DC30 Clone Debugging Help Required

[milkyBK370]

Hi good folks of the Amp Garage forum. I'm back again with another question about my DC30 (Ceriatone layout) build.

I have posted some pics to help with this problem. Here's exactly what I did on first power up.

No vavles installed.
Powered on.
Fizzing sound and burning smell coming from the pilot light wires.
Powered off immediately.

The wires connecting the pilot light to the heater supply standoff were completely melted. This cable is rated at 1000v, 10 A so there must have been serious current/voltage to burn the cable. Needless to say I almost shit myself when it happened. With the voltages drained on the caps I went back in and cut the burned cable out. I was reluctant to power it back on but went ahead and installed the valves and powered on again. No more damage was caused this time and the amp worked ok on both channels. There was quite a bit of hum when the Master pot is in the pulled out position but I can get to that later. There's also an orange cable from the PT marked as "SH" - 0. I wasn't sure if this should just be trimmed and insulated or if it should be grounded.

Any advise on the potential causes of this problem would be greatly appreciated.

Ignore the fact that the FX loop wires and OT aren't connected in these photos. They have indeed been connected but my camera packed in so I couldn't get any more photos.

All the best,
Gary

[milkyBK370]

I forgot to say that the amp has been checked numerous time for continuity and everything seems to be fine there.

The voltages on the valve pins also line up with Ceriatone's figures with the valves installed.

[martin manning]

The orange wire is a shield, which should be grounded. On the other issue it sounds like there is a short in the pilot lamp assembly or wiring. Looks like it's plastic and should be isolated from ground, but I see three solder lugs? The pic is not too clear. Measure across the terminals and to ground as well.

[milkyBK370]

Thanks for the reply. I took a couple of pics using my phone of the heater wire standoff and pilot lamp.

I have now connected the orange wire from the PT to ground.

Yes, the pilot lamp has three solder lugs. I connected the heater supply to the two outer lugs leaving the centre lug free. I check the centre lug for continuity to ground and there's nothing. Should this lug be grounded as well?

[martin manning]

I'm guessing you need to run one of the leads from the filament supply to the center terminal on the pilot lamp, and the other to one of the other two. Can you measure the resistance from the center to the two side terminals and side to side? The bulb (if it's an incandescent) will measure a few ohms.

[Phil_S]

No guess on that, Martin. That pilot has two lugs for the sleeve and one for the tip. One wire goes to the tip in the middle and the other to one side lug. You might be tempted to ask, how am I so sure? Posing such a question might be a source of embarrassment so I won't mind if you don't ask.

[M Fowler]

I ran into a pilot light like that too and burned up wires the hard way

Center and only one side should be connected.

[milkyBK370]

So I feel embarrassed. Will make the corrections and will report back.

[M Fowler]

I'm embarrassed with you

I did the very same thing, once

Mark

[milkyBK370]

I suppose its fair enough to make this mistake. That's how we learn. Thanks for all the help and info guys. I'll get it all corrected tomorrow night.

[Structo]

Not sure if a light bulb current limiter would have prevented that melt down but it would surely protect the transformer or other expensive components.

Do yourself a favor and build one if you plan on building more amps.

[milkyBK370]

Hey Structo. Yeah, that's something I had intended doing. I have the bits to build a 5E5-A but will make the limiter up first I think.

[milkyBK370]

The amp has been gigged (albeit on low power) 3 times since I made the last post. I'm really pleased with it and haven't really had a issue with the amp being too bright, as was suggested on a couple of other DC-30 cone thread on here.

I do have a slight niggle though. When the Master control is in the off position there's a difinite increase in hum from the amp, at all levels on both channels. It doesn't really bother me too much but it's about twice the level of hum you'd expect from the amp sitting idle. When the Master is engaged there's no issue with hum whatsoever. I have a couple of people interested in buying the amp from me so I'd like to resolve this "issue" before I part company with the amp.

I notice that Ceriatone suggest using a shield between the preamp valves and OT. I'm using a standup tranny instead of their normal lay-down one so didn't bother installing a shield. Could this be the source of the problem? I assume not since the hum is only present when the master is taken out.

Please help!!
Gary

[alvarezh]

Try separating the two MV wires shown on the image.

All the best.

[milkyBK370]

I'll give that a go tomorrow mate. Will report back.