Draining Filter Caps - Best place to meter.

[12thfret]

I have been wanting to do some mods on my Epi BC30. Understanding the importance of draining the caps first, I unplugged the amp, removed the chasis, set my DVM to 3000VDC and checked for voltage at the anode resistor (R4) of V1...nothing. Checked every resistor coming off of the power tubes (R40 - R46) ...nothing. I can't get to the pins of the caps without removing the PCB. Anyone who's done the C5, C6 mod, MV mod care to share how they drained the caps? Or maybe a trained eye could take a look at the linked schematic. Is it possible the circuit has bleed resistors that drain the caps off before I can get the tubes cooled and the chasis removed?

I've tested the DVM on several known DC sources...9V battery, 12VDC/24VDC power supply and it appears to be fine. I've never had any issues with it in the past. I was hoping to get this buttoned up tonight. Short of metering the chasis when it's hot, I'm at a loss.

BC30 Schenatic

Peace,
Mark

[defaced]

The balancing resistors (R50/R51) bleed off the HT when the standby is off. Measure between the most positive side of R50 and ground. Or pin 8 of the rectifier tube will work too. Check the other preamp resistors you mentioned, but if this node is showing near zero volts, you should be fine.

[Alex R]

Those are well-built amps for the money, imo.

[12thfret]

The balancing resistors (R50/R51) bleed off the HT when the standby is off. Measure between the most positive side of R50 and ground. Or pin 8 of the rectifier tube will work too. Check the other preamp resistors you mentioned, but if this node is showing near zero volts, you should be fine.

Thanks Mike. That's great news! I'll continue to meter each time just to safe but it's good to know that the amp has a built in provision for draining the caps.

Peace,
Mark

[12thfret]

Those are well-built amps for the money, imo.

Hi Alex,

I didn't care much for the layout and not being able to get to the caps when I was trying to figure out how to drain them but now I see that with the bleeder resistors, there's no need to get to the bottom of the caps unless you're replacing them.

Peace,
Mark

[Alex R]

Yes PCBs are generally a nuisance, but the Epi BC30 strikes me a a well-designed board with nice thick traces a good way apart. Seems pretty durable too though I'm not really qualified to comment on PCB quality. Also I kind of respect the amp design for not going overboard for output watts, and the marketing is a bit more frank than some, selling it cheap because it's made abroad rather than trying to hide the fact and charge a premium price.