I disconnected the down stream end of r37 and the hum from the speaker stopped.
Gibson GA20RVT amplifier hum
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Stevem
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Re: Gibson GA20RVT amplifier hum
Good we’re making progress!
Now let’s see if we can narrow things down even more.
Reconnect r37.
Let’s move on to V4B.
Off of pin 1 there is C9.
Disconnect its down stream end.
Is the hum still present?
If not then C9 is leaky and should be replaced.
Now let’s see if we can narrow things down even more.
Reconnect r37.
Let’s move on to V4B.
Off of pin 1 there is C9.
Disconnect its down stream end.
Is the hum still present?
If not then C9 is leaky and should be replaced.
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!
-
Stevem
- Posts: 5604
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
1 others liked this
Re: Gibson GA20RVT amplifier hum
Yes, lifting r37 unpowered V5A and the phase splitter T3, but then C9 still could also be the source of the hum if it’s passing dc voltage out of it and into V5A.
The other possibility is that socket v5 is leaking some heater voltage .
With v5 out of the socket you should read an open between pins 4 and 5 to pin 2, and an open between pin 9 and pin 2 .
It’s however far more likely that C9 has gone leaky.
One more question, does T3 look like it took a good hit when the chassis dropped?
Another question is this.
I forget if the 20s are built off of one long terminal strip spanning near the whole horizontal width of the amp.
If so then that fall might have fractured one of the strip standoff’s that are used as circuit to chassis grounding points .
Take a real good look at all of those points and Rock them around a bit if you can to see if they give.
Redoldering and of them will take away more than a common 40 watt iron .
I use a big ass plumbers iron .
The other possibility is that socket v5 is leaking some heater voltage .
With v5 out of the socket you should read an open between pins 4 and 5 to pin 2, and an open between pin 9 and pin 2 .
It’s however far more likely that C9 has gone leaky.
One more question, does T3 look like it took a good hit when the chassis dropped?
Another question is this.
I forget if the 20s are built off of one long terminal strip spanning near the whole horizontal width of the amp.
If so then that fall might have fractured one of the strip standoff’s that are used as circuit to chassis grounding points .
Take a real good look at all of those points and Rock them around a bit if you can to see if they give.
Redoldering and of them will take away more than a common 40 watt iron .
I use a big ass plumbers iron .
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!