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Pickup reading open coil on Magnatone Hurricane Bass

HH1978

Member
Messages
330
Hello,

I replaced the tone pot on my 1965 Magnatone Hurricane, and took a reading of the pickup DCR in the process. It reads infinite, which should mean open coil. Yet the pickup is still working. It does not have a tremendous output, but I've never played another Hurricane to compare, and the similar Paul Barth designed pickups used on guitars (Tornado and Typhoon) are low output units.

One thing that doesn't seem right is that the tone control kills a lot of the volume, much more so than on a Precision, which is wired the same and has the same cap value.

Is it an indication that the pickup is shorted and will die soon?
 

jvin248

Member
Messages
6,415
.

Assuming it's a standard wound pickup and you have no active electronics in the guitar, there are two known cases of pickups that read open yet sounded iconic: Paul Buccanan's 'Nancy' Telecaster bridge pickup and one coil of Eddie Van Halen's Frankenstrat bridge humbucker. Effectively the breaks happen where enough wire is next to each other that it creates a capacitor. The break blocks all DCR yet lets AC signals through. You can do the same by wiring in a series cap. What a series cap or this magical kind of break does is cut the muddiness of a pickup giving more brightness and note articulation/clarity.

If adjusting a tone knob drops the volume that often reveals a 'fifties wiring scheme'. Take a good look and see if you have that. If you have a 'modern' wired harness then it could be a problem part in the system.

.
 

HH1978

Member
Messages
330
Thanks for the reply!

I forgot to mention, the Hurricane is a bass, which is why I compared it to the Precision.

The pickup sounds actually quite bright, even with flatwounds LaBella, so you're probably right. That sounded suspicious since Barth pickups tend to sound dark and muddy on guitars.

Not sure if there's a 50's vs modern wiring for bass. It's wired the same as a PB, with the tone pot connected to the same lug of the volume pot than the pickup (as opposed to the LP 50's wiring were the tone control is wired to the wiper/output).
 

nmiller

Drowning in lap steels
Messages
7,451
Barth pickups definitely do not sound dark or muddy on guitars. They're definitely in the Fender-inspired camp, with a little less output than a Tele but not far off in sound. The Tornado and Typhoon's switches introduce a lot of settings with caps rolling off the highs, but on the least-filtered settings there's plenty of treble and upper mids.

The tone knob rolling off lots of volume sounds like the result of a poorly-chosen cap value, something not uncommon on old guitars (and sadly not uncommon on modern ones, either).
 

Highnumbers

Silver Supporting Member
Messages
1,553
I just had a ‘62 Gibson PAF humbucker rewound that’s gave an open circuit/infinite reading. It definitely happens and @jvin248 ’s description of how it happens is right on.

Mine still “worked” in that the pickup amplified the guitar but it sounded extremely tinny and horrible. There was a break in one of the coils and it had to be partially rewound.
 

HH1978

Member
Messages
330
Barth pickups definitely do not sound dark or muddy on guitars. They're definitely in the Fender-inspired camp, with a little less output than a Tele but not far off in sound. The Tornado and Typhoon's switches introduce a lot of settings with caps rolling off the highs, but on the least-filtered settings there's plenty of treble and upper mids.
Sorry, I was a bit too drastic in the way I put my words. I didn't mean they are dark or muddy as if they were unusable. More comparatively to typical Fender single coils. To me they sound noticeably darker than a tele pickup. In the Typhoon switching system, there are positions that involve a 0.01uf cap to ground, which indeed rolls off the highs, but also positions that involve a 0.01uf cap in series, which acts similar as the coil break described above. There's even one position where you get both caps involved, if I remember correctly.
Yet, on a typhoon, you can hear the neck or bridge pickup alone without a cap when the 3 switches are down, respectively on the rythm and lead circuit. On a Tornado, there's no position where you can hear the neck pickup alone.

Also, there were 2 Barth pickups designs in that era. The one used on the Tornado, and the Typhoon in the neck and bridge positions is not the same as the one used on the Zephyr and the Typhoon's middle position. The first is similar in construction to a P90 (with many less turns and smaller bar magnet though), the other has (crudely cut) magnet polepieces hidden under rivets, and is more similar in design to the Fender singlecoils. To me, the second type has clearly a Fender type of sound, the other one not so much (though it doesn't sound like a P90 either).
Other difference must be the coil wire gauge, with the first design usually reading around 5k, and the second one around 11k.

Sorry for the digression, I'm always happy to discuss old Magnatone guitars (and amps).

The tone knob rolling off lots of volume sounds like the result of a poorly-chosen cap value, something not uncommon on old guitars (and sadly not uncommon on modern ones, either).
I agree, I'll try some other values and see how it changes.
But I also think that since the pickup itself seems to roll off the bass frequencies due to the coil break, it seems logical that the volume is reduced when the tone control cuts the highs... So having the pickup rewound would be the first step. I won't touch a vintage pickup myself, but I have a winding machine, so I can make a replacement pickup to dimensions and see how it reacts to the tone control.

Mine still “worked” in that the pickup amplified the guitar but it sounded extremely tinny and horrible. There was a break in one of the coils and it had to be partially rewound.
Well, I wouldn't go as far as "horrible" on mine, but that low end rolloff is not really desirable on bass. I'll have to think of a good winder to send the pickup for repair, preferably in the EU.

Thanks again, @jvin248 for identifying the issue :)
 

HH1978

Member
Messages
330
I made a replacement pickup today. Not really the same design, I went for a Fender type pickup with white forbon plates and .195" alnico 5 rods I had in a drawer. 9000 turns of 42AWG Formvar gave me a DCR of 6,68kOhms.

Anyway, seems like it confirmed the original pickup being the issue. The bass now growls like a precision, with much more volume and low end than before, and the tone control is usable throughout his range, without any significant volume loss.

Upon visual inpection, I think there's a good chance that the break on the original pickup is near the end of the coil, so maybe it won't need a full rewind.

The good news is that I have some time to carefully choose to who I'll send the pickup for repair, because I like how the bass sounds with the new pickup.
 




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