Urgent help needed with replacing output devices

[Sampsa]

The output devices in my Musical Fidelity A300 integrated amp blew out on the left channel and I need to replace them. There are 4 Sanken SAP15 NY 9819 and 4 Sanken SAP15 PY 9013 devices in the amp.

I can get replacement ones from Profusion PLC for $5 each. They're from the same gain group (Y). Or I can send it to the importer for replacement at $25 each + work + 2-way shipping + at least 2-week wait.

So the question is, how tight are the tolerances in a gain group like this? Would it be ok to match them with random ones from the same gain group?

Please, I really need this info.

 

[AndrewT]

Hi,
are there individual source resistors for each FET in the power outputs?
If yes then group them into Hi Vgs & Low Vgs, using the Hi groups in Ch1 & Low groups in Ch2.
If No then closer matching will be my recommendation but await other opinions.
BTW I think the letter code grading will be for admittance(yfs) which you may find difficult to measure consistently. Varies with temp during each reading.
You can easily measure Vgs at a prescribed current. Try to match this to Iq.

 

[Sampsa]

Thanks. The Sanken SAP15N/P are monolithic bipolar Darlingtons with internal temperature compensation diodes. The Y-code is the gain group, but it's really wide, from 8000 to 20000 hfe.

 

[AndrewT]

Hi,
mistakenly thought SAP were FETs.
Just substitute Vbe for Vgs & follow previous.
The crossover distortion is likely to be the most serious concern when replacing outputs and that's why I think matching Vbe @ Iq will be more effective. Current gain disrepancies further up the voltage swing will mean unmatched currents but the emitter resistors (if fitted) will help balance them out.

 

[Sampsa]

Ok. So it seems that it's probably more cost effective to send the unit to the importer than buy a bunch of the devices and match them by hand.

 

[KBK]

Ken's Review of the sonics of this amp in stock form:

Bloated Screech (with lumps).

 

[ostripper]

No , not a bad amp.. in fact ,rave reviews...
http://www.soundstage.com/revequip/musicalfidelity_a300.htm

Can't find a schematic but I don't think matching is a problem
with these sankens (High end- made just for audio- OP devices)

Since these are darlingtons with diode comp.
[IMGDEAD]https://i302.photobucket.com/albums/nn112/ostripper/sap15.jpg[/IMGDEAD]
it's a good bet they are IC driven.
Amazing for the high end (now I really want to build my sanken/
LM4702 amp)
Good luck, OS.

BTW .. something to note ..internal emitter resistor can be bypassed by connecting an external one.
you might have just burned internal resistor-data says
it is designed to fail before transistor junction does(s). strange.