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 R.W.Clarke PA amplifier.
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 Return to top of page · Post #: 1 · Written at 3:41:39 PM on 25 March 2014.
Crite's Gravatar
 Crite
 Location: Helensville, NZ
 Member since 25 March 2014
 Member #: 1533
 Postcount: 4

Good day all!
I am a member of the NZVRS (#206) and recently picked
up one of these 4 channel, allegedly 100 watt systems.
The power amp is already replaced with a Quad 405 copy
but I have had extreme difficulty sorting out the 4 input amplifiers. These use a mixture of PNP and NPN silicon transistors and have a 741 op amp to operate a Baxandall
tone control for each channel.
The circuit appears downright weird!
I am VERY experienced (over 60 years) but this one is a real puzzle. The seems to be nothing on line on this firm at all.
Has any kind Aussie got any kind of manual for this unit?
It is branded Sonart and I want to restore it as a sound system for out local community hall.
Any information gratefully received.
73 ZL1BDA
 
 Return to top of page · Post #: 2 · Written at 10:44:28 PM on 25 March 2014.
Marcc's avatar
 Marcc
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5254

I would not be surprised to see NPN & PNP in the push pull, some configurations are impossible with two the same and it is never unusual in old units, to see a zero point with +15V -0 - (-15V) ( for example) with one amp board PNP and the other amp board NPN

PNP tends to fail short: NPN open.

Quad amp you may have a chance of a circuit. Brand unheard of with me.
 
 Return to top of page · Post #: 3 · Written at 11:58:34 PM on 1 April 2014.
NewVista's avatar
 NewVista
 Location: Silver City WI, US
 Member since 10 May 2013
 Member #: 1340
 Postcount: 977

In the 1970s audiophiles complained that 741 OP-Amps had poor slew rate. MCI published a bulletin attempting to refute the notion that this was audible (their tape multitrack machines were full of 741s)
 
 Return to top of page · Post #: 4 · Written at 12:19:37 AM on 2 April 2014.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6687

Have no experience of the 741, but the Fairchild uA739C was used in the Playmaster 127 preamp (EA Nov 1969) and it was very noisy.
 
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