BA-F1 Output Transistors

[HDJR808]

I've finally gotten around to cleaning and adjusting the BA-F1 that was a craigslist purchase from a year or so ago, and have a question about the output transistors that I found.

The left channel has the NMA1012/NMC1012 combination that is correct for this amp, but the right channel is fitted with a NMA1216/NMC1216 combination. Anyone know which amp would have originally used the 1216 transistors? And whether the specs would be comparable to the 1012 transistors?

No telling when these were installed- the interior is pretty clean, no obvious evidence of ham-fisted repairs. Exterior was pretty tattered. The unit sounds fine, no obvious difference between the channels, offset and bias are stable.

I appreciate any info- Herb

 

[ManyMoonsAudio]

I had one with the same exact setup. The right channel was the oddball ones you mentioned. There is no info on the web about them. I had a channel out on mine and replaced all 8 with 2sa909 and 2sc1586 Sankens and it sounds wonderful! One of the best sounding amps I have.

 

[EchoWars]

The originals are the NMA1012/NMC1012. I'm familiar with the other numbers, but can't recall what they were used in. Regardless, they are all very high-speed devices and contribute a lot to the unique sound of the BA-F1. I'd leave them alone if all is working well.

 

[Nicowico]

I had one with the same exact setup. The right channel was the oddball ones you mentioned. There is no info on the web about them. I had a channel out on mine and replaced all 8 with 2sa909 and 2sc1586 Sankens and it sounds wonderful! One of the best sounding amps I have.

The original replacements for NMA/NMC1012 are 2SA1116 and 2SC2607.

 

[Stene]

The original replacements for NMA/NMC1012 are 2SA1116 and 2SC2607.

as well as NMA1016/NMC1216
For AU-919 Sansui had a note:

 

[EchoWars]

Yeah, I've got a few 2SA1116's and 2SC2607's that I'm hoarding.

 

[Nicowico]

Yes, me too.:yes:

 

[HDJR808]

Thanks for everyone's input.

The amp has been in the mix for a week or so, fed from the preamp output of one of my AU-717's, driving a pair Infinity Renaissance 90's. Sounds fantastic, so I figure I will just not concern myself with the mismatch on the outputs.

Did have a question though, that hopefully someone (echowars?) can help out with. I'm looking to replace the trimpots for the bias and offset, to get rid of the very touchy originals. I plan on pulling the driver boards to check the mounting of the trimpots to match up a multiturn replacement, but if anyone has info on the correct upgrades I would appreciate it.

Also, in regard to my original inquiry, I did find a reference somewhere that the NMA1216/NMC1216 transistors were originally fitted to the AU-819. Being used as a replacement on this amp makes sense I guess based upon the NMA/NMC1012's being common between the BA-F1 and AU-919.

Thanks- Herb

 

[spaghetti]

Since there's already an old thread on this topic I won't start another one. I recently purchased a non working unit and it comes out a couple of NMA/NMC1012 transistors is missing. The others are there and seem fine according to the DMM.

The best subs 2SA1116 and 2SC2607 are a bit hard to find nowadays, I was wondering if there may be some good alternative with high availability. I was thinking MJ15003/15004 or MJ15015/MJ15016 could do the job... the most significant difference with the originals is the lower bandwidth, about 2.2Mhz vs 20Mhz. What is your recommendation?

Thanks,
Andrea

 

[AUD101]

Try searching for "2SC2608 / 2SA1117 Very Rare GENUINE Sanken TO3 transistor NOS" on a certain auction site

 

[Hyperion]

But if you want to pay less money and avoid any possibility of receiving damaged or simply counterfeit devices, then new MJ21193/94 or MJ21195/96 pairs, (bought from a reputable supplier i.e. not an auction site) will do the job, albeit with ~4Mhz bandwidth, which may impact somewhat on the perceived performance of the amplifier in question.

According to the tech's on this site there are a very few amplifiers which depend on the high speed of the originally fitted OP transistors for their unique sound quality. Of the more commonly found vintage SS amplifiers around 6 fall into this category, examples are Sansui AU-919, Sansui AU-X1, Sansui BA-F1, other manufacturers also have examples. I don't know how much difference it makes, but I am prepared to believe there IS a difference.

The vast majority of other amplifiers don't care what OP transistors are fitted, providing the basic spec is met with the replacements. And in many cases replacing the 'original fit' OP transistors with the suggestions above is actually an upgrade as they are extremely robust devices. Such an upgrade is extremely unlikely to improve sound quality, but may significantly improve the ability of the OP stage to take some 'abuse'

 

[ManyMoonsAudio]

I have some 2ST2121 and some 2ST5949 that are absolutely perfect in this amp, and verified to sound exactly like the original outputs in this amp. Sending PM.

 

[spaghetti]

So, I see the best thing would be to find a proper hi speed transistors pair such as 2ST2121/2ST5949, 2SC2608/2SA1117, 2SC2607/2SA1116.

I am thinking that I may try to buy the 2 couples of the suggested MJ pair MJ21195/96 on mouser. Although they're 5x slower than the originals, mounting them on the left channel (the one that's missing one original pair) would allow me to:
1) make sure everything is fine on the left channel, if something bad happens then the original transistors are safe in my drawer
2) get first hand knowledge about the sound difference with the slow transistors
3) have enough time to find the rarer subs without spending top money for them right now

I am going to place my order soon, I already have the mica replacements for the black flag caps in my basket, is there anything else I should replace on sight inside the amp?

thanks,
Andrea

 

[ManyMoonsAudio]

Did the amp have a failure, or did someone just rob the parts out of it? Since you are asking about repairs now, it might be a good idea to make a new thread.

 

[spaghetti]

I purchased it as non working unit. The seller said one channel was not working. After inspection I found out the non working channel was retrofitted with a pair of MJ15004, I mean 2 NPN transistors instead of a NPN/PNP pair. Other than that, the amp is in original conditions, just needs a thorough clean (WIP).

 

[Hyperion]

Would you like to tell us what this 'unit' is?

We are talking in general terms about OP transistor replacements - but what is the unit you are dealing with?

 

[ManyMoonsAudio]

Then aside from replacing all the electrolytic capacitors and the bias/dc offset trim pots, nothing else electrically should be needed.

 

[spaghetti]

@Hyperion of course it's a Sansui BA-F1

 

[spaghetti]

I've not purchased any replacement transistors yet... Since the same MNA/NMC transistors are mounted on the AU-919, I searched the web for that topic as well, and I found some references to the following transistors, that somebody used to replace the original ones. None of them has TO3 casing, but on the BA-F1 this doesn't seem a big issue to me:

2SA1265 2SC3182 (30Mhz, 100W)
2SA1294 2SC3263 (60Mhz, 130W)
TTA1943 TTC5200 (30Mhz, 150W)

They're all pretty cheap compared to the official SANSUI replacements... but apart from wattage, frequency and ampere I don't know if all the above pairs are good replacements for the originals... any opinions?

Thanks,
Andrea