I found that the PMC 649/669 devices had lower THD% in the Marsh headphone amplifier owing to higher hfe, but slightly higher noise. I think that Richard (AKA Dr. Marsh) had used MJE200/210. I sold a few hundred Marsh HPA kits with PCBs and no complaints. (I sell the PCB's at cost in respect of Dr. Marsh's intellectual property, terms which he happily agreed to!)
Good to see this topic is still very much alive. In my (successful) attempt to recreate a NAD3020 from scratch I've stumbled across this forum a little while back. In my journey to find good replacements I ended up using the actual 649/669, bought locally from a little shop here in the Netherlands (Tessatronic.nl). However I have no idea if they are genuine or not. They seem to do the job just fine though, amp is working just fine!
Just out of curiosity, I compared later iterations of that amp and NAD seems to have exchanged some of the 669's with BD139's in the 3020i version. The only thing is that they still use the obsolete transistors as drivers for the main power transistors. I did look into the MJE200/210 combo but found that the collector - emitter voltage might be too low in the power stage. So I've looked at tje MJE243/253 as a step up and those might work out too? Haven't tried them (yet) but they can be ordered from mouser.
Just out of curiosity, I compared later iterations of that amp and NAD seems to have exchanged some of the 669's with BD139's in the 3020i version. The only thing is that they still use the obsolete transistors as drivers for the main power transistors. I did look into the MJE200/210 combo but found that the collector - emitter voltage might be too low in the power stage. So I've looked at tje MJE243/253 as a step up and those might work out too? Haven't tried them (yet) but they can be ordered from mouser.
@jackinnj
I made my own PCB from the figure 11.14 of the last book edition of G. Randy Slone! I know that this thread is may be dead but I took a chance to contact you and I cannot start a conversation because my account is tagged as "Moderated".
I wonder if you still have the 2SD669 and 2SB649 available? I am ready to buy a lot of them depending of the price per unit.
You can contact me in private if you prefer. My bests regards,
Yves
I made my own PCB from the figure 11.14 of the last book edition of G. Randy Slone! I know that this thread is may be dead but I took a chance to contact you and I cannot start a conversation because my account is tagged as "Moderated".
I wonder if you still have the 2SD669 and 2SB649 available? I am ready to buy a lot of them depending of the price per unit.
You can contact me in private if you prefer. My bests regards,
Yves
That REALLY makes one wonder about them. Yes, MJE243/53 are among the many things that will work, but are not really equivalents to the Hitachi parts. They are a lot bigger, closer to the MJE1503x. The Hitachi parts are highly sought after, because their capacitances are lower than any competitor’s version (including the modern Toshiba ones like TTC004). The MJE243/53 defeat the hell out of that purpose (even though they are very good drivers). Not only the driver recommendation, but the interchangeability of MJ15003 and the C2565? They are about as far apart on the spectrum as two sets of output transistors could be these days. MJ15003 is the old-and-slow burnout proof variety, and those Toshibas were darn near the fastest things on the market. They were pretty rugged, but still nowhere near equivalent to the old Motorola. If they can get away with those kind of output transistor changes then nothing is critical in the circuit and anybody’s driver transistors will work.
That sounds great, but I can't PM you hence my profile is moderated. Can you send me a PM? Thanks!
I have also sent you an email if that address is still in use. If you can´t find it, depending on mail provider check the spam folder.
Thanks!