Hi all!
I have one of these I am / have one thru in regards to the normal things a amp this old needs and once I got it up and running I found that the bass channel had a higher level of 120 HZ hum then the normal channel.
Having put some new preamp tubes in it I went about confirming that they where all good by not only testing them as I always do to just rate them, but swap them into my known good bench top test amp.
In taking a good looking at the amps schematic I noticed that the V+ for the Bass channel is taken off right after the amps choke and as such has one less stage of filtering then the normal channel does.
I am getting a noise floor of -45 db out of the amp and so far can't get it any better unless I yank out the bass channels 2nd AX7.
I jumped in a added 47 uf cap which totals the filtering on the bass channel V+ to to well above 60 uf with no , yes no change in the 120 HZ ripple hum level.
Any suggestions besides making a parallel power supply ?
6G6-B Bassman power supply
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Stevem
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6G6-B Bassman power supply
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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sluckey
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Re: 6G6-B Bassman power supply
I would temporarily disconnect the 56K dropper from node B and connect it to node C to see if hum level decreases.
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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: 6G6-B Bassman power supply
I will try that, but just the lesser amount of V+ from that C node will drop the gain which will reduce the hum I would have to think!
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: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: 6G6-B Bassman power supply
So my easy cure for this without lifting up a soldering iron was to swap out the second AX7 for a Strong testing AT7.
The noise floor got near 6 db better with only a minimal gain loss which could easily be made up with the volume control.
The noise floor got near 6 db better with only a minimal gain loss which could easily be made up with the 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!