The 7581A has a 5 watt higher plate rating then a 6L6GC, so you will be fine with a idle current of .041 A / 41 ma.
That being said if you mostly play the amp up at 5 or more then a cooler idle current will extend the output tubes life some.
I would try setting the idle current at 38ma and see if you still get the same basic level of punch out of the amp.
You never know, the amp may sound basically to your liking until you get down to 35ma even!
A lot of the starting point of clipping of the output stage and the punch the amp has is in direct relation to how strong the 12AT7 is that is driving the output tubes.
Biasing a Twin
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: Biasing a Twin
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: Biasing a Twin
Fantastic. I love it when stuff works. Here are a couple of mods I’m planning on doing and would love feedback.
I hooked up the other 2 OT wires to create an 8ohm and 16ohm output. The feedback will always be from the 4ohm. Any problem with this?
I am going to internally wire the reverb to the first channel. I read you can go from the output of the tank to the input of the 1st channel and it gives you more control over the reverb sound. It works and sounds awesome but I want the foot switch to still kill the reverb. My idea was to hook a wire to a spot that would ground out the sound. Any suggestions where?
Also, if I wanted to put in a “master” volume, what would be the best way to do that on this amp?
Thanks
I hooked up the other 2 OT wires to create an 8ohm and 16ohm output. The feedback will always be from the 4ohm. Any problem with this?
I am going to internally wire the reverb to the first channel. I read you can go from the output of the tank to the input of the 1st channel and it gives you more control over the reverb sound. It works and sounds awesome but I want the foot switch to still kill the reverb. My idea was to hook a wire to a spot that would ground out the sound. Any suggestions where?
Also, if I wanted to put in a “master” volume, what would be the best way to do that on this amp?
Thanks
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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: Biasing a Twin
In a real TR the output from the tank goes into basically into a unity gain stage to bring the signal back up to a level to match that of the normal channel.
From there it goes on to the PI section.
Your plan of dumping the output of the tank into the input of the normal channel, while that will get you a tone section on the reverb output , you will have way too much gain and I can foresee that making for a feedback situation.
But that being said you can easy enough try it to see if I am wrong.
In trying this idea I would start out by having no bypass cap on that normal channel first gain stage.
Just short out the output signal with the switch to the ground at the normal channel input jack and see if you get a issue from having a ground loop or not.
The master volume should go in at the same circuit location that you find it on a 1976 and up twin reverb or pro reverb or super reverb schematic.
From there it goes on to the PI section.
Your plan of dumping the output of the tank into the input of the normal channel, while that will get you a tone section on the reverb output , you will have way too much gain and I can foresee that making for a feedback situation.
But that being said you can easy enough try it to see if I am wrong.
In trying this idea I would start out by having no bypass cap on that normal channel first gain stage.
Just short out the output signal with the switch to the ground at the normal channel input jack and see if you get a issue from having a ground loop or not.
The master volume should go in at the same circuit location that you find it on a 1976 and up twin reverb or pro reverb or super reverb schematic.
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!