Repairing The Venerable Crown DC 300

[mlucitt]

Joe, I guess this is mainly for you. As I re-immerse myself back into the electronics, the Crown DC 300 beckons to me. I have a soft hum in the left channel and a loud 60 Hz hum in the right channel. I'm suspecting the power supply caps because they are original (everything in the amp appears original). Do you have a source for these 13,500 MFD/70 Volt capacitors? Anything else I should be looking for? I have the schematics.

Thanks,
Mark

 

[Gepetto]

Hi Mark
It will be a little while before I come up for air. Really busy lately, things run hot and cold, you know how that is.

The last set of those caps I ordered from Crown direct, probably about 6 years back. They still had the caps and the mounting phenolic washers available as well to mount them. I cannot tell you what they are like post H-K acquisition but they were pretty darn good back then.

 

[laatsch55]

THIS THREAD IS WORTHLESS WITHOUT PICS!!!!!!!!!!!!!!!!!! Now that's saying something coming from the reigning pic and post whore!!

 

[mlucitt]

Got Caps?

I received the DC 300 replacement PS caps from Harmon, not cheap. I installed them and brought the amp slowly. The right channel sounds great, the left channel (Channel 1) blew the B+ fuse after a brief hum. I also see that channel 1 had some previous work done to it (non-stock power transistor, burnt spot on the board, and some replaced resistors). I love the way this amp is built with all point-to-point wiring but it is a pain to work on. Lee, imagine if the PL 700 had the transistors all hardwired! Yes, wires wrapped around the pins! Efficient but difficult to troubleshoot with the parts swap technique.

Joe, if you get a chance, can you throw me a bone? I would hate to have to pull all the channel 1 outputs on this animal just to test them and find them OK. Is there an easy test point that would point to a failure. The schematic is clear but not as friendly as the PL drawings. Once I get the other channel running, I will post some numbers. I can say subjectively that I am getting more than 150 WPC, at least out of the right channel.

Thanks,
Mark

 

[Gepetto]

Mark
It has been a while since I have been under the hood on any of my Crowns, the most vulnerable part of the Crown is the current source formed by the voltage doubler and the 2 MPSA92 transistors that are usually labeled Q101 and Q201. BTW that is a beautiful specimen you found Mark.

 

[laatsch55]

Damn sure is.

 

[mlucitt]

OK, small update on DC 300 amp symptoms. Only the B+ 5A fuse blew, not the B- 5A fuse. Also, the B+ fuse did not blow with the amp on the bench and powered up. It blew after I connected the load and then powered it on. I am checking for grounds on the output because the Crown uses class AB + B switching. The outputs stay off until the drivers turn them on, so a short will only draw current with a load connected.

Stay tuned.

Mark

 

[Gepetto]

That should make it a fairly straightforward debug Mark. With those symptoms you should be seeing a pegged or high offset on that channel. Since it is a pure DC coupled amp, unlike the PL amps, it is possible that the offset circuit for that channel is messed up and all else is good. Hope for that as it keeps it contained to the low level board circuitry.

 

[laatsch55]

Talking to Ed on the phone right now. It appears the TO-3's in this Peavey mixing board are RCA 61288--- which is a Peavey # --they cross to a 2N3773---you guys need some spare outputs for your DC 300??

 

[mlucitt]

Yes, Yes, and Yes. I need one right now and maybe more in the future. Mouser has new ones, but NOS is so nice.

If he is still on the phone ask him why the B+ outputs used .33 Ohm emitter resistors and the B- outputs used .27 Ohm emitter resistors, hardly seems worth the trouble for the difference?

Also, because the Service Bulletins were (mostly) not dated, does he have any idea when some of those came out? Do we have them all?

Mark

 

[laatsch55]

Give me your address and they'll be on the way in the morning. IIRC I have some more of those stuffed away in a drawer someplace..... demounting them now Mark.

 

[laatsch55]

BTW--- there are 10 of them.

 

[mlucitt]

I have 10:
1. Meters?
2. Service Bulletin #7721 - 700B Protection Circuit
3. Models 400 Series, 700 Series, and D-500 Amplifier Output Transistors and Output Driver Transistors (2 pages) dated 1-80
4. Service Bulletin #5179 - 400II and 700II Universal LED Display PC Boards
5. Service Bulletin - GES 97 Pin Out Change
6. Service Bulletin - Replacement of Transistor 2N5401 dated 1-76 revised 6-81
7. Service Bulletin - TO-92/TO-18 Transistor Pin Patterns dated 6-76 revised 6-81
8. Service Bulletin - No More XPL909 or FPL909 Output Transistors dated 10-81
9. Phase Linear Amplifier Bridging Information
10. Early 700 Meter Lamp Replacement

All from the Lynnwood address, Is that right?

Mark

 

[laatsch55]

I have ten 3773's , now you funny. A few beers tonight eh?? I've had a couple crown and cokes. A lot of box unused here. What else ya need??

 

[mlucitt]

I read my email and not the blog, I thought you were talking about 10 Service Bulletins, Ha!

My drink of choice tonight was called a San Diego, I invented it myself - Diet Coke and Bacardi Coconut Rum (Coco), it has a unique flavor (don't use Malibu Rum , too sweet). Anyway send me a couple of those 2N3773 thingamajiggers. Did you stock up on PL400 caps from Apex Jr? I will need a pair of those next week. And, I'm still looking for 1 PL400 meter and some PL400 aluminum faceplate bolts/nuts. I'll PayPal you for that stuff, if ya have it.

 

[laatsch55]

DUDE!!!!!!!!!!!! I can't take a dime from you if it's for your personal stuff. Ain't gonna take it. Ed sent me some caps ,yeah.....uh, how about a pair of CD-18,700Uf in the same proflie as the original 400 5900uf'ers?? Got a 400 meter from 1 that I junked out, ok um faceplate bolts and nuts, yep, how many??

 

[laatsch55]

Interesting drink there Laddie. I also have some 80 volt 35,000uf caps in the 2-1/2 by 4" profile.

 

[laatsch55]

Now if you were rebuilding the neighbors Bryston we'd soak im.

 

[laatsch55]

NEED SOME KNOBSSSSSSSSSSS??????????????????????

 

[laatsch55]

OK, there are 10 3773's. 3 read weird, 7 are TOTALLY good. You're getting all of them. I don't have anything but that Bryston that could use em and the Bryston is getting 15024's before it's big lottery day.