Harman Kardon Citation Twelve transistor replacement.. help needed

[JoshHendi]

UPDATE: Final transistors used listed on post #7

I have a Citation Twelve with a bad RCA 4306 transistor. Q703/704

The rest of the transistors are being replaced. 2N5087 for diff pair, 2N5232a for bias, 2N5322 & 2N5320 for drivers, 2N3773 for outputs

Can someone reccommend a good option for Q703/4 pre-driver? (or if there are better options for any listed above)

 

[ecluser]

The same as the NPN driver (2N5320) would be perfect for Q703/Q704

 

[gslikker]

In mine, I used 2N3439 (selected for not too low HFE)

 

[gadget73]

I love how simple early solid state amps are. This has barely enough parts to work.

 

[HandsOnHifi]

Will the pre-drivers and/or drivers need a heatsink? 2N5320 and 2N5322

 

[gslikker]

predriver dissipates around 400mW it will get warm , but it does not need a heatsink and there is not much room for a heatsink, either.

Drivers definately will need a heatsink.
Unfortunately, the original heatsinked transistors are rather unobtainable. Myself, I did choose "fins" .

To the OP: consider whether your amp initially may have failed because of bad connections. Even the original Nelson Pass paper about his citation 12 FET modification mentions bad connections (to be found on the internet).
My Citation 12 had bad connections too, I had to shafe off between 1 and two millimeters (about 0.07") of the circuit card side to have the socket wedges connect properly to the pins.
After restoration but before this action, I heard a loud bang when the amp was moved around a little while power was on. It did not kill it but the bad circuit card connection was the culprit.

I put some info about that on my resto page: http://www.gerardslikker.nl/hkcitation12.htm

 

[JoshHendi]

Just as a followup to the original post...

I did not have good luck properly biasing the 2N3773 outputs. Switching to MJ15001 devices solved this and are working great. So the final transistors used were

2N5087 for diff pair (HFE matched. You will need to buy about 20-30 to achieve 2 matched sets)
2N5232a for bias
2N3439 for pre-drivers (2N54320 also work, tested both)
2N5322 & 2N5320 for drivers (heatsinks needed)
MJ15001 for outputs

All are available at Digi-Key as of this posting.

@gslikker yes I did notice that these pin connectors could cause issues. I was able to get mine fully seated, but it did take a good amount of force to do so. If I were to do another one of these, that couldn't hurt