Hagstrom Corvette / Condor wiring

[Flowboy]

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!

 

 

[Bizman62]

Hi and welcome!

As I had no idea about the guitar I did a quick Google search and found this (which you most likely have already seen): https://www.fetishguitars.com/hagstrom/condor-corvette-impala/

Reading that and your post there's a couple of things that may or may not explain something. First the pots: "There are two separate volume pots for rhythm and solo (the latter being a cool rotary handle below the pickups)". Regarding to that the "cool rotary" may be difficult to find it's understandable that you want to swap the functionality.

Regarding the sound and the potential issues with the switches, "The range of tones extends from the metallic and trebly down to warmer and even darker sounds" - is that synonymous with your "one PU being tinny & quieter & the other 2 bassy"? I mean, could they have meant to be like that?

Hagström has had some interesting guitars over the years and finding out what every knob and switch is supposed to do can be tricky. I used to own a Viking with two humbuckers, four pots(2 vol and 2 tone) and two three way switches. I asked the previous owner what the switches do and the answer was "They produce different tones". Having learned something my wild guess is that the other switch could have been for coil splitting for single coil sounds and maybe that both in series or parallel. All I remember is that with the other switch I could get a sound out of the bridge pickup thin enough not to blow the speakers of my stereo equipment which I used as an amp at bedroom volume. Most likely also the impedance of the microphone input wasn't the most optimized for guitar pickups...

[Flowboy]

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

 

[curtisa]

5 hours ago, Flowboy said:

one PU being tinny & quiet

A pickup with weak magnets could do that. A quick check would be to attach a screwdriver to the pole pieces and see how well it 'sticks' to them, and compare with the other two pickups. Your resistance measurements seem reasonable for a generic single coil, so my gut feel is that the windings themselves are ok. Removing the pickups would be an idea to see if they are marked in any way to indicate that they might be intentionally different.

How confident are you that the schematic is correct? The 'solo' switch does precisely nothing as drawn.

For that matter, how confident are you that your guitar matches the schematic? Some of the faults you list (pickup sounds, HML switches not working) could be down to wiring mods/wiring errors/sins of the past.

[curtisa]

6 hours ago, Flowboy said:

# 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?

It was probably done that way as the intention would be that the 'Acc' setting would be used as a preset lower volume compared to the other settings. The 50k Accompaniment pot would load up the master volume and provide a degree of automatic volume cut when engaged so that the guitar player could duck behind the other band members when it was time for him to stop doing his Jimi Hendrix impersonation and let the organ player do his best Keith Emerson.

Swapping the order of volume/Acc pots would mean that the overall volume would never be any louder than what the Acc pot would provide when set at maximum, which defeats the purpose of the circuit. You could use the volume pot as the Acc pot, but it would have all its adjustability in the first few degrees of rotation near 0-2 (ish), and then no perceptible difference from 3-10.

Repurposing the Acc knob for master volume is worthwhile however, especially if the regular Volume control has that esoteric lever-and-gears arrangement. Exchanging the Acc pot for 250k and re-wiring it to utilise this pot as a master volume instead is possibly good practice simply because (as you say) finding a replacement assembly for the normal Volume mechanism will be nigh-impossible. You could then either leave the lever-and-gear pot disconnected, or wired as the Acc control (and accept that its volume-drop preset function will not work quite as originally intended).

[Flowboy]

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!

 

[henrim]

It is hard to tell from the picture but to me it appears that the solo button is implemented as drawn in the schematic. Not electrically connected to anything. I can think two possibilities. Could it be that it mechanically disengages all the selected tone controls? Like for instance if you have “ACC” and “H” pressed down pressing solo would release both? That or a conspiracy against guitar players. That poor guitar player clicks the button to boost the solo while other band members gives thumbs up and chuckles quietly.

[curtisa]

7 hours ago, Flowboy said:

the Solo switch really seems to operate as a way of cancelling the acc. sw

Ah, yes - that makes more sense, It acts as a 'cancel all' rather than to enable some part of the circuit.

Could that skinny black wire that's lacing underneath the two capacitors be rubbing through the insulation and making contact with the bottom leg of the left-most capacitor? Seems kinked over a little tight.

Generally looks like a pretty grotty circuit board, but probably typical of something of its age. I'm not too keen on the way that black foam material has reacted with the board. It could do with a bit of a clean with some isopropyl alcohol. 

Easiest way I can think of the check the bridge pickup is to desolder the lead from it off the PCB and connect it directly to the tip connection on the guitar lead and see if the sound becomes more normal. That would at least tell you if the fault is with the pickup or with the circuit.

[Flowboy]

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. 

 

[Flowboy]

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]

2 hours ago, Flowboy said:

try detaching the 3kpf cap on H & try a straight connection without cap & possibly test other caps there

That capasitor is paired with a resistor (potentiometer this case) and they together form a high pass filter. So I think you better have a cap there if you want the switch do what it’s supposed to do. It’s probably a good idea to change the capacitor though and maybe try a slightly different value than 3 nf. 

[curtisa]

57 minutes ago, Flowboy said:

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.

Looking at the schematic, the minimum controls you need to engage to get sound out is any one of the three pickups and the 'M' switch. Solo and Acc can be disengaged at it makes no difference. By your description, 'Solo' just mechanically pops out the 'Acc' switch, whereas 'Acc' just engages the low volume rotary pot.

 

19 minutes ago, Flowboy said:

if the colours mean anything at all. 

Maybe to differentiate that they're the higher resistance of the three in the factory for the guys on the assembly line putting it together? Could mean anything.  But probably not anything significantly important from your perspective.

[Flowboy]

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.

 

[henrim]

9 hours ago, Flowboy said:

Cap & pot = high pass filter

Yes, the way signal path goes in this circuit. Not in every combination.

[Flowboy]

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.

[Flowboy]

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!  

[Flowboy]

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

[curtisa]

7 hours ago, Flowboy said:

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? 

The sound should be cut off at zero for either pot. If it gradually tapers off and then suddenly disappears altogether near the very end of the pot's rotation it may be due to the taper of the pot (perhaps it's a linear taper pot where a more appropriate taper would be logarithmic?).

 

7 hours ago, Flowboy said:

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"

It's a ceramic capacitor. They are sometimes manufactured in axial format with the leads exiting either end of the body rather than at the bottom corners. Value most likely 68pF (pico Farad), or 6.8pF if you think there's a decimal point in there. 

 

7 hours ago, Flowboy said:

Am I also correct in reading the colour coded resistor on the right as  1200 ohm. +/- 5%  Brown, red, red, gold at bottom.

You have it correct.

Which particular model is this one?

[Flowboy]

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.

[curtisa]

8 hours ago, Flowboy said:

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! 

The implementation of the volume controls is not typical - normally you'd expect to see all three legs of the pot wired in a variable divider arrangement, but in the Hagstrom's they all appear to be wired as two-leg variable resistance rheostats. The taper of the pot may become more pronounced if it's a logarithmic (maybe linear is more appropriate?). As an alternative you could try re-wiring the volume pot as a variable divider, as just about every other guitar manufacturer would do (more work though):

 

8 hours ago, Flowboy said:

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.

That's quite the rare bird then. I'd also be suspicious that a lot of the 'attachments' to the back of the switch PCB are non-standard. The 6.8 (cap? resistor? I'm having doubts now...) in series with what looks like another cap (the green cylindrical object) is very odd.

Edit: the 'k' used on older caps sometimes signified 'kilo', so '6.8k5' may be 6.8pF x 1000 = 6.8nF (nano). But a capacitor with a 'K' suffix can also mean it has a tolerance of 10%. Not very helpful...

Probably the most foolproof thing to do is grab a multimeter with a capacitance function on it and see if it measures 6.8pF/68pF/6.8nF. Or even if it measures 6.8/68/6800 ohms??

 

 

[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.