He said the amp would likely be worth ~$150-200 in good working order. If you don't have the end plates or bottom cover, expect less.
If he's right, it may not be worth repairing if you're going to sell it to try to make a profit. Of course, for some people, the satisfaction of getting it back into good working order would be enough reward.
If he's right, it may not be worth repairing if you're going to sell it to try to make a profit. Of course, for some people, the satisfaction of getting it back into good working order would be enough reward.
so far I've only spent about 25 bucks.I now have to replace all the transistors that touch the heatsink as well as buy a few others so that I can do some more investigating. Those parts will run me roughly 45-50 dollars. If all goes well with that then I have to buy those mpsu 57's and 07's to get the amp back to stock and I haven't seen either of those for less than 7 bucks a piece and I fear i may need four of each of those parts.I'd also like to redo some of the caps as well.All in all I think i'd be in well over a hundred when its all said and done. I'm not sure how soon I could have that extra money so I may have to wait a few weeks before I can hopefully finish this thing off .
Hey every-one. The U57’s can be had here. http://www.opamp-electronics.com/ 
10 for $4.95 the U07’s are harder to find and cost $. E-Bay 1 for $7.00
Does everyone agree that the Motorola and Central versions do the same thing?
10 for $4.95 the U07’s are harder to find and cost $. E-Bay 1 for $7.00
Does everyone agree that the Motorola and Central versions do the same thing?
Got a quick question for you Perry.I have enough good 6491s and 6488's left over from when the amp had its last blowout to use in the amps output section.If I replace all the 6488's in the power supply with new parts and use mpsa06's and mpsa56's in place of the 07's and 57s in the output section will the old parts(6491's and 88's) be stable enough to use until i get all the amps problems worked out?Whenever I work out all of its demons I would then replace the old 91's and 88's and most likely recap the whole amp.
spooney said:
It sounds like your gutting this fish to fix it, so to speak. You probably don't have that much wrong with the amp to begin with. Replacing everything like you are might fix whats ailing this amp, but there are a assortment of other things that can go wrong that are related to the passive devices.
I mention this because after you spend all of this money on parts and then test fire the amp, you might just still have some or all of what caused this in the first place happen again.
Dead semi's can be a symptom of a smaller problem that most probably will still be there after all of this work has been done.
Heres a suggestion:
1: replace only a single set of output transistor for each channel, 1 P deviced (6491) and 1 N device (6488). This is all you need to troubleshoot the channel and make sure its repaired prior to plugging in all of those parts.
This should simplify your work and allow testing of your work without risking all of those parts. Your not testing at full power so all you need is a single set of outputs to get the channel de-bugged and tested at LOW power <25 watts or less>. <HEATSINKING IS MANDATORY ON FIRE UP
2: the same applies to the power supply, it only needs a single set of transistors to start the amp up and test the power supply for simple functionality. Then install all the rest. <HEATSINKING IS MANDATORY ON FIRE UP
And please replace those big caps they are shot to hades and back, I am almost sure that will smooth out your power supply issues in a single movement.
These older transistor power supplies were power hungary heat generating monsters, and that coupled with bad caps and you have catastrophy just waiting to be powered up.. <HEATSINKING IS MANDATORY ON FIRE UP
Also as for the MPSU07's & 57"s try MPSU06's & 56's they will work fine for most all ops of this amp. You might find issue if your using the amp on loads below 2 ohms, and then its a big MAYBE.
Its been a while since I have had one of the beasts on my bench, but I don't think I have forgotten much about them over the years.
Also be prepared to replace ALL of the tantalum caps used in the amp section. They go shorted and cause excessive current draw on the power supply ( until they literarlly burst into flames like a flare).
About the only other thing i ever saw go wrong on these were the Op-amps used in the frontend input and the channel input stages. But they just cause a scratchy sound on the channel.
Orion in their day built some fairly nice, well designed and built amps. There are a limited number of things that can and will go wrong,
You sound new to this sort of work, so < go slow, crawl before you walk, Use a single set of outputs instead of them all. The amp does not need to fully populated to actually work correctly. Good luck
that definitely helps me out a lot.If I do as you suggested I already have enough parts to trobleshoot some more minus the mpsu's.This is only the second amp that I've attempted to fix.I got lucky on the first one but things have only gotten worse on this one since i began workin on it.When I started almost all of the transistors were in good working order.then while testing one day without a heatsink like a moron I believe it just got too hot and blew out most of the 6488's.
YES, it will, but it will get very hot because of the transistor power supply. That's why all these amp companies went to MosFet power supply's
You also should take Scott's offer of parts (07's& 57's), I can and will vouch for him any day of the year. Save yorself time and get them from Scott.
Or use 06's and 56's like I suggested they are cheaper.
Also for test you can use 6488's and 6491's in there place <just watch out for lead placement they have different lead pin-outs. Look up the pdf's on the web, and download them, them compare the pin-outs and bend some leads to make them fit and use tubular insiulation striped off wire or cable to prevent leads from shorting out on themselves.
This is a simple trick that will pass way more current than the original parts ever did. This will also speed you up some in your quest to repair, It's not a permanent thing to do, just a quick trick to move things along abit.
I have also seen this done on refurbed Autobahn amps. the drivers fail and they replaced them with outputs, go figure.... but it works.
Hope this helps
You also should take Scott's offer of parts (07's& 57's), I can and will vouch for him any day of the year. Save yorself time and get them from Scott.
Or use 06's and 56's like I suggested they are cheaper.
Also for test you can use 6488's and 6491's in there place <just watch out for lead placement they have different lead pin-outs. Look up the pdf's on the web, and download them, them compare the pin-outs and bend some leads to make them fit and use tubular insiulation striped off wire or cable to prevent leads from shorting out on themselves.
This is a simple trick that will pass way more current than the original parts ever did. This will also speed you up some in your quest to repair, It's not a permanent thing to do, just a quick trick to move things along abit.
I have also seen this done on refurbed Autobahn amps. the drivers fail and they replaced them with outputs, go figure.... but it works.
Hope this helps
I just received some 07's from Scott yesterday.I definitely agree that he is a good guy to deal with. He also found a place where I can get some cheap 57's. I'll probably use the mpsa 06s and 56s like Perry suggested in place of those 07's and 57s for testing because if there are any other problems and they blow out they are very cheap to replace.
well after procrastinating for a long time I finally soldered in those mpsa56's and mpsa06's along with the partial power supply and output section as recommended and yet again tried to fire up the old orion.It made a high pitch squeal for a split second upon applying turn on power but to my surprise the newly replaced LED lit up and the 5 amp fuse remained intact.Feeling lucky I decided to run signal to it and for the first time I heard this amp play.It was an awesome feeling.One channel seemed to play fine but the other was very very weak.Just about dead.I checked out the preamp ICs and found that one channel was not receiving much of a signal.I traced the lead back to a small input capacitor directly next to the rca input for that channel.Turns out that this cap is trash as it has good voltage on one side but nothing on the other.I planned on replacing all the caps anyways so its no biggie to replace this one but man I'm so happy to hear this thing play at all even if it was only one channel.This amp has definitely been a positive learning experience for me.I thank all of you for bearing with me and helping me out with this old beast.
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