AA-100 OPT inductance - help?

justinis

justinis

Active Member
I am trying to do a simple model of an OPT from a Heathkit AA-100 in LTSpice. I have no idea what the inductance of the primary and secondary are. The transformer is a Stancor 51-58, but I haven't been able to find any specs online. Does anybody happen to know these numbers? Even a rough estimate would be awesome. Thank you!
 
justinis said:
I am trying to do a simple model of an OPT from a Heathkit AA-100 in LTSpice. I have no idea what the inductance of the primary and secondary are. The transformer is a Stancor 51-58, but I haven't been able to find any specs online. Does anybody happen to know these numbers? Even a rough estimate would be awesome. Thank you!
Click to expand...
the reason your not finding the information your after is that the part number is thats the part number given to the transformer exclusive for heathkit for whom they made it for. you might have to do a search on just stancor transformers and find one thats similar to the output tubes heathikit used or as you said find someone that can measure it for you that has a aa 100 or similar amp that used the same opt as the aa100 ane im sure they used that model transformer in more than one amplifier.
 
Are you looking for "real, accurate" numbers so you can simulate the frequency response, etc., or just something that will allow a basic simulation of an output stage?
 
If anyone would know its a good chance @Tom Bavis would. Send him a note and ask. He's measured dozens of transformers and published their specs. His measurements are on line somewhere I think but I don't have the link.
 
I just happen to have measured one... however, the inductance varies with frequency and audio amplitude, so it's best to take the primary inductance and divide by the impedance ratio (7200 / 8 = 900) for secondary inductance. Leakage inductance will placed in series with the primary, half on each side for symmetry (then use K=1). Magnetizing inductance is about 250 Henries. There's a fair amount of capacitance from primary to secondary, at least a few hundred pF, but I didn't measure it.

And I DO intend to post all my measurements, but haven't gotten around to it.
 

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Tom Bavis said:
I just happen to have measured one... however, the inductance varies with frequency and audio amplitude, so it's best to take the primary inductance and divide by the impedance ratio (7200 / 8 = 900) for secondary inductance. Leakage inductance will placed in series with the primary, half on each side for symmetry (then use K=1). Magnetizing inductance is about 250 Henries. There's a fair amount of capacitance from primary to secondary, at least a few hundred pF, but I didn't measure it.

And I DO intend to post all my measurements, but haven't gotten around to it.
Click to expand...

This is amazing! So much more than I was hoping for. Thank you so much!
 
Tom Bavis said:
I just happen to have measured one... however, the inductance varies with frequency and audio amplitude, so it's best to take the primary inductance and divide by the impedance ratio (7200 / 8 = 900) for secondary inductance. Leakage inductance will placed in series with the primary, half on each side for symmetry (then use K=1).
Click to expand...

Sorry, just one question. The primary is listed in your doc as 256H, but each leg is listed as 68H. Shouldn't each leg add up to equal the total? Thanks!

radioactive said:
Love the ak community and it didn't take long to get answers.
Click to expand...

So true!
 
justinis said:
Sorry, just one question. The primary is listed in your doc as 256H, but each leg is listed as 68H. Shouldn't each leg add up to equal the total?
Click to expand...
Inductance divides in the same way as impedance. Half of the winding has one quarter of the total inductance.
 
Yes, but the situation changes if they're coupled --- as in a single winding.
Click to expand...
Ahh. So when I model this transformer, do I model it as two 68H inductors in series that are coupled together (and coupled to the secondary)?
 
Tom shows the total primary inductance as 256 Hy on the drawing where he also gives the total primary impedance, which is 4 times the half winding inductance.
 
This is how I modeled it. I hope this is correct?

xformer_ltspice.PNG
 
I come up with about 0.28H for the 8 Ohm secondary; about 0.2 for the 8-16 segment. I measured higher than that, BUT those values should give the proper ratio.
 
Tom Bavis said:
I just happen to have measured one... however, the inductance varies with frequency and audio amplitude, so it's best to take the primary inductance and divide by the impedance ratio (7200 / 8 = 900) for secondary inductance. Leakage inductance will placed in series with the primary, half on each side for symmetry (then use K=1). Magnetizing inductance is about 250 Henries. There's a fair amount of capacitance from primary to secondary, at least a few hundred pF, but I didn't measure it.

And I DO intend to post all my measurements, but haven't gotten around to it.
Click to expand...

Tom Bavis said:
I just happen to have measured one... however, the inductance varies with frequency and audio amplitude, so it's best to take the primary inductance and divide by the impedance ratio (7200 / 8 = 900) for secondary inductance. Leakage inductance will placed in series with the primary, half on each side for symmetry (then use K=1). Magnetizing inductance is about 250 Henries. There's a fair amount of capacitance from primary to secondary, at least a few hundred pF, but I didn't measure it.

And I DO intend to post all my measurements, but haven't gotten around to it.
Click to expand...
Tom, do you by a chance have a measurement document for a Harman Kardon 6L6PP output transformer for a HK-250 amplifier? The factory model number is FT2382666. The harman kardon HK-250 outputs NEVER show up on eBay and my HK-250 needs a new one on one side, so I thought to use the Heathkit 51-58 as a sub. A rebuild job will cost me plenty more than buying the 51-58 on eBay. Kindly advise...
 
I can't specifically comment on the HK250 output- but I have actually used the Heathkit AA100 outputs, to substitute for those in an Award A500.

The only thing I noted- was that the output was slightly less- because the AA100 outputs are higher primary impedance compared to the A500 (about 7K as opposed to about 5K or so). I didn't have to make any changes to the stability networks.

I do remember (and just verified, by looking here: https://audiokarma.org/forums/index...rale-output-transformer-666-impedance.485191/ ) that the "666" output transformer also is about 5K- which was entirely typical for Harman-Kardon. There may be other parameter variations (inductance, bandwidth, etc), but I would think there would be a good chance that the Heathkit transformers would work.

The only way to know for sure- would be to substitute the transformers temporarily, fire up the amp, and test for stability. That may be easier than trying to find the data for the "666".

Regards,
Gordon.
 
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