diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Tubes / Valves (http://www.diyaudio.com/forums/tubes-valves/)
-   -   Interstage Transformer Nomenclature (http://www.diyaudio.com/forums/tubes-valves/49655-interstage-transformer-nomenclature.html)

TerribleT 15th January 2005 04:54 PM

Interstage Transformer Nomenclature
 
Hello,
I posted this question in other forums that I thought could help but no one responded so here I am. If you've seen this already excuse my multiple posts. But I really do need to know.
Could someone please explain the nomenclature used to describe an interstage transformer (IT). I've seen various designations like: 1:1, 1:2, 1+1:2+2, 5k:5K, etc... I understand even less about how one would choose an IT for a particular driver tube/power stage tube. I know I'm asking a lot, but please, if you have any insight in this matter, help me out. Regards,
David

Bas Horneman 15th January 2005 05:00 PM

I've seen all your posts at the other forums....as Sidewinder...and I did not reply because I thought someone who knows more than I do would answer.

So I'll try...
1:1 is that the turns ratio is the same on primary and secondary.

thus 2:1 means that there are 2 turns on the primary for every turn on the secondary...this in turn means that if you have a load of 5k at the output side...... the reflected load for the tube on the "primary" side will be 10k. etc. etc. etc.

1+1:2+2 means the same but there are 2 sections on both sides. This can be handy ...because if you connect the 1+1 side in parallel and the 2+2 side in series you would have 1:4 ratios...

I hope this is correct and if it is I hope it has helped... ;)




Cheers,
Bas

SY 15th January 2005 05:10 PM

Just to add on, when impedances are quoted, they're assuming the secondary loaded with the specified resistance. If it's terminated with a different resistance, the impedance presented by the primary will change accordingly. So, if you have a 10K to 10K transformer and load it with 20K, the primary will present a 20K load.

rdf 15th January 2005 05:56 PM

When a manufacturer quotes an impedance, isn't that the optimum operating point for widest, flattest bandwidth and lowest LF distortion? For example, a Hammond 804 (we use often at work) can be strapped one-to-one as either 600:600 or 150:150. Terminating the latter's output with 10K will reflect a higher impedance to the primary but the low end still has to contend with the 804's low number of turns and DCR. I ask because after a couple of decades using line level trannies in a broadcast setting the simple turns ratio ratings used by most interstage manufacturers are still unclear to me.

Sch3mat1c 15th January 2005 07:53 PM

Quote:

Originally posted by rdf
When a manufacturer quotes an impedance, isn't that the optimum operating point for widest, flattest bandwidth and lowest LF distortion?
And/or power efficiency. Which isn't of concern here, but is in OPTs which are just beefy ISTs with a low-Z secondary. Unless you're driving a zero bias class B output and have hair-thin margins for drive capability. But when does that ever happen...

Quote:

For example, a Hammond 804 (we use often at work) can be strapped one-to-one as either 600:600 or 150:150. Terminating the latter's output with 10K will reflect a higher impedance to the primary but the low end still has to contend with the 804's low number of turns and DCR. I ask because after a couple of decades using line level trannies in a broadcast setting the simple turns ratio ratings used by most interstage manufacturers are still unclear to me.
Correct; you also have parasitic (inter-winding and inter-layer) capacitance which becomes a greater concern to higher impedances. Any reactance really, inductive or capacitive, narrowing in the bottom and top end responses respectively.

In a perfect world, you could use 1 turn coupled to three turns for any frequency...sigh... ;)

Tim

TerribleT 15th January 2005 08:11 PM

1:1
 
Hello,
Thanks for the replies. Could you indulge me further? If a schematic shows a 1:1 for an IT, what would the actual impedances be for the primary? 5k or something else?
Regards,
David

SY 15th January 2005 09:07 PM

For a 1:1, the primary impedance will look like whatever impedance is loading the secondary.

TerribleT 15th January 2005 10:17 PM

1:1 IT All the same?
 
Quote:

Originally posted by SY
For a 1:1, the primary impedance will look like whatever impedance is loading the secondary.
I apologize for all these basic questions, but I can't seem to get a firm intuitive understanding of ITs. Thanks for the patience. I kinda understand the concept of impedance reflection, but in an article by George Sanguinetti in Sound Practices Issue 15 he had used a Sowter 8423 IT with a 5k pri 1:1+1 between a 7788 driver and a vv52B that was choke load and parfed to a MQ2004opt. Later after he measured the plate resistance he and Brian Sowter decided that a 2k pri IT would be better. So the question is how are the 2 ITs different? Both are I assume are connected 1:1+1. Thanks
Regards,
David

SY 15th January 2005 10:51 PM

The ratio of the reflected impedances is a function of the ratio of the number of turns. BUT.... this is something determined at midband. At the frequency extremes (for a given transformer), non-ideal elements like primary inductance and interwinding capacitance come into play, changing the frequency response and distortion characteristics of the transformer.

For example, I'm using some Jensen 1:1 input trannies that are optimized for 10Kohm loads. At 1kHz with a 10Kohm load on the secondary, the primary looks like a 10K resistor, the -3dB point at the high end is about 85kHz, and the rolloff is well-damped. Pass a 1kHz square wave through it and it looks pretty good.

Now load that same transformer's secondary with a 100Kohm resistor. At 1kHz, as expected, the primary reflects that load faithfully and looks like a 100Kohm load. But now the frequency response has a big bump at 50kHz and that same 1kHz square wave shows ringing on its leading edge.

rdf 15th January 2005 11:35 PM

Exactly, but for me that still leaves the question how to approach a transformer when the specifications are listed as simple turns ratios. Is normal practice in this case to contact the manufacturer for an opinion on the specific applicationin mind?


All times are GMT. The time now is 09:19 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2