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Retrofitting speaker for Philco 84
#9

I think you are correct Ron and Terry. It is not as bad the other way (8 Ohm speaker on a transformer with a 1 Ohm secondary), at least for fidelity. However, empirically, they say it is better to run a tube style amp with a shorted output transformer secondary than with an open one. It is very important not to run a Pentode tube with a transformer with an open primary, the screen grid will melt and short. For solid state amps, the exact opposite is the case; one should never short the output of a solid state amp. As a kid, I replaced a slew or transistors for friends who hooked up 3 or 4 8 Ohm speakers in parallel.

Remember, resistance and impedance are 2 different things. I am not a radio engineer (Ask me questions about clinical chemistry, I'm your guy) but do understand a lot of it. I think that the members who are General or Extra Class HAMs could explain impedance better. It has to do with reactance, inductance and capacitance as well as resistance. There is an "Impedance ratio", however, if you try to run a transformer from a 6L6 (impedance of 2500 Ohm, 6W output) output transformer on a 50L6 Output stage in an AA5 (2500 Ohm impedance, 1 W output), the 50L6 will be drawing more current then with the correct speaker due to the resistance of the 6L6 transformer being lower than the one designed for an AA5 using a 50L6 even though the impedances are the same.

I think that if the schematic lists a value of 400 Ohm for a primary and 0.89 Ohm as a secondary, they are describing the DC resistance and not impedance. After all, they give the Field coil resistance in Ohms, not the inductance in Henries. (Is that the plural of Henry?)
By the mid 1930s, speaker voice coils were either 3.2 Ohm, 4 Ohm or 8 Ohm impedance (at 400 Hz or 1KHz). I don't know what the original Philco "Pie Plate" or G E "Kellogg Rice" speakers as used in the Victor early RCA, Majestic, etc. units used.

HAMs, jump in here (and save me).

"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis

Best Regards, 

MrFixr55


Messages In This Thread
Retrofitting speaker for Philco 84 - by Ctkid - 09-25-2022, 06:39 PM
RE: Retrofitting speaker for Philco 84 - by Ctkid - 09-26-2022, 09:57 PM
462ron - by 462ron - 09-29-2022, 08:29 AM
RE: Retrofitting speaker for Philco 84 - by MrFixr55 - 09-29-2022, 05:34 PM



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