Spectro Acoustics

[Robin]

That's a great price for the amp. A couple of months ago, I bought one on E-Bay for our PA system at MidNite. I paid more that they sold for 35 years ago.

[onanparts]

Well........sure sucks when people have no idea on how to properly pack heavy items. Particularly vintage/classic audio gear.

What was a very nice condition 200SR showed up with severely bent rack mount ear ends. Bezel/display area is OK though. Right SCAMP is DOA. left side is good but Led Zepp in Mono does not cut it.. Pulled the bad SCAMP last night and will check the transistors today.

Robin, you posted earlier those are/were Motorola MJ15024 if I recall? Same ones used on the 500SR? And Robin when cleaning out the garage don't forget about that NOS 200SR double faceplate in a box back in the corner......

boB thought maybe it was Jeff at Optimum that did those plates for Spectro way back but Jeff says it wasn't him.

[Westbranch]

parcel loader thinking to self...." Hmmm, it's heavy!  Must be tough.  I'll test that for him...."

[onanparts]

parcel loader thinking to self...." Hmmm, it's heavy!  Must be tough.  I'll test that for him...."

Test is right! Seller was kool and refunded about half so at this point I'm in it about $50 so a decent reduction in pain. Still ticks me off when careless folks are allowed to leave the hospital after birth.

Found two of the output transistors on the SCAMP board dead. I plan on rebuilding both SCAMP's since I'm in this far anyway. All the caps too.

Robin, do you still have the schematic in PDF for the 200SR?

[Robin]

I do have some sort of 200 schematic. All I have to do is find it! The transistors are indeed MJ15024's. We usually had to replace the T0-220 drivers on the stand up heat sinks also.
I will keep looking. We have those transistors at MidNite, so if you have trouble finding them, come on up and we will give you some.

[Westbranch]

so who was this "boB was Here"??

[onanparts]

I do have some sort of 200 schematic. All I have to do is find it! The transistors are indeed MJ15024's. We usually had to replace the T0-220 drivers on the stand up heat sinks also.
I will keep looking. We have those transistors at MidNite, so if you have trouble finding them, come on up and we will give you some.

Well dang twist my arm! Planning a trip up maybe next week and will bring that HD I loaded up with a gazillion tunes for your PA.

Noticed somebody put a bridge on the bad SCAMP, not there on the good one and doesn't look like anything spectro would have done.... Couple pics of it.

[Robin]

Here are a couple of diagrams of the 200. There is one more that may be a duplicate. I will send it in a separate message. Files too big.
You might be able to talk Bob into helping to fix your amp. Bring it up.

[Robin]

Here is the last 200 diagram I have.

[onanparts]

Here are a couple of diagrams of the 200. There is one more that may be a duplicate. I will send it in a separate message. Files too big.
You might be able to talk Bob into helping to fix your amp. Bring it up.

Thanks for finding those Robin! The only thing I would need to bring up would be the SCAMP that has been modified with that wire bridge. boB should be able to finger it out just seeing it. pics here may be enough too. R n R bad devices and old caps is easy but when somebody has gone off the reservation with the original design is where I get lost...

[Robin]

Bob may not be able to do anything without the rest of the amp. He may be able to get it running. I do not think those other two parts were ours.

[onanparts]

Bob may not be able to do anything without the rest of the amp. He may be able to get it running. I do not think those other two parts were ours.

I know the power supply and other SCAMP are OK. Wired up a 220R to my 217R and cranked it up. Sounds great and display functions correctly. Just the one dead and bastardized SCAMP.

I catch him several days a week in the mornings on his way in and we swap lies on one of the VHF repeaters near Everett. I'll try to catch him tomorrow or early next week and see what he thinks. Did talk yesterday about it briefly so he is in the loop.

[boB]

Just for the record, that resistor in the tubing soldered to the back of the board was most likely
done at Spectro.  It is a resistor tied from one of the power voltage rails to one of the diff-amp
inputs to mitigate too much DC offset on the output of the amp.

I remember this trick for several amplifiers, not just Spectro Acoustics.
But I seem to remember that we did this at Spectro once in a while.

boB

[onanparts]

boB had looked around but did not locate any of the MJ15024 output transistors. He gave me a couple of great sites to check though, one is https://octopart.com/ you can punch in almost any device number and they return numerous hits on other sites that stock them. Thanks for that link boB!

I stumbled on an ebay seller that had them at a good price and their feedback was 100% excellent history etc. so I purchased 10, 2 spares just incase...along with one of the two drivers they had available. 2N6474. Found on ebay also what "appears" to be original RCA 2N6476 drivers. How do you really know?

Anyway....here is a pic of the 15024 tranny's as received, shipped in an...envelope! Seller replied promptly and is sending replacements in a "box"! Yes, I could straighten the pins but that's a pain and several are tweaked badly. Plus I would not trust them.

[Mtn Don]

Now you'll have lots of spares...