Durability of Leach Amp (how mean can I be)

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hi all!

I've blown a hand full of output transistors (and others as well) in my attempts to get a Leach Amp up and running. The first ones went away with a big pop when I powercycled the amp really fast. (off, wait one second, then on again)

The transistors I had was of the type earlier discussed in a recent thread about counterfeit (fake) Motorola MJ15003/MJ15004, so after a couple of tries I just gave up on my local supplier and ordered some from a more reliable source. My new ones are branded with the "ON" logo instead of "Motorola", which I believe is a good thing.

Since my last attempt was so _unsuccessful_, I'm not sure if the new amp (new PCB's, new circuits) will be just as fragile, or will I be able to put my amp out in my living room? In my workshop nobody else have access to it, but if I have it somewhere else, my family will most likely be tampering with it.

Is the Leach Amp in general really that sensitive and break for sure if I powercycle it too quickly, or was it just my last one with the "fake" transistors?

Retired diyAudio Moderator
Joined 2002
Just an observation on the leach amp... (assuming you have real parts)

Dr. Leach has had his first leach amp running every day for the last 30 years with no problems. It is a solid circuit. I see it everytime that I go to his office. He turns it off each night at 9pm and on each morning at 11am. It is the same as the one in the original article. See the picture in the article:

Build a low tim amplifier ('76)

I have talked to others who have used theirs daily since the 80s with no problems.

I do not think that the circuit has stability. I have ran mine constantly for over 2 months with no problems.

Well, I agree with you, that the amp (if built with proper parts) should last long (for decades), but my question is on how mean I can be, turning it on and off a couple of times.

I don't see a problem with the powercycle if the filtering caps are fully uncharged, but since my last amp didn't make it very well, I'm just curious on what will happen if a four year old kid starts to fiddle around with the power switch.

I've got a whole bunch of the output transistors (including the 2n21193 and 2n21194 (that someone said to be more durable) laying around now. After the last disaster I ordered some fifty devices.

If the power supply is large with alot of capacitance and you cycle the power repeatedly, the inrush current could blow some fuses, diodes and perhaps damage the transformer .... if these problems are dealt with promptly, no damage should be done outside of the power supply and maybe the mains fuse which would probably blow.
I think you should try some inrush suppressor on the AC line

I sugest you to try with a power thermistor as seen in the DIGIKEY catalog under the reference CL 60

If a kid plays with the main AC switch it shouldn't be a problem after implementing it
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.