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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Tue Dec 26, 2017 2:06 pm
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strayedstrater wrote:
I've never personally experienced this, but I've read that if the ESR of the filter caps has drifted upward, they can let power line buzz enter the signal path.

We both suggested lead dress and other things as being more likely than the filter caps.

Stratele52, you've previously posted that you consider 30 years to be the safe lifespan of electrolytics.

I keep harping on the caps simply because if he's going to take it to a tech anyway he should make sure they're not the original caps. If they're ancient, might as well have it done while it's in the shop rather than bring it back again later.


Hi!

Thanks!, As soon as i can i will open it and make a picture to the caps. If i have the courage enough i would change it myself :)

Many thanks as always!


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Tue Dec 26, 2017 3:26 pm
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melpi65 wrote:
[youtube][/youtube]
stratele52 wrote:
Filter caps did not make this kind of noise.

Did you change all tubes ?
Don't forget other tests I wrote yesterday ;


I'll test and clean all input jacks's normaly close contact to ground. Often they are bad
12XX7 noisy tubes
Unbalanced 6L6 tubes
Bad wiring dress acting like antenna
____________________________


Hi bro!

Thanks for this, i don't know how to test the rest, the best it will be to take it to a professional guy, it's very funny because in the recordings it doesn't appear the noise so much as here look:



Again, lovely playing and lovely tone. I hear some hiss in the recording but the amp sounds perfect.

Back to my first reply. It was very hard to judge the relative volume of the buzz in the first recording. I took your word for it that the buzz was annoyingly loud and wasn't interference being picked up by the guitar or cable.

But in the second vid the amp sounds healthy.

If the noise is worse sometimes and better other times, are you sure you've ruled out the possibility that some device that broadcasts noise is on sometimes and off other times?

The device could be in a different room, even outside your house.


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Wed Dec 27, 2017 11:04 am
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Good afternoon,

Sorry but i forgot to mencione something which i don't know if it's important or not. The amp has been made in USA, so it's 110v, so what i do it's connect it to an adaptor of 350w 220 to 110 and it works. I don't know if this would be the reason of this noise, but the last owner had something similar and it worked perfectly. No mods on the amp.

Cheers!


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Thu Dec 28, 2017 12:07 am
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350 watt rated converter should be fine. The amp's PT is 50/60Hz rated. So, difference in wall-output power Hz should not matter.

My bet, it's the main filter caps. They are prolly the original ones. Main cap replacement should do the job.

:)


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Thu Dec 28, 2017 9:14 am
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I didn't really hear the issue over the net at volume played. Definitely some fine playing.

I would spot tighten/check all the nuts/screws as well, sometimes they will contribute to secondary frequencies when slightly loose. And would agree w/ everyone else that the PSU caps are prolly ready for an update.


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Thu Dec 28, 2017 10:29 am
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One thing about a big step-down transformer is that it can broadcast a lot of RF/EMF noise.

Ultralinear Twin has a great big power transformer that can also send a lot of noise over the air.

I notice in the second vid you're sitting within arm's length of the amp.

In my first reply suggesting guitars/cables, you may have misunderstood what I was suggesting.

Guitars and cables don't make buzzing noises. They can pick up radio/magnetic noise being broadcast from other sources.

Your guitars may be quiet with other amps because those amps don't have giant transformers.

If you change position while playing -- turn the guitar in a different direction, or move farther away from the amp -- does the noise change?


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Thu Dec 28, 2017 2:25 pm
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strayedstrater wrote:
One thing about a big step-down transformer is that it can broadcast a lot of RF/EMF noise.

Ultralinear Twin has a great big power transformer that can also send a lot of noise over the air.

I notice in the second vid you're sitting within arm's length of the amp.

In my first reply suggesting guitars/cables, you may have misunderstood what I was suggesting.

Guitars and cables don't make buzzing noises. They can pick up radio/magnetic noise being broadcast from other sources.

Your guitars may be quiet with other amps because those amps don't have giant transformers.

If you change position while playing -- turn the guitar in a different direction, or move farther away from the amp -- does the noise change?


Hi Bro!

Sometimes i think the bzzz gets slow but i don't know if it's my perception or that i'm getting use to this sound.

I will try to put the amp in different zones of the house to see if it gets better.

Thank you very much for all the advices. I'm learning really a lot with all this troubleshooting, thanks!!! :):)


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Thu Dec 28, 2017 6:33 pm
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"Sometimes i think the bzzz gets slow..."

You think it maybe related to the VIBRATO section and the SPEED control? Could be an opti-coupler or wiring lead-dress issue with that part of the circuit.


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Fri Dec 29, 2017 12:26 am
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BMW2002Ti wrote:
"Sometimes i think the bzzz gets slow..."

You think it maybe related to the VIBRATO section and the SPEED control? Could be an opti-coupler or wiring lead-dress issue with that part of the circuit.


Hi bro, I don't use the vibrato or speedd or intesity, in fact i took the pedal off because i really don't use it.

By the way, i just discovered the amp it's for 1980 and not 1978, is it something to be worried about it? can something change from one year to another one?

Thanks!


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Fri Dec 29, 2017 7:02 am
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As far as I know, after they introduced the Ultralinear 135 watt version they didn't make any electrical changes.

Sometime around '81 they changed the faceplate from silver to black but that was just a cosmetic change.

----------------

When you say the amp worked perfectly for the previous owner, did you hear it before you bought it? Or has the previous owner just told you it worked perfectly?

When did the buzzing start? As soon as you got it home, or did it start later?


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Fri Dec 29, 2017 7:07 am
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A couple of posts back I asked an implied question. Do you always sit so close to the amp?

Also asked if the noise reduces if you move farther from the amp while playing?

And if you point the guitar in a different direction while playing, does the noise reduce?


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Fri Dec 29, 2017 9:28 am
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strayedstrater wrote:
A couple of posts back I asked an implied question. Do you always sit so close to the amp?

Also asked if the noise reduces if you move farther from the amp while playing?

And if you point the guitar in a different direction while playing, does the noise reduce?


Hi!

Sorry i forgot about it. About noise it doesn't matter if i plug the guitar or not, after i press on the Stand by button couple of second after the bzzzz starts.

I tried to put the amp in many parts of the room and take it away from the 220-110 conversor or the bluesbreaker but the bzz stills remains

After new year i will try to change the caps to see if the thing comes better, and when i can change the tubes because they are not the original but i guess they are very old also.

Cheers!


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Fri Dec 29, 2017 9:34 am
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strayedstrater wrote:
As far as I know, after they introduced the Ultralinear 135 watt version they didn't make any electrical changes.

Sometime around '81 they changed the faceplate from silver to black but that was just a cosmetic change.

----------------

When you say the amp worked perfectly for the previous owner, did you hear it before you bought it? Or has the previous owner just told you it worked perfectly?

When did the buzzing start? As soon as you got it home, or did it start later?



Hi!

When i went to buy it, i tried it and i don't remember this noise happening, perhaps i didn't realize due the emotion :)...so i would say 50/50 i would be wrong in this.

The previous owner told me it needed a little of work but i thought he reffered to the estetic of the amp. Anyway it's not an issue for me to change that caps if it's only that, i will gladly do it :)

I will open the amp as soon as i can and check where are the caps and how many i should change.

Here i think it should be arround 60€ of caps.

Do you know any brand or models i should chosse? Is it neccesary to change the BIAS after this?

thanks!


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Fri Dec 29, 2017 11:26 am
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If it buzzes with nothing plugged in, the problem is definitely in the amp.

The main filter caps aren't inside the chassis. They're underneath where the tubes are, under the metal box cover. If I recall correctly the cover is soldered on, and takes a really big soldering iron to remove.

Visual inspection of the caps won't tell you much, except possibly the age.

Old electrolytics can bulge or leak at the ends, which indicates they're about to die. They can also burst and spray out the liquid inside them, but then your amp would hum loudly, not buzz.

If the caps' ESR has risen there won't be any visual signs.


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Post subject: Re: Fender Twin Reverb Silverface 1978 humm issue
Posted: Fri Dec 29, 2017 11:34 am
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"Lead dress" -- the way the wires are arranged -- has been suggested several times as a possible cause of the noise.

Fender got very sloppy with wiring in the '70s. And with decades of sonic vibrations, getting bounced around inside cars, bumped and dropped, those wires can move around and start causing problems.

The filter caps can hold hundreds of volts, even when the amp is turned off. If you're not experienced with working on tube amps, let a pro do the work.

A tube amp that's turned off and unplugged can possibly kill you if you stick your hands inside the chassis.


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