part # for Sansui 1000A OPTs

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Indy1K

Member
Joined 2021
I

Indy1K

Member
Joined 2021
Sansui 1000A Hashimoto OPTs

Yes, I would like to stay with the same specs and try to find transformers that will work.
You dont happen to know the specs on those OEM xfmrs? I would like to ohm them out to see if the one I do have is good.

Thanks a bunch.

Kevin
 
D

duncan2

Member
Joined 2013
I suppose you already know the plate to plate load resistance is 6600 ohms-P-P.

In the Eico ST-70 which uses the 7591,s the output transformer impedance is (approx ) 6500ohms -P-P.

Now it just so happens that the circuit diagram for that amplifier is available online ( hi-fi engine ) and even better it gives the metered resistance of the output transformer primary input , which as far as I can see is --- 120ohms/130ohms .
 
Francois G

Francois G

Member
Joined 2004
Paid Member
Indy1K,

Thanks for your patience. OK, I unpacked my Sansui 1000A output transformer pair and measured the resistances on the different taps. I used a Fluke 179 that I believe is in good calibration. Hopefully this will be helpful to you to determine the condition of you output transformer. This is what I measured:

Transformer #1 Primary
Orange to yellow 121 ohms
Orange to blue 142 ohms
Blue to yellow 263 ohms

Transformer #2 Primary
Orange to yellow 123 ohms
Orange to blue 138 ohms
Blue to yellow 261 ohms

#1 Secondary
Black to blue 0.6 Ohms
Blue to yellow 0.4 Ohms
Black to yellow 0.7 Ohms

#2 Secondary
(Identical)

Compared to other transformers I have measured I consider these primary measurements a good match across transformers and two coils for each primary. The secondary measurements are probably not very useful.

My transformers have only three secondary wires, for 8 and 16 ohm loads, and I believe this was “standard for the 1000A receiver. However, I noticed in Hifi Engine’s archive they have an official-looking 1000A schematic that shows a 4 ohm load also. Their scanned Sansui 1000A service manual shows only the 0-8-16 ohm outputs. Anyone with information on this variation?

In my files I discovered a post from a (now) unknown poster that I have copied. This poster also measured Sansui 1000A transformers. Here are those measurements for comparison:

“Sansui 1000A output transformers.

Each one has two sets of wires--3 from each side. One side has a blue, an orange, and a yellow wire.

On one transformer, I get these measurements:

Orange to yellow 120 ohms
Orange to blue 135 ohms
Blue to yellow 255 ohms

On the other transformer I get these:
Orange to yellow 120 ohms
Orange to blue 247 ohms
Blue to yellow 367 ohms”
 
I

Indy1K

Member
Joined 2021
Francois,
This is excellent information! Thank you!
Do you know if these are good transformers? I dont know what the static impedance readings should be. I mean, the specs say 6600ohms. Is that in circuit with an 8 or 16 ohm load applied?
I will measure the one OPT I have and report back.
Kevin
 
I

Indy1K

Member
Joined 2021
Francois G said:
Indy1K,

Thanks for your patience. OK, I unpacked my Sansui 1000A output transformer pair and measured the resistances on the different taps. I used a Fluke 179 that I believe is in good calibration. Hopefully this will be helpful to you to determine the condition of you output transformer. This is what I measured:

Transformer #1 Primary
Orange to yellow 121 ohms
Orange to blue 142 ohms
Blue to yellow 263 ohms

Transformer #2 Primary
Orange to yellow 123 ohms
Orange to blue 138 ohms
Blue to yellow 261 ohms

#1 Secondary
Black to blue 0.6 Ohms
Blue to yellow 0.4 Ohms
Black to yellow 0.7 Ohms

#2 Secondary
(Identical)

Compared to other transformers I have measured I consider these primary measurements a good match across transformers and two coils for each primary. The secondary measurements are probably not very useful.

My transformers have only three secondary wires, for 8 and 16 ohm loads, and I believe this was “standard for the 1000A receiver. However, I noticed in Hifi Engine’s archive they have an official-looking 1000A schematic that shows a 4 ohm load also. Their scanned Sansui 1000A service manual shows only the 0-8-16 ohm outputs. Anyone with information on this variation?

In my files I discovered a post from a (now) unknown poster that I have copied. This poster also measured Sansui 1000A transformers. Here are those measurements for comparison:

“Sansui 1000A output transformers.

Each one has two sets of wires--3 from each side. One side has a blue, an orange, and a yellow wire.

On one transformer, I get these measurements:

Orange to yellow 120 ohms
Orange to blue 135 ohms
Blue to yellow 255 ohms

On the other transformer I get these:
Orange to yellow 120 ohms
Orange to blue 247 ohms
Blue to yellow 367 ohms”
Click to expand...

Ok, I measured my OPT.
Primary
Orange to Yellow 120ohms
Orange to Blue 133 ohms
Blue to yellow 254 ohms

Secondary
Black to Blue .5 ohms
Blue to yellow .5 ohms
Black to Yellow .8 ohms

None are shorted to the iron and nothing is shorted from Primary to the secondary,


They are very close to your readings and the other gents readings. So, do this mean this OPT is good?
 
Francois G

Francois G

Member
Joined 2004
Paid Member
Indy1K,

Good progress! I believe you have one good transformer! One to go!

Unfortunately I’ve packed my transformers away already, so I’m not going to check primary impedance now, but I believe the Sansui 1000A OT are actually specified for 5.5K! Some folks speculated that they are 6.6k, based on other OTs used with 7591 tubes, so it would be good if someone has definitive input on the impedance.
 
I

Indy1K

Member
Joined 2021
I did manage to find a pair, but they are both marked "B" I am still looking for an "A" OPT.
If you have one and want to sell it, let me know how much you want.
Since I have 2 of the 5234-B OPTs, maybe you have 2 "A" s and want to trade one for one.
Either way, let me know.

Thanks,

Kevin
 
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