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Acoustic Research AU amplifier - transistor substitution

SiCo Amp

SiCo Amp

Member
Hello folks, I have been restoring an Acoustic Research AU amplifier for a friend and have almost completed the task. The one problem that I have run into is locating a drop in substitution for the obsolete RCA 40311 that is used in the regulator. The unit's 40311 has a short between E-C. If any of you have worked on one of these and know of a reliable drop-in replacement I would greatly appreciate the help. I'd prefer not to re-design the circuit - though that may end up as a last resort. Thank you in advance.
 
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It seems like a pretty ordinary part, but our choice of TO-5 packages is limited. I'm guessing a 2N3053 would drop in. Hfe is a bit low, but a TIP30 is likely to work if you can stand a TO-220. As always, compare datasheets and see what you think.
 
For the life of me, I can not find any information on the 16A1700 transistor used in the AR AU amp. Does anyone know what the recommended modern substitute for the 16A1700 would be? (and the 2N3900a, 2N5567 and 2N3645 for that matter - I have found some generic recommendations, but would appreciate recommendations from folks with actual experience with these transistor substitutions)?
 
SiCo Amp said:
For the life of me, I can not find any information on the 16A1700 transistor used in the AR AU amp. Does anyone know what the recommended modern substitute for the 16A1700 would be? (and the 2N3900a, 2N5567 and 2N3645 for that matter - I have found some generic recommendations, but would appreciate recommendations from folks with actual experience with these transistor substitutions)?[/Q
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If I were doing this restoration I would substitute a general purpose transistor for amplifier or switch purposes. You are right, there are no specification for the 16A1700 but looking at the circuit it looks like a general purpose transistor would work as long as the Collector Emitter breakdown voltage is high enough and the power rating is high enough. I have had good luck substituting transistors based on these properties.
 
Hi just came across this post and I also blew this transistor by accident. I made short and I was frustrated since I just finished restoring.
I could not find any info so I did some trial on error with different transistors I had at home.
I had BC461-CDI and it worked. its also TO39 package with same pinout. Info I found on 40311 is that is NPN? BC461 is bipolar PNP 60 V,1A, 10W
 
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VinAudioRev said:
Did the KSC1845 Work for this? I am working on the same amplifier and Can't find any other information.
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Hello. I don't want to hijack this thread, but I have the same problem. I picked up a nice looking on the outside AR amp. It looks like the whole thing caught fire inside. I have replaced all the caps and resistors, and done the recommended updates. I replaced all the 2n3900a and 16A1700 with KSC1845. The amp works, but there is alot of crackling. I plan on replacing the 2N3900a with BC169, unless someone has a better solution. Has anyone found a modern equivalent for the 16A1700, or any specs?
Thank in advance for any advice, Andrew Chang
 
Put your replacements into chat gpt and see what it returns. I have been using it quite a bit and it has been quite accurate sharing pros and cons. It has access to just about everything that has been posted and verified one way or the other. Include the model and board number and it will zero in.
 
jefferylhenr, you are a genius, or at least have done this before. I have scoured the web for days looking for specs for the 16A1700 and found absolutely nothing. I just tried AI and I was rewarded with a few potential matches, and much data. Though I have done the comparisons yet, I am anxious to give them a try.
Thank you very much for the insight into the modern world.
I will report back with what I try and what works, for the two or three other people who have these amps.
 
andrew c. said:
jefferylhenr, you are a genius, or at least have done this before. I have scoured the web for days looking for specs for the 16A1700 and found absolutely nothing. I just tried AI and I was rewarded with a few potential matches, and much data. Though I have done the comparisons yet, I am anxious to give them a try.
Thank you very much for the insight into the modern world.
I will report back with what I try and what works, for the two or three other people who have these amps.
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It combines data from multiple sources and cuts through the forum phlegm. It’s hard to get a straight answer asking a question in these forums. And you can ask it vrs questions between various alternatives
 
I just tried this, not sure if it's a good answer though... Great idea to use Chat though and then compare to other forums if there is something. Since both the 2N3900a and 16A1700 are in the Phono amp among other places, I'd look for a low noise transistor. I see that the 3900a has an Ic of 100mA, but is very low voltage (18 IIRC). My "vote" would be for the BC550C, just be very careful with the pinout. Do you have at least one good Q of each type to verify with a tester? If you want higher voltage than the BC550, go with the BC546C...it should still be low enough noise figure.

You're asking about replacing a 16A1700 transistor. After digging, I'm confident that you meant the 2SA1700, a PNP silicon transistor used in high‑voltage driver applications. Key specs include:


 
SiCo Amp said:
Hello folks, I have been restoring an Acoustic Research AU amplifier for a friend and have almost completed the task. The one problem that I have run into is locating a drop in substitution for the obsolete RCA 40311 that is used in the regulator. The unit's 40311 has a short between E-C. If any of you have worked on one of these and know of a reliable drop-in replacement I would greatly appreciate the help. I'd prefer not to re-design the circuit - though that may end up as a last resort. Thank you in advance.
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When this amp was designed (1966), this RCA 40311 transistor seemed appropriate. RCA is now long out of the semiconductor business, so exact replacements will be scarce and old. This is an under rated part for this application (it overheats) and will often fail; if working it urgently needs an added T05 heat sink as a reliability improvement. You can replace it with almost any medium power NPN transistor with a 5W or better dissipation rating, Vce of 60v or more and Ic current of 700ma or more. It is used as a series regulator with 40v input, 20v output and current of probably under 50ma. You can replace it with a modern medium power NPN like a TIP31 or better, and I would also add a small flag heatsink for insurance.
 
jheu02 said:
I just tried this, not sure if it's a good answer though... Great idea to use Chat though and then compare to other forums if there is something. Since both the 2N3900a and 16A1700 are in the Phono amp among other places, I'd look for a low noise transistor. I see that the 3900a has an Ic of 100mA, but is very low voltage (18 IIRC). My "vote" would be for the BC550C, just be very careful with the pinout. Do you have at least one good Q of each type to verify with a tester? If you want higher voltage than the BC550, go with the BC546C...it should still be low enough noise figure.

You're asking about replacing a 16A1700 transistor. After digging, I'm confident that you meant the 2SA1700, a PNP silicon transistor used in high‑voltage driver applications. Key specs include:


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No, this 16A1700 is an NPN transistor, not a PNP. I can't find a datasheet for it, so it may have been an AR manufacturer's selection special marked 16A1700. That's just my guess. Since I can't find the 16A1700 as a new part, I'd try replacing it with a modern part with appropriate Vce, Ic and beta. In this amp, the small signal sections operate with Vc of 20v and very low current, a few ma. I'd try a 2n3904, but I have not done that so that's just my first guess. You may prefer others, fine with me. Be mindful of the board pinouts with any substitutions. Similarly, the 2N3900 number does not correspond to a modern low signal transistor. It is used in the phono preamp and power amp input stages. In my opinion, and good low noise high gain small signal transistor will be fine if it meets the voltage/current needs (try 2n5089, and again watch pinouts).

Incidentally, AR recommends putting ferrite beads on the base leads of most of the small signal transistors in the amp if RF noise problems occur. They also recommend adding 3 0.1 mF bypass caps at the phono connector, and several other bypass patches if switching noises occur. You need the AR amplifier manual to know these recommendations.
 
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