NeoVibe transistors again !!!!

[Aharon]

Still populating the board on my Neovibe (75% finished)and one of the things I'm short of is transistors......I have lots of pulls but I want only new stuff going into this rather involved build,so shopping I go.
I have been looking into the specs of the transistors and specially the lamp driver since is the one giving more troubles more often.
Seems like the 2n2222A metal can could make a good driver and I also wonder if you could even use something like an MPSA13 darlington in there?
The collector max current of these are 1A and 1.2A respectively.

I have decided to go the true bypass route so I have implemented the gain increase mod (R8/R9) and the mixer mod (R35/R36) by using the 200K trim instead of fixed Rs.
Driver transistor socket, "grain of wheat" lamp (although the mA are unknown to me !!),heat-sinked voltage reg. and "Kodak"  lamp shield.
Power supply is 24VAC/1000mA.
Geez.....I really hope it works for me!!!!!!!!
Any suggestions welcome.
Aharon

[RedHouse]

...Seems like the 2n2222A metal can could make a good driver and I also wonder if you could even use something like an MPSA13 darlington in there?
The collector max current of these are 1A and 1.2A respectively.

I have decided to go the true bypass route so I have implemented the gain increase mod (R8/R9) and the mixer mod (R35/R36) by using the 200K trim instead of fixed Rs.
Driver transistor socket, "grain of wheat" lamp (although the mA are unknown to me !!)...

Well here's my 2¢ worth, while not speaking directly of the Neovibe (more generally to univibe clones) the MPS-A13 works great in the LFO but I havent tried it as the bulb driver, the data sheet does say it can handle 1.2A...but...

I've tried the 910/3.6k (R8/R9) feedback resistors mod which works fine too.

I haven't tried using a 200k mix pot, but I have tried a 47k-trim/82k/82k mixer-mod and it works (ok) but IMHO I'm not sure it's worth the extra parts or board space (I make my own boards based off JC Maillet's design) it's minor'ly effective (is that a word? "minor'ly") not a huge key-to-the-universe mod if you know what I mean. Seemed to me a nice pair of 1% 100k resistors worked just fine there but I have some further A/B testing to do on that myself.

JC Maillet's bulb driver offset mod has much more to contribute to benefit the basic Univibe than all the above mods IMHO, but I don't think you can add it to the neovibe PCB, I'm fairly certain you'd have to make it an off-board addition to use it on the Neovibe build.

[R.G.]

I have been looking into the specs of the transistors and specially the lamp driver since is the one giving more troubles more often.

I did that when I did the original layout. That's why I put in pads to put a TO-220 transistor on the layout.

Seems like the 2n2222A metal can could make a good driver and I also wonder if you could even use something like an MPSA13 darlington in there?

The problem is not current rating as much as it is power dissipation. Power dissipation is more a function of the physical package than it is the chip inside. A TO092 plastic pack is marginal for the lamp driver. I've repaired many real Univibes, and a dead lamp driver is often the problem. I think that's because over time the heat simply degrades the lamp driver.

A metal can package is certainly better than a plastic one, so the 2N2222 is a good choice. But the 2222 is a lowish gain device, so you might want to go darlington on it if you use that one.

I'll take a look and see if there's a common TO-126 or TO-220 package I can recommend.

[Aharon]

Thanks RG and RedHouse !!!!!!!!!!!!!.
Great info.
Aharon

[R.G.]

I think the following are suitable driver transistors that have packages that would help with the power dissipation issue.

TO-126:
2SD1691/KSD1691
2SD2582/KSD2582
MJE800 ... MJE803 (D)
BD675, BD677, BD679 (D)
2SD985/KSD985, 2SD986/KSD986 (D)

TO-220:
2SD1942/KSD1943
TIP100 - TIP102 (D)
TIP110 - TIP112 (D)
TIP120 - TIP122 (D)
BDW23 (D)
BDX33 (D)

There are many others, I just found these easily.

Look for Hfe>100 at low current, Vceo>30V, package = TO-126 or TO-220 and relatively low power rating for these packages, under 50W or so.

[Aharon]

Thanks!!!!!,I'll look for those tomorrow ,with all those possibilities they are bound to carry at least one of them.
I was testing hfe on the ones I have....any specific value better suited...for the buffer for example?.
Thanks
Aharon

[jball1985]

Sorry couldnt find this one earlier. Has anyone used a tip112 typed tran. for the driver. its huge!

[lonewolf]

I tried every mod as far as the mix/driver and oscillator goes and settled on:
250k trim for the mix..easy to find..works great....2 2n3904 darlington pair for the bulb driver and oscillator
I tried several bulbs but the radio shack 12v 25ma was the only one I could get to sound right..with a 250k 20 turn trimmer for the bias offset
tried several ldr's but the small bear hermetically sealed ones sounded best ..placed them flat on the board with a light box I made using  roof flashing ...very easy to work with and very reflective..2n5088 for everything else..also had an a100k dual pot for the speed..changed it to a c100k ..made a huge difference..no true bypass..used the cancel switch....I was going for that frank marino 1977 mahogany rush sound...I got pretty close..sounds like a cross between marino and leslie west....I think they had the most intense guitar tone