20-02-2019, 06:32 PM
(20-02-2019, 05:17 PM)LyntonP Wrote: If I measure the voltage across C29 it is 1.42V.
R16 out of circuit measures 5.0 ohms.
R15 out of circuit measures 6.5 ohms.
Current flow to S7 100mA.
Resistors R15 and R16 are sizeable components is this due to their age? If 100mA flows through a 3.9 ohm resistor would this produce only 0.3W? (Power is IxV watts)?
So would a 1/2 watt resistor be ok?
The current flow should be 125mA unless there is a battery economy switch but that should be inoperative for mains use.
This range of valves has 25mA filaments but the DL96 has two filaments! (Actually a 2.8V filament with a centre tap.) The two sections are connected in series in many mains operated receivers (but not this one!) so effectively there are five 1.4V filaments in series. For parallel connection, as here, the two sections are also connected in parallel, so it draws 50mA with the other 3 valves drawing 25mA each, a total of 125mA. It would be worth looking at the connections to the DL96 to check it is connected ok. Also check the valveholder pins from above for damage.
If you can find that missing 25mA, it will bring your excess voltage down!
Those resistors were very common at one time. The size of the resistor is quite small but what you are seeing is the relatively thick ceramic tube that surrounds it.
Power is I x V watts but for the figures you are using, current and resistance, you need to transpose the formula to find V. V = I x R, so the formula now becomes W = I² x R (normally written as I²R)
So 0.125 x 0.125 x 3.9 = 0.061W - so yes ½W would be more than adequate! Even 125mW would be fine! However, it looks at the moment that you need higher values than 3R9.
A thought that crosses my mind is that you measured the voltage at around 1.1V when the set stopped working and those resistor values are high - which could account for it but you are now missing 25mA somewhere so try this as an experiment: connect the meter across the LT line and place a finger on the top of the DL96 and move it around with a circular motion whilst keeping your eyes on the meter. If it suddenly drops to 1.1V, you've found your problem - either a faulty of just dirty valve holder or a dry joint under the chassis.
I'm assuming you are using a modern electronic meter and not an old analogue meter which is badly out of calibration?
Find that missing current because something isn't right there, then we can address the subject of replacement resistor values.
Oh - nearly forgot. No need for the apology - we all have to start somewhere and if you'd upset anybody you wouldn't be getting all this wonderful advice, would you?
