Bias setting for Sansui 1000A

[SAM]

Does anyone know the correct bias setting for the Sansui 1000A? The manual
that I have does not include this information.

Thanks,
Scott M

[Mikkel C. Simonsen]

SAM wrote:
>
> Does anyone know the correct bias setting for the Sansui 1000A? The manual
> that I have does not include this information.

The Sansui 500 circuit I have specifies a grid voltage - is it the same
for the 1000A?

Best regards,

Mikkel C. Simonsen

> Thanks,
> Scott M

[SAM]

>he Sansui 500 circuit I have specifies a grid voltage - is it the same
>for the 1000A?

I don't know what the 500 uses for outputs, or if it is set up the same. The
1000A uses push pull 7591s.

Scott M.

[Gregg]

This isn't it - but this is what I do - use headphones and play a soft
piano concerto and bias the amp (winthin PdMAX) until it sounds
"right" to your ears.

--
Gregg

*It's probably useful - even if it can't be SPICE'd*

Check out the cool electronics forum at:
http://www.dutchforce.com/~eforum/index.php

[Mikkel C. Simonsen]

The 500 and 1000A are not the same at all. I just thought that since the
500 schematic includes a bias voltage setting (-19V as can be seen here:
http://stiftsbogtrykkeriet.dk/~mcs/Sansui_500_Amp_g.gif), the 1000A
schematic might include the bias voltage also (assuming you have the
original schematic).

Best regards,

Mikkel C. Simonsen

> Scott M.

[Jon Yaeger]

Scott,

First, I recommend that you install 10 ohm 1/2 watt resistors between the
cathodes and ground for each tube. This does two things - it will provide
some protection in the event of tube or transformer failure. You can also
measure the voltage across each resistor, which corresponds to the
current, e.g. .375 V = 37.5 ma. The 7591s like to operated with about 38
ma of current per tube. The bias voltage that this corresponds to varies
with the age of the tube. Others recommend about 20.5 V negative bias.

By the way, virtually all of the coupling caps in this amp will be bad - I
tested mine and was quite suprised. It is imperative to replace the
coupling caps to the output tubes BEFORE you adjust the bias. Failure to
do so may result in tube or XMFR failure; you'll certainly never get the
bias right with bad caps.

Once you change the caps, lube the pots and switches, bias the tubes, etc.
you're in for a treat. With two Nuvistors on the front end, the
sensitivity is terrific. The amp section is real nice, too. The solid
state phono section sucks - it has loads of noise. Other than that, it's
my favorite receiver, and I own several tube units . . . .

Hope that helps.

- Jon

In article <20020902120136...@mb-fx.aol.com>,

[Robert Sarbell]

Sam,
The original manual does not specify (as Jon has stated); however,  very close to -21 is what I have been running on both of my units. The RCA manual calls for -19 grid voltage for a plate voltage of 450 . . .the schematic for the early 1000As have VR₁₀ and VR₁₃ to adjust the grid bias. I also have a schematic for the 1000A which shows a fixed bias circuit for the 7591s.
Regards,
Bob

[SAM]

Thank you Jon and Bob. I appreciate the information and advice. I, too,
tested the caps and as you said Jon, all were bad. It didn't surprise me given
the age and heat that these units produce. I was seeing greater than 50 uA of
leakage on the coupling caps. I am just about done replacing them, hence the
need for the bias setting.

Scott M

[Jon Yaeger]

Scott,

You're welcome!

After rereading my first post, I may have been unclear on the capacitor
issue - ALL of the coupling caps are suspect - not just the ones on the
outputs. Even the small noise shunting caps across the A/C line have been
know to fail explosively! The disc, mica, and large electrolytic cans are
typically ok.

I generally replace coupling caps in the amps I restore, and I usually
test the ones I remove. Suprisingly, most caps seem to hold up - but not
those grey axial "Japan" caps!

If you get further along an want to consider another SS phono section, let
me know and I'll send you a copy of a schematic I found. Heck, with a few
Sansui 1000A owners, it might be a good idea to lay out a replacement PCB
. . .

- Jon

In article <20020903092647...@mb-cv.aol.com>,

[Mikkel C. Simonsen]

Jon Yaeger wrote:
>
> The disc, mica, and large electrolytic cans are
> typically ok.

But don't count on the cans beeing ok. Both the main 200湩 caps in my
Sansui (500) were bad... I haven't touched the third smaller
multisection cap.

[SAM]

>But don't count on the cans beeing ok. Both the main 200湩 caps in my
>Sansui (500) were bad... I haven't touched the third smaller
>multisection cap.

The electrolytics were all bad in this one. The disk and mica caps are all OK.
Finding the 4 x 20uF was a challenge. I used (2) 2 x 100uF for the 200s
which were readily available.