(04-29-2017, 02:18 PM)gregb Wrote: I think you still have something wrong in your radio as there are lots of similar radios out there that use a resistor or two in the power supply and they are rarely more than a couple watt units and they work just fine. You can be absolutely sure that Philco did not install a 20 watt resistor in this radio originally. Have you done a current measurement through this resistor to see what the total set current is? If not you should as something does not seem right to me.
Greg,, how did i miss this post?
i couldnt agree with you more.. something is odd, yet my transformer voltages are all good.
radio plays on AM , no shortwave yet.
there is some risk but im willing to power up and spend the min time i need to gather section by section the voltage readings you all need.
While i had one meter reading each side of this resistor, i had my amp clamp set on "MAX" to gather and hold the max current draw and the display never caught a number. i can redo but that tells me the current is likely under or at an amp.
any other time i amp clamp using min/max scale it works like on mult-2000AH -48v battery strings, automatic transfer switches, Gensets, hvac etc.
dono man,, maybe i will open the circuit and put my meter inline with the input side of this resistor.
If needs to be measured very accurately, the voltage across the resistor can be measured on AC, then on DC, then the results are squared, summed and the square root extracted. That willbe the RMS of the voltage. Before extracting the root, same sum of the squares times 300 ohm is the power dissipated.
Again, only possible with true RMS DMM, else the averaging DMM can gve anywhere 10 to 40% error on complex AC forms.
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.
(This post was last modified: 04-30-2017, 12:17 PM by morzh.)
It seems this discussion is going around in circles.
The real question is whether the radio is drawing excessive B+ current from the power supply. It is very easy to measure. Just connect your DC voltmeter across R100, indicated on your photo. This is the wirewound bias resistor and the full B+ supply current flows through it. The current here is pure DC, so there are no complicated waveforms to worry about. Measure the DC voltage across this resistor, then divide the voltage you read by the resistance of R100. You can measure the actual resistance of R100 if you want to be very accurate. The voltage divided by the resistance will give the current draw in amps. Multiply by 1000 to get mA.
If this current is close to 0.1 Amp or 100 ma, then the radio circuits are fine and there is no excessive current drain.
If the current is ok, then the 300 ohm series resistor is getting as hot as it is supposed to. Remember, wirewound power resistors are designed to operate at very high temperatures (several hundred degrees) at their rated power dissipation. If you want a cooler running resistor, derate it ( use a higher power rating resistor) or use one which can be heat sinked to the chassis.
SOmetimes,,,that resistor ,,that is bolted to the chassis,,,with the tin wrap around body,,,get real hot,,,and burn thru the insulation,,,and kind -of burn out,,,but --not really,,,and will really drive you nuts with stuff like this----Cheers
communications error on my part.
my resistor that is getting too hot is called out as R102.
R102 *IS NOT* the speaker field coil replacement. R102 is spoken to in the code 125 update as simply "added" off pin 8 of my rectifier tube.
the resistor that replaces the field coil is R103 and is the original with code 125 called out PN#
additionally i have the original R101 with the correct code 125 call out PN but its leads were too short, replaced with the blue one in the pic.
My candohm is shown as well, as R100... its pn upgrade to code 125 is also correct.
going to get the information requested now.
I have provided updated prints & picture to help. does this change any opinions?
(This post was last modified: 05-01-2017, 10:40 AM by jcassity.)
additionally, something that has bothered me,,,
the error i think i find in the filter capacitors shown to the far right on code 122.
I assume that the first filter section cap off pin 8 of the rectifier tube is C101.
I assumed that the text "C101" was correct and that the text of the 10 & 25 uf caps was meant to be C101A & B.
I have to wonder if the diagram isnt bass akwards.. a few terminations i made reinforced my assuptions were correct though.
voltage reading results
again, R102 is the one getting very hot
Part AC across AC IN AC Out DC across DC in DC Out OHMS Comment
R100 O 0 0 0 0 0 271 could be intermittant / candohm
R103 4.6 4,5 1.2 50 226 175 1341
R101 4.5 4.7 1.4 63 226 162 10024
R102 65.5 66.9 4.8 74 301 226 511 substituting/300ohm call out
v6-3 -- 4.3 -- -- 214 -- -- 6k6, from chassis to pin 3
v7-3 -- 5 -- -- 212 -- -- 6k6, from chassis to pin 3
Green -- 0 -- -- 0 -- -- T6/T100 green highV center tap
(This post was last modified: 05-02-2017, 07:50 AM by jcassity.)
Something is wrong with your measurements on R100. Is is connected correctly?
One end should connect to chassis ground, the other to the can of C101 and the center tap of the power transformer. You measured a resistance of 271 ohms which is correct, but there is no DC voltage across it? That makes no sense unless it is not connected properly.
on the candohm R100, i was also at least expecting something like -15v per the diagram- 46-1226 code 125 power supply update to the far right.
T100 center tap of the hv secondary (green) to>
terminal strip to>
white wire to>
C101 filter cap group (parallel caps with negatives tied to>
one side of R100 candohm to>
chassis.
if you look at the prints... Filter cap C102 negative can bond to chassis direclty.
Filter cap C101 can not be bonded directly to chassis, it must go through R100 before getting to chassis.
(This post was last modified: 05-02-2017, 08:07 AM by jcassity.)
Something is wrong with the connection of the green center tap wire.
It should not connect to ground, but to the end of R100. You should measure 271 ohms from the center tap to chassis ground. You should also read 271 ohms from the can (negative) connection of C101 to chassis.
Confirm that you so not have a short from the green center tap wire or C101 negative terminal to the chassis.
Yes, that is correct. The center tap and C101 negative should only connect to chassis through R100.
Thats why I said to measure the resistance from the center tap to ground. You should read 271 ohms, the resistance of R100.
If you do not read 271 ohms there is a problem. There must be 15 to 20 volts at the center tap to provide bias for the output tubes. This voltage is developed across R100 so if you have no voltage across R100, then the center tap is somehow bypassing R100 with some other path to ground.
