ua739 Op Amp Replacement

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#42
I have had several ua739pc (plastic case) ic's fail in crown dc300a amps,

The ceramic case option was common in the earlier dc300a amps,

There is a fair amount of heat around the top of the dc300a main board, the only thing i have had to do re the ic power supply was to replace the tired zener and resistor associated with the ic supply....

I have no idea about the marantz problems, so i just cant comment. the dc300a runs 10volts into the ic , so i dont think its a huge voltage by any means.

The ceramic option seemed the way to go, i have 25+ year old dc300a's still running virtually untouched.

Some of the earlier r's and c's were bullit proof....

shame we cant say the same for some of the newer gear!
 
#43
Hi krmaudio,
The Marantz 3600 / 3800 run a uA748 at 17 V bipolar. What's nice is Marantz utilized a current sink to lower distortion. The high supplies can kill these if the internal ambient gets too high.

-Chris
 
#44
hi chris,

17volt sounds a little high, the ic in the crown's seems to go quite frequently, and some of the pre driver transistors are a little iffy!

i think a lot of the problems were down to component availability at the time, there appears to be no logic in transistor choice.

it amazes and amuses me the parts people use as "equivalents" at times, the range of available components seems to lessen every year .......

cheers chris
 
#45
Hi krmaudio,
17volt sounds a little high, the ic in the crown's seems to go quite frequently
Click to expand...
I've always thought that. All in the name of headroom.

i think a lot of the problems were down to component availability at the time, there appears to be no logic in transistor choice.
Click to expand...
There is if you look at a catalog of that time period. I think they did amazing things back then with what was available to them.

it amazes and amuses me the parts people use as "equivalents" at times, the range of available components seems to lessen every year .......
Click to expand...
Well, yes. Me too. Then again, you have to clean up after these amusing folk. So much needless destruction. Getting good parts for old gear is getting more difficult year by year.

-Chris
 
#54
UA739/749

The replacement part in metal can from NTE, 949 www.nteinc.com

See the att.

Best regards, R Amandi
 

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#55
billg here hi all:i was chking the d40/d44 transistors for a crown dc300a-the d44c7,8,9 are rated at supply volts of 60v.but the d40 comes up as an darlington..the data sheet specs the compliment at d44c7,8,9 same specs as the npn.thought i would add this.
 
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