Kenwood L-07M II Issues

[cchean]

I did this mod several years ago and it works perfectly. I still have some of the mica caps lying around. I noticed the price of mica caps have increased significantly, it will cost almost $80 to do a pair. Has anyone tried multi-layer ceramic caps? Murata has caps that will cost a fraction of the mica caps.

 

[Broesel02]

as you see i need only 4 glimmer capacitors for the driver board. The Murata caps are not the solution for the best sound

 

[sae-7125]

looks like asr/amir did a vintage review recently:
https://www.audiosciencereview.com/...kenwood-l-05m-vintage-amplifier-review.43409/

 

[Bumpalump]

I wonder if the stability issues are affected by long speaker wires, high capacitance wires or interconnects that might tend to pick up RF and present it at the amp input.

Yes, speaker cables above 2m affect the stability

 

[sae-7125]

it would be interesting to measure how LCR variances with speaker cables, interconnects and source device output impedance (preamp output or whatever) change the oscillation behavior that has a habit of burning up the txf primary (not an easy repair). one forum post, either echowars or another, indicated the sensitivity when positioning connection wires inside the chassis (not much breathing room). perhaps a family pack of ferrite beads strategically placed would help.

 

[Thierry]

Hi,

I have bee reading this thread since I was asked to repair a dead Kenwood L-07M.

Two Sanken outputs, Q3 and Q5, were fried (2SA747A, 2SC1116A), along with Qe11 NPN driver (2SC1913).

The original transistors being unobtainable I decided to pickup and try replacements. Those are the ONSEMI MJ211193G and MJ211194G (https://eu.mouser.com/datasheet/3/101/1/MJ21193-D.PDF)

Luckily enough, they seem to be perfectly suited to this amp, as shown in the attached oscillograms. Amp is perfectly stable and sounds as nice as its counterpart.

I hope it helps one who is seeking replacements.