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Migrating from AU717 to BA-F1 combo

Southbus

Southbus

New Member
Hi Folks,
First of all, I want to thank you for the possibility of joining this prestigious forum.
For about 15 years, I have had a Sansui AU 717 amplifier powering Bose 901 series 4 speakers. Very happy with my team but always wanting a little more definition and power for those hungry 901s.
Now I am about to buy a BA/CA-F1 combo in perfect condition, with all its original electronic elements (I opened both components).
Somewhere I read (maybe it was in this same forum) that it is highly recommended to change the capacitors and I want to start there once I get it. Should I change all the capacitors or just the ones in the power supply?
Only the electrolytic ones or also the ceramic or polyester ones?
What are the recommended capacitor brands?
The Nichicon brand available today, has the same quality as always?
Is there a kit for this amp?
The recap process, I must also do it in the preamp?
I look forward to your valuable advice and recommendations for this new sound life in my living room.

Cesar
 
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For a proper restoration at their present age, all the electrolytics should be done. But even more important than that are the infamous black flag capacitors (so named for their physical appearance). These drift way of value, and in the power amp especially, are dangerous, as they cause instability that can instantly blow a channel, taking the output devices with it.

In order to preserve the OE outputs - which are generally unavailable, but subs do exist - it is imperative to get out all the black flag caps. There are multiple threads here on the subject that can be searched for. Most pertain more heavily to the AU-919, but are also relevant to the BA-F1, which is very similar to the 919, less the control amp stage.
 
I have restored one of these, you might find this interesting.

BA-F1 restore

I have been entrusted with a really nice BA-F1 to restore for an AK member, I collected it last night. It is in at least a 9/10 condition overall, and appears un-molested inside apart from a replacement set of OnSemi output transistors for one channel. He is not expecting it to be finished until...
audiokarma.org

And another by skippy124

BA-F1 on the work bench

A little while ago I was lucky enough to score a BA-F1 albeit in need of a little TLC operationally.... it came to me with the description of "one channel dead". Recently I also acquired a CA-F1, so it was time to get the BA-F1 on the bench Top view with cover removed Evidence...
audiokarma.org

There are other threads too, as well as ones covering the CA-F1 in similar detail.
 
Sansuiman said:
For a proper restoration at their present age, all the electrolytics should be done. But even more important than that are the infamous black flag capacitors (so named for their physical appearance). These drift way of value, and in the power amp especially, are dangerous, as they cause instability that can instantly blow a channel, taking the output devices with it.

In order to preserve the OE outputs - which are generally unavailable, but subs do exist - it is imperative to get out all the black flag caps. There are multiple threads here on the subject that can be searched for. Most pertain more heavily to the AU-919, but are also relevant to the BA-F1, which is very similar to the 919, less the control amp stage.
Click to expand...
@Sansuiman, thank you for your forceful answer, you are very kind, it is already clear to me that I will change all the capacitors, although initially I will work in the BA, there are approximately 30 individuals who will "retire".
Doubts: What are OE outputs?
What are black flag capacitors?
I am very interested in knowing more about the interior of this F1 combo.
Cheers!
 
OE=Original Equipment (factory parts). In the case of the BA-F1 (as well AU-919 and AU-X1) the particular output transistors used were purpose made for Sansui by Sanken. These have been out of production for decades now, so finding legit replacements (rather than counterfeits, which do exist regrettably) is both difficult and - if they do turn up - quite expensive.

Black flags are a particular type of low value styrene capacitors used in the driver stage, among other purposes, of several Sansui amps of the roughly 1978-81 timeframe. These drift far of their original value, which causes instability in the affected circuits, this in turn can cause self oscillation, loss of proper bias current, and thermal runaway, destroying the output devices in the process.

The upshot of all that is if one has an AU-919, BA-F1 or AU-X1, if it hasn't already been serviced to remove and replace ALL the black flag caps at a minimum, the unit is not safe to use without presenting serious risk of damage to the circuitry, most notably the output transistors.

Therefore, the reason I was so emphatic is that I was hoping to prevent anyone reading this thread from having to deal with the cost and aggravation of a full output stage rebuild. This is all common knowledge for longtime readers here, but newer arrivals may well not know about this issue. So, I considered a strong caution a worthwhile reminder.

Once these issues are resolved, the CA/BA-F1 is an exceptional combo, that I'm sure you'll find quite enjoyable to listen to.
 
Perfect, it is very clear to me, although the purchase of this combo is imminent, I will not have it for a month, for this reason I would like to know the list of capacitors, quantity and value of each one to ask my wife to be in New York until the end of July. I am based in Chile, South America. So I can buy them online and she will bring them to me, obviously scolding me for my new "weird project" (for her).
@Sansuiman I understand the emphasis with which you have explained the importance of not making this team work without replacing those damn black flags.
I think I will also need the repair manual for Sansui BA/CA-F1, i appreciate any link where I can buy or download it.
Thanks
 
Dear friends, I want to thank anyone who can help me with the list of capacitors that I should change in a BA-F1, especially the black flag caps. It would be very beneficial for me because my wife is returning from New York to my country (Chile) next week and I expect her to bring them with me.
I appreciate that list of sensors and quantity to order in an online store, maybe they sell the kit especially for this enlarger.
Thank you so much.
CESAR
 

Elektrotanya for electronics experts

Electronics forum for electronics experts to repair defective appliance.
elektrotanya.com

Elektrotanya for electronics experts

Electronics forum for electronics experts to repair defective appliance.
elektrotanya.com

Links for the service manual.
A list of replacements is not so simple. A lot of choices. Going up in voltage and/or capacitance, concerning lead pitch, diameter, height.
I have to do my CA/BA-F1, I know it will cost more time to select capacitors then replacing them!
 
For the CA-F1 you will need 2*33 pF, 6*22 pF and 4*3 pF.
This is taken from the schematic and component list of the service manual so can be more, or less.
 
Southbus,
I found this post below by member Sivo to be very useful. He included a spreadsheet of parts that I’ve used to figure out what to buy.

So far, I only replaced the black flags in the BA-F1, and I’ve been running it for 8 months. It sounds good, eventually I’ll get to the restoration.


Sansui-ba-f1-restoration

Mark
 
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