Sunn Concert Bass Output Transistors

[nsubulysses]

Hey quick Q about Sunn Concert Bass output transistors. This amp has 2N3055 output transistors like most 60s and 70s SS amps it seems. I know Acoustics are particular about using old 2N3055 which I believe have 0.8MHz current-gain bandwidth (?). I think new 2N3055 are 3MHz and will not work in old Acoustics because of high frequency noise, but is this true for all old amps with 2N3055s or are only Acoustics sensitive to this. I'm about the resurrect a red knob Sunn Concert Bass that has 4 output transistors shorted.

I got some OTs from weisd.com -- NTE130. Datasheet shows 2.5MHz current-gain bandwidth. Is this a poor choice for this amp?

I have never found a schematic online for this amp. I was able to get a physical copy from a friend who works at a repair shop though. I can post a pic if needed, but it is NOT the silverface version that has 3 bridge rectifiers, if that helps.

Any thoughts?

[Audiotexan]

Hey quick Q about Sunn Concert Bass output transistors. This amp has 2N3055 output transistors like most 60s and 70s SS amps it seems. I know Acoustics are particular about using old 2N3055 which I believe have 0.8MHz current-gain bandwidth (?). I think new 2N3055 are 3MHz and will not work in old Acoustics because of high frequency noise, but is this true for all old amps with 2N3055s or are only Acoustics sensitive to this. I'm about the resurrect a red knob Sunn Concert Bass that has 4 output transistors shorted.

http://music-electronics-forum.com/t37014/ A great thread to read, and addresses what you seek right on target IIRC.

I got some OTs from weisd.com -- NTE130. Datasheet shows 2.5MHz current-gain bandwidth. Is this a poor choice for this amp?

Personally NTE/ECG is a bad replacement for *anything* in my opinion (unless there is absolutely no other alternative), as I've heard time and again from different sources that their practice as a company was to buy up the factory rejects from OEMs at a substantial discount, and then relabel them and cross reference them (sometimes quite loosely). Now this may be an old tech "superstition" or perhaps I'm repeating (in error) an old tech "urban legend" however....I'm inclined to believe it given my experiences with NTE/ECG silicon-based components (IC's/transistors especially). Someone here will correct me if I'm wrong.

I have never found a schematic online for this amp. I was able to get a physical copy from a friend who works at a repair shop though. I can post a pic if needed, but it is NOT the silverface version that has 3 bridge rectifiers, if that helps.

Any thoughts?

New schems (or alternate versions) are always welcome, post away!
Regards
AT

[nsubulysses]

I used NTE123 as a replacement for MPF161 in an old Gibson G-10 that was noisey. Wonder if that's why it came back 3 weeks later noisey again .....

I will check that thread thank you

[J M Fahey]

This amp has 2N3055 output transistors like most 60s and 70s SS amps it seems. I know Acoustics are particular about using old 2N3055 which I believe have 0.8MHz current-gain bandwidth (?).

True

I think new 2N3055 are 3MHz and will not work in old Acoustics

True

because of high frequency noise,

No, that´s not the problem.
*Maybe* some marginally stable amp will oscillate with faster modern ones but that´s not the point.
Low bandwidth is a secondary effect of old technology Hometaxial building technology which gave you relatively "thick" base dies, which were slower but stronger.
Later ones are Epitaxial, a different technoogy, faster, cheaper and efficient but the much thinner layers are less strong if abused.

but is this true for all old amps with 2N3055s or are only Acoustics sensitive to this. I'm about the resurrect a red knob Sunn Concert Bass that has 4 output transistors shorted.

AFAIK most if not all amps used hometaxial ones; even if they didn´t specifically ask for them the standard was the very robust RCA and second the Motorola version.

I got some OTs from weisd.com -- NTE130. Datasheet shows 2.5MHz current-gain bandwidth. Is this a poor choice for this amp?

NTE in general are an expensive and poor choice for anything.

[Enzo]

This amp has 2N3055 output transistors like most 60s and 70s SS amps it seems. I know Acoustics are particular about using old 2N3055 which I believe have 0.8MHz current-gain bandwidth (?). I think new 2N3055 are 3MHz and will not work in old Acoustics because of high frequency noise, but is this true for all old amps with 2N3055s or are only Acoustics sensitive to this.

Don't try to make it more complicated than it is. Some very wise advice, and don't recall who said it first:

When you see hoof prints in the dirt, think horses, not zebras.

Acoustic was particular about 3N3055 because that was the transistor everyone used in those days. Name another transistor with similar specs that they could have used in 1969. Even then they were iffy. They are a 60v part, and Acoustic was using them in 90v circuits. The reason any new 2N3055 might not work is because the ones today are shadows of the original, and won;t hold up. Nothing to so with freq range. If you want to go all spec sheet on us, look at SOA - safe operating area - on the data sheet for any power transistor. The old orignal parts had more space in the SOA than new 2N3055.


NTE130? If you are going to order something, why not just order the original instead of the NTE? Mouser sells 2N3055 for $2, and I see Mouser has dropped the NTE line altogether. Newark still sells NTE. and they ask $4.89 each for them. SO the NTE130 costs two and a half times what the real part costs.

These circuits, in my opinion, are not concerned whether the transistor is capable of operating at 3MHz, because the circuit doesn't ask it to.


MY often stated view on NTE. Although we don't know who made them or what they really are, I do not object to NTE because I think their parts are crappy and won't work. I object because they are only sold as approximations of what you want, and at a steep price. We already looked at the NTE130. MY favorite transistor is the MJ15024. Mouser sells those for $5.87. Newark sells the NTE388 that subs for it at $16.55. I expect their transistor to work, especially is alone. But when I have a row of power transistors, they have to work together. An NTE130 in a row of 2N3055 is not likely to share current evenly, nor is it likely to track thermally. That means the part will either hog current or not carry any. SO why pay triple or more for the price?

[loudthud]

Some time ago I tried to post Concert Bass schematics on Ampix in GIF format. The bugware on the site blew the files up to about four times the size of the files I uploaded and you can't download them. There is no thumbnail shown, only a silver trash can. I sent a message to tboy about the issue and never got a reply. Attached below is the power amp. The Concert Bass, Lead and Slave should all have the same schematic.

Edit: the attachment won't download on my computer. Arg!

[Enzo]

Opens for me. Power amp GIF.

A later version:
http://bmamps.com/Schematics/Sunn/sunn_concertbass.pdf

[loudthud]

Enzo, that's the earlier version (D1003) with the eight wire power transfomer and bridge drive output. The one I posted has the five wire power transformer and conventional totem pole output (D1079). There is a separate schematic for the preamp that I can't find just now.

[Enzo]

Oh, sorry, the file name in my computer says "later", so I I accepted it.


Is this the preamp you want or is this a wrong one?

[loudthud]

Yes, that's the later Concert Bass preamp drawing number D1085 dated 9-24-1975. They cut off the title block.

[nsubulysses]

Alright, as I was saying I hit the mother load in service info for this amp. I was unable to find red knob schematics but a kind repair shop shared their whole Sunn Concert bass file with me. Finally got around to scanning it -- all in all 14 pages of schematics, parts lists, and service updates including "shake proof" speaker jack mod and a power amp stability mod.

Sunn Concert Bass Schematics and Service Info.pdf
Linked here if attachment doesn't work

I believe pages 1 and 2 are for red knob Concert Bass and all the other pages are for the silver face version.


As some of you suggested the NTE130s did not work out. I needed 4 so I ordered 6. 3 matched pretty good; 1 was very strong; 1 was very weak; 1 did not work at all.

I ordered RCA 2N3055Hs from electronicsurplus.com for <$2 each and the amp seems to run great, putting out 144W at clipping into 4 ohms. No matching issues with these.

Thank you for your input.

[loudthud]

Thanks for sharing the pdf. The mod info is something I have never seen before.

[Audiotexan]

Thanks for sharing the pdf. The mod info is something I have never seen before.

Seconded! TY!