this amp work?

tadiam · 5th February 2008, 06:57 PM

Old circuit old transistors..70w

unclejed613 · 5th February 2008, 07:18 PM

yes, it works, it's been used by many pro-audio manufacturers. it's a quasi-complementary amp with a diode stack for bias and a single ended input. it was common in the late '60s and early '70's.
Dynaco used a similar design, except theirs had a single ended power supply and a huge coupling cap on the output. the jack plug in the collector circuit was for inserting an ammeter to adjust the bias current. most pro audio designs don't have adjustable bias. they "err on the safe side" and set the output bias just at cutoff, since pro audio amps are rarely driven at low levels, so these vintage pro audio amps have a bit of crossover distortion.

tadiam · 6th February 2008, 10:27 AM

thanks ...how sound this?
mid hi fi.....

latala · 6th February 2008, 05:39 PM

Early Wem 100 watt power slaves as used by bands such as the (cream ) i.e.
Jack Bruce,Eric Clapton Ginger Baker etc used a schematic very like this !
I used to repair them I can see no advantage in going back to this scheme
Dc offset was always high and thermally unstable but I am talking re very early days in transistor amplification
regards Trev

5th February 2008, 07:18 PM	#2
unclejed613 diyAudio Member Join Date: Dec 2006	yes, it works, it's been used by many pro-audio manufacturers. it's a quasi-complementary amp with a diode stack for bias and a single ended input. it was common in the late '60s and early '70's. Dynaco used a similar design, except theirs had a single ended power supply and a huge coupling cap on the output. the jack plug in the collector circuit was for inserting an ammeter to adjust the bias current. most pro audio designs don't have adjustable bias. they "err on the safe side" and set the output bias just at cutoff, since pro audio amps are rarely driven at low levels, so these vintage pro audio amps have a bit of crossover distortion. __________________ Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net spammer trap: http://www1284177414881.v-dc.net/

6th February 2008, 10:27 AM	#3
tadiam diyAudio Member Join Date: Mar 2007	re thanks ...how sound this? mid hi fi..... __________________ audio

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6th February 2008, 05:39 PM	#4
latala diyAudio Member Join Date: Feb 2006 Location: staffordshire	Early Wem 100 watt power slaves as used by bands such as the (cream ) i.e. Jack Bruce,Eric Clapton Ginger Baker etc used a schematic very like this ! I used to repair them I can see no advantage in going back to this scheme Dc offset was always high and thermally unstable but I am talking re very early days in transistor amplification regards Trev

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