Thank you to Nelson Pass for providing instruction on converting the HK Citation 12 to a mosfet output. I have one sitting on the shelf and this is a project I’ve been wanting to do for fun for awhile. I had a couple of questions and was hoping to get direction.
First, the instructions are older, I’m guessing not, but are there any layout pics that are a little clearer? The schematic is no problem at all though.
This design being older I was thinking I’ll have to substitute parts. The outputs used are IRF-130 which are TO3 packaged MOSFETs. I was thinking I would swap to a TO3p package and use the IRFP240, would that be a good swap for the outputs?
The transistors being used are MPSL01 and MPSL51. What would be a good replacement for these? I have a bunch of 2N5401c and 2N5551c and was thinking maybe those would be appropriate. MPSA92/MPSA42? I have thousands of the 2N5401/2N5551 though so would prefer to use those.
Dan
First, the instructions are older, I’m guessing not, but are there any layout pics that are a little clearer? The schematic is no problem at all though.
This design being older I was thinking I’ll have to substitute parts. The outputs used are IRF-130 which are TO3 packaged MOSFETs. I was thinking I would swap to a TO3p package and use the IRFP240, would that be a good swap for the outputs?
The transistors being used are MPSL01 and MPSL51. What would be a good replacement for these? I have a bunch of 2N5401c and 2N5551c and was thinking maybe those would be appropriate. MPSA92/MPSA42? I have thousands of the 2N5401/2N5551 though so would prefer to use those.
Dan
Why do you want to do this (change from BJTs to Mosfets)?
I ask because I run a pair of Hugh Dean-designed Class A amps; they were designed to have Mosfet output devices (IRFP240C) ... but later on Hugh suggested I would get better sound by changing the +DC rail mosfet for a BJT.
There were a couple of component value changes required for this - so it wasn't just a simple swap.
I ask because I run a pair of Hugh Dean-designed Class A amps; they were designed to have Mosfet output devices (IRFP240C) ... but later on Hugh suggested I would get better sound by changing the +DC rail mosfet for a BJT.
There were a couple of component value changes required for this - so it wasn't just a simple swap.Well as we all know, Nelson likes MOSFETs. I figured it would be a fun project to do since the amp needs a full rebuild anyways. One of the filter cans has spilled its guts.
Nearly all of the electrolytics on the amplifier board are split down the side and measuring completely open, meaning no capacitance at all.
Plus I’ve already cleared the board lol.
Also in the past this amp has a failure, so one channel had an assortment of NTE silicon and I’m not a big fan so I would have had to replace all of the transistors anyways. So a bigger job either way.
Dan
Nearly all of the electrolytics on the amplifier board are split down the side and measuring completely open, meaning no capacitance at all.
Plus I’ve already cleared the board lol.
Also in the past this amp has a failure, so one channel had an assortment of NTE silicon and I’m not a big fan so I would have had to replace all of the transistors anyways. So a bigger job either way.
Dan
Sure Dan - but I suspect changing to Mosfets will require some component value changes ... how will you know:
a. which components, and
b. what values?
Huh??? Maybe you did not see my first post? I posted there that Nelson pass provided all the component changes and everything. He’s the one that designed the circuit. I’m Just wondering if I can substitute my suggested MOSFETs and transistors (IRFP240 and 2N5551c/2N5401c) since the originals are not readily available, that’s what my thread is about. Yes, there were many changes made to the circuit, but Nelson Pass did all of that for us.
Exactly, anytime I see something with their name on it, immediately pulled out.
Dan
Do my suggested replacements look appropriate?More modern devices might require some tinkering with compensation to make it stable. (Currently 20pF + zobel) Interesting project.
Dan
If anyone could possibly suggest the best replacements for the MSPL01 and MPSL51. The 2N5551c and 2N5401c looks like great replacements though the Ft is quite a bit higher at 300 MHz. The MPSA42 and MPSA92 look great also, much closer Ft at 50 MHz, but slightly lower Ic at 500 mA. Any other recommendations? What would you all use?
Thank you,
Dan
Thank you,
Dan
I was reading some threads about replacing these and the advantage of going with low noise devices. Someone suggested the KSA992/KSC1845. Looking at this circuit, I don’t know what the current demand is going to be on them, but these being rated at 50mA I don’t know if I want to take that chance. Another mention was the ZTX694b and ZTX795a, if higher gain was needed, these are supposed to be low noise as well. I have plenty of them. Am I overthinking this and should just go with the MPSA or 5551/5401 devices? I have this problem where I want to ensure I’m using the absolute best devices I have available, when I really even hear a difference?
Dan
Dan