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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

4EH7 opinions anyone?

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bacon665

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Joined 2009
#1
I acquired a box with a couple hundred miniature and subminature tubes the other day for $5
ive found i have 8 of the amperex 4EH7.
i looked up the datasheet there doesnt seem to be much on the frequency response but it says its a remote cut off pentode designed for use as a wideband IF amplifier.

my plan at the moment besides finding more info is to see what people think of these if anyone has used them and maybe to build a small equalizer/preamp using this tube.

a futterman wouldnt be out of the question either but as i dont fully understand the design it might not happen anytime soon

-edit-
also if anyone would be interested in buying some of these i have a spreadsheet available
 
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#6
bacon665 said:
IVe also got 8 6fq7's they seem to be listed as general purpose.
i seen a design using these as the grid driver for some 300B's and also as a driver for an EL84.
Click to expand...

Looks like a variation on ECC82 theme. Using it as a driver tube (wired as cathode follower) is a no-brainer, but you mentioned you're interested in building a preamplifier. Have you decided on specific parameters (load impedance, amplification factor, input type) for your preamplifier yet ?

ECC82 is often shunned when it comes to linear amplification (because there are many other alternatives avaliable, which perform better in one way or another), but if all you wanted of your "preamplifier" was a tube buffer, I'd say go for it with this tube - you'll definitely get your $5 worth out of this thing alone 😉

Low mu is an obvious limitation, so you'd be better off finding some other candidate if you wanted to get huge amplification factor.
 
#7
I went over your list quickly and I noticed you got some 6AQ5-As there. This is essentially a 7-pin version of EL84. You could combine a pair of those with two of your 6GH8s (use pentodes as CCS for the triode sections) and get a couple of watts of single-ended goodness per channel out of them.

There is plenty of fun to be had with the stuff you purchased 🙂
 
#8
Arnulf said:
Looks like a variation on ECC82 theme. Using it as a driver tube (wired as cathode follower) is a no-brainer, but you mentioned you're interested in building a preamplifier. Have you decided on specific parameters (load impedance, amplification factor, input type) for your preamplifier yet ?

ECC82 is often shunned when it comes to linear amplification (because there are many other alternatives avaliable, which perform better in one way or another), but if all you wanted of your "preamplifier" was a tube buffer, I'd say go for it with this tube - you'll definitely get your $5 worth out of this thing alone 😉

Low mu is an obvious limitation, so you'd be better off finding some other candidate if you wanted to get huge amplification factor.
Click to expand...

6FQ7s are essentially 6SN7s in a miniature bottle. They are much more linear than a 12AU7, and IMHO a much better sounding tube.
 
#9
so if i find another one in the box then I could build an 8 band stereo equalizer (pump them to a fet mixer) and then use another one for the preamp output?

-note
i havent pulled all the datasheets yet if I find I haven enough pentode/tetrode or maybe even a heptode (doubt it) then i could use tubes for the mixers. if im not mistake you just feed the output of the eq bands into grids and it mixes them on its own right? I've heard tale that mixing with tubes diminishes bass response (eew distortion) clear that up before I get too far into this.
 
#11
An externally hosted image should be here but it was not working when we last tested it.

heres my proposal for one channel one band
B+ = +35
cathode = -35
or ground the cathode and place 120 on B+ ?
Im still not sure about the ganged pots its not just the price there is also the chance that r1 and r2 in the unit have slightly different values.

Im not certian on this but bipolar transistors are current devices right?
so i should be able to use one pot between the + voltage and the transistors allowing me to control both channels with one pot correct?
 
#12
bacon665 said:
my main source is my pc so 3.55mm plug and rca jacks will be the input ...
Click to expand...

In that case my question is why ? All music programs for computers have built-in equilization panel which handles everything in software (DSP). If you do not want tube distortion, stick to equalizer controls in your computer.

Regarding your picture above: potentiometer should have one of its ends conencted to ground, not as rheostat. Yes, BJTs are current devices, but volume potentiometer would still be connected in normal manner (brush up your Kirchoff's laws and Ohm's law knowledge !).

Do yourself a favor and stick to implementing things from existing schematics until you figure things out. Tubes usually work with high voltages (= lethal) and you could pay dearly for beginner's mistake.
 
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