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 Post subject: Vertical blocking transformers as audio transformers?
PostPosted: Nov Wed 20, 2019 12:14 am 
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Location: Dos Rios, CA. region
Can vertical output or blocking oscillator transformers ever be used for audio circuits with same ratio of windings as audio specified transformers?
Say 1 to 3.5 ratio for example...
Thanks all


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 Post subject: Re: Vertical blocking transformers as audio transformers?
PostPosted: Nov Wed 20, 2019 4:19 am 
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Location: Rochester NY USA
I would say they wouldn't be very good for the purpose. If you have an LCR meter, two measurements of inductance will tell you most of what you need to know: measure primary inductance, measure again with secondary shorted. First measurement tells you the low frequency limit - f= Z/(2*pi*L) (Z is impedance of drive source - i.e. 7K for 6J5 or 6SN7) So for instance 10 Henries works out to 137 Hz. Inductance may be lower with DC current through the primary.

Second measurement (leakage inductance) is a major factor at the high frequency end. Same formula - 100 mH gives 11 Khz. It won't do that well due to stray capacitance.

A GOOD audio transformer will have 1000:1 or better ratio between primary inductance and leakage inductance.

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 Post subject: Re: Vertical blocking transformers as audio transformers?
PostPosted: Nov Wed 20, 2019 5:22 am 
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Thank you very much Tom for the explaining the differences!

-Kent


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 Post subject: Re: Vertical blocking transformers as audio transformers?
PostPosted: Nov Fri 22, 2019 11:33 pm 
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Location: Long Island NY
I've used vertical output transformers as audio outputs and they do work, but the results are about the same as using a doorbell transformer. In other words, you can get away with it in a pinch if you are fixing a small table radio, but do not expect any high performance. This should not come as a surprise since vertical output transformers were optimized to work at TV vertical sweep frequencies (i.e. 60 Hz, 59.97 Hz, or 50-Hz).

Blocking oscillator transformers were designed for pulse operation and most would not offer enough inductance to work successfully as audio outputs.

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 Post subject: Re: Vertical blocking transformers as audio transformers?
PostPosted: Nov Sat 23, 2019 12:37 am 
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Location: Dos Rios, CA. region
Thank you Chris, appreciate the "doorbell transformer" comparison for audio purposes :lol:
Just thought I'd ask, since they are more commonly found in Ham radio estates, flea mkts, etc, (Or my junk drawers)
than audio interstage, etc.
I've read the older (20's, 30's, etc) interstage audio transformers are not as robust fidelity wise for more modern circuits (say late 40's, 50's)
than the newer made interstages, what's your opinion on that?
regards,
Kent


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 Post subject: Re: Vertical blocking transformers as audio transformers?
PostPosted: Nov Sat 23, 2019 1:10 am 
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Location: Long Island NY
I would tend to agree with that, though with some exceptions. Certainly if you are talking about the interstage transformers that went into battery radios like the old three-dialers, they were optimized to produce maximum voltage step-up (often misstated as "gain"), which meant they were only efficient over narrow frequency ranges. There were some better fidelity audio transformers developed in the late 1920s and early '30s when sound systems became popular in movie theaters and other commercial venues, and some of them did make it into elaborate high end radios and phonographs. But grain oriented silicon steel, which has superior magnetic properties, was not invented until 1934, so it is not until the mid to late 1930s that high(er) fidelity audio transformers became more commonplace.

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 Post subject: Re: Vertical blocking transformers as audio transformers?
PostPosted: Nov Sat 23, 2019 7:13 am 
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In other words, try it and see if you like it. It won't hurt anything but the time you invest. But you can get some value out of that by telling us your results.

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 Post subject: Re: Vertical blocking transformers as audio transformers?
PostPosted: Nov Sat 23, 2019 1:18 pm 
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As Jim mentions, its good to experiment!

I learned alot of my radio and electronics knowledge by just "Giving it a try" :D
many things failed, and I learned from it.

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 Post subject: Re: Vertical blocking transformers as audio transformers?
PostPosted: Nov Fri 29, 2019 12:29 pm 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
The inductance of transformers varies with the DC current
that the AC current rides on. For blocking transformers, the
natural resonant frequency of the effective inductance, and
the distributed capacity will affect the bass audio response.



When practical NTSC television sets arose from the tiny electrostatic
CRT oddities to wider screen magnetic deflection types, there was
a scramble to make them work , and the technology was dodgy.

Turns ratio was easy. Making a circuit work as the oscillator tube aged,
was another. Those in the trade knew the complaint. The vertical hold
control just ran out of room. So a new vertical oscillator tube was needed,
but the old one probably would work in another set just fine.

Wonderful to tell the audiophile that the transformer coupled stage needs a
fresh new tube, to deliver the characteristic purest of sound.

If you have a stash of blocking oscillator transformers in boxes, try and
link them to the TV sets they were used in. Then fish out the schematic
of the set to see which tubes they were used with, and the type of
circuit used.
Attachment:
Blocking transformer  Fink DG  16 165 1957  TV engr.jpg
Blocking transformer Fink DG 16 165 1957 TV engr.jpg [ 414.72 KiB | Viewed 685 times ]
Attachment:
Blocking.jpg
Blocking.jpg [ 313.5 KiB | Viewed 685 times ]

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