I want to build a small amplifier which has a BC179 in the schematic. I would like to use a more up to date PNP transistor such as the 2N2907A. Will this transistor sub for the BC179? 😕
???
2N2907A is about the same age as a BC179.
It may sub for a BC179, but the BC179 is low noise.
It depends on the circuit, but the 2N2907A has similar gains at 1 mA so probably yes.
John
2N2907A is about the same age as a BC179.
It may sub for a BC179, but the BC179 is low noise.
It depends on the circuit, but the 2N2907A has similar gains at 1 mA so probably yes.
John
Thanks for the quick reply. I guess I should have said a more readily available transistor since I already have plenty of 2N2222A and 2N2907A transistors. When looking on a transistor data sheet, what do I look for to determine the noise factor of a given transistor or FET? Or is there anything?
Hi
The noise figure is given for low noise transistors but not necessarily for other types. So if it isn't there it isn't. If it is, it will have something like N or Nf and should be specified in dB for a given frequency or range, input impedance and bias current.
More to the point is this transistor in a preamp stage or power amp - if not a preamp, it probably won't matter too much.
John
The noise figure is given for low noise transistors but not necessarily for other types. So if it isn't there it isn't. If it is, it will have something like N or Nf and should be specified in dB for a given frequency or range, input impedance and bias current.
More to the point is this transistor in a preamp stage or power amp - if not a preamp, it probably won't matter too much.
John
I was able to find cheap surplus FPQ2907, FPQ2222, and also 3906 in quad DIPs.
In my app I don't care too much about the beta match, only VFWD BE matching.
I'm assuming 3904 must be common as quads too, but I didn't see any...
I have baggies of 2n4403, but only singles. A little too small to clip pairs together
with a TO5 heatsink as the clip. Dunno why they are smaller than normal TO92?
In my app I don't care too much about the beta match, only VFWD BE matching.
I'm assuming 3904 must be common as quads too, but I didn't see any...
I have baggies of 2n4403, but only singles. A little too small to clip pairs together
with a TO5 heatsink as the clip. Dunno why they are smaller than normal TO92?
Thanks for the replies. Actually, what I am building is a low level preamp to overdrive the front end of a SS guitar amplifier. I posted here because I figured you folks would have more info on SS components. The original circuit uses a J201 FET input and a BC179 on the output. I have a bunch of 2N2907A transistors and was just wondering if it would be a good sub for the BC179 but from further research, it appears the 2N2907A will produce more noise than the BC179 according to folks on some blogs. I found some data on the BC179 which shows it having a typical noise reading of 1.2dB and a maximum of 4dB. I also find a data sheet for the 2N2907A that showed a maximum of 4dB but no minimum or typical. I think I'll just go ahead and order a few BC179 PNP's and build it. If you're interested I have attached the schematic. Also available at:
JFET_preamp_schematic_s.gif picture by Soapboxsam - Photobucket
JFET_preamp_schematic_s.gif picture by Soapboxsam - Photobucket
Attachments
Thats a darn good circuit topology.
Might even be a decent tube emulator for reasons of voltage feedback to source.
I'd be tempted to put a diode drop in series with R5, but probably just fine without.
Recommend reading: OHSchade, RCA Beam power tubes 1939, especially Fig 35.
Observe how Triode curve set is constructed from Pentode curves. Same theory.
Your PNP is located where the component noises you speak of are not a problem.
I'd be far more worried about the guitar's cable.
Might even be a decent tube emulator for reasons of voltage feedback to source.
I'd be tempted to put a diode drop in series with R5, but probably just fine without.
Recommend reading: OHSchade, RCA Beam power tubes 1939, especially Fig 35.
Observe how Triode curve set is constructed from Pentode curves. Same theory.
Your PNP is located where the component noises you speak of are not a problem.
I'd be far more worried about the guitar's cable.
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Thanks for the info Ken. I found a listing of 10 BC179s on eBay and bought them. Cheaper than buying just one plus the shipping. I got the J201 FETs in yesterday. I already have a small project board wired so I'm gonna go ahead and install the 2N2907A and see how she works. I'll replace it when the 179s come in to compare. It's small enough to fit into my bass guitar as the pots have an access plate on the back. Another thing I'm thinking about doing is installing a 50K pot in place of the 47K - R9 resistor, so I can have some control over the amount of signal presented to the input of the amplifier.
I am using what I know are very good cables. I built them over 20 years ago. I can't remember who I got the cable from but I do know the cable is Belden low capacitance and the connectors are Switchcraft. They have never failed and have never been noisy.
I'll post here when I get it finished and working. Thanks again to all for your help in clearing up my concerns on this project. 🙂
I am using what I know are very good cables. I built them over 20 years ago. I can't remember who I got the cable from but I do know the cable is Belden low capacitance and the connectors are Switchcraft. They have never failed and have never been noisy.
I'll post here when I get it finished and working. Thanks again to all for your help in clearing up my concerns on this project. 🙂
If thats going inside your bass, no problem.
Can't pickup cable noise where none exists.
Got plenty low output impedance to drive long cables after the fact.
Can't pickup cable noise where none exists.
Got plenty low output impedance to drive long cables after the fact.
In the 1980's I spotted a tube emulator in Wireless World.
I took it and adapated it for my own guitar.
I found it needed a bit more gain on the front end and also some treble boost so came up with this circuit.
softlimiter | harrabylad | Flickr
I took it and adapated it for my own guitar.
I found it needed a bit more gain on the front end and also some treble boost so came up with this circuit.
softlimiter | harrabylad | Flickr
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