Replacements for workhorse transistors

[GregH2]

Hi all,

I'm about to place another big digikey order to stock up on components and am hoping to get some advice from you all on some possible transistors before I do.

For every transistor amplifier I have built, I have used BC550C/560C transistors for the signal stages and BD139/140 transistors for driver stages. I use them because the first amplifier I ever built used them, and i am comfortable and familiar with them. They are also cheap and easy to come by. With them and a few power transistors or fets, I can make pretty much any amplifier I want.

After reading the forums it would seem that these transistors a not held in particularly high regard both performance wise or sonically. So, what do you all think are the best substitutes that are currently in production and relatively easy to get hold of?

I look forward to your thoughts.

Greg.

[Ian Finch]

Hi
This has been the topic of several threads in the last year at least. There are quite large numbers of suitable through-hole types available but the question I always ask is: Will it be available in 6 months or six years time or is the price cheap enough to buy up stocks?

For amplifiers, small signal input types need to be very quiet, relatively high Vceo or need cascoding or protective resistors to be added. Medium power types for the VAS need to be blindingly fast and high voltage types and so on but the prescriptions are not really for that many types, more for a reliable supply. There is nothing wrong with universal ss types as you mention, but it may be to some advantage to keep low noise level with higher working voltages with something like 2SC2240/2SA970 or 2SC1815/ 2SA1015. These have much higher voltage ratings too so can be used without extra protective components. For NPN only, the Renesas 2SC2547 is quite a gem. Higher voltages imply lower Hfe but these types have it all. When browsing, check noise figures from the spec. sheet and you will knock out about 95% of contenders there.

Drivers to replace the BD139/40 are not easy but the voltage limit is restrictive of power so the MJE15003x series from On-Semi is highly recommended, if expensive. There are a number of puny TO126 types but On semi MJE243/53 and 181/2 are not bad at medium power. Don't underestimate current requirements here, 1.0 amp drivers are seldom up to even only 2 TO3P 0/P devices, IMHO.

A good guide to supply is to study Fairchild's site and catalogue for all the classic audio types they have cloned, and cloned cheaply and well. They can appear under original or Korean (Samsung) equivalent codes prefixed by KSC..etc. They also have several variants of Toshiba's 2SC5200/2SA1943 under various codes and all are excellent high gain and Ft output types. No doubt you are familiar with types like the excellent KSC 3503 etc. as VAS.

There are folks who would never build any output stage that was not 100% "On-Semi" or Toshiba for reliability or perhaps overload confidence but that is not necessary with 2nd source modern types that also meet the required specs. Let's not forget that On-Semi still clones Toshiba's mighty 2SC3281/2SA1302 in their multi-package audio types.

Don't forget Greg Erskine's site for a good list of amplifier semis that was built early in the BAKSA thread, just this way, from forum suggestions. It's good! .

[GregH2]

Thanks for that informative post Ian. You've given me a good place to start. I'm going to go research those parts and track down those websites.

Regards,

Greg

[sakis]

for low voltage applications you might try for drivers the Bd 829 830 combo that was tested in a P3A and give by far excelent results

Off topic
Better late than never my friend Ian i got now plenty of those and if you please resend your postal data i will be mor ethan happy to send you some

Kind regards sakis

[Michael Chua]

Originally Posted by swordfishy

For every transistor amplifier I have built, I have used BC550C/560C transistors for the signal stages and BD139/140 transistors for driver stages....

After reading the forums it would seem that these transistors a not held in particularly high regard both performance wise or sonically.

There's nothing wrong with them. Sonically, they are excellent. Just use them within their parameters and you'll be fine.

[Ian Finch]

Hi Swordfishy
I realised finding the thread/ post is not so easy, so here's a link, initially to just small signal types. http://users.tpg.com.au/gerskine/gre...ransistors.htm

Hi Sakis
Nice of you indeed. I will P.M.

[jaycee]

The newer parts do have the edge and can ease design especially the likes of KSA1381/KSC3503 which are pretty ideal VAS devices with high voltage, good speed and low Cob, but the old bd139/140 can serve too

Sanyo also have some good devices, and hopefully now they have been bought by Onsemi they will become more readily available.