Hi, I'm working on an old Supro head and cab amp that has a hard to fix hum. It would be helpful to find a schematic. I put 2 small pictures up here: Group: alt.binaries.atest Subject Line: suprotest Upload/Download took about 10 secs on DSL. (finally moved into the 21 century,..) The model# is worn off but I think it says, "62-9018". It might be 9058. I've searched for hours with no result. These may have been sold under several different names: Supro, Valco, Airline, Montgomery Ward, Gretch and so on. Normal channel: 2 inputs. Reverb/Trem channel: 2 inputs. 4x total 12ax7: 1 for reverb recovery, one phase, one each for the inputs. One 6v6 for the reverb driver, 2x 6V6 output stage. 4 diode rectifier section. Heater string is CT grounded. The speaker cab is enclosed and houses 2x 12" speakers. It sounds wonderful except for a loud hum that doesn't change with volume. No crackle or scratchy pots. Reverb and Trem work perfectly. I've reworked all the PS caps and a couple of interstage caps. Replaced the diode section. I replaced the mains cord with a 3 prong and removed the hot-to-ground cap. The cab sounds fine with another amp. Is there an actual method for finding a hum? You know, a system, a routine? I normally just shotgun the cap section and blocking caps and that's it. If anyone remembers these amps it would be great to hear from you. It really sounds cool. Thanks as always, s. p.s. I have already heard the one about how the amp is humming because it doesn't know the words,..
First: is the hum 60Hz or 120Hz? The former suggests grounding problems, the latter power supply problems.
Second: When you added the three-prong power cord, are you sure you got the right polarity with the hot and neutral wires? When you measure between chassis ground & wall ground with an AC voltmeter, what voltage shows up?
Finally, when you shotgunned the supply caps, did you change anything about the grounding wiring?
> Hi, I'm working on an old Supro head and cab amp that has a hard to > fix hum. It would be helpful to find a schematic. > I put 2 small pictures up here: > Group: alt.binaries.atest > Subject Line: suprotest > Upload/Download took about 10 secs on DSL. (finally moved into the 21 > century,..) > The model# is worn off but I think it says, "62-9018". It might be > 9058. I've searched for hours with no result. These may have been sold > under several different names: Supro, Valco, Airline, Montgomery Ward, > Gretch and so on. > Normal channel: 2 inputs. > Reverb/Trem channel: 2 inputs. > 4x total 12ax7: 1 for reverb recovery, one phase, one each for the > inputs. > One 6v6 for the reverb driver, 2x 6V6 output stage. > 4 diode rectifier section. Heater string is CT grounded. The speaker > cab is enclosed and houses 2x 12" speakers. > It sounds wonderful except for a loud hum that doesn't change with > volume. No crackle or scratchy pots. Reverb and Trem work perfectly. > I've reworked all the PS caps and a couple of interstage caps. > Replaced the diode section. I replaced the mains cord with a 3 prong > and removed the hot-to-ground cap. The cab sounds fine with another > amp. Is there an actual method for finding a hum? You know, a system, > a routine? I normally just shotgun the cap section and blocking caps > and that's it. If anyone remembers these amps it would be great to > hear from you. It really sounds cool. Thanks as always, s. > p.s. I have already heard the one about how the amp is humming because > it doesn't know the words,..
Is it possible either the power or output transformer was replaced ? If so, improper orientation can cause AC to directly couple from the power tranny to the output if they are close enough to each other. You might test for this with a sheet of metal between them.
How hot is the bias ? The tubes aren't red are they ?
That amp is old enough that it should know the words by now ;->
> Hi, I'm working on an old Supro head and cab amp that has a hard to > fix hum. It would be helpful to find a schematic. > I put 2 small pictures up here: > Group: alt.binaries.atest > Subject Line: suprotest > Upload/Download took about 10 secs on DSL. (finally moved into the 21 > century,..) > The model# is worn off but I think it says, "62-9018". It might be > 9058. I've searched for hours with no result. These may have been sold > under several different names: Supro, Valco, Airline, Montgomery Ward, > Gretch and so on. > Normal channel: 2 inputs. > Reverb/Trem channel: 2 inputs. > 4x total 12ax7: 1 for reverb recovery, one phase, one each for the > inputs. > One 6v6 for the reverb driver, 2x 6V6 output stage. > 4 diode rectifier section. Heater string is CT grounded. The speaker > cab is enclosed and houses 2x 12" speakers. > It sounds wonderful except for a loud hum that doesn't change with > volume. No crackle or scratchy pots. Reverb and Trem work perfectly. > I've reworked all the PS caps and a couple of interstage caps. > Replaced the diode section. I replaced the mains cord with a 3 prong > and removed the hot-to-ground cap. The cab sounds fine with another > amp. Is there an actual method for finding a hum? You know, a system, > a routine? I normally just shotgun the cap section and blocking caps > and that's it. If anyone remembers these amps it would be great to > hear from you. It really sounds cool. Thanks as always, s. > p.s. I have already heard the one about how the amp is humming because > it doesn't know the words,..
i'm not sure, but a 6V6 for a reverb driver seems a little odd. Does it still hum if you pull it out?
On Sat, 7 Nov 2009 13:41:50 -0800 (PST), PStamler <pstam...@pobox.com> wrote:
>First: is the hum 60Hz or 120Hz? The former suggests grounding >problems, the latter power supply problems.
I think it's 120Hz. I can't really tell, all octaves sort of sound the same to me. I mean it's like I tune my hearing to whatever's there. That probably doesn't make any sense. The Peterson SAM tuner was equally as confused. Either B3 or B1. The drone tone is one of the lower B notes. After all this part replacement I now have a buzz component that might not have been there or as noticeable when I started.
>Second: When you added the three-prong power cord, are you sure you >got the right polarity with the hot and neutral wires?
Not sure. When I made up the 3 prong cord and wall connector I made the narrower wall slot correspond to the black wire. Wider slot to the white and green went to ground. Inside the amp I wired the black to the incoming side of the fuse, removing the cap to ground and the white to the on/off switch. Green went to a screw through the chassis near the entry. I'm in the PacificNW, North America.
>When you measure between chassis ground & wall ground with an AC voltmeter, >what voltage shows up?
.1ma using the same outlet. (that's point one ma AC).
>Finally, when you shotgunned the supply caps, did you change anything >about the grounding wiring?
No, I made sure not to. It's possible because two 4 segment cap cans became 8 individual caps on terminal strips. I'll check again but all the voltages are as expected all over. Everything works as you'd expect, there's just this loud hum. The phase reverse switch doesn't have any active parts, it's just a dual 3 tab switch which has always done nothing in terms of changing the hum. I've swapped out all the tubes. Replaced some more old paper caps. Checked for DC at all the interstages. Is there a way to check if the heater string is interacting somewhere it shouldn't? It's CT at the transformer, not a stand off. Thanks for your time.
>On Nov 7, 2:46 am, spud <g...@gfhf.com> wrote: >> Hi, I'm working on an old Supro head and cab amp that has a hard to >> fix hum. It would be helpful to find a schematic. >> I put 2 small pictures up here: >> Group: alt.binaries.atest >> Subject Line: suprotest >> Upload/Download took about 10 secs on DSL. (finally moved into the 21 >> century,..) >> The model# is worn off but I think it says, "62-9018". It might be >> 9058. I've searched for hours with no result. These may have been sold >> under several different names: Supro, Valco, Airline, Montgomery Ward, >> Gretch and so on. >> Normal channel: 2 inputs. >> Reverb/Trem channel: 2 inputs. >> 4x total 12ax7: 1 for reverb recovery, one phase, one each for the >> inputs. >> One 6v6 for the reverb driver, 2x 6V6 output stage. >> 4 diode rectifier section. Heater string is CT grounded. The speaker >> cab is enclosed and houses 2x 12" speakers. >> It sounds wonderful except for a loud hum that doesn't change with >> volume. No crackle or scratchy pots. Reverb and Trem work perfectly. >> I've reworked all the PS caps and a couple of interstage caps. >> Replaced the diode section. I replaced the mains cord with a 3 prong >> and removed the hot-to-ground cap. The cab sounds fine with another >> amp. Is there an actual method for finding a hum? You know, a system, >> a routine? I normally just shotgun the cap section and blocking caps >> and that's it. If anyone remembers these amps it would be great to >> hear from you. It really sounds cool. Thanks as always, s. >> p.s. I have already heard the one about how the amp is humming because >> it doesn't know the words,..
>Is it possible either the power or output transformer was replaced ?
not likely.
>If so, improper orientation can cause AC to directly couple from >the power tranny to the output if they are close enough to each other. >You might test for this with a sheet of metal between them.
>How hot is the bias ? The tubes aren't red are they ?
>On Nov 7, 3:46 am, spud <g...@gfhf.com> wrote: >> Hi, I'm working on an old Supro head and cab amp that has a hard to >> fix hum. It would be helpful to find a schematic. >> I put 2 small pictures up here: >> Group: alt.binaries.atest >> Subject Line: suprotest >> Upload/Download took about 10 secs on DSL. (finally moved into the 21 >> century,..) >> The model# is worn off but I think it says, "62-9018". It might be >> 9058. I've searched for hours with no result. These may have been sold >> under several different names: Supro, Valco, Airline, Montgomery Ward, >> Gretch and so on. >> Normal channel: 2 inputs. >> Reverb/Trem channel: 2 inputs. >> 4x total 12ax7: 1 for reverb recovery, one phase, one each for the >> inputs. >> One 6v6 for the reverb driver, 2x 6V6 output stage. >> 4 diode rectifier section. Heater string is CT grounded. The speaker >> cab is enclosed and houses 2x 12" speakers. >> It sounds wonderful except for a loud hum that doesn't change with >> volume. No crackle or scratchy pots. Reverb and Trem work perfectly. >> I've reworked all the PS caps and a couple of interstage caps. >> Replaced the diode section. I replaced the mains cord with a 3 prong >> and removed the hot-to-ground cap. The cab sounds fine with another >> amp. Is there an actual method for finding a hum? You know, a system, >> a routine? I normally just shotgun the cap section and blocking caps >> and that's it. If anyone remembers these amps it would be great to >> hear from you. It really sounds cool. Thanks as always, s. >> p.s. I have already heard the one about how the amp is humming because >> it doesn't know the words,..
>i'm not sure, but a 6V6 for a reverb driver seems a little odd. Does >it still hum if you pull it out?
Yes it does. Pulling tubes out can reduce the volume somewhat but it's still the same old hum. 6V6 was the choice Fender made early on for the stand alone unit. (Well, 6K6, pretty much the same thing). The verb is super surfy! It's instant "pipeline". I found Supro drawings that showed a 6V6 reverb driver but 6L6 output and a tube recifier. Thanks.
> I think it's 120Hz. I can't really tell, all octaves sort of sound the > same to me. I mean it's like I tune my hearing to whatever's there. > That probably doesn't make any sense. The Peterson SAM tuner was > equally as confused. Either B3 or B1. The drone tone is one of the > lower B notes.
Maybe record five seconds of the hum and put up an MP3 someplace?
> >When you measure between chassis ground & wall ground with an AC voltmeter, > >what voltage shows up?
> .1ma using the same outlet. (that's point one ma AC).
That's current. What happens when you set the meter to V instead of A and measure again, one probe going to the amp chassis, the other to the ground hole in the plug?
>> I think it's 120Hz. I can't really tell, all octaves sort of sound the >> same to me. I mean it's like I tune my hearing to whatever's there. >> That probably doesn't make any sense. The Peterson SAM tuner was >> equally as confused. Either B3 or B1. The drone tone is one of the >> lower B notes.
>Maybe record five seconds of the hum and put up an MP3 someplace?
I uploaded a small wav file to: alt.binaries.atest Search: suprobuzz Took about 15 secs to up on DSL. No guitar plugged in.
>> >When you measure between chassis ground & wall ground with an AC voltmeter, >> >what voltage shows up?
>> .1ma using the same outlet. (that's point one ma AC).
>That's current. What happens when you set the meter to V instead of A >and measure again, one probe going to the amp chassis, the other to >the ground hole in the plug?
My mistake. That's .1mv on the AC setting. This is the $39 dollar craftsman meter.
|
