Spectro Acoustics

[Ingot worx]

So interesting hearing all of this history right from the guys that designed and built these products. I have had Spectro stuff since the very beginning. I had a 217 a 200 series amp and a 210R. I kept the 217, and now I just picked up a second one (my favorite sounding preamp of all time). I also have three versions of the 210 now.

I just picked up a very tired 202 amplifier with the midnight blue logo graphics on the faceplate. I decided to recap everything and upgrade the connectors etc. I stumbled on what look to be four three leg transistors? The are attached to what i am guessing are small heat sinks (two on each driver board). The parts are so old now that only one of them had any visible markings on them. I have tried to find anything that resembles the part numbers and no luck. I was hoping that possibly someone here would know what these are and what would be a suitable replacement for them?

Thanks in advance.

[Robin]

That is indeed a very early unit. We switched to different driver transistors and power transistors later on. The replacement drivers would be 2N6474 and 2N6476. The power transistors switched to Motorola MJ15024.
All of those are still available.
Good luck with your amp. We were just dumb kids back when we built that stuff. We really didn't understand how good and simplistic the gear was.

[Ingot worx]

Robin. Thanks so much for this information. Greatly appreciated. Is there much difference between the 2N6474 and the 2N6476?

I think what you did back then was pretty impressive. The products were superb, and they brought great hi fi to people at an affordable cost. I still remember the quote from Len Feldman that was included in the 217 brochure "The little unit tends to dispel the myth that a really superior separate control unit preamplifier has to cost a small fortune".

Someone had to design the electronics circuits, parts had to be sourced and purchased, metal fabricating and artwork, logos, names, distribution, marketing. This is a huge undertaking to produce something like that, and at that level of built quality. The preamps and the EQ's are still going strong today. The Alps pots in the 217 are top notch. My 202 amp was worked on by a guy called "Little Diablo" He left his sticker on the power transformer.

Thanks again for the help Robin.

[boB]

Hello Ingot !

FYI, here is the schematic for the amp module.
The original module did not have the op-amp in the input
and had a 27K Ohm feedback resistor rather than the 8.2K.

http://fusion.midnitesolar.com/spec202a.gif

and the LED circuit for the 200SR...

http://fusion.midnitesolar.com/200SR-LED-circuit2.gif

The 2N6474 and 2N6476 were NPN and PNP complimentary pairs for the drivers.

boB

[Robin]

Yes, we did design circuits and products, buy parts, stuff boards, test units and all that. But remember boB and I were still pretty young back then. All that work tended to get in the way of drinking beer and chasing skirts. Now we are too old to have that kind of fun anymore so we just work.

[Ingot worx]

Hello Ingot !

FYI, here is the schematic for the amp module.
The original module did not have the op-amp in the input
and had a 27K Ohm feedback resistor rather than the 8.2K.

http://fusion.midnitesolar.com/spec202a.gif

and the LED circuit for the 200SR...

boB....thanks so much for that information. I will post some pictures of the amplifier when i finish everything. My first Spectro amp had an all mesh cover on it. This 202 is thin anodized aluminum with a few vent slots near the output transistors.

http://fusion.midnitesolar.com/200SR-LED-circuit2.gif

The 2N6474 and 2N6476 were NPN and PNP complimentary pairs for the drivers.

boB

[Ingot worx]

Yes, we did design circuits and products, buy parts, stuff boards, test units and all that. But remember boB and I were still pretty young back then. All that work tended to get in the way of drinking beer and chasing skirts. Now we are too ld to have that kind of fun anymore so we just work.

You guys are pretty modest. never too old to chase skirts....but harder to catch now. 

The Spectro stuff will have a lasting legacy. The 217 is really an inventive design with the cartridge loading section. The sonics are as good or better than the best available today. And it's built like a tank without looking like a tank. It's like the "MiniMoog" of preamps.

[Ingot worx]

After completely gutting my 202, I decided to replace everything except the power transformer. The way this thing was designed is beautiful. A lot of fun to work on.  I decided to recap my 217's  and then I looked at trying out new op amps that weren't available back in the day. I love the sound of the 217, but I have ordered some new ones to try. Then I noticed that the faceplate is separate from the base chassis. That means rack or non rack, and make your own. Like the 202, the 217 is all right there. nothing hidden, even the pC mount rca connectors can be replaced easily. It disassembles easily. No doubt designed to assemble just as easily. I spent a couple of hours designing a new front panel. (not finished yet). I will do the same for the 202 so that they both look like cousins. (which they are). The 217 that I have in my office ( I spend a lot of time there) is running into two Rane ME30 graphs ..into a Hafler DH220 and then into a pair of EAW JF80's.. For me it's a magic combination. The 217 is a huge component of the sound, so it will be interesting to find out how more modern rev op amps factor into it. Quite possibly I will end up keeping the original 4136PC.

[Ingot worx]

My Gold 217

[boB]

Ingot, I LOVE that new screen job !  Looks nicer than the original !

boB

[Ingot worx]

boB, Thanks for the comment. I wasn't sure if this would be sacrilege or not. I'm waiting for some parts for the 202 and I'll post some pic's of it when I'm finished (hopefully there won't be any smoke).  I'm using new 18000 uf caps and i installed a higher rating bridge rectifier. Is it necessary to use a variac when I first plug it in? or does this only matter with tube amps?

[boB]

boB, Thanks for the comment. I wasn't sure if this would be sacrilege or not. I'm waiting for some parts for the 202 and I'll post some pic's of it when I'm finished (hopefully there won't be any smoke).  I'm using new 18000 uf caps and i installed a higher rating bridge rectifier. Is it necessary to use a variac when I first plug it in? or does this only matter with tube amps?

Variacs are handy for these types of things either way, but, I think that if you have a fuse in there, that should be enough.

The larger caps ~may~ have more of a tendency to blow with the greater turn on surge though.  For that reason alone,
it might not be a bad idea to use the variac I suppose.

boB

[niel]

the caps themselves or the fuses? i was into using a bit more capacity in an old lafayette receiver/amplifier to try an ease the pumping effect from the power supply when one channel draws heavily causing a bit of thd in it due to the common supply. i didn't get too far with it though and lacked the equipment to see the results of my efforts. ideally, separate supplies should be used to eliminate this pumping of the supply and thd you don't need. it was a quad amp setup (remember those?)

anyway, if there is a problem with the cap values you have chosen you can either go closer to the original design caps or place a tad of resistance inline to the caps to act as a bit of a limiter.

[boB]

the caps themselves or the fuses? i was into using a bit more capacity in an old lafayette receiver/amplifier to try an ease the pumping effect from the power supply when one channel draws heavily causing a bit of thd in it due to the common supply. i didn't get too far with it though and lacked the equipment to see the results of my efforts. ideally, separate supplies should be used to eliminate this pumping of the supply and thd you don't need. it was a quad amp setup (remember those?)

anyway, if there is a problem with the cap values you have chosen you can either go closer to the original design caps or place a tad of resistance inline to the caps to act as a bit of a limiter.

I meant the fuses might blow because of the surge that charges up the caps.

[Ingot worx]

boB, thanks for the advice. I will use the variac when I get ready to fire it up (someone also mentioned using some light bulbs in series as an alternative).

here's where I'm headed with the look of the 202. It has such a forward thinking design already with the clever backlit midnight blue logo. That was really well done back when LED's were almost unheard of. When that thing is on it really looks appealing.

I'm just tweaking what already exists (you guys did the heavy lifting and invented the concept). I am just going to do a simple overlay on a new faceplate with some tempered glass or plexi and FX lighting gel behind to get the color (I'm going with a gold for now, but I like the blue a lot too. I won't use through bolts to fasten it all, just some hot melt glue for the covers behind the faceplate. The grey overlay to trim out the whole thing could be anodized aluminum or powder coated steel (very thin), or you could do a 3D print of something with 3d contours.