Spectro Acoustics

[Robin]

We used very standard panel mount fuse holders. I would try E-Bay or some of the online electronics stores. Heck, Radio Shack may even have them?

[1ajs]

has a lip on the cap that extrudes into the holder and the metal part of the cap is longer then any fuse holder i have ever seen ive gone through all my 40 yr old computers and such hoping to find one even looked at new stuff none of them seem to match thought i would ask
also tried local repair shops none of them have or seen one quite like it


just noticed the low searial  m0028 could be meaningless but could be neat history i have no idea

[Robin]

The 500SR used 3AG fuses. Very common. You can replace these fuse holders with any panel mount fuse holder meant for 3AG style fuses.
The 0028 serial number means it was the twenty eight one built. Pretty low serial number.
Nice amplifier.

[Sardobang]

This is for boB, Robin or any other Spectro Acoustics team members.

I love old tube and solid state gear (grew up w/tubes and ham radio) and am now rebuilding the SA 202 power amp.  Nice vintage piece without much damage so far.  I've read every post I can find, and thanks to you guys I got the schematic.  However, the 202 has a clipping meter whose circuit I cannot find.  I think I can guess how it works, but it would be nice to get the schematic for this little circuit.  Any help would be appreciated.

Jim aka Sardobang

[Robin]

I do not think we have a schematic of the clipping indicator circuit. It was very simple though. It has a neon light and a transistor or two. If it doesn't work, try replacing those parts. The transistor was nothing special and part numbers should be on the parts. I believe the parts are on a circuit board right next to the neon lights. Do the clipping indicators have a plastic back to direct the light forward?
We contacted a major plastics supplier in Seattle early into production on the P202. We needed some thermal form type of plastic to continue production of the light shields. The plastics salesman asked us what type of thermal forming machine we were using. We weren't quite ready for this question, but we answered him truthfully and waited for the laughter. We told him we were using a toy machine made by Mattell! To our surprise he said that the toy machine was actually quite good. We used that toy machine for years until the P-202 turned into the 200SR and we no longer required Clipping indicators.

[boB]

I don't know what the circuit was behind the front panel but on the scamp module schematic,
Q3 is the clipping sensor in the upper right corner.

I think the "toy" was called a Vacu-Form ?

[1ajs]

aww fooy the 500sr right channel just faded all the sudenl to realy quiet guesing recap time?
got any electrical drawings and recomendations on what i should be using for replacement caps?

[boB]

aww fooy the 500sr right channel just faded all the sudenl to realy quiet guesing recap time?
got any electrical drawings and recomendations on what i should be using for replacement caps?

Did you try smacking it ?

If the caps somehow go away (stop being good capacitors), the rail voltages should be different plus and minus voltages.
I think the voltage was something like +- 80 volts ?

Might be a bad connection somewhere or a bad volume pot if the audio just kind of faded down behind your very ears.

[1ajs]

after pulling out the 2 moduals and cleaning and checking them over its all working in fine order now. and the mild hum i was having is completely gone. really enjoying the design of the 500sr and doesnt run stupid hot like the dynaco qsa300 i used to have.. witch is nice for summer use. sept in the winter i want the heat o -40 winters

counted 5 stamped names so far
ZORRO & DJ also found some of the boards were not stamped by anyone or signed as far as i could tell

thanks for your opinion
and the history of the company
also just noticed the link to the schematics for the 500r sr stuff sweet wish i had earlyer.
txs again

[onanparts]

My 500SR finally made it to the bench.. First up is a very good cleaning!

Found a few names had not seen before. Tinker Bell & Short Cakes. 

And forgot about an old ad I had for it.

Was going to replace the 100K Ohm level pots but the ones I got do not have enough thread length. 

[Robin]

Short Cakes was a short cute blond lady names Suzie. She was bob's girl friend back then. Tinker Bell was a cute little red head. I rented a 23 foot camping trailer from her dad and lived in it.
For some reason we had a lot of very cute girls at Spectro?
Those Spectro transistors are actually MJ15024 transistors.
The 500SR is by far my favorite amplifier. I wish I had one!
The lights were very well done.

[onanparts]

Short Cakes was a short cute blond lady names Suzie. She was bob's girl friend back then. Tinker Bell was a cute little red head. I rented a 23 foot camping trailer from her dad and lived in it.
For some reason we had a lot of very cute girls at Spectro?
Those Spectro transistors are actually MJ15024 transistors.
The 500SR is by far my favorite amplifier. I wish I had one!
The lights were very well done.

Who was in charge of hiring those "cute girls" ? 


Since you mentioned the transistors....

The specs in the manual, FTC etc. are all at 8 ohms. But under output capabilities minimum recommended load is shown as 4 ohms.
I know the protection circuit should kick in at loads less than 2 ohms but this is my question:

Why no specs at 4 ohms? Higher THD numbers? The 70's were all about watt wars and THD etc. The only speakers I have that are rated to handle the 500's max output are 4 ohm JBL's.

Note: My ears can't hear the difference between .005% THD and .25 THD etc. 

Just wondering....

[Robin]

FTC ratings were to be done into 8 ohms. I do not know why we didn't also rate them into 4 ohms. The amplifiers work just fine into 4 ohms. Lots more power too.

[JimPat]

  Hello, I am new to this forum. I hope I have posted in the correct place, please forgive me if I've done wrong.
  I recently purchased a Spectro Acoustics Model 202 amplifier and preamp at a local thrift shop for just $20. I was very excited as I love old amps from this era. My wife was probably not as excited as me. I just tell her that they all do something different so I need them all.
  Upon hooking the pair up I discovered that one side of the preamp is not working. I put it aside and used another preamp I've got for the time being. The amp sounded fantastic, probably the best I've ever heard, up until Friday evening when it shut down. I investigated the fuses and it seems that the one nearest to the bottom has blown. Please, bOB and or Robin, please help if you have time, as I really love this amp. I am using one of my old favourite amps for now, a crown d150a, and I miss the Spectro already !! I am posting from Vancouver, BC, Canada and had never heard of Spectro Acoustics until I found these two gems. I've read up on the history, cool stuff! Now I wish this cool amp would run again. Please help if you have time, thanks in advance.
Best Regards,
J

[CDN-VT]

Jim , If you get a response & need a go between , I live in WA & BC and travel monthly . I can only help if no money/ value  is exchange !!
FREE !


I'm just putting it out there , if I may help .

VT