Thanks Stevem
I look forward to hearing how it goes.
I also have another slight question - what is the centre tap of the power transformer is no good. How can I test this? I guess I could yank out the centre tap and put two 100r resistors in for a fake centre tap and see if the hum goes, but I'm also intrigued to understand how you test if the power transformer centre tap is shot?
Help me identify the hum and buzz
Moderators: pompeiisneaks, Colossal
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Help me identify the hum and buzz
A simple resistance test from each of the winding legs to center tap is all that needed to prove that out.
If you yank your output tubes is the hum still there?
For output tubes to hum cancel heater voltage hum like they should the pin 2 of one tube should feed / go to pin 2 of the other output tube and the same such thing with the pin 7 connection points , so check this.
With my hum issue amp last night I unbolted the speaker jacks from the chassis and I removed the OT fully from the amp and I still have the hum!
This is with the only thing hooked up to the primary side of the OT being the center tap, no plate leads.
When I then installed the OT into another amp there was no hum issue.
In fact when I hook up a voltmeter between chassis ground and ground on the speaker jack in the problem amp I am reading .116 VDC so that's my hum.
This voltage reading is at 125 HZ so the root of this amps hum issue is in its power supply and I am still on the hunt as to why!
If you yank your output tubes is the hum still there?
For output tubes to hum cancel heater voltage hum like they should the pin 2 of one tube should feed / go to pin 2 of the other output tube and the same such thing with the pin 7 connection points , so check this.
With my hum issue amp last night I unbolted the speaker jacks from the chassis and I removed the OT fully from the amp and I still have the hum!
This is with the only thing hooked up to the primary side of the OT being the center tap, no plate leads.
When I then installed the OT into another amp there was no hum issue.
In fact when I hook up a voltmeter between chassis ground and ground on the speaker jack in the problem amp I am reading .116 VDC so that's my hum.
This voltage reading is at 125 HZ so the root of this amps hum issue is in its power supply and I am still on the hunt as to why!
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: Help me identify the hum and buzz
If I pull out my power tubes the hum is gone. If I pull out the PI tube the hum is gone. So I cant help but think the problem has to be in the preamp and/or reverb driver circuit. Just cannot fathom what the problem could be.
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Help me identify the hum and buzz
A this point I would say that you have a bad power supply filter, likley one of the main stacked 220 UF @ 300 volt filters.
Get at least one new one of these and jump out what you have there.
Get at least one new one of these and jump out what you have there.
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!