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5k:8 ohm vs. 10k:16 ohm output transformer. What is the difference?

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However, the impedances listed are different, thus a different inductance, distributed capacitance, leakage inductance is necessary for the same frequency response.

Checking deeper, more specific, using the RCA Radiotron Designers Handbook, 1960, page 213.

Approximate inductance required for -1db at 40hz, under conditions "approximately equal to the load resistance RL in parallel with the effective plate resistance of the valve" (listed as Ra).


5K 42 henries
10k 87 henries

As stated earlier, the information given by the manufacturer is confusing. They cost the same, weigh the same, same frequency response into different loads, yet the primary inductance is the same??

Cheers.
 
The secondary wire colour is different (green vs yellow) although they look the same in the pictures. The two pictures come from different file names, but that would be easy to arrange even if they were the same picture originally. Given that the details we would need to check for differences are not given (for no apparent reason), I am beginning to suspect that they may be the same apart from the wire colour. The wire could be greeny-yellow in both too!
 
Originally Posted by Positron
5K 42 henries
10k 87 henries

.......yet the primary inductance is the same??



not seen that claim anywhere
only detailed specs for the 10K

Right, the original question is what is the difference between the two trannies, if any, with one 5k:8 and the other 10K:16. (I will leave out the high frequency discussion in this particular response.)

The transformers must be different since
the impedances, 5k and 10K are different by definition. Hence the
primary inductances are different in order to obtain the same low frequency response. This is what the data presented from the RCA Radiotron Designers Handbook reinforces. The equation is approximately: wLo = 2Ra

If the primary inductances are the same for both transformers, then the low frequency response must be different, using the same core material.

The claim is the low frequency response is the same for both OPTs, therefore the primary inductances are different, as such different transformers.

Hope this clears things up. Cheers.
 
Ex-Moderator R.I.P.
Joined 2005
The transformers must be different since ........

they use the exact same spec sheet drawing(pfdf) for both



The claim is the low frequency response is the same for both OPTs,

hmm, they claim that both achieve 40-18khz, +/-1db

not that they wont behave differently beyond that
which you have clearly stated they definately will

question is, will it be even worse ?
 
Case A:- 10K:16

This transformer is designed to match a 16ohms load into 10K. That means your output tubes will see a 10K load when you connect a 16ohms speaker to the output. This is at the lowest point of operating frequency. Lets say 25Hz.
DC resistance of the primary is mainly based on the out put power of the transformer, higher the power more turns in the primary. That gives you more DC resistance.

The same rule applies for the case B.

All depend on the applications, design and tube and your speaker specs. What tubes are you using?

Cathode biased circuits operate better with higher primary impedance as they stop shunting the output tubes. Fixed biased circuits can operate with lower impedance primaries.

This the equation to calculate impedance ratio

(N1/N2)=Squroot (RL/Z)

N1 = Primary turns, N2 = Secondary turns, RL = Speaker imp, Z= Primary imp

N1, figure depends on the output power of the Transformer.

Hope this helps :)
 
Just thinking and trying to get inside the head of Mr. Westin, the designer at Edcor. There are certain assumptions and parameters that get plugged into the transformer winding machine. We know that at least one is constant for both transformers, the core. We also assume that the turn ratios are the same. Some things that could change are wire gauge and the absolute number of turns. Plus the magnetic gap can be adjusted. (add more of your own)

I am going to go out on a limb to assume a couple of other things. The performance specifications are stated as a minimum and the actual performance for either or both transformers may exceed the minimum specification and that they may not equal each other in performance.

Given the constraint of using the same core there is limited ability to adjust the inductance of the primary and not exceed the limits of flux density and go out on the shoulder of saturation.

More musings, these are nominal 15 watt transformers when operated at 3 or 4 watts where most of us would use them they are most likely interchangeable. (within the specifications)

DT
 
Positron said:
The point is different primary inductances are required for 5K and 10K for the same low frequency response.
Different inductances for the same response, but not necessarily for the same response claim. Frequency response could be better than the claim for one of the transformers, as long as both meet the claim.

Just noticed that DualTriode has made the same point.
 
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Different inductances for the same response, but not necessarily for the same response claim. Frequency response could be better than the claim for one of the transformers, as long as both meet the claim.

Just noticed that DualTriode has made the same point.

Unfortunatley, that does not compute with the claim of 25 henries primary inductance. As the RCA Radiotron Designers Handbook bears witness, the inductance of 25 henries is not enough inductance for a -1db spec at 40hz. However, may be a misprint by the manufacturer as that does happen from time to time.

Cheers.
 
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Ex-Moderator R.I.P.
Joined 2005
As the RCA Radiotron Designers Handbook bears witness, the inductance of 25 henries is not enough .....

could the difference come from different 'type' of SE ?

the 15watt is specced with UL tap, and as such for pentode
doesnt this 'imply' a more effective design, with lower voltage than would normally be needed for 15watt triode SE
or is it no different :confused:
 
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