Ampeg Portaflex solid state reverb

[pontiacpete]

I have one of these here that has a broken reverb. I have not been able to find a schematic for this anywhere. This one has reverb, tremolo and vibrato.
My question is simple. My signal stops at the first transistor on the input. It's an old type 2n3391A. I was wondering if the pinout on this transistor is the same as the modern version of the the 2n3391A?
Thanks

[Jazz P Bass]

It's a '2N' type so it should be ECB.
Standard fare.

[pontiacpete]

Thanks JP,
The base has the signal on it and the collector has 63v. The emitter has nothing. The emitter is connected to the next transistor(in the picture).
I've already tried a new 2n3391a with no change. This can top transistor has 274 and 10008 written on it. What is it? And it's pinout?
I'm wondering if it's open or something. It does seem to be shorted. There's no signal on it. Two of the pins have about 12v on them.

edit: mistake on the numbers for the unknown transistor, it reads 10000 not 10008

[Enzo]

You will have to tell us WHICH portaflex you have for us to help find your drawing.

2Nxxx are EBC, by the way. ECB would be right for 2SCxxxx

[pontiacpete]

It says model "ST" on the back of the unit and it says 'solid state portaflex'

[Enzo]

Ampeg ST

Try this:

http://el34world.com/charts/Schemati...0Schematic.pdf

[Enzo]

Any decent NPN signal transistor will work here. Note the next one is PNP.

[pontiacpete]

Ampeg ST

Try this:

http://el34world.com/charts/Schemati...0Schematic.pdf

Thanks for the schematic. Lame of me not to find it myself.

[52 Bill]

Every 2N3391A that I've ever seen has a ECB pinout. The original TO-98 cased one were that way and newer TO-92 ones that I have are that way as well.

[pontiacpete]

Thanks 52bill,
How about that second transistor 10000 is that PNP? The drawing says it's not. The only PNP I'm seeing is the 40410.
The 2n3565 is not used in the first position, but are they interchangeable with the 2n3391a?

Unfortunately, I was probing that 2nd transistor and I touched something and the 100R resistor with the 73v on it burned and took out the 40409 and 40410. Now I have them on order.

[52 Bill]

Thanks 52bill,
How about that second transistor 10000 is that PNP? The drawing says it's not. The only PNP I'm seeing is the 40410.
The 2n3565 is not used in the first position, but are they interchangeable with the 2n3391a?

No, the 10000 is shown as an NPN. It's also used in the main power amp as a pre-driver. My guess is that because it drives a small power amp circuit used as the reverb driver, it needs to be rated with a higher current rating than the smaller input transistors. It also needs to have a voltage rating high enough to handle the 40 volts used in that part of the circuit.

The 2N3565 is just a basic NPN transistor just like the 2N3391A. The big difference will be the pinouts. Almost any NPN should work as a replacement.

[pontiacpete]

Thanks again 52bill for the above information. The reverb is working. I went back to using the 10000 transistor after replacing the 40409 and 40410(turns out I had a pair of these afterall) and now there's reverb. Good thing I didn't have to replace the 10000, don't know what I would have done.

[52 Bill]

Good thing I didn't have to replace the 10000, don't know what I would have done.

Yes you do, you would have found a transistor to use as a replacement and fixed it.

Everything that I see that uses the RCA 404XX series of transistors seem to use the same parts in one combination or another. The usual predriver transistor is a 40408 (I think). So my guess would be that the Ampeg part 10000 is probably a house numbered RCA 40408.

Congrats on getting it fixed.