JLH 10 Watt class A amplifier

[cumbb]

Evidence photos;-)
To close the lack of imaginations - repeatedly;-)

 

[Ian Finch]

..... 32w disipation for a bd139 like transistor is like melting hot capsule dont you think? ...

Fair comment but we can't be sure what current cumbb is talking about - could be for both channels....or, uh.. something different/relative,-)

 

[sergiu2009]

I think it depends on many things (passive and active components, psu, wiring and tastes) and as a matter of fact i do have a 69 jlh with a bunch of upgrades aded and listened to them both and at the end of the day i cannot choose beetween them. I like them both. To me, if i where to build one of them again the winner will be the jlh but not because of its sound, its just because i'm more laisy now and i dont have to sort and painly match tons of transistors like the hiraga.
None of them is sounding 'very very ugly' neither to my ears neither to 30 other people who compared them to push pulls pentodes and triodes at a valve amp meeting in 2017 in Romania... They just sound very very good and have a different sound signature. You cannot choose the best, you just want them both.
Cheers
Sergiu

 

[cumbb]

Speakers and sources? Which do you use?

 

[cumbb]

Bootstrap removed;-?

May be, the JLH runs after warm up with just a trimmer and a resistor. Per switcher the resistors ...-? Audible the difference of more or less circuits-salad is;-?
"Electrons"-"physics"-?

Earache at a glance in a Krell or ML or ... power amp;-))) Or multiways or soooooo many many, much much more;-)

 

[fredbloggstwo]

Evidence photos;-)
To close the lack of imaginations - repeatedly;-)

Cumbb, there is no lack of imagination, belief of disbelief. I think there is a problem about communication.

We come to this site because we have an interest (some might say a passion) about building and listening to audio equipment.

We read/listen, discuss and learn from each other. To do so we communicate and share. If you cannot communicate and share with the community, (which is genuinely what other members are asking you to do) I think you are wasting your (and our) time with you posts.

Regards

Mike

 

[gaborbela]

Cumbb, there is no lack of imagination, belief of disbelief. I think there is a problem about communication.

We read/listen, discuss and learn from each other. To do so we communicate and share. If you cannot communicate and share with the community, (which is genuinely what other members are asking you to do) I think you are wasting your (and our) time with you posts.

Regards

Mike

I agree with you, I follow these tread and I would love to see Cumbb schematics also. Genuine interested but it is up to him if he decides does not share that is too bad to all of us. I want to learn also.

 

[freddi]

hi Ian Finch - fwiw I ordered an amp "like" yours as was less than $200 shipped. Is there a schematic which likely represents most of the amp? - the seller had posted a FET schematic.

would it be pretty much - ? http://www.startfetch.com/jlh/jlh-1969-amplifier.gif

What would you estimate for the case and heatsink temperature relative to normal room temperatures after an hour or so of heating? I hope some fans under it can keep it going for awhile.

my right hand stays numb a lot of the time - just can't do much of anything anymore

 

[Ian Finch]

....... - the seller had posted a FET schematic.
would it be pretty much - ? http://www.startfetch.com/jlh/jlh-1969-amplifier.gif....../QUOTE]Yes, that's the schematic of the basic amplifier without the power supply or capacitance multiplier filter that are included in the clone. Parts now fitted will be substitutes if its an honest clone. If the smaller transistors look like 1960s metal case transistors that are strangely brand new looking, they may work OK but they will be fakes, good or bad. The semis in my clone may be all plastic types but likely to be fair substitutes.

Today the indoor temperature rose to a humid 33C and the thick front panel was up to 46C. The heatsinks were hotter by 9C, about 56C in the centre. Of course, it depends where you live as to how hot it will get but in the UK for example, temperatures seldom go much above 22C in the Summer and there wouldn't be much of a problem. I think slow fans are probably the solution, boxed in one or two little housings under the amp and supporting it, exhausting towards the sinks and upwards, but out of harm's way. It only remains to check that the volume pot, doesn't lose its lubricant and become noisy over time so I'm planning on insulating the shaft on mine - maybe it will help.

Have you looked at The Class A Amplifier site I linked to? It's archived here from the main index under articles and information. Tons of details, originally from JLH and from later contributors too. Lots of suggestions for DIY builds of most versions. You can also download the original Wireless World magazine articles archived at this great US site - virtually a complete magazine library: WIRELESS WORLD: Technical and experimenter magazinefrom the UK 1913-1986 'hope this is helpful.

 

[Jonathan Bright]

Thank you Ian for WW link.....very helpful. I am old enough to recall the '70's and 80's where you were allowed access to the "stacks" at several libraries at tertiary institutions in Melbourne and photocopy WW and JAES etc to your hearts content. Those days are gone. Here in Brisbane I think I can buy copying rights at UQ for around $240 per annum at least that was the cost 5-6 yrs ago. (They have a good collection of HFN/RR).

Thanks again. Jonathan

 

[Ian Finch]

Hi Jonathan, glad you found what you were looking for and lots more, I imagine. I found it quite by chance, after searching through Keith Snook's "DC to Daylight" website collection of WW magazines without a result.

 

[sergiu2009]

Thanks Ian. I have searched in the past for this collection without any result, but now i'm really glad that you shared it. Thanks!

 

[fredbloggstwo]

.....

You can also download the original Wireless World magazine articles archived at this great US site - virtually a complete magazine library: WIRELESS WORLD: Technical and experimenter magazinefrom the UK 1913-1986 'hope this is helpful.

Hi Ian

thanks for posting the Wireless World archive link - what a goldmine of electronics 'stuff' and trip down memory lane.

Best regards

Mike

 

[Ian Finch]

'Seems we're onto a good thing here - enjoy and save what you need to, as free library sites may not to be up forever.

 

[stevec67]

this jlh amp kit is a PNP and i do not know if stevec67 is able to tell the difference between a pnp jlh and npn.
I risk having trouble explaining him in English, could you please?

I think I can tell the difference. I have a schema, it shows 1 x PNP tranny on the input stage, the input feeds straight onto its base. There's another NPN making up a Darlington pair with the lower 2N3055 and the upper 2N3055 makes up the other half of the voltage divider that drives the speaker. I imagine that this makes it an NPN version.

The 3rd 2N3055 is part of the PSU, it's an odd arrangement comprising a Darlington pair with a heavy bias current to the base of the small transistor. What's the point of this? Surely it's just going to turn on permanently, in which case why bother?

Finally Huggy, don't worry about communication. I've lived in France, I speak the language. Ne t'en fais pas, si besoin y est dis le moi en francais. .

 

[Ian Finch]

.....The 3rd 2N3055 is part of the PSU, it's an odd arrangement comprising a Darlington pair with a heavy bias current to the base of the small transistor. What's the point of this?....

I believe the third power transistor on the clone board is used in a power supply circuit referred to as a "capacitance multiplier". This acts like a large, low impedance filter cap on the single power supply. For the purpose, it's more efficient than a voltage regulator at cleaning up the power supply noise.

With such a simple amplifier circuit running at constant high current, a clean power supply is a must if you want low noise audio. In fact, the original April 1969 WW article has the capacitance multiplier circuit included as fig 9b. Archives of the magazine and the articles have been linked a few times here, over recent pages.

 

[nigel pearson]

I went to help repair a 1978 ( ? ) Luxman L55a. I tested the power supply and found 57.5V on each side which says it could be OK. Next a base emitter base collector diode test on the output transistors ( 20 MHz ft ). They looked to be OK. Do collector to emitter also ( I forgot ). DC offsets were 1 to 2 mV. I saw some 4558 op amps. The next thing above 741. I think they are DC servos. The input is JFET and the preamp is a fancy mini power amp. How did it sound? To be honest it was nothing special. It looked so much like the threads on DIY Audio that don't interest me. Having spent my life with similar designs to repair I don't get excitied when I see them. That's not to say I believe there won't be a good one out there.

The amp looks hot roded by the owner. No, that was Luxman. I wonder if they were cloning the amplifiers of the day and were fighting hard to get back to their better past. There were plastic films capacitors everywhere when an electrolytic was used ( try it, it will do no harm, 1uF 250V types work well ).

As everything was going nowhere I soldered directly to the power amplifier which is very easy on the L55. Same with the speakers. It worked. For some reason the previous owner had removed the speaker ground wires ( ? )

Not happy with this I looked at the 1969 Luxman SQ707. 17 watts, 1% THD and almost exactly like a Leak amplifier. Luxman, why didn't you copy JLH? The L55 diagram I found was hard to read. It looks like the simplest output triple possible. That is Douglas Selfs better Darlington quads which clear out the base charges ( and simplest ) only with 6 cascaded followers.

I can now see how Meridian and Naim became sucessful, the market had gone a bit wrong. Sadly some still seek this type of perfection. To me it''s like over cooked food. An exception I can name was Sony TA5650 as long as the bias was set high.

 

[stevec67]

Thanks Ian. Never heard of a capacitance multiplier before. The WW mags are fascinating, must print off the relevant bits and have a close read. I'm pulling the bits together, a friend has given me an old AV amp with a useful 16-0-16 toroidal, so I shall steal that and the case. The trafo is good for a power consumption of 140w so that's enough and 32V is good enough. The heat sink is a little weedy and only on one side but I have a better one and can do some construction to make it work. This promises to be interesting, I need a trip to Farnell and/or Maplin for the bits. One bit of luck, I have an old 2N3055 in the bits box from Year Dot, I imagine that will be OK.

 

[huggygood]

Finally Huggy, don't worry about communication. I've lived in France, I speak the language. Ne t'en fais pas, si besoin y est dis le moi en francais. .

 

[cumbb]

Sometimes the eyes do listen ...-)))

A "JLH" too;-)