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Replacement OPTs for Sansui 1000A

Kevin Croak

Kevin Croak

New Member
Hello,
I am trying to locate OPTs for my rebuild of a Sansui 1000A. I have a line on two Sansui OPTs that I could purchase, but they are of unknow status at this point. The Gentleman will check them when he returns in a few days.
I have found a pair of OPTs out of Kyiv, Russia that are reasonably priced, but the Primary impedance is higher that the Sansui/Hashimoto's.
These are 8Kohms. I know the Sansui OPTs are 6600ohms.
IYHO's is this too high impedance for the 7591 output tubes to drive?
Tell me if I am way off base here.

Thank you all.

Kevins-l1600 (1).jpg s-l1600 (2).jpg s-l1600.jpg .
 
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The problem I see is the phrase "Transformer for tube guitar amplifier." If the translation is correct, that would imply a limited frequency response.

Jack
 
I had an open primary on an HH Scott 299, second edition transformer. I got Transcendar to make one for me; cost was about $100. But it seems that they are in and out of business lately, possibly because of the pandemic (Just my opinion). They did an excellent job, reused my end bells and it fit perfectly. If you are interested in them, just do a Google search for them.
 
Someone posted in another thread that the owner of Transcendar has retired. Maybe Heyboer or Musical Power Supplies could help.
 
Kevin Croak said:
Hello,
I am trying to locate OPTs for my rebuild of a Sansui 1000A.
I have found a pair of OPTs out of Kyiv, Russia ...
Click to expand...
Kyiv (Kiev) is in Ukraine, which USED to be part of the defunct USSR. Ukrainians may take offense to the oversight, due to tensions between the two today. Have you considered subscribing to AK? That would enable you to access Bartertown for the wanted section where you could post an ad looking for one. Likely someone has a carcass they could pull for not much $$$ or even less. Well worth the $25!
 
If it were me I would not put in anything except the originals or exact copies of the originals (as in rewound to the exact specs of the originals). Amps that use feedback that encompass the transformer secondary (like the 1000A) are quite particular in tuning, and it is very likely you will destroy or at least marginalize the amps stability by putting in some other transformers that were not designed for the amp. Guitar transformers especially are not typically designed for high frequencies, and yet that is exactly where you need it with a hifi amplifier.

I'd just keep looking until you find a pair of original 1000A's that someone is parting out. They do show up from time to time but you may have to be patient and they may not be exactly cheap. I purchased a pair this way four or five years ago and built a custom amp out of them mostly because I wanted to try the Hashimoto/old Sansui iron.

By the way (slightly off topic) my experience with the Sansui 1000A transformers tells me that these transformers are only so-so in their performance. They sound fine, but they don't measure the best, especially in the HF areas where my two samples show some significant phase shift. But the Sansui engineers were obviously aware of that and designed/tuned the amp around those limitations.

Anyway, just my thoughts/opinions.
 
^^ is pretty much why I was thinking re-winds, but didn't have the time to get into the finer bits of why.
 
if those are identical or at least pretty close, then I'd expect them to work just fine. Things with completely different properties though :dunno:
 
kward said:
If it were me I would not put in anything except the originals or exact copies of the originals (as in rewound to the exact specs of the originals). Amps that use feedback that encompass the transformer secondary (like the 1000A) are quite particular in tuning, and it is very likely you will destroy or at least marginalize the amps stability by putting in some other transformers that were not designed for the amp. Guitar transformers especially are not typically designed for high frequencies, and yet that is exactly where you need it with a hifi amplifier.

I'd just keep looking until you find a pair of original 1000A's that someone is parting out. They do show up from time to time but you may have to be patient and they may not be exactly cheap. I purchased a pair this way four or five years ago and built a custom amp out of them mostly because I wanted to try the Hashimoto/old Sansui iron.

By the way (slightly off topic) my experience with the Sansui 1000A transformers tells me that these transformers are only so-so in their performance. They sound fine, but they don't measure the best, especially in the HF areas where my two samples show some significant phase shift. But the Sansui engineers were obviously aware of that and designed/tuned the amp around those limitations.

Anyway, just my thoughts/opinions.
Click to expand...

^^^ This * 10

- Even rewinding does not garantee the same interwinding capacitance or leakage inductance
- I did not like the non-potted Hashimoto PP OPT, could not get a square wave at 15+Khz with an original Sansui HF-VK6 amplifier. The Audio Note kit 4 clone (based on the Sansui HF-VK6) also had marginal stability.
- If replacing a transformer with something not original it is best to replace both
- When replaced you'll have to check square wave performance and you may have to adjust the feedback loop / stability. (see attached files and below link)

https://www.angelfire.com/electronic/funwithtubes/T-E-Smith-NFB.html
 

Attachments

Thank you all for all the great information. I was able to check out the one original OPT I do have against values from two other sources, and this one is good! So I only need to find one matching OPT.
I will join AK officially, so I can enter Bartertown.

Kev
 
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