Lorenz Mic-Pre

[Ericbazaar]

Output Transformer (18:1) and Plate Choke, booth shielded. And the big DC Cap (8uF) on the left.

 

[Ericbazaar]

better View from the Gain Switch

 

[rock soderstrom]

Thanks Eric! The "Frag Jan zuerst - ask Jan first" labeled PSU capacitors are funny!  ;D

 

[abbey road d enfer]

@Abby
The voltage drop on  R18 (47k) is 50V so I think that 1mA for first tube's cathode current is a good assumption.
I agree that in later measurements first and second kirchhoffs are not so happy.

OK, but according to the voltages on g2 and anode, R5 (g2) draws 0.11mA and R6 (most of plate current) draws 0.46mA. Where is the difference going to?
The mystery is further reinforced by the fact that the voltages are measured with a device of 20kohms/Volt, which would result in the plate, and particularly G2 voltages actually being higher in operation, which in turn would indictae lower currents. The most credible figures are the various HT and the cathode voltage.

 

[Ericbazaar]

Sorry, is not original anymore. Booth Units was in horrible shape intern. So i've changed all broken components.

 

[Ericbazaar]

C3 (25nF), W1 (2M) and W4 (1,6K) for the EF86 Tube. These three Components are shielded too with a little Hood.

 

[Ericbazaar]

These are the Modifications i've found in booth units. Eckehard Dux (a german specialist for tube Gear) told me, this was a standard Mod in the DDR for HF Freq Blocking. Hmm, not shure if its right...

 

[Ericbazaar]

Thanks Eric! The "Frag Jan zuerst - ask Jan first" labeled PSU capacitors are funny!  ;D

, these are made by "Fischer & Tausche" Germany i think.

 

[abbey road d enfer]

C3 (25nF), W1 (2M) and W4 (1,6K) for the EF86 Tube. These three Components are shielded too with a little Hood.

Shouldn't the wire coming from the common connection of the gain RC circuits be shielded too? If not, what's the point in shielding the cathode? Unless it is inadvertantly, just a consequence of proximity to the sensitive grid area...

 

[rock soderstrom]

, these are made by "Fischer & Tausche" Germany i think.

Most likely, as far as I know they are the only extant german manufacturer for that kind of capacitors. I am a great fan of their products, I use them in all of my tube gear. The got a great range of axial high voltage capacitors, too!

Here a close up photo of their tripple cap package.

 

[Ericbazaar]

Pictures from my rebuild V241, i used an old RFZ N345 24V PSU Case, that looks indentical to the V241 one.

 

[Ericbazaar]

I just found a much to big Power Transformator. I installed in the back, not the best option but it works and it have exactly the Voltages i need.

 

[Ericbazaar]

It works and sounds really good, but this is a prototype! i build in other Transformers with lower Ratios, so the Workpoints of the Tubes musst be changed. i tested different settings in the last weeks, i am soon on target.

 

[rock soderstrom]

These are the Modifications i've found in booth units. Eckehard Dux (a german specialist for tube Gear) told me, this was a standard Mod in the DDR for HF Freq Blocking. Hmm, not shure if its right...

I guess, this is true. It is a typical grid bleeder which forms together with the Miller capacity of the tubes a low pass or high cut.

 

[rock soderstrom]

It works and sounds really good, but this is a prototype! i build in other Transformers with lower Ratios, so the Workpoints of the Tubes musst be changed. i tested different settings in the last weeks, i am soon on target.

Saugeil!!! What kind of transformers and inductor did you use for that build?

 

[Ericbazaar]

Saugeil!!! What kind of transformers and inductor did you use for that build?

Lundahl 1935 at the Input (wired 1:10), was installed for testing, but i like it. Output Transformer is a 8:1 russian Made from a Guy Named Petrov from Sgt Petersburg. This Trafo is designed for REDD47 Preamps (similiar to the 241)
The Plate Choke is from Hammond (150Hy) but with lower DC resistance, so the ECC85 is running with higher current, i think is better for lower ratio transformers. i am not a specialist in electronics, but i build gear for a couple of years. and i'm learning every day more and more... :

 

[ruffrecords]

> to hit the car directly in front of you

Not used that way in America.

What is the equivalent us term - rear ended??
[qjuote]
I suspect your use comes from shunting railroad cars, and your railroad car bumpers/buffers which are not used on American railroads.
[/quote]

Almost certainly.

Cheers

ian