AC wiring heaters, A or B ? - diyAudio
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Old 1st July 2008, 08:13 PM   #1
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Default AC wiring heaters, A or B ?

Which would you choose? I lean towards A, as it minimizes loop area, though it does have a closer proximity to both triodes, not just one.
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Old 1st July 2008, 08:36 PM   #2
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I always use A. But didnt have problems with B either.
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Old 1st July 2008, 08:46 PM   #3
Svein_B is offline Svein_B  Norway
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I like to use B, since I lay down the heater wiring first close to the chassis, and keep the area between pins open for p-p components added later.

Svein.
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Old 1st July 2008, 09:34 PM   #4
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Definitely B for the reasons above.
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Old 1st July 2008, 09:52 PM   #5
kevinkr is offline kevinkr  United States
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Well I tend to use DC... JK When heating with AC I may use A or B depending on circumstances - have also twisted tightly together as far as possible and looped up and then straight down the middle.

These days I mostly use types with adjacent filament pins and therefore do not have to deal with the issue specific to 12XX7 series stuff.

Minimizing loop area seems to be the key in most cases.

Floating the filaments and biasing them up to some dc level above ground often makes more difference than anything else.
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Old 2nd July 2008, 08:43 PM   #6
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Quote:
Originally posted by Svein_B
I like to use B, since I lay down the heater wiring first close to the chassis, and keep the area between pins open for p-p components added later.
Same here. I always connect the heaters first before completing the rest of the circuit, and like to keep the heater leads out of the way. Other than that, it probably doesn't make much difference.
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Old 2nd July 2008, 09:24 PM   #7
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This brings up a point that I have not seen addressed. Routing of heater wires is easy for a guitar amplifier since all line level signals enter and exit the amp on the front and the controls are also on the front. Thus the heater wires can be routed along the back and they are kept far apart for the most part.

The hifi amp is a little bit different as the controls are on the front but the line level signals come in and out of the back of the amp. So it becomes more difficult to keep the signal wires away from the heater wires.

I see several options and would like your input as to the best approach.

You could keep all of the signal inputs at one end of the chassis and route them around an into the tube sockets from the front while keeping the tubes as far to the other end of the chassis as practical. The down side is that the chassis must be larger and will be visually unbalanced.

Another option is to put the heater wires against the back as in the guitar amp and just run the shielded signal wires over the heater wires exactly perpendicular to each other. Thus you would be depending on the shielding, twisting and orthogonality of the wires to keep the hum out of the signal wires. This has some amount of convenience to it but I wonder about the effectiveness of this approach.

The other idea is to run the heater wires down the center and loop the signal wires around one end of the chassis. The concern here is that the heater wires are only up against one chassis side instead of two and though the wires are far apart they are parallel for a lot of the wire's length.

Your thoughts?
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Old 2nd July 2008, 10:20 PM   #8
chrish is offline chrish  Australia
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I just keep the IEC socket on the rear of the chassis on the left hand side as viewed from above. Run the 240v live down the left hand side to the front power switch. All heater wiring down left side, then along front of chassis, tucked in to corners, tightly twisted.

On right hand side at rear RCA inputs. Input shielded signal wire down right hand side to input circuitry of first valve stage, keeping away from mains and heater wiring.

B+ down centre of chassis. Zero volt bus parallel to front of chassis behind valves.

Followed this basic pattern for the last couple of amps and have had no hum or buzz problems.

This is my latest, finished yesterday. Heater wiring is tucked in to corner, so not visible, but it is the blue and yellow twisted pair. Power supply is on the right, signal circuitry on the left. Did not take too much trouble to keep wiring neat, but there is zero noise.

Click the image to open in full size.

This one is a little more complex, constant current for input and driver. Main power supply upper left. -15V supply for CCS lower left (as viewed). Heater wires run on the top and down right edge as viewed, then directly from corner to valve socket. Sockets are orientated so that pins 4 & 5 are towards the front of the chassis to allow heater wiring to remain clear of signal wiring.

Click the image to open in full size.

I think this is pretty much as recommended by Morgan Jones in his books.

Chris.

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Old 2nd July 2008, 10:31 PM   #9
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Great input. What do you do about controls (vol and selector etc) on integrated amp or preamp?
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Old 3rd July 2008, 08:04 AM   #10
chrish is offline chrish  Australia
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I avoid that tricky problem Mike by only building power amps

Seriously, the only amp I built with a volume control followed the same pattern above, but with the shielded inputs running down right hand side to the volume pot on the front of the amp on the right side, then from there to the input valves. My main system has a Rotel surround sound pre amp, and the other amps for office use have been hooked to computer or iPod, so just using the volume control on the source devices.

Cheers,

Chris
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