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Finished up my Mk II Poseidon yesterday, have some questions and observations:

Have the Poseidon (Auricaps) and SDS cap boards: 50/50/50/50, using hexfed diodes in HV and bias, no 5AR4.

Shannon, your schematics don't show the 680 ohm resistor to ground; but you list it in the BoM. might want to add that for the inexperienced builder. BTW, one of my "680s" measured 792, a reminder that everything should be replaced.

Initial listen with 12AX7, 12AU7 and EL34 was harsh, no bass (no break in). Rolled into 5751s and 12BH7s, much better bass and much smoother. Exchanged EL34s for KT77s and better all around, especially in the mid-bass to bass region. Still experimenting: haven't decided whether to go with ECC99s or 12BH7s, both have advantages Yellow_Light_Colorz_PDT_02

Only problem I have at this point is with the HV supply, having removed the 5AR4, replacing it with Hexfeds and a CL190 surge limiter on the 110v side, my voltages are about 50 volts too high: any suggestions? I was thinking of adding a 50ohm 10 w resister in series with the C354 choke, but that would only drop abouth 10 volts based on a guess. Any other suggestions?

Thanks,

Ed

I have used a smaller (preferably film or paper/oil) caps immediately following the rectifiers and before the choke to tune the voltage I wanted without burning up energy in a resistor. I guess the value will be between 3-10 uF. One could then rewire the previous first cap on the board to be added (in parallel) to the second cap. In stead of 50/50/50/50/ you then have ~8/100/50/50

Perhaps you could try Duncan's PSU calculator to check this out, get an input cap value and see if you like the results. See PSU Designer II on http://www.duncanamps.com/software.html

Good luck with you Poseidons. I am listening to mine (Mk IIIs) and like them a lot.

EdStiles wrote:Shannon, your schematics don't show the 680 ohm resistor to ground; but you list it in the BoM. might want to add that for the inexperienced builder. BTW, one of my "680s" measured 792, a reminder that everything should be replaced.

Thanks for the heads up, Ed.

EdStiles wrote:Only problem I have at this point is with the HV supply, having removed the 5AR4, replacing it with Hexfeds and a CL190 surge limiter on the 110v side, my voltages are about 50 volts too high...

If all your caps meet the higher voltage rating, why not just leave it alone? The driver circuit will be fine, and you'll have that much more headroom for the power tubes.

BTW, does anyone know if the A-430 practically a A-431?

separks wrote:BTW, does anyone know if the A-430 practically a A-431?

It is in the sense that the primary impedance and size are identical.

The actual winding inside is probably slightly different in the A431, to accomodate having a 4 ohm tap (A430 only has 8 & 16 ohms).

If you're just using the 8 ohm tap it's very unlikely you'd hear
a difference between the two.

Uncle Ned wrote:

separks wrote:BTW, does anyone know if the A-430 practically a A-431?

It is in the sense that the primary impedance and size are identical.

The actual winding inside is probably slightly different in the A431, to accomodate having a 4 ohm tap (A430 only has 8 & 16 ohms).

If you're just using the 8 ohm tap it's very unlikely you'd hear
a difference between the two.

Thanks for the confirmation, Ned. I was swagging this.

Question:

Anyone tried using an EDCOR CXPP60-4-4.2K in a Mark II / III ? Since it looks like the speakers are going to change, the A430 transformer with its 8 / 16 ohm outputs is not going to match up very well.

I like the idea of a dedicated winding, no compromise, but just don't know much about the company or its products by reputation. The price is right, can anyone help?

Thanks,

Ed

I used a pair of CXPP25-8-7.6K OTs in a project and was very impressed with the build quality and the sound. A bonus for me was that they were close and the shipping charge was minimal. They are rated for 25w but from their size I would speculate that value is conservative.