Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on May 04, 2023, 01:40:22 pm
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Hola amigos ! It's been a while...
I have an old Traynor YBA1A which is noisy even when nothing is plugged in with volume at 6 and over. Kinda hiss and hum mixed
I checked all voltages, bias, lead dress, unsuccessfully.
The heaters are elevated , power tubes are good, .....so I dont know where to check now ,
my skills disappeared , too many hours practicing..
Thanx
Colad
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start with the 1st tube after the input jack, remove, test, Noise still there?
IF so;
leave tube out, remove "next" tube in line, still noise?
STOP before the PI
hiss is "typically" noisy plate R's, but that just the beginning.... :icon_biggrin:
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Ciao Colas
Is the switch on the female input jack OK ? Does it connects the input to ground when nothing is inserted ?
The same for the ground connection
Franco
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Do you play un-plugged?
Why care about power tubes? Hiss/hum normally comes in a LOW level. Swap small tubes!!
Do any knobs do anything? (You gave a partial clue but more info helps.)
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PRR, I just want to reduce to minimum the noise of my amp. The tubes are good.that s the first thing I tried. While playing I don't hear it ( I am deaf anyway) but when I turn on my 12V tube stompbox which is near dead quiet on my high gain little amp, the hum is just too loud on the Traynor because the amp is unstsable.
I swapped the 220k plate resistor.on V1 for a 100k which helped a bit.
Kagliostro,, I've redone the input jack and.discovered a noise when moving the shielded cable from volume pot to V1 second control grid. Replaced the cable just to make sure that it is not the issue.
Shooter, tubes are good.
Overall noise has definitely diminished.
Thanks for tips . Linda will be happy too !!!
Colas
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Shooter, tubes are good.
you're pulling the tubes to ISOLATE the noise, you can put them back when you figure out which stage is the problem child
when I turn on my 12V tube stompbox
without it being plugged into the amp?, just powering on?
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Sorry Shooter, I .meant to say the first stage was the offending one. The amp is dead quiet without the first tube. I tried that tube in another amp to make sure it was nott the issue.
In that sense I answered you that the tubes were good.
At first I thought it was a ground loop since I m' using two amplifiers with 3 prong cords but it's not cause I am using a lineout with a transformer.
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Layout is:
Hi gain low wattage amp------ transformer line out------regulated 12v 12au7 stompbox ------digital delay--------traynor 50w, in that sequence. Tonight, I have replaced V1 capacitor for a new one. Hiss and hum are reduced but still there at vol set to 7. When I switch off V1 first cathode bypass cap, the noise is almost gone at full volume. It s not too bad but .I want the traynor to be perfectly noiseless so more investigation is goin on, while I have a bit of time ahead of me.
Colas
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bad cable?
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......very simple thing to check first, but I haven t thought of it.....
Nope, all jacks are good thanks anyway.
It s very weird, go back to the post "layout".
When the amp goes noisy and unstable, turning on the 12au7 stompbox makes a loud pop , otherwise we hear only the click of the switch itself. I think I'll do a cap job on the Traynor.
The stompbox is good, well filtered and regulated 12V, shielded signal cables , guitar ok too ...
Colas