Electrically, would R1 see any voltage difference depending on the locations of the two banks of resistors (R5,6 and R4,7)
(U1-U4 are Diodes) in the image below ? (rhetorical)
I don't believe it should, yet after going through great lengths to choose 8 matching resistors, and actually wiring as shown below
I have a 1 volt difference to R1...
The circuit on the left gives me 5V while the Right one gives me 4V ?
BOTH circuits are fed exactly 5.98V AC...
R2+R3 on both sides measure within an ohm of each other...
Using LT spice, to get almost a volt difference at R1 all (4) 1ohm resistors need to be about 2.5 ohms ?
I know measuring low value resistors is not as simple as it sounds, but my leads have a .2 ohm "zero" and all 8 resistors below measured .8 multiple times.
Thats hardly 2.5 ohms!
I just dont understand what I need to do to get these heater voltages the same..
To make this more complete, I had to wire both as shown above as there was only 1 short jumper on the board to one channel (Was real tight getting (4) 1w resistors so they had room to radiate heat without affecting nearby caps)
The other channel had 2 jumpers which allowed a little more room so could add before and after the load.
Again, I didn't think it mattered on a DC circuit...
Basically I had to add resistors where there was none originally
Would a 10 turn 5 ohm 4w pot work better ?
Is there a simpler way ?
EDIT; (R1 is the filiment in the 300B)
(U1-U4 are Diodes) in the image below ? (rhetorical)
I don't believe it should, yet after going through great lengths to choose 8 matching resistors, and actually wiring as shown below
I have a 1 volt difference to R1...
The circuit on the left gives me 5V while the Right one gives me 4V ?
BOTH circuits are fed exactly 5.98V AC...
R2+R3 on both sides measure within an ohm of each other...
Using LT spice, to get almost a volt difference at R1 all (4) 1ohm resistors need to be about 2.5 ohms ?
I know measuring low value resistors is not as simple as it sounds, but my leads have a .2 ohm "zero" and all 8 resistors below measured .8 multiple times.
Thats hardly 2.5 ohms!
I just dont understand what I need to do to get these heater voltages the same..
To make this more complete, I had to wire both as shown above as there was only 1 short jumper on the board to one channel (Was real tight getting (4) 1w resistors so they had room to radiate heat without affecting nearby caps)
The other channel had 2 jumpers which allowed a little more room so could add before and after the load.
Again, I didn't think it mattered on a DC circuit...
Basically I had to add resistors where there was none originally
Would a 10 turn 5 ohm 4w pot work better ?
Is there a simpler way ?
EDIT; (R1 is the filiment in the 300B)
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If the source is floating, the voltage across R1 will be the same either way, since it's a series circuit with
all elements on the same branch, so the same current is in all elements. But measure the DC voltages
directly across the ends of each resistor.
Could the two filament windings have different AC voltages? Measure them.
all elements on the same branch, so the same current is in all elements. But measure the DC voltages
directly across the ends of each resistor.
Could the two filament windings have different AC voltages? Measure them.
Just for the filaments like resistors it doesn't matter , but 300B is a direct heated tube ... so it is trickier
Anyway it should be done the same for the sake of symmetry
Anyway it should be done the same for the sake of symmetry
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Rotated tubes, and same issue. Exact values not exactly the same but the right circuit still is down in voltage...
All 8 diodes recently replaced and all 8 tested identical (or as close as I could measure with my fluke) as well
Actually bought 25 diodes and 50 resistors just to see how close I could get them.
Measuring the voltage drop in circuit really hard, I didn't leave much leg on one side and its tucked way back behind ..
Will try though...
rayma, no the filament windings from the power transformer both measure 5.98 VAC (Im guessing the fluke is rms)
All 8 diodes recently replaced and all 8 tested identical (or as close as I could measure with my fluke) as well
Actually bought 25 diodes and 50 resistors just to see how close I could get them.
Measuring the voltage drop in circuit really hard, I didn't leave much leg on one side and its tucked way back behind ..
Will try though...
rayma, no the filament windings from the power transformer both measure 5.98 VAC (Im guessing the fluke is rms)
The 300B filament takes 1.2A, so if there is 1V missing, that's nearly 1 Ohm.
It's in there somewhere.
It's in there somewhere.
Lampie519, the lower filament voltage tube is at 50ma and the 5v filament tube is at 70ma.. switched tubes and pretty much the same...
Looked for an affordable 10 turn low ohm pot that can withstand 4 watts, no luck... unless i want to withdraw from my retirement plan!
Looked for an affordable 10 turn low ohm pot that can withstand 4 watts, no luck... unless i want to withdraw from my retirement plan!
Do you use a pcb ?
I had a case where the copper had a connection via a screw to ground ( on a dual layer board ). It was a pain to troubleshoot as it was on an unexpected place.
I had a case where the copper had a connection via a screw to ground ( on a dual layer board ). It was a pain to troubleshoot as it was on an unexpected place.
Did you measure the voltage drop of each resistor ? It could be that a component is defective and it only shows under load.
Haven't used LTSPICE n a while, but I recall that all voltage sources were ground referenced- no floating voltages. Bridge requires floating input or floating load. If your heater winding is grounded and heater is grounded, there's a short across part of your heater circuit! Not to mention half-wave rectification...
Update...
If I didn't do the work myself, Id swear an amateur was behind the soldering iron. Wait, I am the amateur !
Found 1 diode had a less than perfect solder job. As soon as the solder was heated, it literally jumped off the pad and onto the iron tip...
that's the 2nd bad solder joint I have found from the work I did that day...
Lesson, no matter how clean you think you have made it, use liquid flux EVERY time.
To sleep well , I redid every part I did that day, just to be 100%. Will verify tomorrow to make sure there are no more surprises ...
If I didn't do the work myself, Id swear an amateur was behind the soldering iron. Wait, I am the amateur !
Found 1 diode had a less than perfect solder job. As soon as the solder was heated, it literally jumped off the pad and onto the iron tip...
that's the 2nd bad solder joint I have found from the work I did that day...
Lesson, no matter how clean you think you have made it, use liquid flux EVERY time.
To sleep well , I redid every part I did that day, just to be 100%. Will verify tomorrow to make sure there are no more surprises ...