The BA-3 as preamp build guide

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Russellc

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Hikari1 said:
Yeah...its hard to tell from that pic. Looks ok though. Where are your rectifiers? Under the little pcb behind your reg board?
Click to expand...

Here are the rectifiers:
 

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Russellc

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6L6 said:
This diagram is for your attenuator? --

An externally hosted image should be here but it was not working when we last tested it.
Click to expand...

Its a diagram Hikari1 found on the web...it sure looks like the way mine is laid out. Hikari1 apparently used this diagram in hooking his up I guess.

Looking at this, would this likely be the way it is wired?
 

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Russellc

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Getting tired last night. One channel on power supply not operating correctly, misconnection of one transformer lead...easy fix. Started variac, was getting P1 and P2 adjusted, then realized I didn't have the variac all the way up, only about 70 volts....turned down bias, went to bed. Should have it up tonight.
Thanks for all the help! Much appreciated!

Russellc
 
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Russellc

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BA-3 as pre playing, pot setting question (P3)

its alive and playing music. Volume pot and all. Let's see if it self destructs burning in. While off (thank goodness) I inadvertantly turned P3 a bunch of times trying zero P1 and P2. It seems to turn forever (tried one unused left over) without any clue of when "at the end" of its travel. Is there somewhere to measure (with pre off) to put P3 back in the middle? Short of removal, zeroing and reinstallation? I just want it middle of the adjustment range, not trying to find any "sweet spot" just want it recentered.

like many others have commented, I dont find it to have all that much gain, my tube pre goes way louder and I can run this thing full throttle with my large econowaves and using a 60 watt tube power amp that has WAY more gain than F-5. Is something wrong here? (bias is only at .875 right now)

Thanks,

Russellc
 
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delecoy

delecoy

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Joined 2011
Those pots look very similar to mine, which clicked at the end of their range in ether direction and, if I recall correctly, was 25 turns. So I turned it all the way to one side, counted the turns in the other direction til the clicking started again the went half the count back.
 
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Russellc

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Well,maybe I left a ground off somewhere, I just switched to an input that didnt have anythinghooked to it and got quite a pop and back ground hum. Switching it back seems ok and plays fine. Should selector switch have a wire to ground.

Its new and I am listening to spotify out of my computers output for a sound source...finding it a bit scratchy compared to my tube unit. Does this thing require breakin or do I need to kepp playing it and reset bias and offset. I am surprised with the gain, not that crazy high as I thought it might be.

Russellc
 
6L6

6L6

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I suspect it's that your computer sounds scratchy and the tube pre was compensating for it...

As for the gain, which Mosfet did you use?


Russellc said:
Well,maybe I left a ground off somewhere, I just switched to an input that didn't have anything hooked to it and got quite a pop and back ground hum. Switching it back seems ok and plays fine. Should selector switch have a wire to ground.
Click to expand...

Use shorting plugs on the unused inputs.
 
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Russellc

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delecoy said:
Those pots look very similar to mine, which clicked at the end of their range in ether direction and, if I recall correctly, was 25 turns. So I turned it all the way to one side, counted the turns in the other direction til the clicking started again the went half the count back.
Click to expand...

Thanks, they are Bourns pots, maybe I need to listen closer! I will give that a try.

Russellc
 
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Russellc

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6L6 said:
Normal? Probably. Mine did that. Some cheap RCAs from radioshack turned into shorting plugs fixed the issue.
Click to expand...

I think I have some of those around, I'll make some. The low level hum was only when an input was selected that didn't have anything hooked up to it, other wise its quiet as a mouse.

As to the gain issue, I think that was source related. Next selection was much louder. I then took it upstairs to the system with F-5 and some mid 80 db speakers, and it drove them just as well as the tube pre up there did.

Russellc
 
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