I'm sure to have a few questions about this JTM45 schematic

[mort]

Haven't posted in a while. I'm back into project land again for now. Building a 5F1 for my boss and a JTM45 for me(). I'm much more familiar with Fender amps than Marshalls, so as I'm studying this schematic I may throw a few questions out in this thread. Thanks in advance for any help. I've only built two units and done a vintage rebuild, so these will be my 4th (and 5th) full on amp projects. So basically, I know a little but always have questions.


I'm looking at this schem- http://www.pleximods.com/images/66JTM45Schematic.gif


-- Does the filter section really only consist of those 2 8uF caps?? In Fenders it's usually 3 at at LEAST 20uF or so.

-- Also, is there a good layout image that matches this schematic? It seems like every jtm45 schematic I look at is very different from one another and I've yet to find a layout to match this one.

[big_teee]

I think you are looking at the negative bias voltage.
Look at the top right hand corner at Lead A.
there is a 32uf before the Choke, and another 32uf after the choke.
Then you have a pair of 16uf Caps between V2, and V3.
T

[mort]

Ah, I see. It's drawn out differently than the drawings I'm used to(Fender). Thanks

[mort]

http://www.pleximods.com/images/66JTM45Schematic.gif


ok, at the lower left corner, there's a 250uF cap parallel to an 820 ohm resistor. What is the suggested voltage rating for that cap? Is 25V ok?

[mort]

And one more stupid question for now...

On the pots, a 250KB designates that pot as linear, is that correct?

If it were an A, then audio taper.... right?

[Jazz P Bass]

That is correct.
B is a linear taper.
A is a logarithmic taper.

[soundmasterg]

http://www.pleximods.com/images/66JTM45Schematic.gif


ok, at the lower left corner, there's a 250uF cap parallel to an 820 ohm resistor. What is the suggested voltage rating for that cap? Is 25V ok?

25V is overkill on the cathode in the preamp since it is biasing up to maybe 2v max, but it is always nice to have a little safety margin to cover spikes and initial turn on. 25V is what was used for years on fenders, and since the JTM45 is at its core a Bassman 5F6A clone with some minor changes, then using what fender used would be sufficient.

Greg