Spectro Acoustics

[Westbranch]

amazing they are almost straight!  must have been 'gently' handled by the delivery agent...

for future reference, was it a bubble envelope?

[onanparts]

amazing they are almost straight!  must have been 'gently' handled by the delivery agent...

for future reference, was it a bubble envelope?

Yes on the "bubble envelope" 

[onanparts]

It's alive!  Replaced the drivers and power transistors last night on the dead SCAMP. Brought it up slowly on a variac......no magic smoke! 14mv DC on the repaired SCAMP output and about 67mv Dc on the other one. Want to get that a bit lower and might try the resistor trick boB mentioned in a prior post.

It was late and I was getting tired but I did a brief test with some input. LedZep sounds much better in stereo!! Next step is replacing all the caps and see about making up a new faceplate. 

[onanparts]

The way it should be...

[Robin]

The display we did on the 200SR is pretty cool for the time. How does it sound?

[onanparts]

The display we did on the 200SR is pretty cool for the time. How does it sound?

It sounds great! Been running all day at low volume and keeping an eye on temps etc. It's staying cool but I'm uncertain on how to adjust the bias? Tried using the same procedure as the 500SR manual shows, but no difference on the fluke voltage wise. Did not turn the pot on one side much either direction and ended up putting it back where It was.

I did crank it up to all of about 25-30 watts for a short period and again no abnormal temps. At low volumes all 8 of the 15024 collectors are at 80-85F.

The drivers on the unrepaired SCAMP are about 10-15F higher though than the repaired SCAMP side.
105F Vs. 115-120F. Not sure if that's a big deal or not. Ambiant room temp is 78F right now and the big heatsinks on both sides are cool to the touch.

No distortion, very clean audio. At least to my ears. 

Display is still KOOL today! Timeless design..

[Robin]

If my memory serves me correctly, we used to set the bias pot using a distortion meter. Too much one direction and the Scamp runs cool, but has higher distortion. Too much the other way and it runs too hot. I don't think it would hurt to try to make the repaired Scamp run the same temperature as the old one/ Just watch for run away temps.

[boB]

If my memory serves me correctly, we used to set the bias pot using a distortion meter. Too much one direction and the Scamp runs cool, but has higher distortion. Too much the other way and it runs too hot. I don't think it would hurt to try to make the repaired Scamp run the same temperature as the old one/ Just watch for run away temps.

The ear also does (usually) a pretty good job of detecting distortion.  In this case, the bias controls zero-crossing distortion
which ~should~ be most discernible at a low-ish level because then, the zero-crossing will be more of a signal compared
to the whole signal.  Applying a sine-wave to the input at a frequency of around a couple kHz should be good.

Could make one on the computer OR download a .WAV file from the internet somewhere.  Just make sure it's a good sine-wave
used.  Then, turn down the playback volume until you can just hear it and then turn it up a little bit more.
Adjust the trim-pot until you can hear some distortion.  If you can NOT hear any distortion, then maybe bias turned
down is good enough ?

There may also be some speaker noise or rattling in some cases.

The newer "modified" SCAMP modules that have the 8 pin op-amp near the input of
the module are the ones with more negative feedback, which makes the crossover
distortion better with a given trim-pot setting.  That trick significantly reduced the THD
including crossover distortion.

It may be that these modified amp modules are so good that you actually CAN turn the trim-pot
down all the way or almost all the way.

Your value may vary with age etc....

boB

[onanparts]

Thanks boB & Robin! I'll give the sine wave to the input a try and see if my old ears can detect any distortion. 

I did run it again all day today at an increased volume...almost enough to rattle the windows and no abnormal temps. Was going for a moderate stress test and it's holding up fine.

During the "stress test" ....I came across some more SA "GOLD" literature as luck would have it. Here it is...First up the 210

[onanparts]

Have to mutli post to get these to fit. Rest of the 210.

[onanparts]

Next up the 101B

[onanparts]

101B part 2

[onanparts]

Next up the 217

[onanparts]

Time for some amps....202

[onanparts]

And now....the 500/500SR.