Hi, Gang,
I'm digging up an old Dynaco project and am thinking of these replacement transistors. I'm looking for 'yes, good enough' replacements, not making a new, different version of the amp. Comments?
Orginal Replacement
2N4889 2N3906
BF257 2N5551
BC308B BC556
SE6020 BC63916
MPSA20 KSD1616AGTA
TIP31C TIP31C
TIP32C TIP32C
2N5630 MJ15003
2N6030 MJ15004
Thanks,
Cheers,
Frank
I'm digging up an old Dynaco project and am thinking of these replacement transistors. I'm looking for 'yes, good enough' replacements, not making a new, different version of the amp. Comments?
Orginal Replacement
2N4889 2N3906
BF257 2N5551
BC308B BC556
SE6020 BC63916
MPSA20 KSD1616AGTA
TIP31C TIP31C
TIP32C TIP32C
2N5630 MJ15003
2N6030 MJ15004
Thanks,
Cheers,
Frank
Last edited:
ST400 perhaps?
If you are scratch building, fine, but I don't see why the front end transistors need replaced on an existing unit. I've got 50 year old transistors except the outputs on one channel of my dynakit ST120 and they work fine. In fact the surviving TO5 drivers sound better on top octave piano & tinkly bells than NTE49/50 and TIP31c32c I tried as replacements. TIP31c/32c have too low a Ft to reproduce 10k-20k hz without IM distortion. I found better sound with MJE15028/29 as drivers and as VAS too. Dynaco used heatsinks on the drivers and I did too, also VAS.
2n3906 is a bit light on Vceo for ruggedness. I prefer MPS8599 or MPSA56. Not available, use 2N5400 or 2n5401 which are more expensive. I was getting gain of about 300 out of a MPS8099, gain is not expensive these days.
KSD1616 is not available to me, not looking it up. What is that, a VAS? If pinout matches use MJE15028/29 as above.
BC556 from Telefunken or Phillips have great noise specs, but if you check the fairchild datasheet of what you can actually buy fairchild left that out. I found very low noise with MPS8099/8599, but not specified. However my units were from Phillipines; fab has moved to ***** now that On bought Fairchild.
MJ15003/4 are fine output transistors but MJ21193/4 have more SOA & are cheaper. I've got some NTE181 which have same soa specs as MJ15003 (which they probably are) and they are 38 years old, used 2000 hours a year some years.
If your amp is original and ailing, concentrate on electrolytic caps, dirty pots and oxidized connectors, geriatric mica washers, is my advice. Also if kit built, bad solder joints. campsquire just refurbished a 35 year old Peavey CS800 Making a Vintage class A/B Lighter
and he didn't use any transistors, mainly replaced transistor sockets ecaps thyristor and fan.
If you are scratch building, fine, but I don't see why the front end transistors need replaced on an existing unit. I've got 50 year old transistors except the outputs on one channel of my dynakit ST120 and they work fine. In fact the surviving TO5 drivers sound better on top octave piano & tinkly bells than NTE49/50 and TIP31c32c I tried as replacements. TIP31c/32c have too low a Ft to reproduce 10k-20k hz without IM distortion. I found better sound with MJE15028/29 as drivers and as VAS too. Dynaco used heatsinks on the drivers and I did too, also VAS.
2n3906 is a bit light on Vceo for ruggedness. I prefer MPS8599 or MPSA56. Not available, use 2N5400 or 2n5401 which are more expensive. I was getting gain of about 300 out of a MPS8099, gain is not expensive these days.
KSD1616 is not available to me, not looking it up. What is that, a VAS? If pinout matches use MJE15028/29 as above.
BC556 from Telefunken or Phillips have great noise specs, but if you check the fairchild datasheet of what you can actually buy fairchild left that out. I found very low noise with MPS8099/8599, but not specified. However my units were from Phillipines; fab has moved to ***** now that On bought Fairchild.
MJ15003/4 are fine output transistors but MJ21193/4 have more SOA & are cheaper. I've got some NTE181 which have same soa specs as MJ15003 (which they probably are) and they are 38 years old, used 2000 hours a year some years.
If your amp is original and ailing, concentrate on electrolytic caps, dirty pots and oxidized connectors, geriatric mica washers, is my advice. Also if kit built, bad solder joints. campsquire just refurbished a 35 year old Peavey CS800 Making a Vintage class A/B Lighter
and he didn't use any transistors, mainly replaced transistor sockets ecaps thyristor and fan.
Last edited:
ST-150. I'm laying out a new PC-43 with the Audio Amateur mods from 1981, except the voltage regulators. I haven't had the original PC-43 in years. Thank you for both your suggestions and reasoning!
I've made a PS board that mimics the intent of the Dyna C-100, that is, current limited charging of extra capacitors. That board has tested out perfectly, I'm pretty pleased.
I've made a PS board that mimics the intent of the Dyna C-100, that is, current limited charging of extra capacitors. That board has tested out perfectly, I'm pretty pleased.
Well, if you laid out board for any bce TO5 transistors, do it again, you can't buy those anymore. Best substitute is TO18 bce transistors with a big honking heat sink. newark usually has one pnp and one npn TO18 transistor, number varies from year to year. they are multicomp, house brand, so I don't know about Ft, noise level, or gain. ****ese. But if you change layout to bce you can use MJE15028/29 or bc139/140. Or some ks TO126 transistors that fairchild gave an actual Ft spec to. Like Ksa992, 1220, 1381. Also Ksc1845,2690, 3502/3
Watch package codes, On freely substitutes TO220 for TO247 and TO92 for TO126, just by putting a suffix on the package code and insisting you download the datasheet everytime you buy to not get *****ed.
Watch package codes, On freely substitutes TO220 for TO247 and TO92 for TO126, just by putting a suffix on the package code and insisting you download the datasheet everytime you buy to not get *****ed.
Last edited:
Fairchild BC139/140 don't come with an Ft spec. Phillips/Telefunken did, but I can't buy those here. I didn't find out about KSA/KSC Jap numbers until 2018, and the ones I ordered from Mouser UK came in TO92 ins tead of TO126 I thought I was getting. Which would be useless for VAS or drivers.
Whereas the MJE15028/29 that came in the TO220 package the datasheetcatalog sheet specifies, sound great as VAS & drivers both.
Those dire warnings I get about high Cob on TO220 VAS don't translate to bad high frequency sound the way that TIP31c/32c that were so bad.
On VAS & drivers, a half inch of window frame with holes drilled in works fine as heat sink. No need to spend $1. At least up to 70 w/ch which is where my ST120 maxes out. The $1 is not so annoying as the $9 freight charge everytime I forget to order something I needed. All the vendors have huge gaps in stocked items when I order. Couldn't get silicon TO247 heat pads for < $2 each at newark for years, and mouser sticks me $.18 each for 1/2 watt resistors and $14 freight nearly every time. The order last Friday newark absolutely could not find RCA jack to 1/4 phone plug adapters. Until I asked for RCA jack to jack barrels, then the RCA to phone plug adapters showed up. Never did find RCA jack to jack barrels, released the order and salvaged some RCA 3 way input jacks from an old TV & soldered the pins together to make female to female.
Whereas the MJE15028/29 that came in the TO220 package the datasheetcatalog sheet specifies, sound great as VAS & drivers both.
Those dire warnings I get about high Cob on TO220 VAS don't translate to bad high frequency sound the way that TIP31c/32c that were so bad.
On VAS & drivers, a half inch of window frame with holes drilled in works fine as heat sink. No need to spend $1. At least up to 70 w/ch which is where my ST120 maxes out. The $1 is not so annoying as the $9 freight charge everytime I forget to order something I needed. All the vendors have huge gaps in stocked items when I order. Couldn't get silicon TO247 heat pads for < $2 each at newark for years, and mouser sticks me $.18 each for 1/2 watt resistors and $14 freight nearly every time. The order last Friday newark absolutely could not find RCA jack to 1/4 phone plug adapters. Until I asked for RCA jack to jack barrels, then the RCA to phone plug adapters showed up. Never did find RCA jack to jack barrels, released the order and salvaged some RCA 3 way input jacks from an old TV & soldered the pins together to make female to female.
Last edited:
I only checked the first item. Do you think you should replace a 150 Volt transistor with a 40 Volt transistor?
It might work if it's running less than 40 Volts but as a designer, why use a 150 Volt device when a 40 Volt
unit would do? Simple rule. Never sub a lower Voltage device for a high Voltage device. The last 2 subs
look fine to me.
G²
Stratus46 - thank you for catching that - I meant 2N5401, my notes are cluttered. To your point; no, I would never (intentionally) lower any voltage rating. Again, thanks!
Indianajo - everything is laid out with what I have suggested, the pinout for 2N3906 is the same as 2N5401. Plus, it's easy to change devices and / or footprints in Eagle, as it should be. Also, once I think I have the correct devices, I order them and check them against a printout of the board before I order the board.
Indianajo - everything is laid out with what I have suggested, the pinout for 2N3906 is the same as 2N5401. Plus, it's easy to change devices and / or footprints in Eagle, as it should be. Also, once I think I have the correct devices, I order them and check them against a printout of the board before I order the board.
THe KSA1220A amd KSC2690A would be a good choice for this project. Toshiba also has a similar set of devices.
Better than TIPs in all respects. But beware that you have to flip them around. ECB instead of BCE. Also suitable for VAS duty.
Well, yeah...
My go-to devices before the KSCs were the 2SA965 and 2SC2235, 120V devices in the TO-92L package. The TO-92L is good for about 1//2W if you want to keep the junction temperature below 100C. I also used some Panasonic devices in the TO-220F package, though those have been discontinued.
Note - the Panasonic devices were the 2SA1535A and the 2SC2944A, now discontinued, though the specs are still viewable at the Digikey web site.
My go-to devices before the KSCs were the 2SA965 and 2SC2235, 120V devices in the TO-92L package. The TO-92L is good for about 1//2W if you want to keep the junction temperature below 100C. I also used some Panasonic devices in the TO-220F package, though those have been discontinued.
Note - the Panasonic devices were the 2SA1535A and the 2SC2944A, now discontinued, though the specs are still viewable at the Digikey web site.
Last edited:
My go-to devices were the C3902/A1507. Still are, because I did a lifetime buy. Before that there was the C2344/A1011 in TO-220. Long gone for 20+ years now. Did a lifetime buy on the C2316/A916 too, so I’ve got giant TO92’s.
For lower power amps, another possible option is the MPSW06 and MPSW56, though those 2 devices are limited to 80V Vceo. They are still available NOS if you know where to look.
Thanks everyone! Here's where I am based on suggested, comments are welcome:
Original Proposed
2N4889 2N5401
BF257 2N5551
BC308B BC556
SE6020 BC63916
MPSA20 MPSA56
TIP31C MJE15028G
TIP32C MJE15029G
2N5630 MJ15003
2N6030 MJ15004
Original Proposed
2N4889 2N5401
BF257 2N5551
BC308B BC556
SE6020 BC63916
MPSA20 MPSA56
TIP31C MJE15028G
TIP32C MJE15029G
2N5630 MJ15003
2N6030 MJ15004
It can sometimes cause problems upgrading transistors.
I bought in a Maplin "disco" amplifier without output transistors.
I bought in replacement 2n3055/mj2955 from RS, a reputable dealer.
The amp started oscillating quite a bit.
I had to increase the VAS capacitor a bit to stop the oscillation.
I can only guess the newer transistors had higher gain or wider bandwidth or both.
I bought in a Maplin "disco" amplifier without output transistors.
I bought in replacement 2n3055/mj2955 from RS, a reputable dealer.
The amp started oscillating quite a bit.
I had to increase the VAS capacitor a bit to stop the oscillation.
I can only guess the newer transistors had higher gain or wider bandwidth or both.