Hello all. I just assembled 2 each of the Coleman DHT regs with his raw dc supplies and I am having trouble with one of the regs. I have 9.5 volts DC on the inputs and while one reg adjusts down to 5 volts on the outputs no problem, the other settles at about 6.2 volts on the outputs and is not adjustable via RV1, the adjustable resistor on the pcb. Is this a case of a bad RV1, or are there other issues to check besides RV1, before I replace it. Hopefully Rod or someone else familiar with these can lend a hand. Thanks!
Are you measured it (and the current) with appropriate dummy load at required current?
For example 5V, 1.25A: dummy load 4R.
If the tube's heater very weak (increased resistance), the fixed current set results higher filament voltage.
The other possibility of error may due to the R1 value.
For example 5V, 1.25A: dummy load 4R.
If the tube's heater very weak (increased resistance), the fixed current set results higher filament voltage.
The other possibility of error may due to the R1 value.
The filament regulators are easy to debug. Euro21's points are good, and should be confirmed first. Also, please check it over with a magnifier, to be sure the joints are all soldered around R5, R7, Q2, R11. If any solder flux is visible, please remove it with some IPA, as flux can leak current.
If there is still any trouble, we can track it down with DMM measurements on some test-points.
I sent an email with the points to measure, please check them & email back.
If there is still any trouble, we can track it down with DMM measurements on some test-points.
I sent an email with the points to measure, please check them & email back.
Thanks for the response, Euro21! Yes, I have it loaded with a 4.3R. I will recheck R1.
Lesson learned: be extremely diligent cleaning flux off the pcb! I recleaned with IPA, this time inspecting with a magnifying glass to make sure all was gone. That did the trick. Works perfectly now.
Glad it's working!
Some solder fluxes are very good at leaking current. 'No-Clean' fluxed solder is an improvement.
Some solder fluxes are very good at leaking current. 'No-Clean' fluxed solder is an improvement.