What output transformer will work? - Printable Version
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What output transformer will work? - KCMike - 05-09-2013
After searching for months for an H-16 speaker for my Philco 144 console. I found an H-29 with the 660 field coil.Now I will need to purchase a single ended O/T . Would a hammond 125d work? This chassis uses the single 42 output tube. Right now I just want to get something so I can safely power up the unit. I recapped & rebuilt the bakelites months ago and put on shelf till now. Thanks for advice.
RE: What output transformer will work? - morzh - 05-09-2013
What is the voice coil impedance? It looks like it is 1.1 Ohm.
The Push-pull transformer has finer grained impedance matching; unfortunately 125 SE series does not. The highest you will get at 1.1 Ohm voice coil is 2.5K Ohm primary impedance and 42 tube needs 7K Ohm.
Also Hammond SE is very expensive.
I used this with my Zenith
http://www.ebay.com/itm/OT8SE-Tube-Output-Transformer-5K-7K-to-3-2-8-16Ohm-8VA-/150881062084?pt=Vintage_Electronics_R2&hash=item2321364cc4
It's half price.
However, this is not a match either.
What is exact voice coil impedance?
RE: What output transformer will work? - KCMike - 05-09-2013
Voice coil impedeance is 1.25 I figured I might have trouble finding exact match. I was hoping to get ideas on what would work for power up of unit for now, that won't damage anything. I plan to keep looking for the original speaker with correct tranny. Thanks morzh
RE: What output transformer will work? - Mondial - 05-09-2013
You can use just about any output transformer just to get it to work. It certainly won't do any damage to the set. About the only thing that will happen is that you might get lower output power or higher distortion because of the mismatch, but that's probably acceptable until you find the right transformer.
RE: What output transformer will work? - morzh - 05-09-2013
The transformers like those won't damage anything, they simply will not correctly transfer the power.
RE: What output transformer will work? - KCMike - 05-09-2013
Thanks morzh & Mondial. I went ahead and ordered the one you used in your Zenith morzh. Just wanted to ask the experts first. I did figure what ever I got that wasn't exact match would sound bad. But at least I can test some of the work I did so far with out worrying about burning out the output tube or worse.
RE: What output transformer will work? - morzh - 05-09-2013
Did you see if the mechanically the transformer is a good fity? It is not terribly important though.
RE: What output transformer will work? - KCMike - 05-09-2013
I have not measured the distance btwn. the rivets yet but it looks close to the new one. I have read that you have to be very careful not to get any shavings in the voice coil if you drill them out.
RE: What output transformer will work? - morzh - 05-09-2013
Yeah....but where's the voice coil and where are those rivets. You have to really try. Though nothing's impossible
RE: What output transformer will work? - KCMike - 05-09-2013
The O/T is on the speaker frame and with it out in the open should'nt be too much trouble to drill out.
RE: What output transformer will work? - Arran - 05-09-2013
Generally speaking it's the primary to secondary ratio that's more important then the primary impedance, that's why those universal output type transformers have multiple taps on the secondary side but not the primary side. The #42 has the same plate impedance as a 6F6 and is fairly close to a 6V6/6BQ5, and close enough to a 6L6, so a salvaged transformer for any of these will work fairly well. What will not work well is an output transformer intended for a type #41, 6K6, or a 6AQ5, those are way off the beam. The only wild card is the weird voice coil impedance of some Philco speakers, most are either 4 or 8 Ohms impedance not 1.1 Ohms, that is if the 1.1 Ohms is an impedance and not a DC resistance.
Regards
Arran
RE: What output transformer will work? - KCMike - 05-09-2013
Thanks Arran, That 1.25 I quoted in earliar post I got off the philco speakers compatibility spread sheet that was on the philco phorum. It was under the voice coil impedance columb. There is also an out. trans. pri. DC ohm columb. that says 260 ohm. which is the original o/t .