• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Any EF184 users?

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Gluca

Gluca

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Joined 2004
#1
Ciao,

I am considering a EF184 (used as pentode) in a DAC IV-preamp. Bias should be in the 10-15mA/150-200V region.

Does any of you have experience with this puppy in critical low level applications? I used it a while ago as CCS and I was quite impressed by the build quality (I think they were tunsfgram) and sound.

Would you point me to other small pentode that can be biased at that current? I am not used to those tubes, sorry.


Thanks
Gianluca
 
#2
The only small current pentodes i use are E180F/E280F/D3A. Very suitable for low level signals and work at similar currents. Higher transconductance than EF184. Out of curiosity: why as a pentode? Voltage gain is sufficiently high as triodes and you won't need an extra stage to get acceptable output impedance.
 
#3
I can vouch for the D3A, very quiet in general.. For this application I would think triode connection would be fine.. The tube has a mu of 77 and an rp that is <2K IME.. Who needs pentode partition noise in an application like this? (I am not sure how big an issue it would be, but as a pentode connection is probably not required....) Ideal for a single stage low noise amplifier with low output Z. Use a CCS or choke load and it will drive a 10K load quite happily..
 
#7
Does any of you have experience with this puppy in critical low level applications?
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Is a guitar amp a critical low level application?🙂

Can't help you with your project, all I can say is this tube sounds great. Geek knows this too.

I was quite impressed by the build quality
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When I was looking at the build quality I thought: thanks God there are plenty of NOS available.
 
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#9
Gluca said:
GG? Hum... yes actually. With a servobias. It seems it works pretty on spice and as I have most of the parts (but the EF184) I'd like to give it a try.
Click to expand...

It should work if implemented properly..(Common grid from an AC standpoint, dc servo bias applied to grid) 😀 Gain may be insufficient with some dacs, as you really want close to virtual earth behavior at the input, however a 1:2 step up transformer (triode connection only!) will generally remedy that at the expense of rather higher output impedance. (Like 4 x rp) Perhaps a high transconductance pentode used as a pentode is the way to go with an output buffer of some sort. Can't hurt to try it. (which I haven't)

You ought to post your proposed circuit.
 
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