Sony TA-E88 Preamplifier Voltage Regs

[slimecity]

Hi all -

I found a great little Sony preamp that Im listening to right now.

I've replaced all electro's in there and want to proactively replace the transistors serving as power regulators. There are two sets of each on the main boards and the same in the little vertical boards feeding power to the head amps - schematics attached - relevant transistors are Q704 and Q715 on the main board, and Q7 and Q10 on the headamp PS boards.

Other pics taken from the web for context and are not of my preamp. The main board regulators are heatsinked.

These are all 2SC1061 & 2SA671 pairs. They work pretty hard and have been known to fail in these preamps.

I've been suggested to replace these with the standard MJE pairs (ie: MJE15034 & MJE15035). I dont have these on hand.

What I DO have on hand are KSA1220A and KSC2690A. The pinout is reversed and the package is different to the original TO220 types (but this is still workable for the heatsinks).

Specs on the KSA1220A and KSC2690A is improved from the originals - but speed is higher. Any potential concerns with oscillation if I use these in the shown circuit positions?

thanks!

 

[dlucy]

Oscillation (motorboating) comes from too much signal getting through a transistor. This means "frequency higher than designed for". Using a replacement transistor with a high speed, higher fT, higher slew rate... only is a concern when the transistor is amplifying. Most times, I would assume even though I'm not an E.E., has to do with the CoB or capacitance of a given transistor... an aspect that limits how high a frequency gets through the transistor.

Transistors used in voltage regulation are not amplifying, so this particular aspect should not be a concern in your application.

I'm looking forward to all the Ak'ers who know more about this than me chiming in here and correcting me.

 

[slimecity]

Great, thanks for clarifying that Dlucy.