J. L. Linsley-Hood 1969 Amplifier - Part 8A

This is amplifier Number 6 of this series. It seems to be the best of the series. When operated at 26 VDC it easily supplied 10 VRMS into the 8-ohm load, or 12.5 WATTS!
Part - 7D I discuss the “regulator” function and discover that it is a form of “soft start”, as wel as supplying 24 (really 22) VAC to the amplifier.
Part - 7C This is the same amplifier powered with 15VAC.
Part - 7B Here I power-Up the #5 Amplifier with a heat sink and apply some inputs and display the output on an Oscilloscope.
Part - 7A Well, AliE notified me that a different version of the venerable JLH 1969 amplifier was available. This one had an on-board power supply circuit. So, I bit and purchased two of them.
Part - 6 I try to clear up the biasing of the signal input amplifier.
Part - 5 I had great hopes for this one, it uses two FET’s in the final stage. Some damped oscillations caused by the amp were found in the input and these caused some residuals in the output.
Part - 4 This is amplifier No. 3, it was from Ebay and I have updated the Sellers info to show the vendors name. Note that the shipping was not mentioned in the video, it was $9.
Part - 3 This is Amplifier No 2, also from AliExpress, sold, by ZERO ZONE as their Model N1969. The test is what it is, pretty nice.
Part - 2 In this Part I look at the Amplifier designated as “No. 1”, a completed amplifier from AliExpress, I destroy the first amplifier and then test a second one (I had purchased 4 of them),
Part - 1 I have purchased four clones of the well-known JLH 69 Amplifier. I will test them all. One was a completed unit three were kits. I have an HP Distortion Analyzer that I intended to use but it failed when powered up, so I will be using a square wave generator and an oscilloscope for testing.
Link to files;
gswagner.com/A...

[@mickwebs]

Great Work Steve

[@mikewhelan5992]

I was an electronics student in the late sixties and built this amp after reading the original article in Wireless World. Mine had poor HF performance and I contacted JLH by letter. He thought that the reason was down to a different o/p transistor manufacturer. I recall that he favoured Motorola. I built many other amplifiers during those years. Your video brings back a lot of memories. After many years with a soldering I final gave up and bought a QUAD 303 Amp and a QUAD33 preamp and settled down to listen to music not the Hi-Fi!!!

[@cuongnguyenquoc6356]

video nice!.

[@fixnreview]

I prefer watching toturials from an older electronics veteran rather than thus young engineers.

[@bobshifimods7302]

That driver transistor looks like it's been reclaimed from another board. As others have discovered component type and quality is very important with this amp. That's a consequence of the simple construction and it might explain the difference in the measurements on these different kits.

[@macchi205]

2x2sc 5200 are you sure they are not fake transistors ??

[@michaelmounts1269]

I really love this series on the venerable "1969"...but...no review like this is complete without a test run with speakers and music...maybe give us some examples...

[@Mikere5]

The identifying number on the PCB is added by the board house when they make your blank boards.

[@bobshifimods7302]

Surely with one amp flowing the maximum power is IsqR =1sq8 for an 8ohm speaker that's 8 watts. If you can show more using your scope then the power delivered occurs because the amp has become cals AB no longer class A. The transistors used can go to 15 amps so I don't get why the amplifier has been limited to only one amp These transistors are also interesting because they have an ft of 30Mhz. On the ESP amplifier site Rod Elliot states that the output transistors for the 1996 version should not exceed an Ft of 3Mhz for stability reasons. I would have thought the same reasoning would apply to the 1969 version. There's no stability components on the schematic.

[@mikepxg6406]

His name was. John Linsley Hood. not Leslie . Mike.