What are you using for PL400 bias transistor replacements?

[porkchop61]

One of my bias transistors (the ones in the metal loop mounted to the chassis) came out of the metal loop.
These:

I put some thermal compound on it and slid it back in. Since I'm going to be changing the driver board to the White Oak board soon, I think I'd like to change both of them out. What are you all currently using as replacements? 2N3405? Brand, NTE?

Thanks.

 

[laatsch55]

2N5088's...

 

[grapplesaw]

I take a razor knife and slide between the ears all the way down then use Joe‘s idea to knock them out with a wood punch and a hamer while holding tone ear in a vase.. clean out all the old glue and the slide in the new 2n5088 with 5 minutes epox. Pinch the two mount tabs together in the vase and let dry. You can do both at the same time. There is sometimes a pinch divot in the transistor hole to watch out for. Also orientation off the transistor legs may be important for your amp

 

[porkchop61]

Thanks for that!
I can definitely change them out of the metal loops.

What's the advantage of the 2N5088 over the 2N3405? Some higher ratings I assume?

 

[Gepetto]

Thanks for that!
I can definitely change them out of the metal loops.

What's the advantage of the 2N5088 over the 2N3405? Some higher ratings I assume?

Much higher Hfe, lower noise...

 

[porkchop61]

Thank you.
do these need to be matched for Hfe?

BTW: It took me only about 10 minutes to put your cap kit in on Sunday!

 

[Gepetto]

Thank you.
do these need to be matched for Hfe?

BTW: It took me only about 10 minutes to put your cap kit in on Sunday!

Nope...no matching required.

 

[porkchop61]

I'm doing this right now, and in post #20, the attachment say's to match the 2N5088's. I'm just looking for clarification before I epoxy the transistors into the metal loops.
Nice write-up BTW, thanks!

Bias transistors

 

[laatsch55]

No need to match. The bias pots would take care of any differences..

 

[porkchop61]

Okay, thanks for the clarification.

Hopefully I'll get my freshly built White Oaks driver board in this weekend! I'm looking forward to hearing it. Maybe the amp will be quieter with this board.

 

[laatsch55]

90 % depends on wiring runs and placement. The board itself is deathly quiet..

 

[porkchop61]

Well, I haven't moved anything, all factory wiring placement. I only re-did the grounding around the input-output jacks to get rid of the ground loop issue (the jumper between the speaker jack and the input jacks). I also ran a new ground wire from the old driver board to the PSU copper buss bar.
I already have the relay board installed and working properly.

 

[laatsch55]

Werll, should be fairly quiet then....

 

[grapplesaw]

Watch the pin out. The legs are not oriented the same with some brands.

 

[porkchop61]

Thank you.
I did catch that. The 2N5088's I have are different from the factory 2N3403's that are currently in-place.

I de-soldered all the connections to the factory driver board last night and installed ferrules on the wires.
I bought the connectors with the new board, so I like using ferrules with those types of connectors.

 

[porkchop61]

I successfully replaced the bias transistors last night, and installed them this morning (along with the White Oaks driver board).
No smoke, so that’s good
Worked perfectly after I fixed the left channel input wiring boo-boo I made (minor).

Sounds a lot quieter than the original board! Minuscule amount of DC on both speaker outputs to boot.
I could only get the meters to go to -10db with the meter board jumpers in the -20db position.

Amy one drive Magnapan speakers with these amps (4 ohm)? I’m tempted, as they are power hungry.

 

[laatsch55]

I'd think you'd want a 700 driving the Maggies. The 400 will drive em,. maybe not to Nirtvana, but it'll get you in the neighborhood. If you run a 400 on 4 ohms, keepa fan handy. Reach down and feel the heatsinks, add fan as needed...

 

[porkchop61]

I’m currently running them with an Adcom 5400, and they need a little more power
I’ve been watching the auction site, and there are some sheet metal fan shrouds available. Someone is actually remaking new ones.

That will be a good use for the FLIR camera

I’ve been testing the 400 on my A7’s, but they’re only rated for 30 watts. They are not the right speaker for that amp.

Thanks for the information!

BTW: I’ve only been to Casper, but it was a nice little town.

 

[laatsch55]

It needn't be a form fitting , expensive, retro PL fan. Anything that moves air accross the heatsinks is a good thing..
There is no such thing as too much clean power....there are however, consequences to using too much of it...

 

[AngrySailor]

It needn't be a form fitting , expensive, retro PL fan. Anything that moves air accross the heatsinks is a good thing..
There is no such thing as too much clean power....there are however, consequences to using too much of it...