___________________And earlier in this thread...
"If you don't want to gut it, try MJ15015. It has the Vceo and an actual SOA rating . MJ802 and MJ15003 would work but cost about 3 times as much. All these fast transistors could oscillate, so do the part of the TIP mod that involves putting 10-20 pf capacitors from b to e on the driver transistors."
___In another thread the "TIP MOD" is referenced to Greg Dunn's website...
"If you use faster transistors, install the output resistor and the 50 pf base to emitter capacitors of the dynaco "TIP mod" documented in greg Dunn's dynaco history website. Faster transistors could oscillate, and I have done that, tacking the capacitors to the bottom of the board without drilling any holes."
Problem is Greg Dunn's website is not accessible anymore.
In 2008, I copied all I could from Greg Dunn's history website.
And, I have found at that time all factory revisions ever made by Dynaco.
That was after I did a complete overhaul in 1996 described next...
All new electrolytics and semiconductors, plus new 1% metal film resistors,
2N3772 outputs, 2N3442 PSU, TIP-31c, TIP-32c, etc. plus C13, C14, C15, & C16.
In 1996, I had upgraded my ST-120 to the then-latest TIP-MOD listed parts (not including the last revision I was unaware of) and it has worked great for the last 20 years... but is now running very hot as in HF oscillation.
I had built the ST-120 from a kit in 1973 and it ran for 23 years beautifully.
The 20 year cycle seems apparent. I'm preparing another overhaul again, but this time I would like to make it more "bullet-proof".
I intend to use MJ15003s for the outputs instead of 2N3772s, all others the same as originally in the "TIP mod".
So, question... where exactly does one tack the 20 to 50pF cap across b to e on the driver transistors??? which driver transistor, Q3 or Q4 or both?
Q3 is the NPN driver, Q4 the PNP.
This cap was not mentioned on the factory "TIP mod".
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You put 50 pf b-c of both drivers, q3 & q4. Probably 51 pf these days. use ceramic. They are not very big, I just tacked them on the bottom of the boards after bending out the leads to make feet.
There is a zobel added on the back of each speaker jack, 1000 ohms 2 w series a .1 uf.
The base stopper resistors, I just flew 10 ohm 1 watt resistors from PC15 to the output transistor base instead of the wire.
here is the text of the dyna service bulletin: FROM THE DYNA SERVICE BULLETIN:
Q1 replace 40233 (100-250 beta) with BC108A (130-180 beta)
Q2 replace 2N3053 (100-200 beta) with 2N5320 (160-260 beta)
Q3 replace 2N3053 with TIP31C
Q4 replace 2N4037 with TIP32C
Q5, Q6 replace 2N3055 (17-25 beta) with 2N3772 (60-90 beta @ 1A)
D1 replace with 1N4733
D2,3 replace with 1N4004
C1 replace with 5 µF 10V tantalum
Add C13 68 pF from Q2C to Q2B, both channels
Add C14 0.01 µF from Q3C to GND, both channels
Add C15 27 pF from Q2C to Q1E, both channels
Add C16 .01 µF across xfmr secondary at rectifier bridge on PC-15
Replace C6 (30 µF, NP) with .47 µF mylar
Add 3.3 Ohm ½ watt emitter resistor to Q4, both channels
Add 1 kOhm 1.2 watt resistor across the red/black output jacks
For circuit stability, several capacitors and resistors were added to stabilize the circuit configuation. These changes kept the amplifier stable as the components aged. Whenever I work on equipment that is over 20 years old, I always replace the electrolytic capacitors. This takes just a few dollars and a few minutes per channel on the Stereo 120. There are several large, high voltage capacitors in the ST-120, three in the power supply, and one each in each channel. I've never seen these fail, but if they do, replacements will be expensive and physically smaller.
end quote
I find TIP31c/32c as drivers have no highs compared to 40409/40410 which survive on one of my boards. MJE15028/29 solved the dullness.
The djoffe bias control mod really helps cold low wattage crossover distortion. I highly recommend it. Or if you don't want 7 more transistors, just replace PC15 with an AX6 board. My PC15 was so damaged I did on one side. I used heat sinks on drivers as original, also q2 the vas. I put extra heat sinks on the output transistor flanges, and pointed a PCAT fan at each, for 18 hour a day survivability.
My PC14 was acting weird, limiting output to 30 watts due perhaps the wrong gain of the replacement transistor. I replaced it with a 5 parallel TIP142 regulator to 69.5 v (72 v base zener) on a Pentium2 heat sink. I replaced the current protection function with two 10 amp fuses to the output transistor collectors. I havn't blown any output transistors since 1990? tens of thousands of hours use. Peaks at 70 w/ch both sides for 5 seconds with only 3300 resevoir capacitor as designed.
There is a zobel added on the back of each speaker jack, 1000 ohms 2 w series a .1 uf.
The base stopper resistors, I just flew 10 ohm 1 watt resistors from PC15 to the output transistor base instead of the wire.
here is the text of the dyna service bulletin: FROM THE DYNA SERVICE BULLETIN:
Q1 replace 40233 (100-250 beta) with BC108A (130-180 beta)
Q2 replace 2N3053 (100-200 beta) with 2N5320 (160-260 beta)
Q3 replace 2N3053 with TIP31C
Q4 replace 2N4037 with TIP32C
Q5, Q6 replace 2N3055 (17-25 beta) with 2N3772 (60-90 beta @ 1A)
D1 replace with 1N4733
D2,3 replace with 1N4004
C1 replace with 5 µF 10V tantalum
Add C13 68 pF from Q2C to Q2B, both channels
Add C14 0.01 µF from Q3C to GND, both channels
Add C15 27 pF from Q2C to Q1E, both channels
Add C16 .01 µF across xfmr secondary at rectifier bridge on PC-15
Replace C6 (30 µF, NP) with .47 µF mylar
Add 3.3 Ohm ½ watt emitter resistor to Q4, both channels
Add 1 kOhm 1.2 watt resistor across the red/black output jacks
For circuit stability, several capacitors and resistors were added to stabilize the circuit configuation. These changes kept the amplifier stable as the components aged. Whenever I work on equipment that is over 20 years old, I always replace the electrolytic capacitors. This takes just a few dollars and a few minutes per channel on the Stereo 120. There are several large, high voltage capacitors in the ST-120, three in the power supply, and one each in each channel. I've never seen these fail, but if they do, replacements will be expensive and physically smaller.
end quote
I find TIP31c/32c as drivers have no highs compared to 40409/40410 which survive on one of my boards. MJE15028/29 solved the dullness.
The djoffe bias control mod really helps cold low wattage crossover distortion. I highly recommend it. Or if you don't want 7 more transistors, just replace PC15 with an AX6 board. My PC15 was so damaged I did on one side. I used heat sinks on drivers as original, also q2 the vas. I put extra heat sinks on the output transistor flanges, and pointed a PCAT fan at each, for 18 hour a day survivability.
My PC14 was acting weird, limiting output to 30 watts due perhaps the wrong gain of the replacement transistor. I replaced it with a 5 parallel TIP142 regulator to 69.5 v (72 v base zener) on a Pentium2 heat sink. I replaced the current protection function with two 10 amp fuses to the output transistor collectors. I havn't blown any output transistors since 1990? tens of thousands of hours use. Peaks at 70 w/ch both sides for 5 seconds with only 3300 resevoir capacitor as designed.
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Hi Joe,
"Whenever I work on equipment that is over 20 years old, I always replace the electrolytic capacitors."
I do so as well, 50+ years experience.
The ceramic caps across b to c or b to e ?
As quoted above...
Originally Posted by indianajo View Post
The ON Semi MJ15015 datasheet I have shows Ft between 800 khz and 6 mhz. The parts, if they perform at 5.9 mhz, are very fast, and should be protected by the driver b-e capacitor and the output resistor of the TIP mod.
___________________And earlier in this thread...
"If you don't want to gut it, try MJ15015. It has the Vceo and an actual SOA rating . MJ802 and MJ15003 would work but cost about 3 times as much. All these fast transistors could oscillate, so do the part of the TIP mod that involves putting 10-20 pf capacitors from b to e on the driver transistors."
___In another thread the "TIP MOD" is referenced to Greg Dunn's website...
"If you use faster transistors, install the output resistor and the 50 pf base to emitter capacitors of the dynaco "TIP mod" documented in greg Dunn's dynaco history website. Faster transistors could oscillate, and I have done that, tacking the capacitors to the bottom of the board without drilling any holes."
"Whenever I work on equipment that is over 20 years old, I always replace the electrolytic capacitors."
I do so as well, 50+ years experience.
The ceramic caps across b to c or b to e ?
As quoted above...
Originally Posted by indianajo View Post
The ON Semi MJ15015 datasheet I have shows Ft between 800 khz and 6 mhz. The parts, if they perform at 5.9 mhz, are very fast, and should be protected by the driver b-e capacitor and the output resistor of the TIP mod.
___________________And earlier in this thread...
"If you don't want to gut it, try MJ15015. It has the Vceo and an actual SOA rating . MJ802 and MJ15003 would work but cost about 3 times as much. All these fast transistors could oscillate, so do the part of the TIP mod that involves putting 10-20 pf capacitors from b to e on the driver transistors."
___In another thread the "TIP MOD" is referenced to Greg Dunn's website...
"If you use faster transistors, install the output resistor and the 50 pf base to emitter capacitors of the dynaco "TIP mod" documented in greg Dunn's dynaco history website. Faster transistors could oscillate, and I have done that, tacking the capacitors to the bottom of the board without drilling any holes."
b-c gives negative feedback at high frequencies.
b-e filters the input at high frequencies.
I can see the capacitor but it is too hard to take apart to see what legs they are attached to. Its summer & the city will cite me if I don't get my mower to run. Which it does for 2 seconds every fifth pull!@#$$%%^&
b-e filters the input at high frequencies.
I can see the capacitor but it is too hard to take apart to see what legs they are attached to. Its summer & the city will cite me if I don't get my mower to run. Which it does for 2 seconds every fifth pull!@#$$%%^&
clean your LM spark plug and air filter.
I use carburetor cleaner on the air filter.
When you are able, please clarify b to c or b to e.
I can see a cap on b to c of the PNP, Q4 would help with local neg feedback. On the NPN, Q3 it may not be needed.
For the OT base-stopper resistors, I would use 4.7ohm, 1w, but only if needed.
I know others that like to use 10ohm, but that adds to slew-rate limiting.
I have seen others use a ferrite bead on the OT bases, a more preferred method.
To keep all the info in thread, I'm waking up this thread.
This is what I did to an original factory wire Stereo 120 . I installed the Update My Dynaco power supply kit and the big caps upgrade kits. Had to do all the Dynaco mods on amp boards and totally rebuilt them, All new resistors, Q1=NTE123A, Q2 =2N5320, Q3=TIP32, Q4=TIP31, Q5=NTE130, Q6=NTE130. The amp sounds good, and everything appears to behaving but more listening is required. My question is are NTE130 a good choice ? Thanks
This is what I did to an original factory wire Stereo 120 . I installed the Update My Dynaco power supply kit and the big caps upgrade kits. Had to do all the Dynaco mods on amp boards and totally rebuilt them, All new resistors, Q1=NTE123A, Q2 =2N5320, Q3=TIP32, Q4=TIP31, Q5=NTE130, Q6=NTE130. The amp sounds good, and everything appears to behaving but more listening is required. My question is are NTE130 a good choice ? Thanks
How deaf are you? Probably sounds like sludge. My hearing goes to 14 khz still. My PC14 replacement had no highs with TIP31c/32c drivers. The original surviving pair 2n5320/22 (private labeled) on a PC14 were sparkling if driving epi output transistors. 50 mhz ft of 5320/22 instead of 6 of TIP31/32. Replacement MJE15028/29 drivers returned the highs. 30 mhz Ft. I never owned any homotaxial outputs, four were blown when I bought the ST120 about 1986.
Hard to go wrong with any epitaxial npn TO3 output transistor (all of them post 1985). All have higher Ft (1 to 2 mhz) than the OEM 40636 which had 400 khz. Original outputs were 2n3055 selected for better Iceo performance at higher voltage. All silicon TO3 outputs have Vce >50 these days. Stereo120 was slammed in the original 1966 review for no highs versus Stereo70 (tubes), and the slow output transistors was the cause. Not going to look up NTE130. Any epi output transistor is an oscillation risk, be sure to check with a scope or analog VOM on 20 VAC scale. If oscillating the cure is use a 1 ohm 10 watt resistor instead of a wire for the base drive to Q5+Q6. To preserve any output transistors, put more heat sink on, install fans on the heat sinks, or run at no more than 2 watts.
BTW the mower problem post 25 was a missing carburator spring, pulled off by a tree limb.
Hard to go wrong with any epitaxial npn TO3 output transistor (all of them post 1985). All have higher Ft (1 to 2 mhz) than the OEM 40636 which had 400 khz. Original outputs were 2n3055 selected for better Iceo performance at higher voltage. All silicon TO3 outputs have Vce >50 these days. Stereo120 was slammed in the original 1966 review for no highs versus Stereo70 (tubes), and the slow output transistors was the cause. Not going to look up NTE130. Any epi output transistor is an oscillation risk, be sure to check with a scope or analog VOM on 20 VAC scale. If oscillating the cure is use a 1 ohm 10 watt resistor instead of a wire for the base drive to Q5+Q6. To preserve any output transistors, put more heat sink on, install fans on the heat sinks, or run at no more than 2 watts.
BTW the mower problem post 25 was a missing carburator spring, pulled off by a tree limb.
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My TIP31/32 were Fairchild. Maybe the ones you bought had more Ft.
If your nte130 has more Vce than 50, they can't low ball anything else these days. 2n3773, 2n5629-30-31, 2n6254, 2n6338-39-40-41, BUY69c, MJ802 MJ15003 MJ15015 MJ15024 MJ21194 nearly everything TO3 is better than a 1966 2n3055. No darlingtons.
You can't tell die temperature with your finger. I ran my ST120 at 10 w/ch for 3.5 hours at a choir rehearsal and the output transistors shorted, vaporized the 1 ohm 10 w resistor I was using for base drive. Why I bought my unit for $50, everybody knew ST120 was garbage in 1985. Built to pass the FTC 1 hour watt test, and nothing more. Now ST120 are drawing $600 up on ebay, ha ha. I've got Pentium 2 processor heatsinks for my unit, plus fans. 1 watt into 8 ohms is about 2.8 vac.
If your nte130 has more Vce than 50, they can't low ball anything else these days. 2n3773, 2n5629-30-31, 2n6254, 2n6338-39-40-41, BUY69c, MJ802 MJ15003 MJ15015 MJ15024 MJ21194 nearly everything TO3 is better than a 1966 2n3055. No darlingtons.
You can't tell die temperature with your finger. I ran my ST120 at 10 w/ch for 3.5 hours at a choir rehearsal and the output transistors shorted, vaporized the 1 ohm 10 w resistor I was using for base drive. Why I bought my unit for $50, everybody knew ST120 was garbage in 1985. Built to pass the FTC 1 hour watt test, and nothing more. Now ST120 are drawing $600 up on ebay, ha ha. I've got Pentium 2 processor heatsinks for my unit, plus fans. 1 watt into 8 ohms is about 2.8 vac.
NTE130 = 2N3055. Like Indianajo said - nearly anything is better. Some switching types might blow up, but sound better until they do.
NTE128/9 are very close to original 2N5320/22.
MJE15028/9 are oversized. Not that there is anything wrong with them, but an 8A device is not really needed. Modern Jap TO-126 types (which are slowly but surely going away) are more “direct” driver replacements.
NTE128/9 are very close to original 2N5320/22.
MJE15028/9 are oversized. Not that there is anything wrong with them, but an 8A device is not really needed. Modern Jap TO-126 types (which are slowly but surely going away) are more “direct” driver replacements.
Fit ! the Updatemydynaco lm3886 boards.
Much , Much better Audio than Dynaco could ever achieve... cheaply and easily done.
ST120 was a Very poor circuit using the fewest and cheapest of parts that could be sourced .. It's sound was stuff of legend Poor.
But Hey! the Shills at Stereopile said it was Great
Much , Much better Audio than Dynaco could ever achieve... cheaply and easily done.
ST120 was a Very poor circuit using the fewest and cheapest of parts that could be sourced .. It's sound was stuff of legend Poor.
But Hey! the Shills at Stereopile said it was Great
I'm changing out the NTE130's for 2N3772's. The Vcer is 70v and 80V on the 2N3772. I don't know what Vce the outputs see or how close to the rail voltage(72V) it is . Also are the 2N3773's too fast? The ft is not listed on data sheet. I think the craping sounding Stereo 120's may have been because of the power supply.
NTE130 had Vce of 60 which is more than the original of a 1966 2n3055 but aprox equivalant to the Vce of a 40406 selection dynakit used or 60 of a modern 2n3055 from Thompson.
There were two problems with the original ST120 PC14. One, no highs, was inherent in the 400 khz Ft selected 2n3055 output transistors. There was nothing better in 1966. Now there is nothing that slow. Somebody did a simulation, proving the highs improved with epi TIP3055 instead of homotaxial 2n3055. All epitaxial output transistors made now have 2 mhz ft or better. Drivers in 1966 were fast enough, 2n5320/22 had 50 mhz Ft and the surviving pair still sound good in my unit on MJ15003 OT equivalents. I've been warning you, your TIP31/32 drivers are NOT fast enough unless they exceed the TIP31/32 datasheet in ft. Wgski was worried about the waste of that big bond wire in the MJ15028/29 preferring some mythical Japanese transistor not sold in the US except by counterfeiters. You can buy real On Semi MJE15028/29 all day at newark, mouser, digikey.
Another problem with PC14 was crossover distortion at low volume and cold. The dingbat idle crossover control circuit built up idle current as the volume ramped up and the transistors heated up. C6 didn't have enough voltage on it starting out cold. One improvement is a 7 transistor closed loop idle bias circuit covered in this thread: https://www.diyaudio.com/forums/solid-state/156627-dynaco-stereo-120-beautiful.html
I built two of those but several times it blew the sense transistor and went open loop 200 ma idle bias current. With fans on the heat sinks that was not a problem.
Another solution is replace the PC14 with an Apex AX6 board, maintaining the output transistors remote from the driver board. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html
That has been more reliable, with fewer parts even than PC14. I destroyed one PC14 by lifting the lands after a NTE49/50 driver broke the twisted legs. My AX6 is point to point, on Nema CE board, requiring no PC boards sourced from a troublesome source. I didn't have to rent a $400 deposit 55 gal drum from Safety Klean to dispose of the PCB etchant legally either, if I had made the PCB myself.
There were two problems with the original ST120 PC14. One, no highs, was inherent in the 400 khz Ft selected 2n3055 output transistors. There was nothing better in 1966. Now there is nothing that slow. Somebody did a simulation, proving the highs improved with epi TIP3055 instead of homotaxial 2n3055. All epitaxial output transistors made now have 2 mhz ft or better. Drivers in 1966 were fast enough, 2n5320/22 had 50 mhz Ft and the surviving pair still sound good in my unit on MJ15003 OT equivalents. I've been warning you, your TIP31/32 drivers are NOT fast enough unless they exceed the TIP31/32 datasheet in ft. Wgski was worried about the waste of that big bond wire in the MJ15028/29 preferring some mythical Japanese transistor not sold in the US except by counterfeiters. You can buy real On Semi MJE15028/29 all day at newark, mouser, digikey.
Another problem with PC14 was crossover distortion at low volume and cold. The dingbat idle crossover control circuit built up idle current as the volume ramped up and the transistors heated up. C6 didn't have enough voltage on it starting out cold. One improvement is a 7 transistor closed loop idle bias circuit covered in this thread: https://www.diyaudio.com/forums/solid-state/156627-dynaco-stereo-120-beautiful.html
I built two of those but several times it blew the sense transistor and went open loop 200 ma idle bias current. With fans on the heat sinks that was not a problem.
Another solution is replace the PC14 with an Apex AX6 board, maintaining the output transistors remote from the driver board. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html
That has been more reliable, with fewer parts even than PC14. I destroyed one PC14 by lifting the lands after a NTE49/50 driver broke the twisted legs. My AX6 is point to point, on Nema CE board, requiring no PC boards sourced from a troublesome source. I didn't have to rent a $400 deposit 55 gal drum from Safety Klean to dispose of the PCB etchant legally either, if I had made the PCB myself.
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with just a single pair of outputs
T0-126 driver agree is easier and faster anyways.
the gain and Ft of modern devices is extremely good.
surprised nobody has just done a complementary upgrade.
and just use a basic " Hi Fi" differential input.
the case, transformers and heatsinks are what is valuable.
everything else can be tossed.
T0-126 driver agree is easier and faster anyways.
the gain and Ft of modern devices is extremely good.
surprised nobody has just done a complementary upgrade.
and just use a basic " Hi Fi" differential input.
the case, transformers and heatsinks are what is valuable.
everything else can be tossed.
The ST120 heatsinks are garbage. one piece of aluminum angle, no fins. Enough to pass the 60 w/ch FTC one hour soak test - only. 10 watts/ch cooked my MJ15003 outputs in 3.5 hours. You can add fins like a https://www.digikey.com/en/products...sion-of-boyd-corporation/506007B00000G/265413
under the TO3 transistors (aavid HS228-nd), but if the plastic feet are missing (mine were) or it sits on carpet, there is still no airflow. I added PCAT fans on each side like Mickey Mouse ears, but you have to hide the amp behind a couch to kill the whine.
Frankly, quasi-comp versus full comp is a Ho-Hummer. I have a full comp no capacitors in sound flow CS800s, I have the djoffe modified ST120 with 20 ma idle bias current on quasi-comp outputs. They sound the same at 1 to 70 w/ch. Got money to burn, buy some better speakers. Or maybe a better MM phono cartridge.
For a no fan amp, I'm using a Peavey M-2600 now. Heat sinks 5.5"x13"x1" with fins all across the back. Can sit out right on top of the schober organ case, no fan noise, 70 w/ch. Also quasi-comp.
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I'm not a tech so I learn by reading. I have found other threads on these amps and slow output transistors are needed here due to oscillation problems. I now have the 2N3772's and TIPs. Why would you need a fast driver with a slow output transistor? I have to hook this up to preamp and play it and check the frequency response. I have software program somewhere. My120 doesn't run hot at all, but we shall see about that.
In December 2000 Thompson 2n3772 was showing minimum Ft of 0.2 Mhz, but that doesn't mean the Ft hasn't been exceeded by 10 or 20 times. There was no maximum Ft. Epitaxial processes are much faster than homotaxial. Mooly suggested 1 ohm 10 watt base stopper resistors to prevent oscillation in other 1966 2n3055 amps (Maplin) and I installed them instead of wire from PC14 as a sacrificial part to prevent blown drivers if the output transistor overheated & blew again. All the other antioscillation parts mentioned in bak064s illustration post 24 had been applied in my 1970 version ST120. The PC14 schematic supplied by Greg Dunn had all those parts on it.
If you wish to experiment with drivers $.005 cheaper than MJE15028/29 you can try TO126 drivers BD139/140 which from Phillips had Ft 190 mhz. We don't get phillips parts in USA, I've only found Fairchild & later On BD139/140, and last time I downloaded the datasheet they had no Ft spec at all. Plus dynaco put heat sinks on the drivers for a reason, and I think going to a smaller part with no heat sink risks burnout. One pair of my TO5 drivers were shorted when I bought the unit for $50 about 1986. I put bits of aluminum as heat sinks on my MJE15028/29 and they survived 14 hours/day for several years (with fans) when I used the ST120 to play FM radio in my music room. Note my speakers were SP2-XT, well capable of high frequencies up to 17 khz.
My unit came with TO5 RCA drivers in heat sinks, and the surviving pair driving NTE60 OT's (likely MJ15003) sounded fine on top octave piano & tinkly bells. The blown drivers I replaced with NTE49/50 and later TIP31c/32c when the legs broke on an NTE. That side sounded like **** on highs. Later I replaced the drivers with 30 mhz MJE15028/29 and the high frequency sounds became equivalent to the side with the original RCA TO5 drivers (likely 40409/410 or 2n5320/22). It is obvious from modern simulations and comments by reviewers in 1966 that dynaco 1/2% HD specification didn't include 15-20 khz. Probably 1/2% HD was true also after the unit was well warmed up, and only at maximum power. Since since early owners noted the unit sounded bad cold at very low watts.
If you wish to experiment with drivers $.005 cheaper than MJE15028/29 you can try TO126 drivers BD139/140 which from Phillips had Ft 190 mhz. We don't get phillips parts in USA, I've only found Fairchild & later On BD139/140, and last time I downloaded the datasheet they had no Ft spec at all. Plus dynaco put heat sinks on the drivers for a reason, and I think going to a smaller part with no heat sink risks burnout. One pair of my TO5 drivers were shorted when I bought the unit for $50 about 1986. I put bits of aluminum as heat sinks on my MJE15028/29 and they survived 14 hours/day for several years (with fans) when I used the ST120 to play FM radio in my music room. Note my speakers were SP2-XT, well capable of high frequencies up to 17 khz.
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be interesting to model it.
Its single supply so dc offset is often ignored since you have half supply on output anyways.
But the topology is susceptible to having poor offset.
So with poor DC the CFP side of the quasi will ring, heat up like crazy.
if good its not more than 1 to 2 watt to drive power transistor.
Bd139/140 could work too. Far as I remember the Motorola have better thermal.
Likely use a MJE243/253 or any of the newer Toshiba repros from OnSemi 2SA/2SC , KSA/KSC 1381 / 3503
yes and you would use a heatsink, since a 4 or 9 watt ...ish transistor derated at 70% or 50%
would want a heatsink for 1 to 2 watts.
Ironically its less AC current to drive power transistors if the amp had 4 outputs instead of 2.
and would push a little better with 4 ohm loads.
T0-39 think is the suffix would also be fun metal can drivers to use too.
Which are still currently manufactured by Central Semiconductor.
Its single supply so dc offset is often ignored since you have half supply on output anyways.
But the topology is susceptible to having poor offset.
So with poor DC the CFP side of the quasi will ring, heat up like crazy.
if good its not more than 1 to 2 watt to drive power transistor.
Bd139/140 could work too. Far as I remember the Motorola have better thermal.
Likely use a MJE243/253 or any of the newer Toshiba repros from OnSemi 2SA/2SC , KSA/KSC 1381 / 3503
yes and you would use a heatsink, since a 4 or 9 watt ...ish transistor derated at 70% or 50%
would want a heatsink for 1 to 2 watts.
Ironically its less AC current to drive power transistors if the amp had 4 outputs instead of 2.
and would push a little better with 4 ohm loads.
T0-39 think is the suffix would also be fun metal can drivers to use too.
Which are still currently manufactured by Central Semiconductor.
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