Sansui BA-303

bogadocarlos

New Member
Hi All,

I bought a very nice condition BA-303. Amazing tube amp with four KT88 on triode connection.
Apparently never was used, was in a box by 20 years, all original and the only problem was a resistor on V4 KT88 that was broken.
I'm testing it, the sound is incredible, but I have a problem with BIAS setting. The BIAS meter is not functioning or, maybe, is not well seted.
I was reading on net about to set AC BIAS first and then set V1 to V4, but I don't know the procedure for it.
I have the schematic and there is two pots (VR11, 1K and VR12, 10K ohms) that can adjust AC BIAS, but I don't know wich to use. Sorry because I'm not a technician and sure I'm having a mistake.

Somebody know the procedure or have user or maintenance manual of this amp?

Some help will be very appreciated.
 
Nice find.

Sorry, I can't help. Perhaps the guys that hang out in the tube forum could assist you?

Rob
 
Hi All,

I bought a very nice condition BA-303. Amazing tube amp with four KT88 on triode connection.
Apparently never was used, was in a box by 20 years, all original and the only problem was a resistor on V4 KT88 that was broken.
I'm testing it, the sound is incredible, but I have a problem with BIAS setting. The BIAS meter is not functioning or, maybe, is not well seted.
I was reading on net about to set AC BIAS first and then set V1 to V4, but I don't know the procedure for it.
I have the schematic and there is two pots (VR11, 1K and VR12, 10K ohms) that can adjust AC BIAS, but I don't know wich to use. Sorry because I'm not a technician and sure I'm having a mistake.

Somebody know the procedure or have user or maintenance manual of this amp?

Some help will be very appreciated.

Can this give you some idea?

Once Sansui discovered that triode amplifiers could yield more sensitive sound, Sansui extended this finding into an extreme end with its own way. Sansui specifically redesigned a power and an output transformer for the high-power triode connection. Then, Sansui incorporated the most powerful and best sounding power tube, KT-88 into these iron beasts. The result was the Basic Amplifier BA-303 that was designated for a low frequency power amplifier on tube based active crossover systems that utilize the CA-303 control amplifier. Of course, Sansui did not stop there.


Especially this:

The BA-303 had a specific meter that indicates bias irregularity so that users can replace power tubes or coupling caps before sound starts deteriorating, or worse, worn-out parts start destroying transformers. The BA-303 also equipped a switch that can control dumping factors into six different degrees. This functionality allowed the most sensitive sound control for the most devoted users.
 
Hi Guys,

Sorry my delay, hard work these days.
I found a very good technician that solve the problem. BIAS meter had the stylus touching the surface, he fix it, regulated de AC meter and now all is functioning in perfect condition.

I'm amazed about the sound of it amplifier. I used it with a pair of Tannoy Reds and I'm in love.

Effectively this is a triode configuration and the sound is in between a pure PP and a SE amplifier.
Having the possibility to regulate BIAS, I can use it in Class A and KT88 tubes are the best.

Many thanks for your help/
 
For sure, here some pictures about this baby.
Sorry for quality!
 

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That's a BEAUTY!

Congrats!!

I think it should be restored, as in caps replaced, to ensure reliability but regardless very nice find!

Is this a Japan market only unit?
 
This unit came with 220V power transformer setting. It can be used as 100V because double wired. On bottom of PT you can select different pins (I'll be posting some pics).

I sent it to my trusty technician, he control each component, capacitors and resistors and all is in parameters and have original components.
It use Elna electrolytic and PIO caps, Noble pots and I think Holco resistors (I'm not sure).
The components quality is first class.

When I switch on first time, I use a varistor to protect components, all function in perfect way and, most amazing, all the pots without noise, nothing.
Is the quietter tube amp I had (and I used Mcintosh, Marantz, Leak, Quad, Cary, Dynaco, etc.).

I'm in love with it!

Most interesting feature is possibility to select dumping factor, depending on speaker. I'll be posting pics to show it.
 
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