2N3055 Transistors

[Techman]

I've noted that it seems to come up in various threads about the fact that newer replacements of these transistors can cause problems in older circuits that were designed round the original and less efficient versions of these transistors, due to more recently manufactured versions actually being 'better', thus causing instability in audio output stages.

These transistors are/were also used as 'pass' transistors in many power supplies. I think I would be right in thinking that there has been no noted problems when used in this respect.

I tend to buy these transistors as and when from John Birkett in Lincoln when he can find them - he usually needs a few weeks notice to look some out. I'll tell you a funny story - A few months ago I had gone into the shop and asked John if he had any of these transistors to hand and four would do. He said he would have to have a look at his other 'store' shop and to pop back the next week. I think it was a few weeks later that he actually had the transistors at the main shop. Remember that John is now in his later eighties and struggles a bit with finding and seeing components that that are not within easy reach near the main shop counter unless he has a 'helper' or his daughter there. Anyway, I was in the shop and he said that he had the transistors and that they were in a bag somewhere behind the counter and his daughter was there trying to identify which bag they were in. The bag was eventually identified and a quick look showed that they looked like original old stock individually sealed in military packaging, but I didn't look that hard and left the shop with the transistors and other bits and pieces after paying.

On the way home I called in at a friends house in a village that I had once lived at back in the 80s/90s, who is also a radio and electronics person, although not a member of this forum. When I got out of the car I put my hand into the bag and pulled out one of the military wrapped packets that I'd got from John intending to open it up in the friends house to have a look at the transistor type. Having cut open the thick polythene and unwrapped the corrugated card and waxed paper wrapping, you can imagine my surprise and slight irritation to find a rather nice, but no use to me phono jack socket. I instantly assumed that as all the four packages looked the same that John had given me the wrong bag and that I'd got four jack sockets instead of four transistors. My friend said that he thought he had some old chassis with these transistors on and he'd look them out, although I said not to worry as I'd take them back the next time I went into Lincoln and visited the shop.

Now for the best bit - When I got home I checked out the contents of the rest of the bag and found that the other three packets were in fact 3055 transistors and it just happened to be the one that I had pulled out first that was a jack socket. This was on a Friday, the next day, Saturday, my friend decided to visit and was very apologetic to inform me that when he found the scrap chassis with the 3055 transistors and tested them, they were in fact all faulty except one which he had with him, so of course I then told him of the fact that it was only the one that I was short of and should have brought the whole bag out of the car and into his house and checked the others the day before. When I was next in John's shop I told him what had happened and he said to bring back jack socket when next in and he would find another 3055 to swap for it. Well last Friday I had the socket with me when I happened to visit the shop and John remembered the transistor he owed me without me mentioning it and I said that I had the socket with me and put it on the counter in its now opened packing - I don't actually think he was that bothered about having the socket back. I was expecting another sealed RCA transistor like the previous three, but it was a slightly crusty, but unused Motorola. I'm not complaining as he only charges 50p each for these transistors, although it's a shame that I couldn't have had a nice set of four all the same.

So that's the little story, now for the real purpose of this thread - This single transistor that I got from Johns on Friday and the used transistor that my pal brought me a while ago are both Motorola types, and measuring the forward junction resistance of these compared with both one of the three RCA sealed transistors plus another used RCA transistor also bought from John some time before (he also sells used but tested 'pulls' for 50p, so I was actually quite lucky to get those new ones), the Motorola ones have a higher forward junction resistance than the RCA ones. I would say that this is not perhaps unusual between manufacturers. There's not a lot in it, just a few ohms, but what I'm getting at is can we deduce that one transistor may perform better in a 'older' audio output stage than perhaps another, although I would say that both types would be regarded as 'older types, particularly the sealed RCA types dated 1971.

I tend to buy these transistors for replacement repairing 'blown' power supplies, but I think what I'm asking is would these particular, and at present 'unused' transistors be wasted in this application and would be better saved for use in repairing vintage audio amplifiers?

Also, please don't limit any discussion to just this particular question but feel free to discuss any points regarding the 2N3055 transistor both old and new that may be applicable.

[McMurdo]

I've only come across problems with oscillation of amplifiers when using new ones in old equipment. After a discussion either on this forum or maybe diy-audio I fitted 'base stopper' resistors and it cured it...and it's happened again so I was prepared.

For series pass duty in linear power supplies I'd say a modern one will be fine. Save the vintage ones for audio!

[emeritus]

One of the old hands at Plessey told me that this was a common problem in the early days of transistors, where circuits that were perfectly stable when designed and first manufactured, were often found to oscillate in subsequent production runs using later batches of transistors. A common remedy was to slip a ferrite bead over one or more of the transistor legs, feasible with the construction techniques then in use.

[Oldcodger]

Similar tale to last post. On the bench at GEC, we often found that certain circuits had "problems" with certain makes of IC/transistor. One studious bloke even went as far as to make a list of what problems to expect with different makes of component( and which makes cured the problem).

[Maarten]

The higher fT could give oscillations as said, but another problem would be that the older examples are manufactured with another process and actually have a larger SOA. I think the one with 3055H on it, was manufactured using the new process, one or more of the other samples may be manufactured using the old process.

[fetteler]

I reckon that all the 'old' vs 'new' 3055 discussions result from the transition between the original homotaxial type and the subsequent expitaxial types. A very common misconception is that the recent 2N3055H is a reproduction of the early homotaxial type when in fact the H designation means nothing of the sort. The 2NN3055H is an expitaxial device with higher safe operating area than a standard 2N3055 at V CE >40V.

The myth that the H means homotaxial is especially rife on audio forums...

Cheers,
Steve.

[DangerMan]

I always believed the original inventor's (RCA) 2N3055 devices were all Homotaxial, and were only renamed as 2N3055H after the "other suppliers" new planar type 2N3055 became commonly sold as plain "2N3055" but then had been found to be very much different animals.

This was done so that a user had a way of actually specifying the "original spec" homotaxial, (rugged. but low ft type even if not actually original) but it possibly gave RCA a market for using the cheaper planar process themselves by using the original type number.

Sadly, not all manufacturers (e.g. RCA?) re-described their "old-process" devices from the same date as the new planar ones appeared, so some "2N3055" 's were actually 2N3055H's (which didn't really exist by name yet) after that event.

Still with me?

So, a lot of 2n3055's at that time were now really planar ones so with a higher ft.. and they were, and still are still described the same.
Perhaps better ft was seen as invariably a good thing?

From my experience the original pre Homotaxial (H) types were undoubtedly very rugged, and the newer planar ones were undoubtedy less so but at least these were better for audio, provided you took more care not to blow them up.

Indeed, in my experience Motorola devices the first ones known for guaranteed better ft and therefore improved hole storage effects in audio amplifiers. I think data sheets at the time showed 3MHz from Motorola vs 800 kHz from others.

Wasn't the very rugged, and very slow, RCA 2N3773 as used in the first Quad 405's a proper homotaxial device?

It was certainly very robust and didn't need many of the faffy capacitor tweaks that the later devices needed to stop them going daft.

[MrBungle]

Some interesting discussion of new vs old 2n3055's here: http://www.amplifier.cd/Test_Equipme...NIX%207603.htm

This is in German, which fortunately I speak, read and write, but you can chuck it through Google translator if you need to. At worst, the curve tracer reports of the 2n3055 will reveal some interesting differences.

[G6Tanuki]

The Hometaxial-vs-Epitaxial issue, and extended frequency-response of some variants of the 3055, *can* be an issue in power-supplies: I recall one where a failed transistor was replaced, and the PSU then suffered a 'squegging' type oscillation around 750KHz at certain load-currents.

Managed to source an original-spec 3055 and happiness was restored.


Some 3055s would work tolerably as a top-band PA!

[m0cemdave]

These RCA data book extracts (from 1977) were posted to a previous thread on the subject:

https://www.vintage-radio.net/forum/...8&d=1453837542
https://www.vintage-radio.net/forum/...9&d=1453837542

[percival007]

Originally Posted by McMurdo

I've only come across problems with oscillation of amplifiers when using new ones in old equipment. After a discussion either on this forum or maybe diy-audio I fitted 'base stopper' resistors and it cured it...

What sort of Value did you use?
Do you think 4.7 Ohms for example would suffice?

Cheers,

James.

[Synchrodyne]

Here are some earlier RCA writings that tend to stress the advantages of the hometaxial construction of the (original) 2N3055 for audio amplifier purposes.

The full article is in "Electrionics World", available here: http://www.americanradiohistory.com/...aster_Page.htm.


Cheers,

[Techman]

Originally Posted by G6Tanuki

some variants of the 3055, *can* be an issue in power-supplies:.........the PSU then suffered a 'squegging' type oscillation around 750KHz at certain load-currents.

Having said that I hadn't noted any issues with these transistors in power supplies in my first post, your post above has reminded me that without realising it, I may have actually experienced this myself with a power supply. I had a radio transceiver with an inbuilt power supply running at 14.5 volts. This voltage, although within the desired range, was at the higher end - the nominal voltage would be around 13.8 volts. The power unit would normally be adjustable, but had been re-built and modified by someone in the past and was now fixed at this voltage, probably due to the fact that these radios work at their optimum TX performance at this slightly higher voltage. As this particular set was used mainly as a 'listening' set and left running for extended periods of time and had already suffered a couple of the filament lamps in meters and mode indicators fail, I thought it would be better to run it from an external power supply of just 13.8 volts to save on lamp changing.

An unexpected fault then manifested itself in that when the radio was connected to this external power supply and it was switched on at the mains switch, there was an oscillation at audio frequency. It's hard to say what the frequency was as I never checked it, but it was a high(ish) pitched whistle that transmitted out with the audio on FM and gave a full clock end stopping the RF output meter on SSB with no audio modulation as with a dummy mic plug where there obviously should have been no drive. On receive, the set seemed to be working ok, but if the squelch control was set to cut out all receive noise and the volume control was then set to maximum, the whistle of the oscillation could just be heard from the inbuilt speaker of the set. Powering the set down and switching on again via the sets own internal power supply restored normal operation.

After some experimenting, I found that if the external 13.8 volt power supply was switched on at its mains switch first without the radio connected to the output terminals, the radio would then work fine when connected to the terminals with the power supply already in this switched on and powered up state. This would have been very inconvenient and I found that the radio would work fine with no oscillation when permanently connected to, and powered up from mains switch on, from an old basic 12 volt only, non regulated power supply, which from memory just contained a transformer, rectifier and basic smoothing with some sort of electro-mechanical overload trip. This type of power supply is actually much safer for long term and possibly un-attended receiving use as there's no chance of a PSU fault suddenly chucking 20-30 un-regulated volts at the unsuspecting radio - I have had this happen in the past, but caught it in time before any damage occurred!

At the time, I put this oscillation fault down to a strange 'quirk' of the radio and I never investigated it further once the set was running normally from either its own or the external 12 volt power supply, the latter being even better for the radio being significantly less than the other 13.8 volt unit, but still within the operating spec for the radio when receiving. However, I'm now thinking that this oscillation could well have been due to the power supply, which although I still have, but have never looked inside (it came with one of those job lots of bits from the local surplus equipment sale a while back), should be fitted with a 2N3055. This power supply could have had a more recent transistor fitted by someone - I'll have to open it up and have a look for any signs of work. Having said that, this particular power supply would likely date from the early 1980s, so would this date of original transistor sit with the later type or the earlier type being discussed on this thread - I suspect possibly the later?

There's also now a question with regards to the particular transistors that I've got as I now have a power supply for repair that needs a 3055, so is there any one of the transistor types that I have that could be sacrificed in the repair of this unit, or should I just get a known recent replacement type?

I was wondering about the 'H' suffix RCA one, but was hoping to possibly match that up with the odd non 'H' RCA one if need be, although from what I'm gathering from previous posts, this may not be a good idea. I think the junction resistances measured about the same, but I think I'm going to re-check them later and take more exact readings.

[Boulevardier]

Techman - I remember Birkett's in Lincoln - went there a few times when visiting a friend in the early 1970s. Very good shop, and nice to hear that it's one of the few old-style component shops that are still there.

[Argus25]

One trouble, that happens nearly every time, with any 2N3055, except the some of the early ones, is when they are used to replace germanium power transistors in switch-mode supplies, especially self oscillating Royer types. High frequency oscillations occur due to the transformer's leakage inductance, even with the toroidal transformer versions where that parameter is lower. The transistors quickly overheat. It is worse with some than other variants of 2N3055's, presumably there is a wide variation in the fT's of clone types. It comes right with 0.1uF base-collector capacitance added to lower their frequency response to more like a germanium, but sometimes it requires additional R-C snubber networks on the collector-emitter to get them to behave.

The same type of instability can occur in audio amps with transformer outputs at the point the output stage is over-driven with bursts of oscillations on the leading and/or trailing edges of the clipped waveform.