Phase linear 400 driver replacement

[The Donk!]

I'm rebuilding one channel in a PL-400

One channel already has OnSemi's in it. (MJ15015s)

I 'm going to use MJ15024s for the other channel.

However, I have searched High and Low for a sub for the drivers mounted right underneath the finals.

And no one seams to talk about them.

They are Motorola SJ2741's

Any idears on this.

And if I some how read what I'm trying to find out here, on this site already and didn't realize. My bad.

[wg_ski]

Finding original spec drivers is going to be a real SB. RCA410's, RCA1B05's or 2N5240's are going to be rare - and probably fake if you find them. When I've replaced drivers, I just use the same as whatever the outputs were replaced with. Just make sure the replacements don't have fT's above about 6 MHz or particularly high beta. I have used MJ15024, 2SD424, 2SD555, and VCEO-selected 2N3773.

[bear]

I've just used the same device as the outputs many many times with no bad consequences ever...

_-_-bear

[The Donk!]

I picked up some NOS RCA 138194's

They work.

Does anyone know what the Bias current should be for these amps?

[djk]

"One channel already has OnSemi's in it. (MJ15015s)"

Get those out of there (only rated at 120V)!

Bias should be 0.34V on the base of the outputs.

[wg_ski]

Originally posted by djk
"One channel already has OnSemi's in it. (MJ15015s)"

Get those out of there (only rated at 120V)!

I would at least test them to make good and sure there's no leakage at 150 volts. Whoever fixed it last may have checked this - the VCBO is 200V and most of them will take this C to E. They're good for 3A at 60V, which is probably better than the RCAs or the PL909's (but not the 15024).

They have the same p- poor beta curve as the 2N3055 and only a 2 MHz fT. This would tend to keep stability problems at bay.

[bear]

It's a class B amp - don't recall the factory method for setting the bias. The manual pages are doubtless floating about.

But it has so much feedback and so little bias that it may not matter much within reason - especially if you can't find the xover notch on a scope...

Personally, I'd want the same devices in both channels... but for casual stuff, probably makes no diff...

_-_-bear

[djk]

"the VCBO is 200V and most of them will take this C to E. "

The reverse biased CE voltage is 200V, but that does not describe an audio amplifier. You must use the Vceo, which is only 120V.

I have had failures with the MJ15015 with only ±57V.

If you expect them to work in a PL400 they need to be checked for 170V minimum.

[d3imlay]

The service manual has a bulletin that allows MJ15024's to be used for drivers. Since then the MJ21196's have been introduced which has a better SOA. I now use only MJ21196's for outputs and drivers.

Below is a link to my crude Phase Linear web site.

Phase Linear Bulletin

[poynton]

Originally posted by d3imlay
.......... I now use only MJ21196's for outputs and drivers.........

Hi.

Any problems with fakes ?

There are a lot on Ebay from HK and also France (trays of 100)


I have to repair my 400

Andy