610B preamp build with EQ

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Spencerleehorton

Well-known member
Joined
May 12, 2012
Messages
4,481
Location
Felixstowe, Suffolk, UK
Hi All,

Wanting now to see if I could build either a channel or a pair of 610B tube preamps with EQ.
I have a 610A schematic with the low and Hi cut and boost but not the 610B EQ section which I’m assuming would add into the circuit in a similar fashion?
Could anyone shed any light on the fabled 610B EQ section?
 
Should be able to knock up both input and output transformers.
What’s the best way to do the -15db pad?
Phase switch is no problem and could have that after the output transformers.
EQ selection of 70hz, 100hz and 200hz with +/- 9db on 3 way switch
Along with 4.5k, 7k, 10k with +/- 9db
Don’t know if the original unit had the +/- 12db output ? But I can put a output pot as master.

Is there any similar schematics with the same style EQ section?
 
Maybe you could try a normal shelving feedback EQ, but the different frequencies will require (too?) much switching it seems.

15dB pad is, of course, the easiest after the OT, or in-between stages, but overloading of the first stages could be a logical issue then.
 

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