Wait before ordering, i'll get back toy you...

Craig,

When looking for replacement transistors, it is important to stay close the the original characteristics like the voltages, forward current, heat dissipation expressed in watts, pinout, better but not less.

Regarding the BC550B/560B, they will be good replacement for the black bullet ones found on the pre-amp section but I don't think they will be suitable for the output stage.

For the output stage, you may find modern equivalents into the TO-220 package instead of the TO-92.

Here's my best suggestion for now.

Take the output board schematic, write down the HFE you are measuring for each corresponding transistor and post the picture here.  Same as you did previously for the voltages. 

I will give you the best answer I can and maybe you don't need to change transistors at all, we never know!

What do you think?

Sounds like a plan......I have ordered the BC550B & BC560B for the pre amp black tops and will measure up the driver stage devices and see where we stand...........

Craig

I have some good used original vintage 2N3055 in the drawer.

Martin

Well.....this is an interesting exercise....left stage up first.

Now the right stage......

I will get to the remainder tomorrow...….however 453 looks in trouble

The one you spotted is lower than the minimum spec (HFE 30).

The modern equivalents are:

- 37741 =  2N5320

- 37740 = 2N5322

Ok....so the next question is should I replace all 8 off 37741 and the 2 off 37740 devices? bearing in mind Frede's comment regarding his preference to re-use old RCA parts salvaged from scrapped BL5000 sets over purchasing modern day devices? or should I only replace the one out of spec device 😮