Transformer opinions needed! Size matters?

[VictoriaGuy]

Doorbell rings today and it's the postman with a (little and light) box. I was very surprised when, looking at the sender's address, I realized that this was my new pair of made-in-Japan Tomiko SE UL output transformers, destined for my '$250 Compactron Amp' project.
As the lady famously said, "I expected something larger!"

Details:
Tomiko- 563 grams, rated by seller for 150mA and 12-18 watts Price: $40 + (excessive) shipping
And, for comparison, a couple of others on the shelf here:
MusicalPowerSupplies OT10SE 725g rated for 60mA and 10 watts Price $23.50 + shipping
Transcendar TT-12OT 1865g rated for 90mA and 10 watts. Price- seems to be about $80 these days.

So, does size matter?
And, are there any simple (non-destructive) ways to test my new purchases, without building an amp around them?

Thanks for your input.

John
PS- Yes I do have Edcors on order, but hit the BuyItNow button when my patience grew thin. Even 'seniors' have plenty to learn, I guess....

[Richard Ellis]

I do really believe what you have here is a so-called "guitar" type OPT.........sorry!
I see you don't state the frequency response of your newly acquired OPT.....is there some documentation with your purchase?
In the SE type OPTs' , yes, size does matter....saturation of the core depends largely on core mass. One tip off is the high 150mA rating....with this size core? With this small of a core mass the frequency response quite probably doesn't reach down to the lower registers of 20 Hz either ...falling short of the 'standard' 20-20K. Perhaps it is the "plain vanilla" looks of the unit.....the plain wrapper.....exposed bobbin look. Most will dress up their OPTs as they most likely are going to be displayed prominently.
Testing the performance of an OPT is usually beyond most of us with limited test tools & gear........let alone how to test em.

Just my 2 cents.

__________________________________________________ ______Rick........

[VictoriaGuy]

Originally Posted by Richard Ellis

I do really believe what you have here is a so-called "guitar" type OPT.........sorry!

Oh, yeah! And not even 'guitar-quality', from the looks of it. The MusicalPowerSupplies OT10SE is a guitar transformer (which actually sounds pretty good for (low power) hi-fi - I put a pair in a RH84 a couple of years ago).

Originally Posted by Richard Ellis

I see you don't state the frequency response of your newly acquired OPT.....is there some documentation with your purchase?

You gotta be joking! I looked in the box and there wasn't even a lead (color) ID sheet - not that I will have any trouble sorting that out.


Thanks for your input on core size, etc. It does match with what little I know.

When I build something with the Transcendars, I'll look at some square waves and then sub in a Tomiko and compare. I've got some test gear- scopes,sig gen, etc.

Assuming that I keep the Tomikos instead of eating the shipping costs, as I don't have a lot of confidence about a refund.

I'm not that shattered; it's only some cash.

I would like to stop somebody else from making the same mistake- not sure of the best way to do that.

[Dyna Saur]

They probably meant that the Tiny Tomiko will take 150 mA before it bursts into flames ;-)

Might be OK for a low power SE amp, like a watt or so, might work with a 12B4, try about 245 V B+ and a 1K cathode resistor, bypassed with a 100 uF/ 50V cap - that combination will run the plate current around 25-27 mA, whch should be well below the primary winding's ignition rating. Max power out would be about 1.5W

Dunno about the low freq performance, that trannie's core and winding bobbin are pretty small, and I suspect that the primary inductance is 5H, or less.

If you think the Tomikos are small and light, I have a pair of diminutive Chinese made "5VA" SE OPTs which are lot smaller. They don't even apply the term "Watts" for the power rating.

/ed B in NC

[DF96]

Measure the primary resistance and inductance. Calculate the expected LF point from primary inductance and transformed load resistance. Compare with the others.

[VictoriaGuy]

DF-
Do you have quick instructions or a link on how to do that calculation?
I measured a bunch of inductances earlier today, and the DCR will only take a few seconds.
Thanks
John

[VictoriaGuy]

OK- Here's some data:
All measurements on the 5k windings.
Tomiko from seller 2930luo 21.3H, 442 ohms
OT10SE 11H, 70 ohms
Transcendar 37.1H, 381 ohms
James 6113HS 14H, 295 ohms

oops...transformed load resistance what is that, exactly?

[DF96]

Load resistance, times impedance ratio. You mentioned 5K so I assume this is the intended load to be applied to the anode.

LF point (open loop) is given by f = R / 2 pi L, so for the tomiko this gives 37Hz. However, this assumes that the inductance does not change with current so reality could be slightly worse.

[VictoriaGuy]

So the Tomiko will have better low-frequency performance than the James? In theory.