Sunn Beta Lead power transistor

[cjlectronics]

I am repairing a Sunn Beta Lead. Searching this forum, I discovered a loud hum that is uncontrollable is common on this amp. My problem is no different and I have found an open 2N3055 and an Emitter to collector short on one of the SJ954s. Finding the 2N3055 is not a problem. But finding the SJ954 seems impossible. Is this the right P/N? Is there a cross reference power transistor?

Thanks in advance,
CJ

[Jazz P Bass]

Pre driver

SJ954. Is that the 3055 predriver transistor?
NPN?
2SC1061 might work.

[cjlectronics]

No, it is a power transistor. I'm thinking it is the other half of the push pull amplifier. The 2N3055 is an NPN and the SJ954 would be the PNP transistor. This power transistor is in a TO-3 can.

[Enzo]

I'm too tired to dig out the schematic. If we are just talking the push pull outputs, then if you have 2N3055, the PNP equivalent is MJ2955.

SJ954 is a house number.

[Jazz P Bass]

2N3055 compliment

Datasheet: 2N3055 NPN/ MJ2955 PNP

[cjlectronics]

Thanks Guys... After some research, it looks like the power transistor I am looking for is MJ0954 which, according to the schematic (house p/n 22-0954 per the service manual). The schematic shows it as a PNP. So, I will apply a logical guess and use the MJ2955.

CJ

[unparalleled]

Thanks Guys... After some research, it looks like the power transistor I am looking for is MJ0954 which, according to the schematic (house p/n 22-0954 per the service manual). The schematic shows it as a PNP. So, I will apply a logical guess and use the MJ2955.

CJ

That is the correct device.
I have a Beta Lead combo which I have restored.
You don't happen to have the user's manual for this amp?
Cheers.
Alan.

[gbono]

betabassmanual.pdf

Closest thing to a user's manual I have.

I have often had to replace the transistors in the +-15 voltage regulator(s) (I belive Q1 and or Q11 = TIP30/29) on the power amp board.

[unparalleled]

[ATTACH]7568[/ATTACH]

Closest thing to a user's manual I have.

I have often had to replace the transistors in the +-15 voltage regulator(s) (I belive Q1 and or Q11 = TIP30/29) on the power amp board.

Thanks heaps! I have been looking for that manual for weeks!

[kingnimrod]

I repaired the power amp section of my Beta Bass combo a few weeks ago. As I'm still somewhat of a novice in the world of electronics, I replaced most of the components on the board until I figured out it was a couple of bad output transistors. Don't remember what parts I used exactly, but they were all either matching or equivalent parts, and the amp sounds great now.

there's a service manual and schematic at the sunn amp forum site.

[jrfrond]

Yeah, the complement to the 2N3055 is the MJ2955, just like Enzo said. Or, just substitute MJ15024 (NPN) and MJ15025 (PNP) and be done with it.

[Enzo]

Thanks John, I almost said that too. Or looking through the drawers, MJ15003/15004, or even MJ15015/15016. Or really, most any TO3 pair you got. Just make them all the same in your amp. Don't put an MJ15004 next to a MJ2955.