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Old 13th Apr 2022, 10:45 pm   #1
Chris55000
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Default Heater Wiring on PCB designs using valves?

Hi!

I was looking at the Assembly Book for the Heathkit S–99 Amplifier I'll be doing in the summer, and I noticed that instead of attempting to run heater wiring along copper tracks, two short pads lead off pins 4 & 5 of each valve and ordinary lengths of 1/0.6 solid–core wire run as a twisted–pair are used, run along the topside of the PCB and connected to the pads for pins 4 and 5 of each valve – is this the most effective way of running heater wiring rather than trying to route it along the copper itself?

I've looked at countless valved TV PCBs over many years and the designers have always been able to run the heater circuit as part of the copper pattern, which is a bit easier when heaters are in series, as is almost always the case!

Are thermionic valve circuits generally easier to design on a PCB as a rule than "old–school" wired layouts?

Chris Williams
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Old 13th Apr 2022, 11:25 pm   #2
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Default Re: Heater Wiring on PCB designs using valves?

Yes Chris. Far superior, it's to keep hum to a minimum. You can't do twisted pair on a copper foil pattern on the PCB very easily.
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Old 14th Apr 2022, 7:19 am   #3
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Default Re: Heater Wiring on PCB designs using valves?

Its also more flexible, if you run into hum problems you can experiment with the heater wire layout, not as easy with a pcb.

Peter
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Old 14th Apr 2022, 7:59 am   #4
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Default Re: Heater Wiring on PCB designs using valves?

I spent many years as a teenager resoldering heater wiring on PCB,s way back. They were ALWAYS 6.3 volts parallel heaters, involving SOME amps of current.
MY opinion, and its mine only so far, is PCB heaters are the tackiest, nastiest, cheapest method to make short lived junk.

Series heaters ?? MAYBE in old blighty, not here in Australia, I continue to say, " I have NEVER seen a transformerless TV, Radio, tape recorder or ANY other device. I can always rearrange my heater wiring to reduce hum and noise. When I fold up a PCB it gets all nasty, bitter and twisted.

Chris, you have specifically asked about amplifiers, I am only answering my experiences.
Short as my 68 years may be.

Forgive my rant, but if you want NICE amps, DONT wire the heaters onto the PCB. In fact I wont use PCB's at all with audio.

Best regards

Joe
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Old 14th Apr 2022, 5:27 pm   #5
G.Castle
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Default Re: Heater Wiring on PCB designs using valves?

Quote:
Originally Posted by joebog1 View Post
I spent many years as a teenager resoldering heater wiring on PCB,s way back. They were ALWAYS 6.3 volts parallel heaters, involving SOME amps of current.
MY opinion, and its mine only so far, is PCB heaters are the tackiest, nastiest, cheapest method to make short lived junk.

Joe
Actually Joe I do agree with you! and was answering Chris's first question. (Sorry for the ambiguity), At the very minimum I'd do as the kit and run the heater supply through proper single core wire that can take the current without appreciable voltage drop, can be twisted and arranged around the assembly to minimise hum, and also not leak nasty AC through the board substrate to low level circutry.

To answer the second question...the reason for PCB assembly of such eqipment initially was to ease assembly by unskilled labour, and reduce production costs.

Or, to put it another way maximize profit by cheap manufacturing.

Who hasn't seen valve equipment in its later life that was built on SRBP PCB's that has started to carbonize and develop bad solder joints on the valve holders.

Metal chassis any day over PCB, at least with the fire tubes
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Old 14th Apr 2022, 6:58 pm   #6
Dave Moll
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Default Re: Heater Wiring on PCB designs using valves?

Quote:
Originally Posted by joebog1 View Post
I have NEVER seen a transformerless TV, Radio, tape recorder or ANY other device.
I infer from that that Australian manufacturers have never had to allow for DC mains.
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Old 14th Apr 2022, 7:16 pm   #7
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Default Re: Heater Wiring on PCB designs using valves?

Quote:
Originally Posted by Dave Moll View Post
Quote:
Originally Posted by joebog1 View Post
I have NEVER seen a transformerless TV, Radio, tape recorder or ANY other device.
I infer from that that Australian manufacturers have never had to allow for DC mains.
You can perhaps also infer, that although AC/DC chassis were sold there in small numbers, (mostly imports), and were not actually banned, safety prevailed over profit in most Aussie designs.
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Old 14th Apr 2022, 11:10 pm   #8
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Default Re: Heater Wiring on PCB designs using valves?

There used to be 240 volt DC many years ago in Sydney. MANY years before I was hatched. BUT, I think there was also AC available. Origionally for trams I seem to remember. Only reason I know that, is I read an article in some magazine that was "going back " in time sort of thing. There was even a photograph of a massive battery bank.

Joe
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Old 14th Apr 2022, 11:44 pm   #9
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Default Re: Heater Wiring on PCB designs using valves?

This sums it up for me:

Quote:
Originally Posted by G.Castle View Post
You can't do twisted pair on a copper foil pattern on the PCB very easily.
I've yet to lay out a PCB for a valved circuit, but if AC heaters I'd hard-wire them for this reason! (And I'd use epoxy/glass-fibre board material, not SRBP).

Though, many a TV of late 1960's and early 1970's used heaters tracked on the PCB, successfully. They were series heaters so current wasn't huge. And I have a Pye attaché-case 4-valve battery radio with circuitry built up on a PCB, again, the filaments are tracked-in. But this if course is DC so there's no hum.
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Old 15th Apr 2022, 4:40 am   #10
TonyDuell
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Default Re: Heater Wiring on PCB designs using valves?

Quote:
Originally Posted by G.Castle View Post
Yes Chris. Far superior, it's to keep hum to a minimum. You can't do twisted pair on a copper foil pattern on the PCB very easily.
Nothing to do with valve heaters, but I've seen a twisted pair PCB track. In the HP9820 calculator, the keyboard sense loop (from the electromagnetic keyboard) goes across the controller PCB on a pair of trace that cross each other on alternate sides of the PCB with lots of vias to connect them up. It's one of those things that when you see it screams 'HP!!!'

The HP9810 calculator uses a normal twisted pair of wires for this.
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Old 15th Apr 2022, 7:50 am   #11
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Default Re: Heater Wiring on PCB designs using valves?

Quote:
Originally Posted by Chris55000 View Post
Hi!

I was looking at the Assembly Book for the Heathkit S–99 Amplifier I'll be doing in the summer, and I noticed that instead of attempting to run heater wiring along copper tracks, two short pads lead off pins 4 & 5 of each valve and ordinary lengths of 1/0.6 solid–core wire run as a twisted–pair are used, run along the topside of the PCB and connected to the pads for pins 4 and 5 of each valve – is this the most effective way of running heater wiring rather than trying to route it along the copper itself?

I've looked at countless valved TV PCBs over many years and the designers have always been able to run the heater circuit as part of the copper pattern, which is a bit easier when heaters are in series, as is almost always the case!

Are thermionic valve circuits generally easier to design on a PCB as a rule than "old–school" wired layouts?

Chris Williams
With it's "low end" heater current requirement a PCB design would run the filaments on series DC.
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Old 15th Apr 2022, 8:31 am   #12
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Default Re: Heater Wiring on PCB designs using valves?

Personally, I like the Radford approach, pcb to take the bulk of the components. Tagged valve bases with the heaters run by twisted wires, grid stoppers wired direct to the valve bases, PSU electolytics bolted to the chassis.
Best of both worlds.

Peter
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