I purchased my first Old Time Radio and working on restoration. I have already started replacing the old capacitors and ordered a new audio output transformer, Hammond 125C. The speaker is measuring out at 4.6 ohms. In looking at the chart for wiring this up I am a bit confused as to the terminals I need to connect to for the 3 wires. As a side note it has been 30 years since I have worked on electronics so I am trying to clear out the dust in the brain.
Any incite or guidance would be greatly appreciated.
Original symptoms are that when powered on volume was very low and would not change. Prior to powering on for the first time I looked at the caps, all original but not leaking, wires where still pliable, and no dust in cabinet or on electronics. This has been kept in a fairly safe environment here in Colorado.
"There are 3 wires with 6 tabs on the . . . (secondary). . . side."
It looks like Morzh is familiar with this exact transformer.
I found some info on it online, but not the impedance info you need,....only refers to the charts numbers that have the wiring . Without the charts themselves, it's no help.
You need the 8 ohm tap and the common connection. Had I been working totally blind, I would guessed using terminals 1 and 5.
I'll have to study a good schematic to fathom that feedback connection.
(This post was last modified: 06-19-2019, 05:48 AM by Jake Blake.
Edit Reason: mispelling
)
Hi and welcome,
You may want to have a look here: https://philcoradio.com/phorum/showthread.php?tid=17076 It's for a 41-300 but the chassis are very similar.
The output transformer requires to be wired w/proper phasing because of the feedback loop. If not the amplifier will oscillate. To acheive the the proper phasing you may have to reverse the brown and blue wire connecting to the transformer (plate leads). This is done w/the fb loop connected.
You may find that none of the secondary taps will give satisfactory performance when the loop is connected to any of them. Low gain or distortion so to get the best performance connect a low value pot (100-500 ohm is fine) across the spkr voice coil connections. Connect the wiper to the loop and adjust the pot for best results. Once this is done measure the pot and replace it w/5w fixed resistors.
GL
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 06-18-2019, 09:15 PM by Radioroslyn.)
Didn't look at the sch and so didn't account for the feedback. The pins I named were for the voice coil connect in case of pentode connection of the output tubes and 4.6 ohm voice coil. .Otherwise what Terry said about the feedback.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
If a standard, battery-operated VOM is used to measure a permanent-magnet driver's voice coil impedance, and measures 4.6 ohms, ( or perhaps as high as 5.-something ohms), you can infer the voice coil is an 8 ohm voice coil.
A 4 ohm voice coil will measure about 2.5 ohms and a 16 ohm voice coil will measure on the order of about 10-12 ohms.
A 2nd look at the schematic shows this radio has a field coil though, so it may be different.
(This post was last modified: 06-19-2019, 06:08 AM by Jake Blake.)
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