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Topic: Tube amp hiss with signal |
David Doggett
From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
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Posted 28 Sep 2005 8:21 am |
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| I just got a 1960 Silvertone 1433 (by Danelectro). It is a sweet little 20 watt amp with a 15" speaker. It had new orange drop caps and other parts and tubes replaced "as needed." It has beautiful tube tone, but there is a noticeable hiss when any signal is coming through. If I set the volume pedal at a reasonable spot, and take my foot off, and am not playing, the amp is quiet. But as soon as I pluck a string you can hear the hiss in addition to the string signal. The hiss dies as the string signal dies. In other words, any noticeable signal starts the hiss, and the hiss dies with the signal. Does anyone know what might cause that, and if there is any remedy? |
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John Daugherty
From:
Rolla, Missouri, USA
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Posted 28 Sep 2005 10:08 am
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David, do any of the controls make noise when you turn them? Could be a dirty pot or a dirty input jack. These are just the obvious simple things to check.
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www.phelpscountychoppers.com/steelguitar
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David Doggett
From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
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Posted 28 Sep 2005 11:07 am
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| The control pots were cleaned when the amp was refurbished. Some of them are still a little scratchy in spots, but the hiss seems independent of that. There are sometimes some squeals and funny sounds when the amp is first turned on, but those go away as it warms up. |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 28 Sep 2005 11:22 am
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I have a speaker that did something similar. You'd hit a note, and it would give a slight distortion sound as the note would decay. Switch speakers, just to be certain. Process of elimination.
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Jay Fagerlie
From:
Lotus, California, USA
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Posted 28 Sep 2005 1:24 pm
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David,
You mentioned in the other post it still has the slvertone tubes in it.
Replace them first.
Let us know what happens
Jay |
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Blake Hawkins
From:
Florida
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Posted 28 Sep 2005 4:21 pm
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I agree with James that you should check the speaker first.
You didn't say if the filter caps were replaced.
The squeals on start up could be caused by defective electrolytic filter or bypass caps.
As Jay said,
It is also possible that a tube is bad.
[This message was edited by Blake Hawkins on 28 September 2005 at 05:22 PM.] |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 28 Sep 2005 4:50 pm
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I'd definitely try some fresh tubes. The hiss may be a bad resistor. You may want to try some freeze spray and go from part to part and see if you can locate a bad resistor or solder joint. I'd also get a plastic pen or something non-conductive and poke and tap around in there. Remember, when inside a tube amp that's on, keep one hand behind your back.
Brad
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David Doggett
From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
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Posted 29 Sep 2005 4:20 am
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| Thanks, I'll try the simple stuff. I don't really know electronics, and don't have test equipment. So I can't really test individual components. I have some extra power tubes and will try them and look for anything obviously loose. Beyond that, I am just looking for ideas to pass on to an amp tech at some point. The speaker wire is soldered to the speaker poles, so I can't easily switch speakers. But it doesn't sound like the speaker to me. It's not distortion, it is just a high background shush, like distant applause, and it comes and goes exactly with the signal. It's volume matches the signal volume, but it is there whether the signal is soft or loud. To me it is not distortion, but is some kind of positive thing the amp is doing in response to signal. It's not too noticeable at first, but after awhile it causes ear fatigue. It's such a distinct thing that I thought somebody might recognize the symptom. But it may just be a characteristic of this kind of cheap amp. [This message was edited by David Doggett on 29 September 2005 at 05:32 AM.] |
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Jim Peters
From:
St. Louis, Missouri, USA, R.I.P.
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Posted 29 Sep 2005 5:24 am
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Dave, even the cheap amps were usually designed properly. Check your preamp tubes first, even a small amount of noise will show up.
Keep us posted. JP |
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Ken Fox
From:
Nashville GA USA
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Posted 29 Sep 2005 6:11 am
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My first bet wpould be a bad preamp or even power amp tube. I had a bad 6V6GT in a Fender Princeton reverb causing such noises!
I have also found filter caps that exhibit a tall and very narrow steeple shaped spike)on the leading edge of the sawtooth pattern. This will show up as a light buzz as a note decays. I have seen this over and over in the older Session 400 amps. A new set of filter caps fixes that.
There are other caps in a tubes amp (electrolytics) that are in the filter area (under the can with main filters in the older Fender Blackface and Silverface amps) but do much more! Their primary job is to prevent one gain stage feeding back to another. They provide a short basically to the signal that develops across the plate load resistor. That can cause an amp to howl out of control.
Also preamp tubes can do everything you described. Caution do not run the amp without a speaker load, it can destroy the output transformer. So if you are going to test with an external speaker, be sure it is connected well!
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