1st Pass at 1st Phono Preamp; Comments?

[SY]

It's in Variac's hands and will be up shortly. (hint: D3a)

[nullspace]

So, I've been looking at the D3A, triode-connected and loaded with a CCS. How does 150Vpk, -1.5Vgk, and 20mA sound in terms of an operating point?

Regards,
John

[nullspace]

Ugh. Such poor typing... I meant 160Vpk, -1.5Vgk, 20mA.

John

[kevinkr]

Originally Posted by nullspace

So, I've been looking at the D3A, triode-connected and loaded with a CCS. How does 150Vpk, -1.5Vgk, and 20mA sound in terms of an operating point?

Regards,
John

If you mean Vp of 150V and -1.5Vgk with ~20mA this sounds like a reasonable choice for the type.

I'm running mine a little colder with -1.2Vgk (diode bias), 15mA and 100V on the plates with very good results. Note that variations in plate current can be rather large with very small changes in Vgk as well as due to the gm spread from sample to sample so if setting a specific operating point is important to you a CCS removes the uncertainty - in practice I use tube based gyrators as loads in my design and while it is not constant current, the load impedance is high compared to the rp so the gain is very consistent over a wide range of device transconductances.

[kevinkr]

Originally Posted by nullspace

Ugh. Such poor typing... I meant 160Vpk, -1.5Vgk, 20mA.

John

While I understand what you mean the voltage from plate to cathode, generally Vpk is taken to mean volts peak. I don't recommend you use this term as it is confusing unless you define it clearly in your post. (The problem is the lack of subscripts that would make it clearer.)

[nullspace]

Thanks for the feedback, Kevin; I appreciate it.

I'll reconsider my use of Vpk; thanks for the perspective.

Regards,
John

[nullspace]

More thoughts...

If I'm going to go with a triode-connected D3A in the first-stage, should I go with another D3A in the second stage or should I pick something else based on my target voltage gain? Given the D3A's mu of ~75, I only need a mu of ~22 for the second stage to get me to 44dB, which is about what I was looking for. How about an active-loaded ECC99? Might that work well as the second stage?

With the D3A, g2 is tied to the anode and g3/shield is tied to the cathode, is this correct? And, I'm assuming that all three grids will need stoppers, is that right?

Thanks for the help.

Regards,
John