Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.electronics.design > #452402

Re: Amplifier transistor substitution.

Show all headers | View raw

On Sat, 18 Mar 2017 10:41:40 +0000, Kevin Aylward wrote:

>>"Sylvia Else"  wrote in message news:ej4csuFe5h4U1@mid.individual.net...
> 
>>The smoke escaped from my old oscilloscope today. I've determined that
>>it came out of R740, to the bottom right of the circuit diagram.
> 
>>https://www.dropbox.com/s/9053dnyr0izv88r/XAMP.PDF?dl=0
> 
>>This is because T711 has shorted out.
> 
>>Not very surprisingly I cannot source a replacement BF472, so I need to
>>find a substitute.
> 
>>This is the final X-axis amplifier, so we're not talking high
>>frequencies.
>>Is it likely to be sensitive to the particular transistor
>>characteristics?
> 
> The key bit about that part is high voltage with low cob, and relatively
> high ft. Its cob is around 2pf
> 
> The BF472 has a voltage rating of 300V. It has a companion part BF470
> with a voltage rating of 250V, its just possible that the design don't
> need 300V. You would have to check.
> 
> So, look for a PNP 300V, 2 Watt,  cob < 4pf ft > 50MHz, I > 50ma
> 
> -- Kevin Aylward http://www.anasoft.co.uk - SuperSpice
> http://www.kevinaylward.co.uk/ee/index.html

Whatever sub you choose, it would probably be a good idea to replace the 
other 472 with the same type as well. A matched pair would be nice.

Back to sci.electronics.design | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Amplifier transistor substitution. Sylvia Else <sylvia@not.at.this.address> - 2017-03-18 20:27 +1100
  Re: Amplifier transistor substitution. "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-18 10:41 +0000
    Re: Amplifier transistor substitution. Cursitor Doom <curd@notformail.com> - 2017-03-18 11:13 +0000
    Re: Amplifier transistor substitution. bitrex <bitrex@de.lete.earthlink.net> - 2017-03-18 18:15 -0400
      Re: Amplifier transistor substitution. Sylvia Else <sylvia@not.at.this.address> - 2017-03-19 12:44 +1100
        Re: Amplifier transistor substitution. Winfield Hill <hill@rowland.harvard.edu> - 2017-03-18 19:03 -0700
          Re: Amplifier transistor substitution. Sylvia Else <sylvia@not.at.this.address> - 2017-03-19 13:14 +1100
          Re: Amplifier transistor substitution. Cursitor Doom <curd@notformail.com> - 2017-03-19 14:11 +0000
            Re: Amplifier transistor substitution. Winfield Hill <hill@rowland.harvard.edu> - 2017-03-20 06:20 -0700
              Re: Amplifier transistor substitution. Cursitor Doom <curd@notformail.com> - 2017-03-20 23:26 +0000
  Re: Amplifier transistor substitution. Phil Allison <pallison49@gmail.com> - 2017-03-18 04:08 -0700
    Re: Amplifier transistor substitution. Sylvia Else <sylvia@not.at.this.address> - 2017-03-18 22:42 +1100
      Re: Amplifier transistor substitution. "Benderthe.evilrobot" <Benderthe.evilrobot@virginmedia.com> - 2017-03-18 22:01 +0000
  Re: Amplifier transistor substitution. Sylvia Else <sylvia@not.at.this.address> - 2017-03-19 16:34 +1100
    Re: Amplifier transistor substitution. Cursitor Doom <curd@notformail.com> - 2017-03-19 14:13 +0000
      Re: Amplifier transistor substitution. John Robertson <spam@flippers.com> - 2017-03-21 08:34 -0700
        Re: Amplifier transistor substitution. Cursitor Doom <curd@notformail.com> - 2017-03-21 18:18 +0000
  Re: Amplifier transistor substitution. Sylvia Else <sylvia@not.at.this.address> - 2017-03-20 13:28 +1100
    Re: Amplifier transistor substitution. Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-03-20 10:59 +0200
      Re: Amplifier transistor substitution. Sylvia Else <sylvia@not.at.this.address> - 2017-03-21 10:57 +1100
  Re: Amplifier transistor substitution - fixed. Sylvia Else <sylvia@not.at.this.address> - 2017-03-22 19:33 +1100

csiph-web