2N2924 vs. 2N3392

[Rhodesplyr]

I know this is a minor technical question, but there's been a discussion on another site I follow about transistor types used in repairing vintage combo organs, some of which were originally built with 2N2924 transistors.

Looking at the datasheets, the *only* published difference between the 2N2924 and the 2N3392 is this:

2N2924 hfe 150-300 @ 2ma, VCE = 10V
2N3392 hfe 150-300 @ 2ma, VCE = 4.5V

I'm not sure how to interpret the difference in VCE ratings. Does that simply mean that you can get the same hfe/beta from a 2N3392 with half the total power dissipation?

[Steve Conner]

That's simply the Vce at which the hfe figure was measured on the factory test rig. hfe depends slightly on the voltage applied during the test, so they have to state what voltage they used for completeness.

I imagine the 2N3392 will have much the same hfe rating at 10V as it did at 4.5V, so there's probably not a whole lot of difference.

[jrfrond]

No, it simply means that is the maximum voltage that can be applied to the transistor between the collector and emitter. The HFE is a constant. FYI- there are a whole bunch of NPN transistors with higher voltage specs that can be used as subs. In fact, I would recommend it.

[Steve Conner]

No, that's not the Vce rating, it's just the voltage they applied for the hfe test. The 2N3392 is a 25V part.

I also agree that there must be some more convenient modern sub for it.

[Rhodesplyr]

No, that's not the Vce rating, it's just the voltage they applied for the hfe test. The 2N3392 is a 25V part.

I also agree that there must be some more convenient modern sub for it.

Both transistor types are still readily available.

So, what you're staying, Steve, is that the 2N2924 and 2N3392 are essentially identical?

The application I'm working on is the emitter follower output of a ~7 Hz vibrato oscillator circuit. Supply voltage is 6.8V, and it drives all twelve tone generator cards in parallel, which means a load of ~5k Ohms. I'll attach the diagram. Q16 and Q17 are both 2N2924.

The original circuit appears to me to be under-designed and has to be tweaked simply to work at all via the resistors marked for "tailoring." This is the American/Thomas Organ version of the Vox Continental. Both the British and Italian versions use an astable multivibrator oscillator, a more carefully biased emitter follower, and an 8.2V supply. Parts count is quite a bit higher, but it works much better.

I've already breadboarded a mod of the Thomas Organ circuit that works much better, using the stock 2N2924s. The way the stock circuit is designed, the oscillator tends to drive the emitter follower into shutoff, resulting in a put-put sound as it switches on and off.

[Steve Conner]

Ugh, what a horrible circuit.

I'd just replace them all with a DSP... er, I mean, 2N3904s.

Edit: To clarify: What I'm saying is that the difference between a 2N2924 and a 2N3392, in the organ application, is probably no greater than the spread in characteristics the manufacturer allows between samples of the 2N2924 or the 2N3392.

It's kind of like the "Men are from Mars, Women are from Venus" thing. That's true on average, but you can always find some particular woman who's more manly than some other particular guy.

[Rhodesplyr]

Ugh, what a horrible circuit.

Here's how your British cousins did it. All germanium transistors of course.

The vibrato circuit was built on its own circuit board in the British version. Thomas Organ tried to get away with just wiring a few parts to a terminal strip.

On the whole, the American version works fine and is pretty reliable. The vibrato circuit was their biggest screw-up.