I got hold of a JLH 1969 PCB and I plan to finish building that amp.
The problem is that the circuit requires 2n1711, D667 and 2n2907 transistors. I can't seem to get D667 transistors for cheap. The real cheap ones are $2 for 50 pieces, so they are obviously fakes.
Can anyone suggest me a good replacement for these transistors? The pinouts should match btw
Thanks
The problem is that the circuit requires 2n1711, D667 and 2n2907 transistors. I can't seem to get D667 transistors for cheap. The real cheap ones are $2 for 50 pieces, so they are obviously fakes.
Can anyone suggest me a good replacement for these transistors? The pinouts should match btw
Thanks
Is your D667 used as the output transistor? I do not think it is suitable if so. These are (if my datasheet is correct) only rated at 1W. If you plan to run the JLH at 10W it needs a 27-30V supply at a current of 1.2A and the transistors will have to dissipate about 15-18W. They need a good heatsink as a result. Your PCB may not be ideal, but you might still use it if the output transistors are wired to the correct pin positions.
You could try TIP3055's.
You could try TIP3055's.
I think the OP is only referring to the early substitutes for the input and phase splitter semis as discussed by JLH and even these are now unobtanium. If he looks at other threads and among the many kits available, there are plenty of substitutes and a common line up of semis in kits that sounds OK and low cost, is 2N3904, BD139-10 or 16 and 2 X 2N3055.
The penultimate JLH schematic used 2SA970, 2SC3421 and 2 X MJ15003 so you can see that nothing was ever set in stone for availability and sound quality. I have used the larger 2SD669 for the 2SD667 with fair results but neither are original parts and neither would those specified in your example design have been original either. The clone design is intended for fakes!
Check all the articles over the many years since 1969 and of course, the changes continue as the old parts sources dry up: The Class-A Amplifier Site
The penultimate JLH schematic used 2SA970, 2SC3421 and 2 X MJ15003 so you can see that nothing was ever set in stone for availability and sound quality. I have used the larger 2SD669 for the 2SD667 with fair results but neither are original parts and neither would those specified in your example design have been original either. The clone design is intended for fakes!
Check all the articles over the many years since 1969 and of course, the changes continue as the old parts sources dry up: The Class-A Amplifier Site
Thank you sir ! I guess I will be replacing the transistors with 2N3904, Bc560 and mj15003.
I would also probably need a giant heat sink.
Class A runs like an oven.
I would also probably need a giant heat sink.
Class A runs like an oven.
I just happened to glace upon this The Class-A Amplifier Site - A JLH Amp for the Quad ESL57
This schematic is made for electrostatic speakers. So naturally these speakers need high current and voltage to work properly.
My question is if this design would work for conventional speakers? If so then do in need to make any mods?
This schematic is made for electrostatic speakers. So naturally these speakers need high current and voltage to work properly.
My question is if this design would work for conventional speakers? If so then do in need to make any mods?
The version to suit electrostatic loudspeakers really only provides higher current to drive the very low impedance at high frequencies of the Quad ESL type (attached graph). It does this just by adding a second pair of output transistors in parallel with those normally used and increasing bias current, so it will certainly need a much larger heatsink. Unless your conventional speakers are very low impedance and you like to play music at maximum volume, you won't get much benefit so you really don't need this level of overkill.
The ESL version is also largely based on the later 1996 version with dual rail power supplies and DC output coupling. It may depend on the other actual transistors used but the specified 2N3055 output transistors are not an easy load to drive, so adding a second pair may prove to be a poor performing method of increasing output current. A standard grade BD139 phase splitter/driver for example, will be out of its depth if tested to full power there so I have my doubts about that design.
I think that for simplicity, just substituting a single pair of MJ15003 for 2N3055 transistors and increasing bias with extra heatsinking to suit 4 ohm loads will be sufficient for any conventional speakers you might want to drive with a 10-15 watt amplifier. It will likely sound better that way too. Another issue is that with later dual rail designs, including this ESL capable one, you'll have to start with a PCB suitable for JLH 1996 or 2001 or build it the hard way on matrix board or P2P.
If this is going to be your first JLH amplifier, try the basic JLH'69 model first before spending on extra features you aren't sure of or perhaps don't yet follow what the supposed upgrades do. It can be bought as a very cheap kit and is cheap to build for a class A amplifier too. Not every design change or mod. to it is in the right direction for everyone though. Having listened to a number of versions and some quite good mods, I'm quite content listening to the original, admittedly using newer and better grade components. It has a certain synergy that allows a very simple but subtle and clever circuit to do wonders with atmospheric kinds of music.
The ESL version is also largely based on the later 1996 version with dual rail power supplies and DC output coupling. It may depend on the other actual transistors used but the specified 2N3055 output transistors are not an easy load to drive, so adding a second pair may prove to be a poor performing method of increasing output current. A standard grade BD139 phase splitter/driver for example, will be out of its depth if tested to full power there so I have my doubts about that design.
I think that for simplicity, just substituting a single pair of MJ15003 for 2N3055 transistors and increasing bias with extra heatsinking to suit 4 ohm loads will be sufficient for any conventional speakers you might want to drive with a 10-15 watt amplifier. It will likely sound better that way too. Another issue is that with later dual rail designs, including this ESL capable one, you'll have to start with a PCB suitable for JLH 1996 or 2001 or build it the hard way on matrix board or P2P.
If this is going to be your first JLH amplifier, try the basic JLH'69 model first before spending on extra features you aren't sure of or perhaps don't yet follow what the supposed upgrades do. It can be bought as a very cheap kit and is cheap to build for a class A amplifier too. Not every design change or mod. to it is in the right direction for everyone though. Having listened to a number of versions and some quite good mods, I'm quite content listening to the original, admittedly using newer and better grade components. It has a certain synergy that allows a very simple but subtle and clever circuit to do wonders with atmospheric kinds of music.
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