Measured VF14 characteristic

[marcus4audio]

As far I can understand EF80 is possible replacement but has 6.3v/300ma filament. Mu number is not so critical unless is much lower than original. So it's not possible to be drop replacement to VF14. Nuvistor replacements are much closer because it can be trimmed to work inside the real U47 with just couple of resistors adjusting. Correct me if I'm wrong

 

[Melodeath00]

Ah yes, I did not mean drop in replacement. I was thinking these graphs possibly told us something about the sound, but I guess I am wrong? Forgive me - I don't know very much about tubes.

 

[bezen4uk]

oops.  sorry. Could you explain why  30 pa input grid 1 current is important? How did you measured this?

Hi,
I'll try to describe grid current measuring method (please, see the attach):
There is voltage drop at the grid series resistor (I use 100M).
If you short this resistor, the grid potential changes and voltage at plate changes too.
So, you can measure voltage change at the plate.
The tube has some amplification k, so the voltage change at the grid is k times lower than voltage change at the plate.
And now you divide voltage change at the grid by resistance of the grid series resistor.
Ig=dVp/(R*k), where:
Ig - grid current;
dVp - voltage change at the plate
k - amplification;
R - series grid resistor.

Why it's important to have lower Ig (imho):
Input grid current has nonlinear nature.
It works like diode that is connected parallel to the microphone capsule and causes additional distortion.

 

[bezen4uk]

So how close if the EF80 to the VF14? Just about all I know is that "mu" is gain, so the EF80 amplifies the signal more? Thanks for the measurements

Hi,
They look like same family pentodes.
Higher gain of EF80 will be reduced due to Miller capacitance, so overall gain in U47 circuit will be close to VF14.

 

[o3misha]

When thetube has higher grid current, the  voltage to the anode is higher than 34?

 

[bezen4uk]

When thetube has higher grid current, the  voltage to the anode is higher than 34?

Higher grid current causes increase of plate voltage.

 

[o3misha]

Yes, I meant plate voltage (anode voltage is also right term?), of course. You mentioned about 30pA grid current. What max grid current is ok for VF14s? Neumann never measured grid current when they tested VF14s.

 

[bezen4uk]

Hi,
I don't know what is the maximum allowable grid current for VF14, but I can compare it to other tubes.
For example, AC701 has 100pA (at Ug=-1.5V, Ip=0.4mA).
Another example: russian tube 6S6B has Ig=1nA (Ug=-1.5V, Ip=0.4mA).

 

[Melodeath00]

I'm posting again because I finally understand a little bit more about how to read these graphs. The question is, is there anything particularly important about the mA output of a tube?  For example, VF14 puts out about .55mA when it has 34V plate voltage and 1.1V cathode. Is there a particular reason to shoot for a tube that also puts out .55mA? It seems there are a lot of tubes that you could bias in a way to output .55mA.

Ignoring the effect of having to run a separate heater, what would be the effect of having an alternate tube in a U47 that output 10mA instead?

The U47 schematic lists 34V on the anode, with .55mA. Is it just coincidence that the VF14 is receiving 34V on the anode at .55mA, and it's idle current at this bias is also .55mA, or am I fundamentally not understanding the electrical flow on this circuit? Is the .55mA listed on the schematic the idle current and not the current of the 34V split off from B+?

Does anyone know how many volts an M7 or K47 puts off?

 

[marcus4audio]

Any progress? BTW, did someone have VF14 Telefunken detailed data sheet?

 

[gary o]

How close to the V14 is the parallell 6028s idea....

 

[BraFra]

I'm also curious about a drop in replacement for VF14. Searching the net I've found this page about a fet conversion: http://www.gothamaudiousa.com/museum/winertemmerdebateu47.htm

It will be possible to use a similar circuit in a drop in replacement? It will be near to the original VF14 sound?

 

[micaddict]

I'm also curious about a drop in replacement for VF14. Searching the net I've found this page about a fet conversion: http://www.gothamaudiousa.com/museum/winertemmerdebateu47.htm

It will be possible to use a similar circuit in a drop in replacement? It will be near to the original VF14 sound?

Andreas Grosser makes a fet version inside a VF14 tube housing.
Drop-in replacement.

 

[BraFra]

I'm also curious about a drop in replacement for VF14. Searching the net I've found this page about a fet conversion: http://www.gothamaudiousa.com/museum/winertemmerdebateu47.htm

It will be possible to use a similar circuit in a drop in replacement? It will be near to the original VF14 sound?

Andreas Grosser makes a fet version inside a VF14 tube housing.
Drop-in replacement.

I've read this too, but from what I've read he doesn't sell it, it's just a replacement part for mics that he repair. So not usable for clone etc and not usable for testing too, if you don't want to send him your mic

Anyhow in every single place where I've read about this drop in replacement they claim about it as amazing, so I think this is the right way.

 

[bezen4uk]

Some update:
there is 8393 nuvistor characteristic.
Unfortunately, it doesn't work at 40mA heater current.
Anyway, it's interesting comparision.
VF14 is much more linear tube (curves are equidistant and parallel).
VF14 has lower Ri, higher mu (28 vs 24).

 

[gary o]

Re the 6028 /408A tubes wired in Parallell as in the MK47, heaters in series, I thought it was a clever solution , not a drop in replacement, worls well in mics I have made from scrarch.....Im no good a reading tube data & graphs so are 6028 parallell similar to V14 ?

Thanks

 

[bezen4uk]

Re the 6028 /408A tubes wired in Parallell as in the MK47, heaters in series, I thought it was a clever solution , not a drop in replacement, worls well in mics I have made from scrarch.....Im no good a reading tube data & graphs so are 6028 parallell similar to V14 ?

Thanks

Hi gary,
I don't have 6028, but I have EF95  and I'll try it.

 

[ricardo]

This http://saturn-sound.com/products/replacement%20valve.htm looks like the closest replacement for VF14m.

Price is a bargain compared to dodgy 'NOS' VF14s on the market.

 

[gary o]

Re the 6028 /408A tubes wired in Parallell as in the MK47, heaters in series, I thought it was a clever solution , not a drop in replacement, worls well in mics I have made from scrarch.....Im no good a reading tube data & graphs so are 6028 parallell similar to V14 ?

Thanks

Hi gary,
I don't have 6028, but I have EF95  and I'll try it.
[/quot

Ef95 I read same as 6AK5 same as 5840 similar to Ac701 I tried them in M49 & Sm269 they work well ...two 6028 in parallell said to mimic V14 again they sound great in a U47 circuit but I not got real U47/V14 to test against tho

 

[bezen4uk]

Hi gary,
6028 tube is the same as EF95(6AK5), but has different heater:
http://www.radiomuseum.org/tubes/tube_6028.html

I attached measured EF95 characteristic at heater 4.41V/140mA (I tried to emulate 6028 at 40mA heater current).
EF95 has same mu as VF14, Ri=20kOhm (VF14 has Ri=14kOhm).
So, double 6028 should be close VF14 characterstic.
Drawbacks are doubling of interelectrode capacitances and increased input current noise.