BA1A4P NPN Transistor or eqiv - UK Vintage Radio Repair and Restoration Discussion Forum

GSBX1220 · 14th Apr 2020, 4:06 pm

Hi Folks

I'm looking to find an BA1A4P NPN transistor or equivalent to fix my Yaesu FT-736.

It needs to be a pin for pin replacement due to the cramped area on the board.

The only ones I see for sale on line are from China, and I'm not keen on buying from there as I'm wary of fakes.

Anyone know where I can obtain some or the equivalent?

Cheers

Richard

SiriusHardware · 14th Apr 2020, 4:23 pm

Big? Small? RF? Medium or high power? Small signal? If you can say which part number it is on the board (and better still post us a link to the circuit diagram) we may be able to suggest pin-compatible alternatives in the same package.

Cobaltblue · 14th Apr 2020, 4:30 pm

Odd device

Has built in bias resistors

https://pdf1.alldatasheet.com/datash...EC/BA1A4P.html

Cheers

Mike T

GSBX1220 · 14th Apr 2020, 4:56 pm

Hi

It looks as it's used to switch Q38

Schematic and datasheet attached. Indeed it is a strange device.

plaka78 · 14th Apr 2020, 5:12 pm

I have seen that type of transistor in video recorders being used as switching transistors, Called a digital transistor in the service manual.

GSBX1220 · 14th Apr 2020, 5:33 pm

OK

I may have made a slight boo boo in my choice of equivalent for the 2SA1528. The equivalent if the 2SA1020 came from here https://www.el-component.com/bipolar...istors/2sa1528

On looking at the data sheet for the 2SA1526, that also has internal bias resistors. The 2SA1020 does not data sheets for both attached.

I presume the lack of bias resistors in the 1020 is causing the BA1A4P to overheat.

Radio Wrangler · 14th Apr 2020, 5:45 pm

Have a look at RS or Farnell. They have a huge range of 'digital' transistors. Choose NPN or PNP, choice of several ratings and several combinations of built-in resistors. Choice of packages too.

Shouldn't be a problem.

David

14th Apr 2020, 5:46 pm

Could you use a mosfet instead?

GSBX1220 · 14th Apr 2020, 6:57 pm

David, thanks. I'll look tomorrow and see if anything comes close.

Merlin, not sure if that would work in this application.

Cheers

GSBX1220 · 14th Apr 2020, 7:08 pm

Maybe I should have explained what is going on.

Basically the rig has a switchable bias tee to feed voltage up the coax for a preamp. The fault was that suddenly I had the incorrect voltage out of the rig on RX, around 7.5 v instead of 12.

I have been working through the path to see what's going on. I think I initially mis diagnosed the 2SA1528's when I tested them as I thought they were normal pnp devices and not having internal bias resistors which skewed my results (Using diode test with neg lead on base they showed 1.2v between base collector & base emitter)
I initially suspected those devices as the voltages I was measuring in circuit were OK until that Q38 2SA1528, on the attached diagram so I thought it was not switching.

However, the transistor may still be suspect. I have since found that Cricklewood have them so I will order some 1528's from them

GSBX1220 · 16th Apr 2020, 4:23 pm

Quote:

Originally Posted by Radio Wrangler

Have a look at RS or Farnell. They have a huge range of 'digital' transistors. Choose NPN or PNP, choice of several ratings and several combinations of built-in resistors. Choice of packages too.

Shouldn't be a problem.

David

Done! Best equivalent was in an smd package but that's fine

14th Apr 2020, 4:06 pm	#1
GSBX1220 Pentode Join Date: Jun 2018 Location: Glasgow, Scotland,UK. Posts: 127	BA1A4P NPN Transistor or eqiv Hi Folks I'm looking to find an BA1A4P NPN transistor or equivalent to fix my Yaesu FT-736. It needs to be a pin for pin replacement due to the cramped area on the board. The only ones I see for sale on line are from China, and I'm not keen on buying from there as I'm wary of fakes. Anyone know where I can obtain some or the equivalent? Cheers Richard __________________ Richard

14th Apr 2020, 4:23 pm	#2
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,556	Re: BA1A4P NPN Transistor or eqiv Big? Small? RF? Medium or high power? Small signal? If you can say which part number it is on the board (and better still post us a link to the circuit diagram) we may be able to suggest pin-compatible alternatives in the same package.

14th Apr 2020, 4:30 pm	#3
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,865	Re: BA1A4P NPN Transistor or eqiv Odd device Has built in bias resistors https://pdf1.alldatasheet.com/datash...EC/BA1A4P.html Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

14th Apr 2020, 4:56 pm	#4
GSBX1220 Pentode Join Date: Jun 2018 Location: Glasgow, Scotland,UK. Posts: 127	Re: BA1A4P NPN Transistor or eqiv Hi It looks as it's used to switch Q38 Schematic and datasheet attached. Indeed it is a strange device. Attached Thumbnails __________________ Richard

14th Apr 2020, 5:12 pm	#5
plaka78 Pentode Join Date: Jul 2007 Location: Salisbury, Wiltshire, UK. Posts: 174	Re: BA1A4P NPN Transistor or eqiv I have seen that type of transistor in video recorders being used as switching transistors, Called a digital transistor in the service manual.

14th Apr 2020, 5:33 pm	#6
GSBX1220 Pentode Join Date: Jun 2018 Location: Glasgow, Scotland,UK. Posts: 127	Re: BA1A4P NPN Transistor or eqiv OK I may have made a slight boo boo in my choice of equivalent for the 2SA1528. The equivalent if the 2SA1020 came from here https://www.el-component.com/bipolar...istors/2sa1528 On looking at the data sheet for the 2SA1526, that also has internal bias resistors. The 2SA1020 does not data sheets for both attached. I presume the lack of bias resistors in the 1020 is causing the BA1A4P to overheat. Attached Thumbnails __________________ Richard

14th Apr 2020, 5:45 pm	#7
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,872	Re: BA1A4P NPN Transistor or eqiv Have a look at RS or Farnell. They have a huge range of 'digital' transistors. Choose NPN or PNP, choice of several ratings and several combinations of built-in resistors. Choice of packages too. Shouldn't be a problem. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

14th Apr 2020, 5:46 pm	#8
Guest Guest Posts: n/a	Re: BA1A4P NPN Transistor or eqiv Could you use a mosfet instead?

14th Apr 2020, 6:57 pm	#9
GSBX1220 Pentode Join Date: Jun 2018 Location: Glasgow, Scotland,UK. Posts: 127	Re: BA1A4P NPN Transistor or eqiv David, thanks. I'll look tomorrow and see if anything comes close. Merlin, not sure if that would work in this application. Cheers __________________ Richard

14th Apr 2020, 7:08 pm	#10
GSBX1220 Pentode Join Date: Jun 2018 Location: Glasgow, Scotland,UK. Posts: 127	Re: BA1A4P NPN Transistor or eqiv Maybe I should have explained what is going on. Basically the rig has a switchable bias tee to feed voltage up the coax for a preamp. The fault was that suddenly I had the incorrect voltage out of the rig on RX, around 7.5 v instead of 12. I have been working through the path to see what's going on. I think I initially mis diagnosed the 2SA1528's when I tested them as I thought they were normal pnp devices and not having internal bias resistors which skewed my results (Using diode test with neg lead on base they showed 1.2v between base collector & base emitter) I initially suspected those devices as the voltages I was measuring in circuit were OK until that Q38 2SA1528, on the attached diagram so I thought it was not switching. However, the transistor may still be suspect. I have since found that Cricklewood have them so I will order some 1528's from them __________________ Richard