Hello
I know that VAS transistors need to be very fast, and maby same for the drivers.
Many do use the 2SC4793 and 2SA1837, but here arround they are hard to find or fake one.
So how about MJL15032 (and MJL15033) or BD139 (and BD140), which one of those are best for VAS and drivers ?
Thank
Bye
Gaetan
I know that VAS transistors need to be very fast, and maby same for the drivers.
Many do use the 2SC4793 and 2SA1837, but here arround they are hard to find or fake one.
So how about MJL15032 (and MJL15033) or BD139 (and BD140), which one of those are best for VAS and drivers ?
Thank
Bye
Gaetan
I'm not so sure I'd use 340/350 for VAS - but for pre-driver they are ok.
I speak from bitter experience!
I speak from bitter experience!
Hello
The MJL15032 (and MJL15033) or BD139 (and BD140) are much easyer to find for me, anyone did try them for VAS and drivers ?
Btw, I live far from any cities in the north of Quebec (Canada) and mail order was always quite bad wen sent here. So wen I go to the far city I buy my stock there but they have limited kind of transistors.
And for output I can have MJ15003 (and MJ15004) or MJL3281A (and MJL1302A).
Thank
Gaetan
The MJL15032 (and MJL15033) or BD139 (and BD140) are much easyer to find for me, anyone did try them for VAS and drivers ?
Btw, I live far from any cities in the north of Quebec (Canada) and mail order was always quite bad wen sent here. So wen I go to the far city I buy my stock there but they have limited kind of transistors.
And for output I can have MJ15003 (and MJ15004) or MJL3281A (and MJL1302A).
Thank
Gaetan
Just about any transistor can be used for a Vas or predriver.
It's a question of what is the best transistor for this application.
Not knowing the circuit specifics makes discussion of part substitution difficult.
It's a question of what is the best transistor for this application.
Not knowing the circuit specifics makes discussion of part substitution difficult.
A little bit of topic, but I try to avoid the MJL15032/33 as I have had the pleasure to have several hundred fakes of those 🙂hot: each time power was turned on) 
Replaced with MJL15030/31 and everything worked just perfect 🙄
Replaced with MJL15030/31 and everything worked just perfect 🙄
gaetan8888 said:
For the VAS, Fairchild's KSC3503/KSA1381. Mouser carries these devices for pennies. They are Sanyo's 2SC3503/2SA1381 clones.
Myhrrhleine,
Here are the requirements:
Faster than 150MHz
Cob less than 2pF
Flat hfe from 1mA-20mA across a wide voltage range
Strong SOAR curves to resist 10-20mA with Vce of 100V
hfe up around 150 minimum
For these reasons I go for 2SC3423/2SA1360, though Syn08's choice is a good one too. I find the NPN has slightly lower Cob and higher beta.
Cheers,
Hugh
Here are the requirements:
Faster than 150MHz
Cob less than 2pF
Flat hfe from 1mA-20mA across a wide voltage range
Strong SOAR curves to resist 10-20mA with Vce of 100V
hfe up around 150 minimum
For these reasons I go for 2SC3423/2SA1360, though Syn08's choice is a good one too. I find the NPN has slightly lower Cob and higher beta.
Cheers,
Hugh
MJL3281A and MJL1302A are good, provided of course you can guarantee getting real ones!
KSC3503/KSA1381 are indeed good devices. Generally, look at any transistor designed for CRT driver use - they are generally fast, high voltage, with low Cob.
KSC3503/KSA1381 are indeed good devices. Generally, look at any transistor designed for CRT driver use - they are generally fast, high voltage, with low Cob.
Hello
I've check and I can have the Fairchild's KSC3503/KSA1381
Typical 150MHz
Cob 3.1pF
I forget to say that it would be for the mini DX for a friend (the transistors I've used for that one was fake) and I will use those KS for an amp for me with a Self type input and output.
Thank
Gaetan
I've check and I can have the Fairchild's KSC3503/KSA1381
Typical 150MHz
Cob 3.1pF
I forget to say that it would be for the mini DX for a friend (the transistors I've used for that one was fake) and I will use those KS for an amp for me with a Self type input and output.
Thank
Gaetan
AKSA is 100% correct - just about any transistor for VAS will defintley not do.
I managed to get hold of some NOS BF471 and 472 and have used these with good results in the VAS position (also in the pre-driver, but this is a less critical role in my view).
However, these will not be available for much longer even as NOS, so I will transition to some avaialble types.
BTW the 471/472 are avaialble as SMD BF871/872 (I think) but I have some concerns over thermal capability of the SOT223 package in this application.
I managed to get hold of some NOS BF471 and 472 and have used these with good results in the VAS position (also in the pre-driver, but this is a less critical role in my view).
However, these will not be available for much longer even as NOS, so I will transition to some avaialble types.
BTW the 471/472 are avaialble as SMD BF871/872 (I think) but I have some concerns over thermal capability of the SOT223 package in this application.
Gee fellas,
ohh, the good old days.
The sentimental journey makes me weep,...almost.
But instead of going back to assembling overpowered amps with loads of antiques lying idle overhere , i'll rather pick NEC A1142/C2682 if more voltage is needed than the Toshiba A1360/C3423 handle.
(and what a relief)
ohh, the good old days.
The sentimental journey makes me weep,...almost.
But instead of going back to assembling overpowered amps with loads of antiques lying idle overhere , i'll rather pick NEC A1142/C2682 if more voltage is needed than the Toshiba A1360/C3423 handle.
(and what a relief)
Attachments
I just tried out the 2sc3953 (Video driver originally from Sanyo, but I tried the Fairchild clone), and it is nearly perfect for NPN VAS use: 120V, 0.2A, 1.3W, 400 MHz, Cob=2.1 pF. Hfe was on the low side at ~60 on a DMM, but they were clustered like peas in a pod - a batch of 10 ranged from 59-62.
It works and sounds extra-fine and super-detailed to me, even with the low gain, in a single-ended VAS with bootstrapped load and 68pF styroflex miller cap. I'll experiment with smaller miller caps later, but it's already exceeded my expectations sonically. The 'tish' sound of cymbals now extends for several seconds, and one can clearly hear inhalations of performers playing pipes and trumpets.
There's nothing to prevent the 2sc3953 from being used as the upper transistor in a cascoded NPN VAS or Wilson Current Mirror - with a high-beta, low Vceo transistor as the lower transistor (almost anything will work here - BC550c, 2sc3112, or maybe even a FET).
Another choice for the upper transistor is the Philips BFQ232, with an fT of 1200 MHz, but that's probably overkill.
It works and sounds extra-fine and super-detailed to me, even with the low gain, in a single-ended VAS with bootstrapped load and 68pF styroflex miller cap. I'll experiment with smaller miller caps later, but it's already exceeded my expectations sonically. The 'tish' sound of cymbals now extends for several seconds, and one can clearly hear inhalations of performers playing pipes and trumpets.
There's nothing to prevent the 2sc3953 from being used as the upper transistor in a cascoded NPN VAS or Wilson Current Mirror - with a high-beta, low Vceo transistor as the lower transistor (almost anything will work here - BC550c, 2sc3112, or maybe even a FET).
Another choice for the upper transistor is the Philips BFQ232, with an fT of 1200 MHz, but that's probably overkill.
linuxguru said:
No PNP complementary.
Easier to order original A1538/C3953 from the Lab in Georgia, even cheaper if you handle Lithuanian
These VHF transistors often have low gain. It seems to be intrinsic to the construction.linuxguru said:
Going to slightly slower, <=300MHz, can usually get a more satisfactory gain.
Sanyo's 2sa1407/c3601 is an example of an exception to this rule but it is rather expensive for VAS & Pre-driver. Cob is slightly high cf Aksa's specification, but I'm told it works very well for this duty.
I like the sound of the 1360. It's cheap and performs.
Aksa,
at what voltage are you suggesting <2pF?
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