PCB Track Width and pad size

Bill and Bertus are quite right, the heater supply voltage can be either 6.3 V DC or 6.3 V AC rms. Traditionally AC is used, but only because it's the cheapest method as the heaters were fed directly from one of the secondaries on the power supply transformer. It has the drawback of introducing mains hum into the signal path, to a greater or lesser degree depending on circuit and layout. Twisted pair wires to the heater supplies are a proven method of keeping the hum field down, but I think for the purposes of this project it would be best to use DC, with the heaters in parallel. Series connections can result in power-hogging if the heaters aren't well matched, but generally it works well if both heaters are in the same valve, and it does work out a little cheaper to implement.

Valves tend to like a soft start on the anode supply, which they used to get with the saggy drive from a valve rectifier circuit. The sudden step input of a contemporary PSU can be a bit of a shock. Supply sequencing can matter too. I'll dig out some old books and see if I can't find some decent cites here.
 

Thread Starter

bumclouds

Joined May 18, 2008
81
This might sound really dumb but how do I wire up the heater? For DC, could I wire it off Vbb and use a voltage divider? Will that do the trick? Or do I need to do something to limit the current going to them..
 

Wendy

Joined Mar 24, 2008
23,415
Feed them 6.3VDC, the rest will follow.

If you have a transformer that has 6.3 VAC, then feed it that. Precision isn't really that critical.

I have to admit, tube circuits look fun.
 

Thread Starter

bumclouds

Joined May 18, 2008
81
Should I put a resistor in series with the power supply to the heater? Or just go directly to it..?

and yeah ;) it is kinda fun
 

Thread Starter

bumclouds

Joined May 18, 2008
81
Ok newest one. Sorry about the delay. I've had two very long shifts at work this weekend.



the traces which aren't connected to anything yet are the heaters. I'm trying to figure out what to do.. and also how to get over to the edge of the board.. lol. Could I make a "jump" using a bit of wire? Or would that be rather un-eloquent..
 

AlexR

Joined Jan 16, 2008
732
Wire links are fine in this situation and probable your best option.
I While you're about it I would beef up the track width for the heaters to somewhere about 1mm - 1.2mm to accommodate the heater current.
 

Thread Starter

bumclouds

Joined May 18, 2008
81
Ok, done. I also realised that i'd made a boo-boo with the valve footprint. I created it using a different grid size to the one I was making my PCB on. I realised this when I printed it out and tried to stick my valve socket onto the paper. Anyway here is the improved version:

 
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Wendy

Joined Mar 24, 2008
23,415
OK, don't forget the center holes. They can be small and still work. They serve the same function as a center punch, they help the drill bit stay in the center of the pad while drilling. Copper is harder than PDB material.

I'd put your name, or pseudonime, and the date on that PCB. You may find others trying to claim the work. The people who do this are lazy, and probably won't change the board layout.

Your Vbb and Gnd need pads for the wires, maybe more than one. I notice you have traces going the length of the board for both. Keep them away from the mounting holes, they don't need to be close at all. You could probably terminate each trace (top and bottom) with a wire pad.

Looking pretty good.
 

Thread Starter

bumclouds

Joined May 18, 2008
81
I can't get my pad holes to show up in the print preview still :( !!

EDIT: Oh wait, I got it. It's in File > Page Setup > Advanced... Then you check the box labelled "Holes"


Here it is.. It's scaled up slightly, so the real thing is not quite this big. (also, ignore not-quite-straight lines, i'll fix those)
 
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Wendy

Joined Mar 24, 2008
23,415
OK, we've hit the limit on what I know about tubes, so I'll ask the question.

So you can have 12.6V on pins 4 and 5...

Or

Ground pin 9, and have 6.3VAC on pins 4 and 5 (with them connected together)?
 

bertus

Joined Apr 5, 2008
22,270
Hello,

You mean you have connected 4 and 5 together and pin 9 to ground.
(the heaters are in parallel connection).
The heatervoltage will be 6.3 volts in this case.

Greetings,
Bertus
 

AlexR

Joined Jan 16, 2008
732
If you beef up the pins 4 & 5 (as you have), you should also beef up the track to pin 9 since it will have the same current flowing through it. In fact it would pay to beef up the common ground rail at the top of your circuit.
 
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