly brighter (first stage cathode bypass cap lowered from 25uf to 1uf, coupling cap after second stage lowered from 47nf to 22nf). both channels will have reverb, which means they'll both be in phase and you can jump the channels (like an old four hole marshall) for more tonal variety. "borrowing" the trem from the original

I'd post my schematic but it's all scribbled in my notebook

[thetragichero]

haven't done much on this but I've got the chassis stripped, normal (not board-mounted) fuse holder, ceramic power tube sockets replaced with micalex). this uses a 3a fast blow fuse for mains which is weird and might end up being changed, we'll see. making the mains wiring closer to where it comes in with a nice long safety ground lead so that if it gets pulled out it'll trip a breaker



filaments will be wired next with the 100r artificial center tap right on the leftmost tube socket

[thetragichero]

decided not to do the filaments yet, makes more sense to get the preamp grids in place first. have to order more 250kA pots for the bright channel tone controls. besides that everything in here is stuff on hand which is cool. slow work as usual but it looks nice. trying out floating buss bars for the preamp grounds. input jacks are isolated from the chassis, the preamp will only have one connection to the chassis at that screw by the rightmost (in this picture) input jack

[thetragichero]

filament wiring done (20awg for preamp tubes, 18awg for power tubes), socket wiring for the reverb driver tube done (parallel 12at7 with a transformer like every fender reverb should be)



working on my garage tomorrow but pots for bright channel tone controls are coming in so i should get them in this weekend and start bias board, filter cap board, and finish preamp board

[thetragichero]

more chassis wiring done, including reverb jacks, footswitch jack (which I've isolated from chassis ground), bright channel tone pots, couple of components in tremolo circuit that are mounted on the socket, output jacks

preamp board is populated, although i have some questions that will require pondering before i wire it up (lots of 'what was i thinking here?'). I'm sure it'll work out

[thetragichero]

rectifier/bias/reservoir cap board made and almost completely installed

[thetragichero]

almost have all the tubes wired up. added an extra 1k5/25uf cathode resistor/cap pair (probably was looking at a schematic and forgetting the led wired from tube socket pin to reverb/tremolo footswitch jack) so i added a submini toggle switch to the front and it'll be a "fat" switch for the bright channel (raises bypass cap from 1uf to 26uf and changes cathode resistor value from 1k5 to 750r so slightly more gain overall and a few more db for low frequencies). useful and then i don't have to have another empty space on the board (like the space on the end for the negative feedback resistor i had already wired from the output jack to a terminal strip
finally figuring out what the heck i did on the board by wiring up what i did know

[thetragichero]

okay pretty much done, just have to connect a few power wires in the doghouse and chassis and clean up about half a pound of flux before testing

[thetragichero]

so it's changed up and sounds GREAT, reverb can get intense (250kB pot with 220k resistor on outside lugs so you can get a little more 'wet' than you'd expect). only bugaboo so far: trem doesn't wiggle the signal (i get 22vac pulsing according to my meter on the trem side of the coupling capacitor but in the intensity pot side i get basically zero). output tubes that came in this are pretty far from matched according to my 1 ohm 1% cathode resistors (off by over 10ma) and the bias voltage is cranked way high to -50v (I'd expect about -32v) so i think trying different output tubes is next on my list. the footswitch is wired like the schematic but the buttons control opposite what they're labeled but that'll be an easy fix
i am digging that the bright and normal channels have their own thang going on

[thetragichero]

still don't have the tremolo working. think I'll copy the brownface vibroverb trem instead of the one that was originally in the custom vibrolux reverb
in the meantime thought this would be a nice touch

[thetragichero]

forgot to post update. this has been finished for a couple weeks and likely to be sold to a studio 5 minutes from my folks' house here after i pick up and install the new power tubes