Hello,
I recently aquired a Philco bread box model 513. It
appears to have been serviced and ready to power up. However, I do not have a speaker for it. Unlike some of my other Philcos this one has two posts to connect a speaker instead of four. I assume it is too early a model to accommodate a pm speaker and I am unsure wether to power it up without a speaker connection. It has a plug in on the front for headphones. any ideas or comments?

:Hi Jim,
you need a high impedeance speaker from this era like a RCA 100A or the Philco Speaker. Some of the other two wire remote speakers are Peerless, etc.
the jack in the front is not for headphones but for a phonograph attchment.

YOu may use a modern PM speaker if you cannot find a high impedance speaker. If you find a cabinet for a high impedance speaker but it lacks the speaker, in this case you can also use a PM speaker. All that is needed is a single ended universal output transformer. Choose the secondary tap for the speaker at hand and choose the primary tap for the tube in use, wattage desired, etc. The lower the primary impedance, the more wattage, but the less bass. Go for best over all tonal response.

You can also use an electro-dynamic speaker, but you will need a way of powering the field coil.

T.

:YOu may use a modern PM speaker if you cannot find a high impedance speaker. If you find a cabinet for a high impedance speaker but it lacks the speaker, in this case you can also use a PM speaker. All that is needed is a single ended universal output transformer. Choose the secondary tap for the speaker at hand and choose the primary tap for the tube in use, wattage desired, etc. The lower the primary impedance, the more wattage, but the less bass. Go for best over all tonal response.
thank you.. I had associated the high impedance speakers/ headsets with battery op farm radios. I did get some of those speakers with the lot and will try one out. This Philco has two 171 output tubes as does another Philco highboy model 511 ( I think ) but it houses and electro dynamic speaker with a voice coil. thanks again

:
:You can also use an electro-dynamic speaker, but you will need a way of powering the field coil.
:
:T.

::Hi Jim,
: you need a high impedeance speaker from this era like a RCA 100A or the Philco Speaker. Some of the other two wire remote speakers are Peerless, etc.
: the jack in the front is not for headphones but for a phonograph attchment.

thank you... I do remember seeing a Peerless and maybe an RCA. I recall reading that some of the voice coils in the electro dynamic speakers were part of the filter choke and that they should never be powered up without a speaker. Or at least I think that was the warning I got with an Atwater Kent. thanks again

It is rare to find a speaker in which the voice coil is part of the field coil.

The main trouble with powering up a radio that requires an electro-dynamic speaker when you don't have the speaker connected, is a possible radio overload. Some radios, especially the earlier ones from the early 1930s and prior, have the field coil wired ACROSS the power supply (just as the radio is wired). With this set-up, the field coil is part of the load across the supply. With its absence, there is less of a load, sometimes causing dangerously excessive voltage to reach the other radio components.

When the field coil is wired IN SERIES with the power supply (between it and the radio), there is not as much of a danger when operating the radio without the speaker. Usually with this set-up, when the speaker is removed, the circuit between the radio and the power supply is opened, which simply causes the radio to not function at all. When variations of this circuit are used, there may be more of a danger of burning something out, depending on how the circuit is wired.

Thomas