Just completed my Add a cap today. Worked first time!
I realised that the 100uF 450V cap might not cut it in my daily guitar amp type repairs. The voltages in these amp are mostly elevated in the range 500V to 750V.
My question is, will the device still work if I add 2x 350V caps in series with 220k voltage sharing resistors across each. ?
Opinions/ ideas please.
Hi, your question is legit but…. it is hard to say for sure for various reasons and I would dear saying the following : 1. At 750V DC there is arcing effect to consider therefore PCB spacing might need to be increased (where required) 2: the relay insulation rating becomes important too. 3. Even the FR4 insulating property/quality (the dielectric leakage level of the PCB) might play a role at those elevated voltages. So…. you are doing so at your own risk but I would suggest that your best bet is to ask MCL directly via PM (on Patreon).
If I were you I wouldn’t venture into such a risky situation unless you surely get some decisive answers from the creator first. I would…anyways. Good luck and if you ask him and get the answer you’re looking for let us know. 🙂 Good luck.
I completed the add-a-cap earlier this week. It works great for straight up test of adding capacitance to a B+ rail. I have noted that the ground path seems to make difference. For example, in an all American 5 radio, using the B- rail as the ground, which is the common ground path in many of these radios, the last relay fires, but then immediately disconnects. When the grounding point is moved to the chassis, this does not occur. More interesting, in a radio where the chassis is direct ground, I attempted to test the effect of adding a cap to the cathode of the final audio amplifier. In less than a second, the final relay disconnects immediately after firing. Any insights on this behavior would be welcome.
thanks!
I found the cause of the premature release of the final relay when the probe is attached to a voltage source under certain conditions. Rejecting the idea that it was a design issue because I thought there was no way Paul would miss that, I assumed it was a build error. It was. While I was constructing the voltage sense board, I substituted 1.2K resistors with 1.0K resistors because I thought I did not have any. I did note to myself to revisit that in case there was a later anomaly. Now, on the voltage sense board, the majority of those resistors are in the circuitry that controls the transistors on the front end, so they can absolutely affect the triggering threshold. So, I located some 1.2K 1206 resistors (it turned out I did have some) and replaced all the 1K resistors on the voltage sensor board with 1.2K resistors as specified by Paul. Problem solved.
So, those values are relatively critical. Don’t do what I did.