heretic build

[bagwell359]

Hi this is a beginner to Bottlehead Crack and tube kits, but lots of transistor kit experience.

Q. Do the connections to the transformer from two AC lines that go to PT10: 15 to 18 and 16 to 13; or can I go AC to 15 & 18 and 13 & 16 with a forked 14 ga cable (two actually - black and white is my coding).

Also I don't get why we should use bare wire for ground early on?  Wouldn't having all ground green jacketed make more sense?

Thanks Folks

 

[Paul Birkeland]

Q. Do the connections to the transformer from two AC lines that go to PT10: 15 to 18 and 16 to 13; or can I go AC to 15 & 18 and 13 & 16 with a forked 14 ga cable (two actually - black and white is my coding).

I would have to ask what you would like to accomplish here?  Why 14 awg cable? Why not use what's provided with the kit?  (if you run into any problems, the more you deviate from the manual, the harder it is for us to help you debug things)

Also I don't get why we should use bare wire for ground early on?  Wouldn't having all ground green jacketed make more sense?

In tube gear, green jacketed wire is traditionally for 6.3V heater connections.  The bare bus wire is very, very easy to solder to, and we sleep better at night knowing that the safety ground in the amp is as easy to solder up as possible.

 

[bagwell359]

I've read and re-read posts, and reviewed my own experience with solid state builds back to the 1970's.  And come up with this as the starting chapter.

I don't like the way the AC cable goes in (visually).  I don't see the IEC as giving the kit much - outside of the fuse.  I'm using two safety measures: cross the line safety cap (V2 X1), and a line to ground Y2.  Beyond the safety one gets from potentially deadly shorts going to the chassis, you also get EMI filtering.  The power switch is a no-op.  If the circuit had enough power to the tubes needing a graduation - great, but it doesn't.  Same thing as sticking the AC power cable in the wall - plus I have need for space on the top side of the amp.

I don't like the long run of incoming single ended inputs from back to front - seems to require an insulated pair.  Also I don't like way the cables stick like rooster feathers out of the amp.  Finally, I want that space on the top of the amp.  Voila - the single ended cable is going in the side under the side with a strain relief to keep the cables safe from pulling.

Using a balanced headphone in, not because the circuit is balanced, but because all my headphones are terminated with balanced plugs.  I may add a SE input to, if so it'll be right there, and I'll have to add a post or two to hold it fast.

So this means AC cable comes straight in by the ground post (14x3 ga), I split the wires (black and white) in half and put in the safety caps there (ground connection at the post).  Then fan out for the 4 transformer points, and the ground connections.

Here it is:



Questions?  Brickbats?

 

[Paul Birkeland]

I don't like the way the AC cable goes in (visually).  I don't see the IEC as giving the kit much - outside of the fuse.

Well, when your captive power cord snags and rips the terminals out of the power transformer, it's possible you might change your mind.

  I'm using two safety measures: cross the line safety cap (V2 X1), and a line to ground Y2.  Beyond the safety one gets from potentially deadly shorts going to the chassis, you also get EMI filtering. 

These are not all that helpful for equipment with linear power supplies.  Typically SMPS that may share the line with your amp will have these caps present in the devices to eliminate the grunge at the source.  EI power transformers do a nice job of filtering this grunge out on their own, but if you wanted to restore an old AA5 radio, these caps would be a good idea (but not as good of an idea as adding an isolation transformer and a 3 wire power cord).  If you believe that your amp is safer with these caps present than it is without them, I'd love to hear why...

The power switch is a no-op.  If the circuit had enough power to the tubes needing a graduation - great, but it doesn't.  Same thing as sticking the AC power cable in the wall

Yes, but the power switch won't wear out like your wall receptacle will when you plug and unplug the amp a bunch. 

In a way this looks a lot like what we sold in the 90s.

 

[Doc B]

You may certainly build the amp any way you wish, that's the cool thing about kits. But we aren't necessarily going to bless changes made, particularly things that don't meet UL guidelines for power entry. As PB says, we did things more like this in the 90s. We have learned a lot about compliance with government safety standards since then. And our stuff performs better now too, more quiet, less sensitive to environmental noise. I'm not saying what you are doing won't work, just saying that I don't want the liability of advising you to remove the power entry as designed.

 

[bagwell359]

There is a cable tie poised to hold the AC wire to the bottom of the top cover, waiting to drill the hole when I figure out how best the various cables will lie after I solder and tape them up.

Hospital grade receptacles shouldn't wear out too fast.  Plus I will only use the amp 3 times or so per week.

Interesting points on the safety caps, I'll have to study that.

Thanks Doc, I understand your point and appreciate the tone it was delivered.

W

 

[bagwell359]

OK, I'll hew to the written plan for my first build.

Still can't figure out why the ground from the AC ground pin to the should be bare wire, but I won't ask.

 

[Paul Birkeland]

Still can't figure out why the ground from the AC ground pin to the should be bare wire, but I won't ask.

I answered this in my first reply to you.

It's also tinned bus wire, not bare wire.