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#1
Hi

I have a 1969 sound city 100w head and a 2x12 laney cab fitted with original 1980 Celestion G12H-65s.

There is a hum when the amp is turned ON coming from both speakers.
When on standby, all is quiet as you'd expect.

I've noticed that the treble knob influences the hum when turned up. But with it right down, still exists slightly.

It won't be a problem gigging, but only when playing at bedroom levels.

Had it checked out a few months ago and all was sound.

Any ideas? Speaker connection perhaps?

Thanks, Luke.
Last edited by moominman2 at Feb 29, 2012,
#4
Can't say how much. I have a 67 Gibson Hawk and the filter cap (40/20/20) is around $45, plus installation. I bought a pack of 22uF caps for $8 and ganged them up to make 44/22/22 and installed them myself. The only way I know to test is to either replace it and see or look at the high voltage (aka HT) with a scope. Even when you look at the HT you have to know how much ripple is acceptable.

BTW, I'm assuming this is a tube amp. Although SS amps probably have filter caps that can go out too.
Last edited by fly135 at Feb 29, 2012,
#10
I take it you're on 220volts.Does it do it everyplace or just home or what?Try superlux.I use their stepdowns for phantom amps on studio mics and they're great.Not sure if they are still in buisness.Are you sure you're not on the same circuit as a flourescent light or something?Hows your crybaby modded?
#11
If its only doing it in your bedroom you got something thats causing it.on that circuit.Refrigerator,light,A?c.Plug it into a line with nothing else on it.And chech the power coming outta your outlets.
#12
Ok thanks for the help. It's not my cry baby as even with a guitar unplugged from the amp, no cables etc it still happens. I noticed it happened downstairs aswell as in my bedroom.

Hopefully will get to see if it happens at band practice but I'm not sure it will be that problem.

Thanks
#13
Quote by moominman2
Never heard of a power conditioner before. What exactly do they do?

They're about £210 here in the UK so for that price I may aswell take it to the tech :P

Power conditioners clean the power up if you have 'dirty' power and give you a nice constant current. I bring this up because it seems similar to your past problems. People buy power conditioners for other things besides amps. IF you have dirty power at your house - taking it to a tech is not going to fix anything.

I personally would try the amp in different places and potentially try a conditioner. You can always return it as mentioned.

And yeah, as mentioned, florescent lights, computers, other electronics can cause hum in your guitar signal.
#14
IIRC you live in the UK. Is the hum somewhere near a G that you take on 3rd fret, low E string?

If yes, it might be bad heater wiring.
Quote by Todd Hart
Shooting your friends with a real gun is a definite faux pas.

Quote by mystical_1
Professor Plum in the Studio with a new Amp

Quote by snipelfritz
If only I were the only one at home right now. I don't need my parents asking who Mr. Wiggles is.
#15
I'll try plugging it in in a different room and check when I get the chance. If it is just the power socket in my house, I probably won't bother with a conditioner as I don't record or anything. But itll be nice to know.

And nah it's not just a string, it's constant. Cheers though.

Thanks
#16
Not what I meant.

From my home built amp (which is still in the trouble shooting.phase) get loads of 50Hz hum from my rubbish heater wiring. 50Hz is around the same as a G note.

My point is, if you get a contant hum that sounds sort of like a G note, it might be bad heater wiring. In any case, that would be AC noise.
Quote by Todd Hart
Shooting your friends with a real gun is a definite faux pas.

Quote by mystical_1
Professor Plum in the Studio with a new Amp

Quote by snipelfritz
If only I were the only one at home right now. I don't need my parents asking who Mr. Wiggles is.
#19
Sounds like something in your room is transmitting the hum which is then being picked up inductively by the amp and/or the guitar. Try turning off everything in the room including the lights and then switch them on one at a time to locate what is the culprit
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#21
Problem still exists through a different cab and at a different power socket.

I did put new speakers in my cab and accidentally wired up one of the wires to the incorrect terminal and tried it. Quickly realised what I did wrong! I did research this and apparently causes no damage? When I played through the cab incorrectly wired up, the volume was damn quiet.

Thanks
Luke
Last edited by moominman2 at Mar 7, 2012,
#26
The only time that will cause a drop in volume is if there are two speakers and you have them wired the opposite way (or any even number of speakers with half wired backwards). There is no actual +'ve and -'ve on a speaker. What is written on them denotes the phase. If you wire two out of phase they cancel each other out. It doesn't result in an absolute cancellation because no two speakers are exactly the same, usually certain frequencies are affected more than others.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#27
Cool thanks.

So what you're saying is that couldn't have caused damage to the amp?

Perhaps it's just a noisy amp? I don't remember it happening previously though from memory. I was always surprised how quiet it was for its age.
#28
That's what I'm saying. Check that it isn't something else in the room causing the noise. Turn everything off including the lights.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#33
Did you try a different guitar? Could be shielding or a faulty pot if it's definitely not the amp...
Maximum volume yields maximum goats.
#34
Does it hum with nothing plugged into the amp's input?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#37
give us the run down again starting with your previous amps and briefly summarize everything you've tried already so we don't repeat things or waste time. What would happen if you took the whole thing to a friend's house?
#38
Ok...

My previous amp experienced other problems , not this.

My original 1969 sound city all valve head hums. It resembles a G note on the low E string. This hum is still the same regardless of any cables plugged in to the amp. And also, when in standby, the hum is not heard...only when fully on. If I turn up the treble knob, it manipulates the hum SLIGHTLY but not enough to believe that it was the cause.

If I took it to a mates house, the hum still remains but as its band practice, cannot hear it. I have tried turning all the lights and other electricals off, changing sockets, but nothing affects the hum.

It was looked at/ biased when I got it around 5 months ago- ish and new tubes put in.

That's it all I think!
Last edited by moominman2 at Mar 12, 2012,
#39
And you're positive it's hum and not hiss? Some amps are just naturally noisy, and I'd be willing to bet that older amps were a bit worse about it.

The gain knob doesn't affect it, does it?
Maximum volume yields maximum goats.
#40
OK, it's just the amp itself. If it was mine I'd be ripping it apart and changing filter capacitors, probably as high as I could go. It's a SS rectifier, no? I'd go crazy and double it or even more. It's most likely a design flaw or sub-standard caps. That would be where I started. I'd at least stick a scope on it and have a look.
But that's if it was my amp. I do that sort of thing just for jolly japes.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
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