Ampeg Solid State portaflex output transistors

[pontiacpete]

This amp is the solid state portaflex without the reverb and tremolo.
http://el34world.com/charts/Schemati...eg_SST_SBT.pdf
The output transistors are shorted. Does anyone know what an appropriate substitute for these transistors would be? And the drivers? Although they don't appear to be shorted.
Thanks

[Jazz P Bass]

Here is the spec sheet: https://www.semicon-data.com/transis.../40/40411.html

[J M Fahey]

Those were king of the hill NPN power transistors ... way back then.
Modern and way stronger ones are the MJ1502x , pick one. (TO3 metallic case)
Same or better current, 200/250Vce instead of 100V, way better SOAR ... reasonable price

As of drivers, the casing is obsolete, if needed get some TO126 (plastic) case transistors which can do the job: 100Vce, 1.5 A minimum (3A is fine) , 15/20W dissipation.
You will have to bend leads to fit them in the proper holes, no big deal..

Caution: the original heat sinks have mounting pins soldered to PCB pads, sometimes they are used as "jumpers" and if pulled some tracks might get disconnected, so just in case jumper mounting holes with a short piece of wire.

[The Dude]

I don't see why you'd replace them if they're not shorted?

[pontiacpete]

Thanks for the responses.
I decided to install 4 new 15024s. The amp now powers up and seems stable, lights on the front panel are lit, but now sound. I think it has something to do with the connector. More work needs to be done. I'll be back.

[pontiacpete]

Thanks for the responses.
I think it has something to do with the connector.

Wrong about this. I found the 10000(40408) shorted and one of the drivers is shorted after all, the 2n3767

Also, found that these schematics are

http://el34world.com/charts/Schemati...5c_15d_18c.pdf

There's another at el34world for the BT15 that has a lot of likeness to this amp

[pontiacpete]

Those were king of the hill NPN power transistors ... way back then.

As of drivers, the casing is obsolete, if needed get some TO126 (plastic) case transistors which can do the job: 100Vce, 1.5 A minimum (3A is fine) , 15/20W dissipation.
You will have to bend leads to fit them in the proper holes, no big deal..

Juan, do I need to mount the TO126 cased drivers to the heat sink as well?

[J M Fahey]

Juan, do I need to mount the TO126 cased drivers to the heat sink as well?

Sorry Pontiacpete, I was thinking the earliest version, derived straight from the RCA suggested schematic just with an extra pair of power transistors, which used 40409/40410 transistors, which are basically "a TO5 case with a spider sheet metal heat sink".

But now I see you have the TO66 drivers version so no need for the TO126 kludge (although technically it can still be done, only caveat is B-E legs are swapped, so it needs to be mounted flipped.).

From what I saw, Mouser seems to have TO66 ones. If so and reasonable price, go ahead.
If not , use TO220 transistors instead, plain vanilla TIP31C/TIP32C (NPN or PNP as needed) will do fine.

TO220 was designed to be backward compatible with TO66 so bending base and emitter legs straight downwards will fit current holes; collector will use just one screw of course.
IF they are in sockets, you might fit these there or pull sockets, mount transistors straight to heatsink and send legs through heatsink holes, just heatshrink wrap them to avoid shorts.
Always mica and grease of course.
Just don´t spend $20/35 on NOS ones, even worse on NTE type "substitutes" , TIP are robust and excellent.

If any doubt post a picture of original transistors still mounted on heatsink.

[pontiacpete]

I tried both MJE182/172 and now I just tried the TIP31/32. I'm getting a fast loud motor boating at this point with both sets of these. Not sure what's going on now. But here are couple of pictures.

[pontiacpete]

Completely stumped at this point. Tried different drivers tip31/32 and ended up finding a pair 2n3767/3741 for a good price. But I’ll still not getting the right voltages.
This what’s happening. I’m getting a good 74v off the power supply, at the top of r49. But on the othe end of the this 300r 20 w resistor there’s only 6v. Top side is of the r47 74v but only 6 v at the collector q8.
Can anyone shed some light on this? I’ve gone over the connections and components many many times
This is the schematic I'm going by it seems to be the most accurate

[g1]

How about post your E,B, & C voltages for Q7,8,9, & 10.

[pontiacpete]

Here they are
Q7
E 5.7
B 6.4
C 5.8v

Q8
E 5.8
B 6.3
C 6.9v

Q9
E 6.3
B 6.9
C 75v

Q 10
E 6.3
B 5.8
C .84v

[g1]

Q7 appears to have a C-E short.

[Sowhat]

From what I know which can be very little and often incorrect... shouldn't there be 39.5 volts on the base of Q9 and the collector of Q8? You show just 6.9 volts there, I might want to take a good look at R47 and R48, maybe one or both has gained a few ohms, that's the voltage source for everything there going all the way down to ground, right?

[pontiacpete]

For Q7 I've been using 2n3415 as it is in one of the schematics that I posted. Changed this out twice with no luck and also tried a 2n3405 in this spot with the same results. No shorts in the 3415.

As for the 2 resistors in series, the 2.2K and the 680r, I've measured and pulled them a couple of times and they're reading as they should.
I can't figure what's holding up the 39.5v for the life of me.
Any other ideas?

Thanks for the suggestions!