Flowboy

That's all useful. Particularly the rethink on the Corvette pot wiring. I did think the pot set up was odd compared to other guitars.. Ive been into a few wiring looms over the years but mostly just fixing what was obviously broken or faulty, rather than with any proper understanding of circuits & how components can work in different ways. Re. the rare bird, it did originally have a number of caps/ resistors (?) on the PCB, but I can't recall what I changed or replaced, it was many moons ago, pre mobile phone & handy camera. I got it to work well enough switching wise at the time, at least better than it had been. Thanks for your thoughts on the possible code marking meanings, I tried to look up info on historic component markings but no luck. I always forget I have a multimeter. I should check the mystery old resistor/cap component to see what it reads. If I was gigging regularly I would want to wire it up to go into failsafe mode & let the signal thru, even if all the switches pop up out of circuit, which used to happen at times, leaving me with a silent guitar. Probably would require some major rethinking tho. I'd just like to get it functional again for now.

Hi, Great, thanks Curtisa. Its a std mini guitar 250k audio pot as I had to replace the failed original anyway. I will check the pot, maybe its lin & not log - although I'm sure I ordered a log! It does cut out quite suddenly, at the far end of movement as you say, unlike other guitars I have had , which smoothly fade to grey... Re the other guitar's PCB, its a Futurama Coronado Automatic, imported in the early 60's by Selmer to their specs. Only 200 were made. I was sent a hand sketched schematic years ago (taken from his guitar) by another owner, with the caps shown as Resistors, from memory the one in question being "R 6.8", hence the confusion. I don't think there is an original Hagstrom schematic that has survived for this model. It was a £50 guitar & I just needed it to work, so messed around with the wiring since it had stopped working after a couple of years. Of course I didn't keep any record of the original set up, it wasn't "collectable" back then! I do know one of the PU's was wired through the switch chassis which seemed mad to me so I repurposed an unused strip of the PCB for that connection, As with the Corvette, switching goes through the switch return springs but in this one, there's like a bus-bar that the "chassis" PU went through, all a bit odd & it took some time to make sense of. Hagstrom had their reasons no doubt! I want to replace that Cap (not resistor as you point out!) with a flat one as it's too fat (& probably not original anyway) & has for years obviously prevented the switch plate from sitting in it's cavity fully, so the screws keep pulling out. (sloppy I know, particularly for a joiner to have put up with!) Life just gets in the way so it's been under the bed a long time! The guitar suffered badly from from buzz at one time so I had little wires running from the bridge to switch chassis for a while. I can't recall if I solved this or not & TBH I've hardly used it for years since it was so annoying, along with the switches falling out at the slightest knock, so that will be another thing I have to look at.

To revive this thread for a minute,,, I have found that the "acc." volume pot (now being used as main vol, since I swapped them round) actually turns off completely when wound right down, I can hear the sound just cut out. Is this a duff pot, does the wiring need further work? Also, on an another Hagstrom guitar I have what I think is a resistor but it has no colour coding. It looks like a slightly shiny ceramic type material, is beige in colour & has (badly printed) either "6 8" or "6.8" (I think poss. the latter) & under that it says "K5". No other markings Or is this a different type of vintage cap? Shown on top of pcb, on the patch of yellow tape. Am I also correct in reading the colour coded resistor on the right as 1200 ohm. +/- 5% Brown, red, red, gold at bottom. I have an old electronics paperback that has a confusing explanation of the codes, including what seems to be a misprint in the calc. Cheers

Thanks for your inputs, its done for now. I might come back to it later when I have more time & try some different caps. I went more extreme than Hagstrom; with a 22nf instead of 10nf (0.01mf ) on the Low tone sw & on the High tone sw., 15nf & 22nf caps in series to give 8.9nf instead of the original 3kpf /3nf. I'll play with this again at some point as it's not quite right but I didn't have any other useful sizes to hand. I really miss our long gone Maplin(Mondo) for these jobs! The tone changes between the HML settings are now more distinctive than the original & the H sw. isn't so quiet as it was. It would be interesting to try (I don't know if its possible), to set up an out of phase position with the switches but haven't really looked at it for that yet. A push pull pot could maybe do it, if there's enough room for it. The body is fairly thin. Interestingly I found a pic online of someone else's switch-plate out, with exactly the same wiring layout as mine including the blue wire run between the cap legs. It was obviously a thing in '65!

Well, small successes on the wiring front. The new 250k pot came today. So this evening I fitted it, I disconnected the radial pot & ran a new wire from the acc. sw. to it. Then connected the new pot to the old radial pot connection point on the pcb. It all worked fine but as Curtisa said, only about he first 25% of the rotation of the Radial pot is useful. From off, to about the same volume as the new main pot, is no more than 1/3 of the lever movement, if that. But it does work as a lower vol. setting so I think I'll keep it that way for now., unless anyone has any suggestion as to how to make the adjustable range wider. I also took the radial pot apart (partially) as I hadn't noticed before that the lever movement was restricted. I think someone had been in there before & reassembled it out of position on the gears. It was a little fiddly but it's in a better position now. Have attached pic to show the pot. I didn't take the main brass mounting plate out of the body, although I was tempted. The actual contact strip part of the pot is recessed underneath & must be very slim to fit in there. It was all held together by 3 fine set-screws, with little washers & 2 red felt pads (to prevent rattle I guess). As everything else in the top section fell apart when I dismantled it (all the little brass support columns were loose) I thought it best not to tempt fate & have the pot contacts do the same! Just waiting for some caps to arrive before trying the next stage.

Yes , the more I've looked at it the more sense I can make of it. It's clear the blue switches are not crucial to basic function due to various other connections in circuit. Cap & pot = high pass filter, will try others. Pickup wire colours may well be for assembly ease if anything, but they work which is the important thing. Thanks, all your comments have helped focus in on it.

Curtisa, Our posts crossed more or less, or at least I didn't spot yours before posting mine. I'll try & clean the board a bit. It's over 55 years old now so not surprising its a bit grotty looking. I think the blue wire has been replaced or at least re-soldered at some point, looking at how it's been done compared to the rest of the loom which is generally quite tidy, cable & soldering wise. The blue insulation isn't worn thru anywhere, so no shorts. That said, it does seem a bit short & tightly stretched. I may replace it later but it's working ok for test purposes. I had the PU's out & they're all the same appearance underneath, no part numbers or anything. The only difference is the neck PU has a green output wire & white to ground & has the lowest resistance of the three. The other two have blue wire & red to ground, if the colours mean anything at all. Attached pic shows the little springs in the switches. They must have had some kind of jig to assemble the things & solder springs to board, it was horrible to repair in situ!

Henrim, you are correct, it is as Curtisa pointed out about the schematic; solo does nothing. As I looked more closely earlier today, the solo switch is definitely not connected to anything & is only there to disengage the acc. sw. due to the way the switches are set up to work mechanically. To operate at all, it has to have the springs soldered to the pcb even if they make no circuit. Pressing it simply disengages the acc. switch, but no other. Regarding your general question about switching; pressing any switch only disengages others in the same colour "block". Therefore black cancels black, red cancels red, blue cancels blue. Black cannot cancel blue or red etc. The switches when engaged make connection from the pcb via their tiny springs to a little buss-bar inside the switch. So they are both mechanical, to pop the switch up when disengaged by another sw. but also make the circuit internally when pressed down & engaged (except the solo sw!) Crikey that all seemed a bit long winded to explain! I discovered today, but don't quite understand how, when BOTH the blue switches (Acc. & Solo) are disengaged, the guitar still works, as does the main radial volume pot. I expected it to cut out. I will have to ring the circuit with my multimeter. Of course this will save a player's blushes! If he rushes to play a solo but miss-hits the solo switch & disengages them both, the guitar still works, even if its maybe not meant to in its original design!? I have attached a better pic of the switch block pcb where I think all connections can be seen. The dark areas are because there was some foam padding (to stop rattling I guess), bonded to the pcb but it had fallen off leaving a sticky stain. What can be seen along the lower third of the board is; each switch has 3 little springs soldered to the pcb, which connect together inside the sw when it's pressed. The centre spring of each switch, (except the solo!) connects to the long bottom strip in the pic. The other springs of each sw. connect to various other parts of the board. Below the wide top strip (ground / red to jack), the second strip is the output (black wire) to jack, So... under test, (with both blue sw' disengaged as they make no difference anyway at present) nothing happens unless a black pickup sw is pressed AND a red sw. H, M or L are pressed. H takes PU signal to output via the 3Kpf cap. (making all pickups quieter & tinny or tinnier.) If M is pressed, signal goes direct to output, If L is pressed, signal goes to output but the other spring on this sw goes to ground via a 0.01uf cap. Whichever of M & L are pressed makes no difference to any PU's basic sound. H makes a distinctive difference. There is a very slight difference between middle, neck & bridge PU, just due to position under strings I guess. It seems that the 0.01uf cap on L isn't noticeably working if it is intended to make a tonal difference. The volume difference between the front 2 PUs & the bridge is a bit excessive when switched via H. The volume difference when H, M or L is a bit more balanced when PU 3 is selected. Does this make sense? If nothing else typing this out has helped me work through it! So I will experiment with different rated caps to ground on L & try detaching the 3kpf cap on H & try a straight connection without cap & possibly test other caps there. Also I'll try swapping connections between the new 250k pot (when it arrives!) & the radial one.

Hi Curtisa, Many thanks for that. Exactly the kind of insight I was hoping for. When looking at the connections on the switch block I wondered if it really would work correctly but I don't have enough understanding of circuits/ electronics to really know why. Hence I thought I might have to modify it to be more usable. The idea that the acc. pot would work (load up) in conjunction with the main one hadn't occurred to me. It's pretty obvious that players would want to switch between strumming and wailing away like Hank Marvin . The old junk acc. pot as wired only operates in the first 5% of its movement (with force applied as it is otherwise nf!), after that, vol is full on thru whatever the main vol control is set at. Looking at it again, if I understand correctly, the Solo switch really seems to operate as a way of cancelling the acc. sw. this diverts the output thru any of the other switches / PU settings that are engaged. Once engaged a switch can't be disengaged by pressing on it again, you have to press an adjacent sw. in each colour / function block. The only exception is: if all the sw' in that block are on, in which case, pressing any one, disengages the others. i.e. if all PUs 1,2 & 3 are on, pressing 1 disengages 2 & 3 etc. Although shown in the schematic as connected to the right hand copper strip, thru all the switches, the Solo sw actually isn't. All the other switches are wired via a copper extension off the strip, linking them to output. So the schematic only shows an implied "virtual" connection as far as I can see! Even with both acc. & solo disengaged, there is still a connection thru the acc. sw to this strip. I am open to any circuit changes / suggestions that would enable the acc. vol to be the main one, with any wiring alterations that would enable the radial vol pot to act as acc. vol. if possible. Obv that might mean some more cables running about inside but that'd be fine. If it's impractical, I could as you say just take the radial out of circuit. The Futurama just had separate vol pots on each PU & everything else on the switch block, so there wasn't the same issue. The Corvette circuit Schematic (off the internet) is the original factory one (faults & all) That said, it is the one that survived; it may be there was an updated one that ironed out the problems that didn't happen to survive, so it's all we've got as a reference. I just need to make the guitar functional, rather than "original" & annoying to use! I think the acc. vol pot had been replaced in the past but in general the wiring is quite neat & original looking to me, even if it doesn't really work very well. The attached pic shows something of the switch block setup, but the wires are coving over the acc. / solo connex. I will try & upload another later. The pickups seem to be equally magnetic but I haven't taken them off yet to see if there are any differences. Thanx!

Hi Bizman 62, Thanks for that. Yes I had seen those promo prints before, but not the accompanying website text. Having owned a Selmer imported Coronado/Futurama, I found out that very few were made but they definitely had a one-piece neck & body like the Impala/Corvettes, not bolt-on. I'm not a Hagstrom expert so there may have been some with bolt-on necks, maybe prototypes or early production line as different headstocks are also mentioned. Perhaps a redesign at some point? Those 3 models (the Coronado in particular) seem to have been top of the range & were probably quite expensive! I can vouch for the switch plates being a risky business on stage - it is very easy to miss hit a sw. & end up with silence! Not something to rush at. Certainly the bridge pickup is a bit like an Ennio Morricone spaghetti western sound. With a fuzz box it would cut thru steel! I just think the levels are so different I might be able to improve that, along with the almost identical sound of the other 2. Regarding the PU's, 3 is the bridge & 1 is the neck. So the difference in apparent volume is not PU resistance related. I haven't tried removing them yet, so I don't know their construction. They may be wound differently but I doubt it. I will have to have a look. It's the only guitar I've come across with a kind of PCB for connections

Hi all, this looked like a worthwhile forum, with so many hands-on projects going on. I have in the past repaired & even completely rebuilt the odd guitar but tbh I claim no expertise at all! just random bits of knowledge picked up over the years. I have no doubt like most, played tolerably ok since I was 11 or 12 which is way back in the mists of time now & really only dabbled in guitar fixing. I have an interesting repair job on the bench at the mo. for which any & all advice is welcome, as there are some quirks about it I haven't really gone through yet. Original Circuit diagram attached + PU detail added. The Guitar is a Hagstrom Corvette / I think AKA Condor, from about the mid 60's. It has 3 single coil PU's. 2 vol pots, one of which is weirdly very flat in shape & radial in action, driven by little gears on pot shaft & lever. (it works which is good as I cannot imagine where I would find another like it!) There are 8 selector switches; 1,2 & 3 for each PU + 3 Tone sw's; H with 3kpf cap, M with nothing & L with 0.01mf cap all going to output via the 250k flat radial vol pot. Plus one for Acc. & one for Solo. The other pot is a std type but only 50k, set up to only control volume via the accompaniment (acc.) switch, so acts like a preset vol. when switching between chords say & solo vol. This doesn't work but at least is easy to replace. I am minded to reverse the pots so the radial one controls the Acc. & the std one that I'm more likely to wear out by violining etc. controls the rest of the main output from PU's. This would be easily put back to spec if ever an originality fetishist got hold of it but see my questions# below! There are other issues: The pickups, (bridge to fretboard), show resistance of 7.79, 7.42, 5.91k ohm (+/- 0.03kohm), I have no idea if those are in a normal range or not for their type. Oddly the bridge one is incredibly trebly & thin & the other 2 are thick, bassy & louder & sound the same to me despite one having a cap on it. I managed to repair the Acc. switch. These are, compared to the common little slide sw. more like some kind of ancient high quality GPO thing with 3 tiny springs in circuit. As far as i can tell, depressing the switch, causes the spring to make a contact (hidden from sight) to make the circuit. One of the springs had snapped. I can tell you it was quite a job to pull the remains into place & solder it, particularly as the little copper part of the PCB was missing. # My question is how will the Acc. vol respond to being put thru the 250k radial pot rather than 50k? Obv. I can replace the 50k with a 250k for main vol control if reversing original set up. I'm interested as to why a 50k was used for Acc. in the 1st place. I suspect it may not be crucial but what do I know? Also Due to the HML switches not seeming to work correctly, one PU being tinny & quieter & the other 2 bassy, what suggestions do you have for changing caps to give more tonal difference on each switch? Might the old (ceramic?) caps be duff? Years ago I repaired an earlier Hagstrom with similar switches etc & got the tone switches to be more distinctive but I can't recall exactly what I did. Possibly resistors were in that circuit. I am quite open to modding the circuit (*within reason) if it sounds better & is more usable in the end. *Excluding the advice I got for the previous Hag, to "rip out those crap PU's & put some humbuckers on it..."! That Hag actually sounded great after repair, although the single coils were a slightly different design visually at least, to the Corvette. Anyway a bit of a long intro but thanks for letting me in!