FS: Vintage genuine Motorola 2N3055 transistors

[Matt Syson]

One version had an H to denote the (by RCA?) which I think was promoted to indicate a more 'robust' situation (they were more resistant to blowing up) and of course no one actually set out to make a 2N5055 but a family of power transistors that would handle up to 15 Amps collector current of which the ones that were 'comfortable' at 60 Volts became 2N3055s. The H versions were (supposedly) suffered less from secondary breakdown where the 'base' region loses control of current flow as I think the revised process removed the possible 'hotspots' across the die. Other variants of what were essentially the same beast with good HF performance, higer Hfe or breakdown voltsage were marked with different numbers so that users could pick devices best suited. Of cpourse a 2N3033 when used in the Neve transformer drive circuit was nowhere near any of the dangers seen in speaker or motor drive circuitry. The 60 Volt rating would probably extend to 80 Volts as long as the SOA wasn't being encroached. The fact it's To3 case represented almost all the heatsink area that it would need for Neve's application was probably just another 'plus'. Reverting back to the discussion, it requires a full test of Hfe curves, frequency response and others to determine what the characteristics that are most important for this job.
There are similar 'discussions to be had over Mullard and Mazda valves with regards to their marking. An old friend who worked for Mullard 'in the day' said that one 'manufacturer would make 'all' ECC83 for example and the other manufacturer might make all ECC82 but as part of the BVA (British Valve association) the parts were 'swapped' so that both could appear to make the full catalogue.
Matt S

 

[31hz]

I can note that homotaxial vs epitaxial construction difference causes a huge issue in "acoustic" amps (running at 70v rail) - my understanding is that the older homotaxial didn't have the bandwidth that the later epitaxial construction did, and caused massive oscillation issues if the later versions were used to repair a blown 370 without an extensive amount of hf filtering in the feedback. It is possible to observe this all day long and we have dealt with that in the past.
I'm not commenting on one thing being better than another - application/implementation is different, definitely operating voltage, but that is a realworld\difference based on HF (below 10kHz in that application) bandwidth capability. it would be interesting to a/b test in the context of the neve doing a frequency analysis. i have stock of homotaxial 2n3055s that i could contribute.

 

[ruffrecords]

Is there a simple circuit that can be used to measure the transition frequency?

Cheers

Ian

 

[blakeyboy]

I still get clients asking about whether the modules they are getting have aluminium RCA 3055's or not...

In old Neve stuff I've seen RCA, Newmarket ( earlier on) , Westinghouse, and BDY20's.
Whether the BDY20 was tried by Neve as an improvement, I don't know....
I've got bagfulls of all types, and I like to change like for like on a 183 etc whether it's a sonically good idea or not.

I particularly use the correct matching old ones in the big ASC1500 and ASC2000 Coutants psu's, and I find I can balance up the series component heatsink temperatures easier that way, so they are reliable. (As well as they can be...! )

 

[ruffrecords]

My Neve colleagues tell me that Motorola was the most commonly used 2N3055 with Newmarket second. It is interesting that the Motorola datasheet specifies the transition frequency as 2.5MHz so these are definitely 'faster' than the original RCA ones. This makes sense because Motorola never had a hometaxial process. The overall parameters of modern replacements seem to be copied from that datasheet which implies there should be no benefit in using vintage parts. In any case, the output stage bandwidth is limited to 146KHz by the 330pF in the NFB loop which is well below the transition frequency of even the original 2N3055s.

Cheers

Ian

 

[JohnRoberts]

Seriously... you guys will argue about anything... remember rule #4. Disagreeing is OK, being uncivil is not.

====

The 2n3055 was the original BSH (brick sh__ house) power transistor... slower than dirt but rugged and reliable. Over the years as power transistor process technology improved, the transistor manufacturers were reluctant to forgo the high sales volume numbers of the original 2n3055 so just shipped new technology ones in place of the old ones ordered under the same original part number.

Engineers rarely complain about receiving improved parts in place of old ones and this probably happens more often than we realize.

I find it difficult to swallow that a slower (lower Ft) power transistor is somehow preferable to a modern device. If the modern device does not work as expected, I am immediately suspicious of the old circuit design not the modern part. That may not be a popular judgement around here.

[edit- for TMI I have even seen power mosfets branded 3055 (like NTF-3055) hoping to piggyback on the popularity of the 2n3055) /edit
JR

 

[blakeyboy]

My Neve colleagues tell me that Motorola was the most commonly used 2N3055 with Newmarket second. It is interesting that the Motorola datasheet specifies the transition frequency as 2.5MHz so these are definitely 'faster' than the original RCA ones. This makes sense because Motorola never had a hometaxial process. The overall parameters of modern replacements seem to be copied from that datasheet which implies there should be no benefit in using vintage parts. In any case, the output stage bandwidth is limited to 146KHz by the 330pF in the NFB loop which is well below the transition frequency of even the original 2N3055s.

Cheers

Ian

Whoops sorry Ian- I meant Motorola rather than RCA! Duh.....

 

[blakeyboy]

Seriously... you guys will argue about anything... remember rule #4. Disagreeing is OK, being uncivil is not.

====

The 2n3055 was the original BSH (brick sh__ house) power transistor... slower than dirt but rugged and reliable. Over the years as power transistor process technology improved, the transistor manufacturers were reluctant to forgo the high sales volume numbers of the original 2n3055 so just shipped new technology ones in place of the old ones ordered under the same original part number.

Engineers rarely complain about receiving improved parts in place of old ones and this probably happens more often than we realize.

I find it difficult to swallow that a slower (lower Ft) power transistor is somehow preferable to a modern device. If the modern device does not work as expected, I am immediately suspicious of the old circuit design not the modern part. That may not be a popular judgement around here.

[edit- for TMI I have even seen power mosfets branded 3055 (like NTF-3055) hoping to piggyback on the popularity of the 2n3055) /edit
JR

Popular with me John, so long as the devices are not the crappy small die copies that won't do more than 5A without blowing up. Modern Motorola MJ series are famous for this. First I know of this sort of thing was amplifiers being returned to the workshop with blown outputs over and over again in the early 90's, and when we questioned the supplier, he admitted they were cheap Hungarian copies of the 2N3773's, and a few years later the MJ15024 and 15025's started to be unreliable, for similar reasons.....

 

[JohnRoberts]

Popular with me John, so long as the devices are not the crappy small die copies that won't do more than 5A without blowing up. Modern Motorola MJ series are famous for this. First I know of this sort of thing was amplifiers being returned to the workshop with blown outputs over and over again in the early 90's, and when we questioned the supplier, he admitted they were cheap Hungarian copies of the 2N3773's, and a few years later the MJ15024 and 15025's started to be unreliable, for similar reasons.....

I think Motorola stopped making TO-3 (metal can) power transistors decades ago. I vaguely recall hearing something about moving (selling?) the TO3 production machinery to Mexico. Counterfeit devices are never to be trusted.

I used 2n3773s in my DIY power amp I designed back in the 70s, a good robust power transistor.

Back last century Peavey bought Motorola power transistors graded for secondary breakdown, and gave them Peavey house numbers. I wasn't the amp design guy inside Peavey, but recall there were complementary pairs in the system recommended for different power points.

JR

 

[ruffrecords]

I think Motorola stopped making TO-3 (metal can) power transistors decades ago. I vaguely recall hearing something about moving (selling?) the TO3 production machinery to Mexico. Counterfeit devices are never to be trusted.


JR

Motorola semiconductors is now On-Semi and they still supply 2N3055s through distribution. Heaven only know where and by whom they are made though.

Cheers

Ian

 

[blakeyboy]

 

[JohnRoberts]

Motorola semiconductors is now On-Semi and they still supply 2N3055s through distribution. Heaven only know where and by whom they are made though.

Cheers

Ian

Thanks, apparently the motorola semi group spun out as On-Semi in 1999 (according to an internet search).

Digikey shows around 4 different vendors selling 2n3055 TO3s, but not motorola. I didn't check every spec sheet but they look like 2.5MHz fT so significantly faster than the old soldiers everyone is searching for. I vaguely recall something like fT more like 200kHz back in the 70s.

JR