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John Linsley Hood Class A or similar

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I would use modern high Ft devices with good gain linearity (and in fact did). The best Japanese power transistors are in a completely different league to all others.
Obviously this advice is not for the novice as you will need to know the best practice in layout and how to tweak the compensation to suit these parts.
2SC2987 are the ones I used in mine.
 
stevec67 said:
Thanks gents. What do you think about these offerings:
https://www.ebay.co.uk/itm/2016-1969-amplifier-class-A-amplifier-HIFI-Board-high-quality-MOT-2N3055-diy-kit/272270848443?_trkparms=aid=222007&algo=SIM.MBE&ao=2&asc=49138&meid=5d3cbd5c55ad4d1eb481d57df34427c4&pid=100005&rk=5&rkt=6&mehot=pp&sd=172237677755&_trksid=p2047675.c100005.m1851
Of which you would need a pair.
Or is this style better (note different O/P transistors)
http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=141684499920

I don't mind using either kit as a basis and binning any dodgy components in favour of something better when I get it under way.
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http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=291643698608

I would expect fake transistors with the cheap kits.
 
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I feared as much. Blank PCBs do seem a safer way to go. I have no fear of buying the bits at Maplin/Farnell here in Leeds. Last time I went to Maplin for some bits I handed the guy a shopping list and off he went. An hour later he came back with 90% of what I wanted, and the bill was £5. Somehow I don't think Maplin have this bit of their business model worked out. Unless their view is that they employ 3 or 4 people in the shop regardless, and if one happens to spend an hour picking a £5 order then that's £5 better than him spending the same hour picking his nose.
 
Fake transistors are rife on eBay. I'd gladly pay a premium for a set (4+4) of genuine NOS Sanken 2SA744 and 2SC1402 or 2SA747 and 2SC1116.
 
:D There used to be a really fit bird serving at the Farnell trade counter in Leeds as well;) It's about 10 years ago since I was last there though.... a regular at one time..
 
James said:
Fake transistors are rife on eBay. I'd gladly pay a premium for a set (4+4) of genuine NOS Sanken 2SA744 and 2SC1402 or 2SA747 and 2SC1116.
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It uses all NPN output devices... but not in the usual way! It can be described as single ended push pull o_O
 
stevec67 said:
I feared as much. Blank PCBs do seem a safer way to go. I have no fear of buying the bits at Maplin/Farnell here in Leeds. Last time I went to Maplin for some bits I handed the guy a shopping list and off he went. An hour later he came back with 90% of what I wanted, and the bill was £5. Somehow I don't think Maplin have this bit of their business model worked out. Unless their view is that they employ 3 or 4 people in the shop regardless, and if one happens to spend an hour picking a £5 order then that's £5 better than him spending the same hour picking his nose.
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Yep, just get a blank PCB and buy the bits from Farnell or RS, MJ21193 could be added to your list of output transistors, plastic packaged versions are fine but TO3 parts look the business, particularly if they have hex bolts to the heatsink.
 
russel said:
... plastic packaged versions are fine but TO3 parts look the business, particularly if they have hex bolts to the heatsink.
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The OEM TO3 transistors in my amp are virtually unobtainium - except from pulled / salvaged parts. There are TO3P equivalents, though. Is there a clever way to adapt these TO3P transistors to fit where TO3s normally reside?

s-l1000.jpg
 
There's no stock way of doing that no... as yours is i believe class A the device to heatsink interface is especially important, also there is the matter of getting the lead out wires connected to the other side of the board without excessive lead length which would likely cause oscillation.
 
Ah, I thought not. I sense a business opportunity for fabricators to make a TO3 shell with the corresponding pair of pins, into or onto which TO3P devices can be securely fastened, electrically connected and thermally coupled. Could such an adaptive thing work?
 
James said:
Ah, I thought not. I sense a business opportunity for fabricators to make a TO3 shell with the corresponding pair of pins, into or onto which TO3P devices can be securely fastened, electrically connected and thermally coupled. Could such an adaptive thing work?
Click to expand...

I don't see why not but I can't see any business opportunity in it either..
 
James said:
The OEM TO3 transistors in my amp are virtually unobtainium - except from pulled / salvaged parts. There are TO3P equivalents, though. Is there a clever way to adapt these TO3P transistors to fit where TO3s normally reside?



s-l1000.jpg
Click to expand...

If it were me, I would use something like mj21193/mj21194 and forget worrying about getting fake parts.
 
russel said:
If it were me, I would use something like mj21193/mj21194 and forget worrying about getting fake parts.
Click to expand...
I was hoping to duplicate the exact specifications of my vintage transistors. Sanken has TO3P encased 2SA1695 and 2SC4468 as substitutes for the TO3 2SA747 and 2SC1116. I know next to nothing about transistors, but note that hFE and fT between the MJs are quite different. I was looking to get plug-n-play equivalents that won't need any circuit or component value adjustments (other than bias and DC offset).
 
TO3P packaged devices are designed to use the same mounting hole pattern as the metal case version, hence the name TO3P(lastic). No need to alter any metal work.
 
It could work but most will be TO246 or TO247 package.. very similar to3p anyway. Thermal conductivity could be an issue with this class A amp.
 
srh said:
TO3P packaged devices are designed to use the same mounting hole pattern as the metal case version, hence the name TO3P(lastic). No need to alter any metal work.
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Well, waddya know! The B - E pins are spaced identically, but how does the C pin work? I imagine that will have to rely on conduction between the mounting screw/bolt.

BTW, those wonderful Sanken trannies I got from you are still working superbly. But it's always good to have a contingency plan if they expire (touch wood).

Arkless Electronics said:
Thermal conductivity could be an issue with this class A amp.
Click to expand...
Surely if they are coupled firmly to the heatsink, they will be fine - yes?
 
James said:
I was hoping to duplicate the exact specifications of my vintage transistors. Sanken has TO3P encased 2SA1695 and 2SC4468 as substitutes for the TO3 2SA747 and 2SC1116. I know next to nothing about transistors, but note that hFE and fT between the MJs are quite different. I was looking to get plug-n-play equivalents that won't need any circuit or component value adjustments (other than bias and DC offset).
Click to expand...


Transistor gain varies by quite a lot between devices of the same type and any half decent amplifier will take this into account as far as I can see they are quite similar anyway. With regards to the transition frequency of the transistors 2MHz Vs 10MHz, if you can hear the difference in a class A design you have better ears than a bat.
 
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