Is the ~460 mA the current in your 40 Ohm resistor? Filament current for the 6-series tubes should be around 0.3 A if I have the correct data.
Other thoughts: The 2M, 47 K resistors and the volume control? I think I read that you checked these, and mentioned that grounding the input to the 6SQ7 doesn't kill the noise, but something could be intermittent.
Clean the socket, and check contacts? This should reveal if you wiggle the valve as the problem develops during warm-up.
(06-29-2018, 07:10 PM)jcassity Wrote: the 40 ohm power resistor is getting extremely hot still
Uhhh that's why it's called a power resistor. Size(wattage) should be at least 2X current, three is better.
463 ma is reading from where? Is that total taken from AC input?
Tube heaters should be drawing 300ma, if significantly higher then there isn't enough resistance in that line. The 25Z6 should also be supplying around 80ma, so a total of 380-400ma would be in ball park. Even if heater string is high, I doubt it has anything to with popping issue.
(06-29-2018, 08:21 PM)jcassity Wrote: I know what you mean Tom but the resistor is starting to smoke if I leave it on too long now
Guess I missed the resistor wattage.
The string consists of five 6.3v tubes totaling 31.5v, along with 75v for the two 50L6 in parallel and the 25Z5 equal 106.5v. To make up difference, one needs to drop a additional 15v. So ohm's law says set needs additional 50 ohms @ 4.5 watt. Since there is virtually no air movement, it's std practice to increase wattage approx 3x. Resistor will still run hot, has to dissipate that 4.5w. If all the set's 460ma is routed through resistor, it's going to smoke. B+ should be derived from AC line, fed from switch directly to 25Z6 plate(s) and B+ from the cathodes. This current should not be routed through above resistor.
Basically I'm saying we can't cheat ohm's law. A 40 ohm resistor @ 300ma is going to drop 12v, that was OK in the 40s/50s but with today's line voltage, ought to be increased. BTW 460 ma through 40 ohms is 8.5w. At 3X it should be at least 25 watt.
Once you have the heater string sorted out we'll figure out why it's drawing a extra 80ma. Correction of string may fix that.
Tom
(This post was last modified: 06-29-2018, 11:38 PM by 35Z5.)
yup,,
so i need to calibrate the power resistor....
i have a few ohmite adjustable R's but i just discovered a little while ago that the "GREEN" resistor in my pic in the lower right is actually a 50 ohm.
the two larger ones next to the green are soldered parallel to make 22 ohms which represents the one resistor with the lamp across it.
so.. on this green ressistor,,,
would you go less on ohms or more or the same?
i have 35 to 40v on the 6sq7 pin 6 when the set is cold but as i believe this resistor starts to get too hot ,, thats whats prob taking my pin 6 voltage down to around 11v,, ive watched it happen several times now.
tom,,,
the power input to the rect tube is wired exactly as the schematic shows.
i gather your saying i should connect the ac line cord differently...? i think your saying connect my 120v lead to rect pins 3/5,, which is for the sake of wiring already done.
my 120v hot leg is tied to the "input side of the 40ohm first power resistor. from that same termination i have a jumper wire going to the rect pin 3/5.
the N leg is wired like the print.
are you saying to move the "cold side of my on/off switch N leg up to the rect tube pins 4/8?
effectively if yes, that would mean my N leg of the chord would be on the + side of the "left" filter cap.
random comment- the print tells me the on / off sw is controlling the N leg of my power cord. I find this kinda odd and backwards.
I will jumper pins 7 & 8 of the 6sq7 *without" a tube installed.
i will then measure the voltage on pin 6 of the 6sq7 to see if my voltage is still degrading down to 11vdc.
This partial schematic shows how heaters should be wired, this is totally independent of any other circuitry in radio. Has no idea there is a pin 6 on 6SQ7. With this circuit can't be more than 300ma through heaters. The Red feed should be connected to pins 3 & 5 of 25Z6 while Blue is return(negative side of filter caps). That circuit should be drawing roughly 70-80 ma.
Yes it'd make more sense if switch was before Red feed in upper leg of circuit, but it'll work same either way. The safety minded often rewire the switch in that position and install a polarized cord.
BTW I forgot about 20 ohm dilal lamp shunt resistor, along with the 40 ohm, values are fine.
with no tube installed on the 6sq7, yet the filament pins 7 & 8 safely jumped, PIN 6 of the 220k ohm resistor has about 20v which will degrade if i let it warm up. so the voltage will continue to decrease.
up to this point i have been lifting the side of the 220k ohm resistor at the 50L6 side which makes the noise / problem go away.
i kept the 220k ohm resistor terminated over at the 50L6 this time and lifted a cap and the 220k ohm resistor off the socket of the 6sq7 pin 6.
with no tube installed and filament pins 7 & 8 safely jumpered, and with the 220k ohm resistor lifted off pin 6 of the 6sq7, my voltage readings are:
-the end of the 220k R tied to the 50L6 is 108vdc
-the free end up in the air that normally lives on pin 6 as i have pictured now reads 84vdc ***THIS IS THE VOLTAGE I need with the resistor terminated.
so as soon as i terminate the resistor back on pin 6, without a tube installed, the voltage will crash and drop.
sounding like a bad socket?????????
or bad solder joint(s)?? ~which i can easily reheat up and recheck.
see picture..
see the resistor and cap i lifted off pin 6
see the jumper wire setup (fused) to the right of the set on the bench to jump the 6sq7 socket filament pins 7 & 8.
(This post was last modified: 06-30-2018, 11:03 AM by jcassity.)
Bad solder joints can break/make connection but probably 99.999% will clear up at any movement, prodding, etc. You've juggled this thing around far to much to have a bad joint issue.
With only the 220K connected to pin 6, voltage drop will be within socket.
That would be an eight pin octal socket. There are several different types made, your set has molded sockets however there are wafer sockets and ceramic sockets too. Sometimes the mounting holes can differ in placement and in size slightly.
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!
