I have a set of four old SK 3079 outputs that I wanted to use in a Dynaco Stereo 120 I'm redoing. But I see that they're TV vertical outputs, and from the info I've been able to find so far, it seems that these aren't good for audio use due to not being very linear, among other issues. I'm fine with using something else, but I wanted some other takes before I trash these.
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Well the main problem is you only have NPN output transistors, which would force using a quasi-complementary circuit topology. They have lower bandwidth than even 2N3055/2955's too... Couldn't find datasheet with curves or secondary-breakdown information either.
The ST120 has feedback so non-linearity of the output transistors is not a problem.
1 Mhz Ft is quite different than the 40406 original. I installed 1 ohm 2 watt resistors series the emitter of NTE60 outputs instead of the wire from PC14 shown in the factory diagram. Mooly suggest this practice to prevent oscillation on 2n3055 amps. The rest of the "TIP Mod" shown on greg dunn's website should be installed. Including 1000 ohm series .01 uf across the back of the output jacks.
The main problem with the ST120 is inadequate heat sinks. I installed fans blowing on the heat sinks. 80 mm PCAT fans driven by an external 9 v power supply.
Mark TIllotson statement concerning converting the unit to PNP+NPN output transistors is irrelevant. I don't know anybody that has done that. 40406 had no secondary brakedown limit either. SOA wasn't invented in 1966, or in 1971 when my unit was built. It can sound great with quasi-comp outputs as shipped. The 1 mhz epitaxial output transistors do improve high frequency response over the 40406 with 400 khz.
The main problem with ST120 sound is the obsolete idle bias current management, which allows crossover distortion when the unit is cold and wattage is low. Replacing PC14 with Apex AX6 driver boards is the best solution, IMHO. But the AX6 artwork wont fit in the case, too tall. P 42 of the link shows my point to point build. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html D Joffe's bias sense closed loop feedback board mod http://www.diyaudio.com/forums/solid-state/156627-dynaco-stereo-120-can-beautiful.html worked but repeatedly blew the sense transistor, going to 225 ma idle bias.
1 Mhz Ft is quite different than the 40406 original. I installed 1 ohm 2 watt resistors series the emitter of NTE60 outputs instead of the wire from PC14 shown in the factory diagram. Mooly suggest this practice to prevent oscillation on 2n3055 amps. The rest of the "TIP Mod" shown on greg dunn's website should be installed. Including 1000 ohm series .01 uf across the back of the output jacks.
The main problem with the ST120 is inadequate heat sinks. I installed fans blowing on the heat sinks. 80 mm PCAT fans driven by an external 9 v power supply.
Mark TIllotson statement concerning converting the unit to PNP+NPN output transistors is irrelevant. I don't know anybody that has done that. 40406 had no secondary brakedown limit either. SOA wasn't invented in 1966, or in 1971 when my unit was built. It can sound great with quasi-comp outputs as shipped. The 1 mhz epitaxial output transistors do improve high frequency response over the 40406 with 400 khz.
The main problem with ST120 sound is the obsolete idle bias current management, which allows crossover distortion when the unit is cold and wattage is low. Replacing PC14 with Apex AX6 driver boards is the best solution, IMHO. But the AX6 artwork wont fit in the case, too tall. P 42 of the link shows my point to point build. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html D Joffe's bias sense closed loop feedback board mod http://www.diyaudio.com/forums/solid-state/156627-dynaco-stereo-120-can-beautiful.html worked but repeatedly blew the sense transistor, going to 225 ma idle bias.
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They don’t have a whole lot more gain at high current than a 2N3055, but are fast enough assuming you put in fast beefy drivers like MJE15032/3. You get 99% of the possible improvement by doing that anyway. They are closest to a 2N3442, BTW.
Most vertical outputs are the 40 watt TO-220 4MHz variety. Any TV manufacturer using TO-3s probably ran the vertical amp class A. That went out of style when trying to miniaturize sets. Vertical outputs in general were often used in audio amps - as both outputs and drivers.
The original 40409/40410 (2n5320/5322) TO5 drivers with the heatsinks are entirely adequate. I have a pair of survivors from 1971 that drove NTE60 (MJ15003) outputs 14 hours a day for a few of years. Sounded indistinguishable to my no-capacitor-in-sound-path complementary output CS800s at 1-70 watts. I used MJE15028/29 as drivers on the AX6 board that replaced the PC14 with the ruined lands. AX6 sounded the same as PC14 with the Djoffe idle bias modification but a little more gain.
I ruined the PC14 by trying to install TO220 NTE49/50 instead of the burned 40409/40410. Twisted legs broke after a year and the lands peeled off when I removed them. I couldn't get TO5 80 v transistors at the local TV parts store in 1985. Newark wouldn't sell to individual in those days and I wasn't up for a $5 long distance call to find out what the freight would be to write a check to somebody else. I still had mail flyers of surplus & junk from Digikey, had no idea why I would trust them to sell factory authorized parts.
BTW if you have to replace the TO3 transistor on the voltage/current regulator board, modern high gain transistors make it regulate to 2 amps, not 6.75. Once diyaudio.com came into my view, I replaced that whole board with a TIP141 voltage regulator holding voltage down to 70 v (5 parallel driven by a 72 v stack of zeners). I replaced the current regulator function with a fuse.
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Not anymore. They are the most respected electronic parts vendor in the US. They got that way by practicing outstanding customer service. Something Newark never understood. Digikey is a fully authorized distributor for all the product they sell. I fully trust them in these days of fake semiconductors.
I too remember the Digikey ads in late 1970s electronics magazines. I went to them for TTL chips in those days.