output transformer for the 12 inch Magnavox speaker for the Sixteen, Masterpiece & early Phantoms - EH Scott Radio Enthusiasts2024-03-29T11:53:16Zhttps://ehscott.ning.com/forum/topics/output-transformer-for-the-12-inch-magnavox-speaker-for-the?feed=yes&xn_auth=noHere are the images of the mo…tag:ehscott.ning.com,2016-09-10:3925821:Comment:540042016-09-10T02:11:31.875ZDavid C. Polandhttps://ehscott.ning.com/profile/DavidCPoland
<p>Here are the images of the modified Hammond output transformer and of the transformer mounted on the speaker.</p>
<p>Here are the images of the modified Hammond output transformer and of the transformer mounted on the speaker.</p> This is my solution. I modifi…tag:ehscott.ning.com,2016-09-09:3925821:Comment:541082016-09-09T17:12:44.248ZDavid C. Polandhttps://ehscott.ning.com/profile/DavidCPoland
<p>This is my solution. I modified the 125E push-pull Hammond 15 watt transformer from Radio Daze.</p>
<p>Available universal output transformers max out at 15 or 16 ohms including this transformer.<br></br>This 125E universal transformer ( lug 1 to lug 6) has a turn ratio of 26:1. I needed 21:1 (measured from another good Scott transformer for this Scott speaker, driven by 6V6 tubes in push-pull). The Scott models Sixteen and earlier Phantoms use the same 12 inch speaker. The Super XII uses a…</p>
<p>This is my solution. I modified the 125E push-pull Hammond 15 watt transformer from Radio Daze.</p>
<p>Available universal output transformers max out at 15 or 16 ohms including this transformer.<br/>This 125E universal transformer ( lug 1 to lug 6) has a turn ratio of 26:1. I needed 21:1 (measured from another good Scott transformer for this Scott speaker, driven by 6V6 tubes in push-pull). The Scott models Sixteen and earlier Phantoms use the same 12 inch speaker. The Super XII uses a different speaker because of field coil design, but I suspect the same voice coil and ( being rated for 9 watts), probably the 10 watt Hammond push-pull transformer could be similarly adapted.<br/>For this particular Hammond transformer I chose, there is room between iron laminations and the core to carefully add a layer of wire. After experimentation, I found 12 feet of #22 gage magnet wire connected to the #6 lug and continuing to the RIGHT of lug 6 adjusted the transformer to about the desired 21:1 turn ratio. The new magnet wire is totally exposed.<br/>Used electrical tape on the metal to protect the wire from abrasion while winding the additional wire around the core. Wind the wire fairly tight and neat, and slip 3 or so inches of spaghetti at the end, so the end of the added wire end can be wedged between lug 1 and lug 2 to become a lug #7. Thus: lug 1 and the new lug 7 is about the ratio I wanted.<br/>This transformer will not fit into the original bracket which also holds the speaker terminal strip.. So I relocated the original bracket enough so I could mount the new transformer tightly agains the original bracket (after removing the old transformer from the old bracket).<br/>Success - the radio sounds good and the impedance is about right.</p>
<p>I will add a couple photos soon.</p> Dave, also check out Edcor US…tag:ehscott.ning.com,2016-08-24:3925821:Comment:538082016-08-24T05:01:53.039Zpalegreenthumbhttps://ehscott.ning.com/profile/palegreenthumb
<p>Dave, also check out Edcor USA, they have some 15W transformers for PP output.</p>
<p><a href="http://www.edcorusa.com/gxppseries" target="_blank">http://www.edcorusa.com/gxppseries</a></p>
<p>-Rodney</p>
<p>Dave, also check out Edcor USA, they have some 15W transformers for PP output.</p>
<p><a href="http://www.edcorusa.com/gxppseries" target="_blank">http://www.edcorusa.com/gxppseries</a></p>
<p>-Rodney</p> Thomas - Thanks. The Hammond…tag:ehscott.ning.com,2016-08-22:3925821:Comment:539122016-08-22T21:58:32.729ZDavid C. Polandhttps://ehscott.ning.com/profile/DavidCPoland
<p>Thomas - Thanks. The Hammond site for classic P-P transformers show the same 15 watt units as AES and Radio Daze, but with more information and a chart of connection combinations. Does not show ratio information.</p>
<p>Norman - Thanks. So I'll repeat my analysis with the Variac and a known good transformer from another Scott speaker. Then calculate plate to plate impedance needed. Then from the Hammond hook up chart, then I would select the lugs closest to the impedance the Scott…</p>
<p>Thomas - Thanks. The Hammond site for classic P-P transformers show the same 15 watt units as AES and Radio Daze, but with more information and a chart of connection combinations. Does not show ratio information.</p>
<p>Norman - Thanks. So I'll repeat my analysis with the Variac and a known good transformer from another Scott speaker. Then calculate plate to plate impedance needed. Then from the Hammond hook up chart, then I would select the lugs closest to the impedance the Scott needs.</p>
<p>I'll try that later this evening.</p> Dave:
I would want to see the…tag:ehscott.ning.com,2016-08-22:3925821:Comment:539902016-08-22T17:20:54.869ZNorman S Braithwaitehttps://ehscott.ning.com/profile/NormanSBraithwaite
<p>Dave:</p>
<p>I would want to see the tables before ordering the transformer. Most of the impedance ratios will be duplicate ratios such as 2500:8 and 5000:16. An impedance ratio of 6000:15 is electrically similar to 15600:39. Unless stated or marked otherwise, the primary impedance of push-pull transformers is plate to plate.</p>
<p>Norman</p>
<p>Dave:</p>
<p>I would want to see the tables before ordering the transformer. Most of the impedance ratios will be duplicate ratios such as 2500:8 and 5000:16. An impedance ratio of 6000:15 is electrically similar to 15600:39. Unless stated or marked otherwise, the primary impedance of push-pull transformers is plate to plate.</p>
<p>Norman</p> Thanks Norman.
So a "ball pa…tag:ehscott.ning.com,2016-08-22:3925821:Comment:540832016-08-22T16:46:32.164ZDavid C. Polandhttps://ehscott.ning.com/profile/DavidCPoland
<p>Thanks Norman.</p>
<p>So a "ball park" output transformer with 15 ohm impedance may be close enough. Then, seems worthwhile to order the 15 watt Hammond P-P universal replacement from AES (or Radio Daze) that can provide 15 ohm impedance - about $40. On AES, part P-T125E has an interesting product review comment: that a Mr. Morris had room to add some additional turns to the secondary to get closer to 39 ohms impedance he needed. (Radio Daze offers the same part.) Larger dimensions than…</p>
<p>Thanks Norman.</p>
<p>So a "ball park" output transformer with 15 ohm impedance may be close enough. Then, seems worthwhile to order the 15 watt Hammond P-P universal replacement from AES (or Radio Daze) that can provide 15 ohm impedance - about $40. On AES, part P-T125E has an interesting product review comment: that a Mr. Morris had room to add some additional turns to the secondary to get closer to 39 ohms impedance he needed. (Radio Daze offers the same part.) Larger dimensions than the Scott original will be a bit of a challenge, but maybe the additional iron is beneficial. Can not tell from the specs on either site what the turns ratio may be for the 15 ohm secondary.</p>
<p></p>
<p>Another thing I do not grasp: push-pull transformer primary evaluation - whether to measure from primary center tap to one end, or to measure from end to end to determine the ratio. I thought center tap to either end (or center tap to both ends and average the result). My original frame of reference was a Scott transformer with primary half open compared to the half secondary that would be connected to the voice coil. Used a Variac applied to half primary and 1) adjusted the Variac to produce 1 volt ac on the secondary and then 2) measured the actual voltage to the primary, then 3) computed the ratio. An additional unnecessary complication to avoid for now: the Scott's original secondary winding is also center tapped - but only half is connected to the voice coil, unless a remote speaker is added. I suppose I could repeat ratio calculations on another of my same model speaker having a good output transformer (after disconnecting the voice coil) to get end-to-end figures.</p>
<p></p>
<p>From Gary Schneider's PTOP site awhile back, I did find an informative 4 page article at this link . <a rel="nofollow" href="http://www.radioremembered.org/outimp.htm" target="_blank">http://www.radioremembered.org/outimp.htm</a> </p>
<pre>Took some thought to understand, but it enlightened me about speaker impedance, reflected load, tips on evaluating old<br/>output transformers you might already have, and some basic calculations to determine the needed transformer ratio. I <br/>recommend this piece to those wanting to understand more about impedance. Learned that the measured voice coil <br/>resistance times 1.25 is pretty close to the voice coil impedance. Hence the measured 30 ohms does yield the 39 ohm <br/>spec of the Scott voice coil. This article got me as far as I got to patch in the universal push-pull transformer I had <br/>and having a ratio near what I had calculated - and attained proper sound from the Scott Masterpiece on my bench. <br/>Wish the article was clearer on push-pull transformers, however.<br/><br/>So if I were to add some turns to the Hammond transformer, what gage transformer wire should try? (I have a selection of gages available.)<br/><br/>Maybe I should try to open up the bad Scott output transformer and explore it.</pre>
<p></p> David:
Check out the Hammond…tag:ehscott.ning.com,2016-08-22:3925821:Comment:539082016-08-22T16:06:21.347ZThomas Dayhttps://ehscott.ning.com/profile/ThomasDay
<p>David:</p>
<p>Check out the Hammond transformer catalog. They make a lot of transformers for older tube guitar amps and also a lot of tube type output transformers. </p>
<p>Thom</p>
<p>David:</p>
<p>Check out the Hammond transformer catalog. They make a lot of transformers for older tube guitar amps and also a lot of tube type output transformers. </p>
<p>Thom</p> The impedance ratio is the cr…tag:ehscott.ning.com,2016-08-22:3925821:Comment:540792016-08-22T14:00:19.770ZNorman S Braithwaitehttps://ehscott.ning.com/profile/NormanSBraithwaite
<p>The impedance ratio is the critical characteristic, not the rated primary and secondary impedance. The impedance ratio is the turns ratio squared. Therefore, having a turns ratio of 20:1, the impedance ratio is 400:1 (full primary to full secondary). The original output transformer, having a specified output impedance of 39-ohms, has a primary impedance of approximately 15600-ohms. If all you can find is a transformer having an output impedance of 15-ohms, look for one having a rated…</p>
<p>The impedance ratio is the critical characteristic, not the rated primary and secondary impedance. The impedance ratio is the turns ratio squared. Therefore, having a turns ratio of 20:1, the impedance ratio is 400:1 (full primary to full secondary). The original output transformer, having a specified output impedance of 39-ohms, has a primary impedance of approximately 15600-ohms. If all you can find is a transformer having an output impedance of 15-ohms, look for one having a rated primary impedance of 400 x 15 ohms or approximately 6000-ohms. So long as it is rated for 15-watts, it will be electrically near equivalent to the original.</p>
<p>Norman</p>