Marantz 250 restoration query

[catrafter]

I have seen that diode both under and on top of Q507. There is also a bias network mounted on the rear of the heat sink on some models.

Tom

 

[ocdecio]

I have seen that diode both under and on top of Q507. There is also a bias network mounted on the rear of the heat sink on some models.

Tom

Correct - the one with a diode is encased in epoxy, the one with another transistor is a regular transistor with a connector.

The ones I saw a diode over the transistor came on top encased in shrink tubing connected through a wire, the one installed in the pcb probably under the transistor - but I think I saw pictures of it going over the transistor (maybe it was a 500?)

 

[quadmatrix82]

I think you did it correctly and I am mistaken:

View attachment 2269081

Sorry for the confusion.

Ok so the transistor and diode should touch based on that so I’ll remount them thanks for pointing that out

 

[ocdecio]

Ok so the transistor and diode should touch based on that so I’ll remount them thanks for pointing that out

The diode tracks the predriver temperature so yes their cases have to be in close contact.

 

[quadmatrix82]

If I recall those are for the current limiting section, probably would've cause some issues shorted but not cripple the thing entirely.

Also, where's your bias diode?

Here’s the bias block transistor diode will reconnect when heat sinks ready to mount back on and board complete

 

[quadmatrix82]

Replaced q518 and 519 2n4250 transistors today with 2n5087, interestingly so far these transistors on both boards were still the most closely matched circa hfe 335 I matched all 4 as close as a could with the stock I had ~530hfe.

I mounted the transistors low so they wouldn’t knock on the wiring

 

[quadmatrix82]

Drivers arrived today anyone ever heard of Malay brand transistors? They were bought from a reliable source and was able to match within 2hfe

I’m happy was able to find t066 replacements to keep the original look

 

[ocdecio]

Never heard of it. The one at Quest Components is from Harris, $20 a piece

 

[quadmatrix82]

Reading the notes from the service manual does point 7 mean that both drivers and pre drivers need to be matched within the same hfe range? Or is it a repeat of above to ensure they are each matched?

 

[quadmatrix82]

Never heard of it. The one at Quest Components is from Harris, $20 a piece

Either had I they look well made the 2n3583 is RCA branded I’m hoping these are fine I’ve bought lots of mje parts already which none were good matches

 

[ocdecio]

Pre drivers need to match, drivers need to match. Predrivers and drivers can be in different ranges. Hope this makes sense

 

[quadmatrix82]

Pre drivers need to match, drivers need to match. Predrivers and drivers can be in different ranges. Hope this makes sense

Got it…that what I did, thanks for clarifying just making sure I got it all right before full assembly and test

 

[egellings]

Looks like a Harris Semiconductor part, made in Malaysia.

 

[ocdecio]

Looks like a Harris Semiconductor part, made in Malaysia.

Yessir, you got it. I should have looked at the logo. Here's one (different) from India.

 

[quadmatrix82]

Looks like a Harris Semiconductor part, made in Malaysia.

Good pick up!

 

[egellings]

A bipolar op amp.

 

[quadmatrix82]

Mica insulators arrived today! Drivers now installed with matched 2n3583 and 2n6211 for each channel

 

[quadmatrix82]

Starting to clean up the heat sinks do the outputs go in the same order on both channels that is top to bottom mj21993g x 2 followed by mj21994g as the bottom two?

Given the driver pnp/npn compliments are on opposite ends on each side would outputs follow too?

 

[quadmatrix82]

One channel with bias transistor remounted all new thermal compound of course on drivers and outputs

 

[quadmatrix82]

Is this order for the outputs the same on both channels? I’m pretty sure it is but want to make sure before I put all back together