E180F Preamp

[Dagwood]

I was looking for a preamp design using a pair of E180F Pentode's and found this on an old website.

My question for the experts is...... from this design what voltage would I expect to see at socket pins 7 & 9 without the E180F fitted.

My transformer has 235 - 0 - 235 outputs and I am seeing 218vdc on pin 9 (Grid 2) and 303vdc on pin 7 (Anode) offload. Is this not on the high side when the E180F datasheet states a grid voltage of 160v (400 max) and the Anode should be 190v (400v max)

Cheers

[Doz]

What voltage is on the cathode?

[Dagwood]

Hi Doz

Nothing, E180F not connected. I was checking the voltage at the socket offload and think they are high?

Cheers

[Doz]

Sorry, I understand.

Until you place the circuit under load, or you know what current is flowing through the tube, and the power supply resistance, you aren't going to know what the cathode or anode are going to be at under load.

The cathode will rise up to a few volts, and the anode will sag. The tube will only "see" the volts between the anode and the cathode, so, as long as that is within your operating parameters.. all is well.

Simulate it in LT Spice or similar first... but, personally , I'd fit the tube and run it up on a variac.

Don't forget your anode may well exceed the max voltage until the tube starts conducting. Have you used a SS or tube rectifier?

[Dagwood]

Thanks Doz

I have only set this up on a test rig at the moment so will complete the rest of one channel tomorrow night and fire it up !!! Was just a bit worried as these tubes look great and didn't want to fry them!

6X4 as per the design

I will follow this up tomorrow night (NZ time)

Cheers

[DF96]

Make sure you use a high quality resistor for the 51k at the grid. Even just the thermal noise from this will be a limiting factor for this design, so you don't want any extra noise too. I'm not sure why the design uses a low noise valve in a high noise circuit, but each to their own!

[Dagwood]

Make sure you use a high quality resistor for the 51k at the grid. Even just the thermal noise from this will be a limiting factor for this design, so you don't want any extra noise too. I'm not sure why the design uses a low noise valve in a high noise circuit, but each to their own!

Thanks, I have not ordered any parts yet, just mocked it up with parts in stocks. I was going to order Vishay/Dale CMF55 resistors Digi-Key - CMF51.1KHFCT-ND (Manufacturer - CMF5551K100FHEB) these are very close spec to there RN55 Military series.
Whould these be up to the job?

Not sure of the exact design details as I'm not a EE, more the point was a pair of E180F's in my stores and the need for a preamp

Cheers

[DF96]

Sorry, I have no idea. I know a bit about circuits, but not component brands.

[Dagwood]

Ok, cheers

Will give it a go

[jez]

This will be one hissy phono stage!