Transistor Cross-Reference 2SD425 2SB555

[LFazio51]

Happy New Year to All!

I'm working to restore a Yamaha CR1020 (http://audiokarma.org/forums/index.php?threads/cr1020-restoration-guidance.798122/) and it appears that the transistors are somewhat out of spec. I'm very fresh into the hobby and have no idea what the appropriate modern cross-reference is and was hoping to acquire recommendations from those familiar with this unit. I've researched an earlier thread where Echowars was recommending the On-Semi MJ21193/94, which is perfect but the thread has a few years of age and I would like to validate that this IS the best choice at the moment or, if newer, better performing transistors are available. As always, thanks in advance for your advice and support!

 

[avionic]

Echowars was recommending the On-Semi MJ21193G/94G,

Thats what I'd use.. Or MJ21195G /96G

 

[sregor]

^^^

 

[BinaryMike]

...it appears that the transistors are somewhat out of spec.

That seems unlikely. How did you measure them?

 

[LFazio51]

That seems unlikely. How did you measure them?

With an inexpensive DIY component tester (you've probably seen them on eBay or Amazon). I attached to both pins as well as the shell, which returned the following data:

From my "Yamaha CR-1020 Restoration Guidance" thread (http://audiokarma.org/forums/index.php?threads/cr1020-restoration-guidance.798122/page-7)

MAIN AMP C. BOARD 1
-TR614 (Toshiba 2SB555) - PNP - [hFE=105 / Uf=576mV]
-TR613 (Toshiba 2SD425) - NPN - [hFE=57 / Uf=588mV]

MAIN AMP C. BOARD 2
-TR614 (Toshiba 2SB555) - PNP - [hFE=96 / Uf=569mV]
-TR613 (Toshiba 2SD425) - NPN - [hFE=66 / Uf=581mV]

 

[gslikker]

Especially older transistors no specification graphs, measuring using low currents is a crapshoot, I am sure many would not be alarmed at all reading these specs. Probably the transistors are good?

Now for people into these ON semiconductor devices, it looks to me several modern TO-3 transistors are getting less available. Like MJ21194 below 100 pieces and MJ21193 out of stock / on order at Mouser (at least over here)

 

[BinaryMike]

The original transistors are very high quality devices, and that's not enough evidence to suspect degradation. hFE has to be measured at the manufacturer's specified current in order to have validity. I would put the originals back into service and be happy.

 

[LFazio51]

The original transistors are very high quality devices, and that's not enough evidence to suspect degradation. hFE has to be measured at the manufacturer's specified current in order to have validity. I would put the originals back into service and be happy

Thanks for the feedback BinaryMike, I really appreciate it. I understand your point but I would have thought that the hFE measurement of the pairs, when tested under the same conditions, would have been more similar than the difference indicated. Should I assume the same when testing much smaller transistors? I guess I need to review Echowars thread on testing transistors with a DMM - it appears to be very indepth and may offer a more accurate way to gain insight just short of using a curve tracer with the proper current applied (I don't have one and will likely not ever own one).

It seems there is a never ending amount of decisions involved with restoring these vintage units along with a wide degree of varying advice. This CR1020 is proving to be quite a challenge, its old and access to certain boards and components can be difficult. I'm also trying to keep the solder work to a minimal; removing, installing, and removing again appears to be increasing the overall risk level of damage, therefore, my thoughts have been focused on replacing items that may be "tired" and "out of spec" while I have access, rather than reinstalling and taking the risk of further damage. It's possible that I may be focused too much in this area due to little knowledge of elements we are discussing in this thread. My thinking was to replace $25 worth of transistors while I have access, however, if suitable replacements are not available, then the risk associated with using them may be one worth taking if I cannot create the same level of performance with new transistors. Again, there are quite a large amount of opinions on this and I guess I'll just have to decide.

 

[BinaryMike]

If you know the hFE test current used by your instrument, and you test transistors that have an hFE spec for that current, then you should get readings within the datasheet spec. But most transistors have very broad hFE tolerance, and hFE varies radically with temperature. Types that are sorted into hFE bins after manufacturing might even have 2:1 hFE tolerance. With audio power transistors, the focus is usually on minimum hFE at a current level high enough to correlate with peak 8-ohm or 4-ohm load current in the intended application. Low-current hFE testing of power transistors only suggests that a device is functional or failed.

 

[restorer-john]

...Low-current hFE testing of power transistors only suggests that a device is functional or failed...

Functional- maybe, maybe not. They may test OK at the low voltages of the tester and breakdown at higher voltages that are way below their rating.

Ring emitter transistors (Sanken, Fujitsu) do that when they get old and most of them (except the new type from Sanken) are ancient now.