FG504 Q1040 equivalent? 151-0438-00 -> 151-0712-00 -> MPSH81


EJP
 

Finally tracked down my clipping FG504 to Q1040 in the gain stage, A1 board, diagram <4>. Part number is 151-0438-00 which xrefs to 151-0712-00 MPSH81. Suggestions for equivalents welcome. This being a push-pull pair of LTPs should I replace its mate? or all four?

Its complement is 151-0424-00 which xrefs to 2N5769, which might give a clue.

TIA

EJP


Tom Lee
 

A PN2369 looks to be a good complement to that PNP. Widely available and cheeeep.

Cheers,
Tom

Sent from an iThing, so please forgive the typos and brevity

On Oct 17, 2021, at 0:15, "EJP" <esmond.pitt@bigpond.com> wrote:

Finally tracked down my clipping FG504 to Q1040 in the gain stage, A1 board, diagram <4>. Part number is 151-0438-00 which xrefs to 151-0712-00 MPSH81. Suggestions for equivalents welcome. This being a push-pull pair of LTPs should I replace its mate? or all four?

Its complement is 151-0424-00 which xrefs to 2N5769, which might give a clue.

TIA

EJP





EJP
 

On Sun, Oct 17, 2021 at 07:15 PM, Tom Lee wrote:

A PN2369 looks to be a good complement to that PNP.
I don't need a complement to the PNP. I need the PNP. 2N5769 is its NPN complement. I've seen 2N5771 suggested but also debunked.

EJP


Tom Lee
 

Sorry. I misunderstood your post.

Is the problem with the 2N5771 its lower BVCBO rating? Otherwise, it is what I would have used. I haven't looked at the schematic to know if BVCEO matters more than BVCBO.

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/17/2021 15:44, EJP wrote:
On Sun, Oct 17, 2021 at 07:15 PM, Tom Lee wrote:

A PN2369 looks to be a good complement to that PNP.
I don't need a complement to the PNP. I need the PNP. 2N5769 is its NPN complement. I've seen 2N5771 suggested but also debunked.

EJP




EJP
 

No details were given by the 2N5771 debunker, and it wasn't a source I would place much reliance on (diyaudio).

Vce is well under 10V in the FG504 so I doubt BVCEO or BVCBO can be an issue. 2N5769 's Ft=650MHz is important as the FG504 switches at over 40MHz.

EJP


EJP
 

In fact 2N5771 is far too slow at 8MHz. How about 2N3906 (250MHz)? I think I even have some.

EJP


Tom Lee
 

The 2N/PN5771 has an 850MHz ft. I've used it frequently, paired with members of the 2N918/2N2857/2N5770 family. With a 10V max VCE, applied, the PN5771 should be just fine as far as breakdown voltage is concerned. What Ic, max and power does it have to support?

Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/17/2021 16:49, EJP wrote:
No details were given by the 2N5771 debunker, and it wasn't a source I would place much reliance on (diyaudio).

Vce is well under 10V in the FG504 so I doubt BVCEO or BVCBO can be an issue. 2N5769 's Ft=650MHz is important as the FG504 switches at over 40MHz.

EJP




Tom Lee
 

?? No, it's an 850MHz ft part!

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/17/2021 17:04, EJP wrote:
In fact 2N5771 is far too slow at 8MHz. How about 2N3906 (250MHz)? I think I even have some.

EJP




Tom Lee
 

I just checked online to see where you might have gotten that wrong number. I see that at least one datasheet has a silly typo. It gives a number, 8.5, and assigns it a unit of MHz. But if you read the text in the middle you see that what they actually mean is that this is the current gain at 100MHz. That extrapolates to a unity-gain frequency of 850MHz; that's ft.

The 2N5771/PN5771 is a very fast transistor. Wavetek used it all over the place in their 50MHz function gen. I've used it all over the place as well. It is certainly a lot faster than 8MHz. :)

Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/17/2021 17:09, Tom Lee wrote:
?? No, it's an 850MHz ft part!


EJP
 

Thanks Tom, well spotted. Now to find them in Australia ;-)

EJP


Tom Lee
 

I imagine that shipping cost could well exceed the cost of the transistors. I hope that you can find a local vendor with a stash of 2N5771s at reasonable prices!

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/17/2021 18:04, EJP wrote:
Thanks Tom, well spotted. Now to find them in Australia ;-)

EJP




Mark Vincent
 

EJP and Tom,

How about a 2N5400? Its ft is 400mc. Mouser has these. The voltage is way higher than you need and may be easier to find.

Mark


Michael Perkins
 

Try a 2N4957.
Has better specs.
Mike

On Sun, Oct 17, 2021, 3:44 PM EJP <esmond.pitt@bigpond.com> wrote:

On Sun, Oct 17, 2021 at 07:15 PM, Tom Lee wrote:

A PN2369 looks to be a good complement to that PNP.
I don't need a complement to the PNP. I need the PNP. 2N5769 is its NPN
complement. I've seen 2N5771 suggested but also debunked.

EJP






um-gs@...
 

Hi EJP,
I could acquire a few MPSH81 originals (to repair my FG504).
I coud give you one if you would pay shipping cost (letter?) from Germany.

Regards, Gordian


EJP
 

I will note that on examination Q1040 is a TO-3, not TO-92, along with its three fellows in that stage. I can't see a wattage reason for that, as the stage is strictly a voltage amplifier, with an output stage to follow. Is it for some stability reason?

EJP


EJP
 

My mistake, I had meant to write TO-39 or similar, got confused. Anyway a metal can package as in many driver transistors. They have large radial heatsinks. Just wondering why.

EJP