Ampeg GT10 Xsistor part number

[Dano]

Greetings, I am working on a GT10 Amplifier. There are two output transistors, one a TO-3, and the other a TO-220. The schematic inside the unit shows pictures that these are the correct case styles for these outputs.

Someone replaced both of these with NTE replacements.
NTE 121 for the TO-3 and NTE 196 for the TO-220.

The TO-3 is shorted. I cross referenced the 121 to a 2SB407, (both are germanium).

The TO-220 tests good with my Fluke 87, and it is Silicon.
As Elmer Fudd would say, "Theres something Scwoowy going on here".

I also have a paper schematic of my own and looking at the base to emitter voltage drops indicate both should be Germanium.

I replaced the NTE 121 with the 2SB407, missing voltages came back
but there is still no output and before I go any further I need to find some good cross references for the original Ampeg numbers.


The schematic has the original Ampeg part numbers for these transistors.

REF. Part # Case Type NTE thats in there now
Q10 610289-1 TO-3 PNP 121
Q11 610289-2 TO-220 NPN 196

Thanks
Dan

[Jazz P Bass]

Germanium to silicone

Here is link to a Germanium/ NTE cross ref.
Link:http://www.logwell.com/capabilities/stock/xistors.html
You might want to consider silicone transistors.
Link:Redesign Germanium Transistor Circuits, Part 1

[nbabmf]

I just picked one of these amps up on CL for a song because it needed work. The transistors in the ouput (Q4, Q9) in mine were silicon, RCA part numbers 40389. According to a spec sheet scan I found online, those are the same as 2N3053 but with a large heat radiator (sink). The schematic I have references a different RCA part number, 40625 "Driver, 16-W True Comp. Univ. Amplifier" according to the sheet.

Someone had literally ripped out Q4, the reverb driver, so I first replaced the missing transistor with a 40409 ("Complementary Driver for 70-W Class AB Amplifier" accord to the sheet). It was a plug and play replacement, and I did not have to change any of the resistor values. The reverb came in nice and clean without any discernable noise. I also switched the Q9 to a 40409 because I thought the old 40389 might be causing the white noise that was only noticeable when not playing. It did reduce the noise considerably, and made the amp a bit louder and also cleaner when dimed. Interesting!

For the sake of reference, since hardly anyone has posted any technical information about these amps anywhere... here are the two transistors you ran into trouble with:

Q10: RCA 40623 (Ge PNP) - my GT-10 has an RCA 2N5373 (Si PNP) in a TO-3 package
Q11: RCA 40624 (Si NPN) my GT-10 has an RCA 2N5955 (Si NPN) also in a TO-3 package

This amp sounds great. The Baxandall tone stack is incredible, the reverb is useable throughout the full range of the pot, and it sounds a lot bigger than a 1x10. I'd even say it sounds better than comparable tube amps with the way the saturation comes in. I wish they still build amps like this with thoughtfully engineered discrete designs rather than op amps and clipping diodes.