I have a 67 YBA-3 ( traynor ) that makes a loud hum when an instrument is connected.
WHere do I look ?
Hum when connecting to input
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Stevem
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Re: Hum when connecting to input
Does it pass audio along with the hum?
Does the volume control effect the level of the hum?
Does the volume control effect the level of the hum?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Hum when connecting to input
Yes, it gets worse as Volume goes up. Not sure what you means "does it pass audio..." If I connect an instrument it goes trough as well.
Is that your question ?
Is that your question ?
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Stevem
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Re: Hum when connecting to input
The volume control is right after the first gain stage in that amp, either that first preamp tube is bad ( V1 ) or the amp has a bad power supply filter cap .
It may just be C34 the 10uf 400 volt filter that powers that tube V1.
My first guess is that it’s that preamp tube.
It may just be C34 the 10uf 400 volt filter that powers that tube V1.
My first guess is that it’s that preamp tube.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Stevem
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Re: Hum when connecting to input
Also note that these amps have a huge power transformer and if your guitar has single coil pickups and your plugged in holding the guitar right next to the power transformer side of the amp then you will get a bunch of hum as you open up the amps volume control.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Hum when connecting to input
NO hum ( except the power tranny ) if nothing in the input.
Changed the tubes, ALso chaged the power supply filtering ( all the 80uF ) I'll check the 10 @ 400v, don'T have one on hand and my Meter does'nt do caps...
Buy the way, I intend to make this amp Guitar friendly, would like hints on changing the tone stack. Looking for clean, Fender like.
Changed the tubes, ALso chaged the power supply filtering ( all the 80uF ) I'll check the 10 @ 400v, don'T have one on hand and my Meter does'nt do caps...
Buy the way, I intend to make this amp Guitar friendly, would like hints on changing the tone stack. Looking for clean, Fender like.
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Stevem
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Re: Hum when connecting to input
Well also any of the coupling caps right after the plate of V1a, V1b or V2a could be leaky and passing low DC voltage down stream to the next gain stage.
Unsolder the down stream end of each of these cap and see if you measure any dc voltage above .035.
If you start by lifting the down stream end of C2 ( .022 uf) on V1a and the hum stops then that cap is leaky.
Unsolder the down stream end of each of these cap and see if you measure any dc voltage above .035.
If you start by lifting the down stream end of C2 ( .022 uf) on V1a and the hum stops then that cap is leaky.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Hum when connecting to input
With nothing plugged in the input grid to V1 is grounded. So, the chance of the noise being internal to the amp is very small. It would have to be comming from the wire between the jack and the grid of V1. Is this run done with shielded cable? That might help.
The other possibility is that the noise is entering the circuit via your guitar/cable. With a guitar plugged in and the amp "huming" does the noise go away (or reduce in volume) when you turn the guitar's volume down to zero?
Mike
Re: Hum when connecting to input
Schematic?
Try a different valve, especially if the input stage cathode isn’t fully bypassed.
Try a different valve, especially if the input stage cathode isn’t fully bypassed.
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Stevem
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- Joined: Fri Jan 24, 2014 3:01 pm
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Re: Hum when connecting to input
In that amp only V1b is not cathode bypassed, and that gain stage is after the volume pot, so it’s not part of his issue .
If you place a short across R12 the 100K plate load resistor off of pin 6 on V1 then that will kill all the gain and signal flow .
If the hum them goes away then you have found the problem gain stage!
If you place a short across R12 the 100K plate load resistor off of pin 6 on V1 then that will kill all the gain and signal flow .
If the hum them goes away then you have found the problem gain stage!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Hum when connecting to input
Two things come to mind. One is AC mains wiring, the other input jack wiring.
I don't have a schematic for that amp, so these are speculative.
If an amp has AC mains leakage, it can sometimes be quiet until the input is un-grounded. Generally amps with three pins on the AC mains cord are immune to this, but if the connection of the third-wire safety ground to the chassis comes loose, it can cause something like this. Likewise if the connection from signal ground to chassis is loose.
Another possibility is that the input jack attachment to the chassis is loose or dirty. Taking all the jacks, pots, and switches loose from the chassis for a good clean and retighten of the panel nuts is a good idea every few decades.
I don't have a schematic for that amp, so these are speculative.
If an amp has AC mains leakage, it can sometimes be quiet until the input is un-grounded. Generally amps with three pins on the AC mains cord are immune to this, but if the connection of the third-wire safety ground to the chassis comes loose, it can cause something like this. Likewise if the connection from signal ground to chassis is loose.
Another possibility is that the input jack attachment to the chassis is loose or dirty. Taking all the jacks, pots, and switches loose from the chassis for a good clean and retighten of the panel nuts is a good idea every few decades.
Re: Hum when connecting to input
Stevem wrote: ↑Sat Jan 29, 2022 11:52 am In that amp only V1b is not cathode bypassed, and that gain stage is after the volume pot, so it’s not part of his issue .
V1b is not used in this amp.
here is the schematic, V2 is the one
Looking at this, I realise it is used in the SChem, but not in my amp !!!
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Re: Hum when connecting to input
Well, you guys put some work omy table ! I will take the inputs out , clean and retight. Also will check for wiring issues. THanks for all the input, I'll follow up ounce I have had a chance to do all this...
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Stevem
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- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Hum when connecting to input
Gut shot from the last one I worked on.
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When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!