Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12, 2025) x

Thread Closed

Excessive Field Coil Voltage in 70 ...
#5

Just because the field coil is rated at 40 mA does not mean that is how much current is actually flowing through it. To measure the current flowing through the field coil, put the VTVM in series with it and measure the current flowing. The power being consumed in the field coil will be the current times the voltage drop across it, on the order of 2-3 watts maximum. This power is used to generate the magent field for the speaker, and a small amount of heat. Given the big metal shaft through the center of the field coil and the air in there, you will not feel it as heat. For interest, go back and check the power draw for the entire radio. It's about 80 watts to my recall, not having the radio in front of me. The rated total plate current for all the tubes is 35 mA. On an average plate voltage of 250 Volts, thats about 10 watts. If you study the plate current draw per tube, 80% of the power is used by the audio output tube 47. You could also figure out the amount of power used to heat the filaments of the tubes, that's about 5-8 watts per tube depending on which one. Most power in the set is consumed heating filaments and as audio power, with small amounts consumed in the speaker field coil, and some wasted as heat passing through dropping resistors, the main choke out of the 80 rectifier ahead of the field coil, and in the dial lamp.


Messages In This Thread
Excessive Field Coil Voltage in 70 ... - by Guest - 11-23-2008, 11:21 PM
Re: Excessive Field Coil Voltage in 70 ... - by Guest - 11-28-2008, 01:14 AM
Re: Excessive Field Coil Voltage in 70 ... - by radiomikee - 12-05-2008, 02:14 PM



Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Philco P45-6365 Universal Transformer Instruction Manual
Can anyone guide me to where this may be found?GRG — 03:00 PM
54C Complete Teardown/Rebuild
I don't think that I have encountered a 12Z3 before, curious how it uses one of those but includes a #43, which is a 25 ...Arran — 02:17 PM
HiFi (Chifi) tube amp build - but my own design.
It's the other forum. I'm also in DIY, but mostly read there. Honestly, I kinda jumped into this without much thought to...TV MAN — 10:43 AM
Philco 71 Code 125
Hello,  I am in need of a schematic for this radio. Mine has the three separate circular tube shields and a shadow me...dconant — 08:06 AM
Stromberg Carlson 1500 Squeal
And life just keeps getting more complicated.dconant — 07:57 AM
54C Complete Teardown/Rebuild
Hello Roy, here is this one sincerely Richardradiorich — 12:45 AM
54C Complete Teardown/Rebuild
Richard, Had grabbed it already but thank you just the same.  I find myself wanting to find some way to block out the...glyphmon — 12:03 AM
54C Complete Teardown/Rebuild
Hello roy, here is a link to the schematic . Sincerely Richardradiorich — 11:54 PM
54C Complete Teardown/Rebuild
Richard, The Silvertone 2014 also is a transformerless set, so I am incorporating a 1:1 600 ohm audio isolation transfo...glyphmon — 11:37 PM
Preliminary work on wife's Silvertone 2014
Did an alignment today which was interesting.  IF alignment went great, almost all was already spot-on.  Adjusting on th...glyphmon — 11:35 PM

[-]
Who's Online
There are currently no members online.

>