I don't see any 22uF capacitors in my DC300A or on the schematics I have. There are 0.0022uF caps and there 25uF non-polar caps and there are .22uF but I do not see these "22uF's". Perhaps you have a different version of the amp than I? Maybe you are calling your large power supply caps 22MFD. That’s it, you Americans and your old nomenclature? Just kidding… we still have some of that here in Canada. I think it more universal to call them 22,000uF. I mention these caps further down in my post.
One of the electrolytic capacitors at the top of the driver PCB has been known to cause problems. It is C5, 10uF radial lead electrolytic. There is an Axial 10uF beside it and you should replace that too. It is C4 but you should keep it at 10uF and raising the voltage of both of these caps is good as Bill says above, 160V to 200V is great. Predominantly the old models had problems with C5. These caps are filter caps for the Op Amp power supply and you can raise the value in capacitance and voltage for this one. The service bulletin from Crown stated that the caps were faulty from a supplier but it may have been specified at too low a voltage rating.
If you have the amplifier open, the driver board off and you are servicing it, then for the love of XXX replace the ceramic disk capacitors with MKP, type caps. 200V rating will work nice. There are various ones like C7, C102, C202, C121, C221...that may be all of them, I think.
If she's an oldie, you will have a heck of a time adjusting input and output bias with those old dirty potentiometers on the board. Replace them if you can and or clean them well.
I have a friend in the UK selling industrial temperature uA739DC Op Amps in the ceramic package. They are not cheap but heck they are NOS inventory and have never been used. Drop me an email and I will hook you up with him. The power supply capacitors hanging off the back of the chassis could easily be replaced by calling Apex JR. and Steve will hook you up with some big caps for the mains. He has all kinds of stock. Google Apex JR. and when you hit his site look for the Hitachi caps as he has posted pics of them. Great Guy, Great Service!
The DC300A is an audio classic! It is an iconic semiconductor amplifier. Perhaps the greatest quasi complimentary design ever made, at least it is the most famous for certain. Go buy one and restore it now before they cost $2000.00 broken on eBay. Preserve our Audio history! After a few key points of restoration, you may have a chance to hear what the original designers heard? Not the shrill tweeter squeaking amp we all heard while listening. What'd ya expect for an old bugger of an amplifier? It needs new parts to sound new again.
I love my DC300A and I'll be cooking up number 2 this year and I can't wait. I hope to have the website looking like a real web site in a month or two and it should be a little interactive for visitors. I need a little more time.
Thanks for a great informative reply!! I appreciate all your information, as I have seen the pictures of your DC300 on the forum and it is outstanding. I hope mine comes out half as cool as yours did. As far as Canada goes, down here in Houston we live by the Red Green slogan "Duct tape, the handyman's secret weapon"
The caps I am referring to are the 25MF nonpolarized C108, 208, 109, 209 radial cans on the main board. I could only find 22MF N/P so I wanted to know how critical the values were. With my limited knowledge, I don't want to get too wierd.
I am going to do all the electrolytics and probably the film caps for sure and now with your advice I will have to get back to Mouser and/or Antique Electronics, Handmade etc, to get some more stuff! I went ahead and got the C1 and C2 caps from Crown Parts department, maybe they also have those diodes you mentioned.
When I opened up my Ebay box and saw the amp, it was like seeing an old friend. I lugged many a rack full of these things in the 70's and 80's, we ALWAYS knew they were going to work no matter how they got bounced around. I had an amp rack fall face first off a 5 foot loading dock. Busted off all the rack mounts, bent some knobs etc... Stood it up, rolled it backstage, plugged the amps in and did the show.
The amp is heavier than I remember
Remember, "Real men solder naked"