A stupid question -heaters in series - UK Vintage Radio Repair and Restoration Discussion Forum

Croozer · 27th Jan 2018, 6:01 pm

I have a stupid question whose answer I can't see.

I wanted to use half an ECC83 and only one of its two heaters. 12.6v at .15A in series, 6.3V .3A in parallel, for use in a 12v parallel heater chain.

1.CONSIDER RESISTANCE OF HEATERS:
I needed the resistance to balance using one heater. So what is the resistance of the heater in one half of the valve 6.3V/0.3 = 21R

But back-checking, 12.6/0.15= 84R

If the two resistances are connected in series, then the two individual heaters' resistances should sum to the total. (84R)

2.CONSIDER WHAT I NEED FOR CIRCUIT:
I have 0.15A traveling through a circuit which needs to drop 6.3V
I therefore need a resistor of 6.3V/0.15 A = 42R

(Which is also half of the 84R total heater resistance)

My brain is tired. It's been a hard week for work, and my mind is stuck in press officer mode, not technical mode.

I'm not seeing something very basic about the difference between the two. Could someone please explain the discrepancy between 1 & 2 above? What is the resistance of half a heater?

Many thanks

Croozer

Croozer · 27th Jan 2018, 6:10 pm

Mistake in context if circuit topography

GrimJosef · 27th Jan 2018, 6:12 pm

Your sums are correct.

Quote:

Originally Posted by Croozer

...

1.CONSIDER RESISTANCE OF HEATERS:
I needed the resistance to balance using one heater. So what is the resistance of the heater in one half of the valve 6.3V/0.3 = 21R

6.3V and 0.3A heats the whole valve with the two individual heater sections in parallel. Each heater section is 42R so the two in parallel are 21R, as you've shown

Quote:

But back-checking, 12.6/0.15= 84R

If the two resistances are connected in series, then the two individual heaters' resistances should sum to the total. (84R)

You're right again. Now the two 42R sections are in series.

Quote:

2.CONSIDER WHAT I NEED FOR CIRCUIT:
I have 0.15A traveling through a circuit which needs to drop 6.3V
I therefore need a resistor of 6.3V/0.15 A = 42R ...

Indeed, one section will be 42R.

Cheers,

GJ

kalee20 · 27th Jan 2018, 6:12 pm

ECC83 has its heater in two sections, you're right.

Each section is 6.3V 0.15A (or 42Ω). So if you put in parallel, you draw 0.15A + 0.15A = 0.3A, obviously all at 6.3V. Effective resistance is half 42Ω, or 21Ω, which is exactly what you get by considering 6.3V and 0.3A.

But if you put in series, you have 6.3V + 6.3V = 12.6V. And the resistance is 42Ω + 42Ω = 84Ω (resistances in series add), which is exactly what you get by considering the 12.6V at 0.15A.

If you're just using one section, then it'll behave like a 42Ω resistor.

Croozer · 27th Jan 2018, 6:14 pm

Mistaken blank post above

barrymagrec · 27th Jan 2018, 6:15 pm

The valve has two heaters, one for each half. Each is rated at 6.3 volts 0.15A. They can be connected in series or parallel..

Why do you want to connect only one half of the heaters and then add a resistor?, why not just connect them as intended?

Croozer · 27th Jan 2018, 6:32 pm

All,
Many thanks for your quick response. I needed someone from the outside to point out a mistake so obvious I couldn't see it.

I was intending to strap all unused electrodes together and thence to earth, in that context it didn't seem sensible to light the heater. But I don't know the correct procedure for using half a valve. Recommendations welcome

barrymagrec · 27th Jan 2018, 6:38 pm

I see no problem with running the heater on the unused half.

Unless others have better data info than I have I am not sure that which heater connection runs which half of the valve - if it is unspecified it may change for different makes of valve or different manufacturing plants.

G6Tanuki · 27th Jan 2018, 6:45 pm

The only downside I can see for running the heater on the 'unused' half is that it introduces additional heat which - if the valve's being used in something like a VFO - could cause additional thermal drift. Using an external resistor located well away from any temperature-sensitive parts of the VFO reduces this problem.

[I'm currently trying to reduce the thermal-drift of the VFO in a Trio 9R-59 communications-receiver which uses an ECC85 double-triode but only one triode is actually needed. The non-centre-tapped heater takes 0.45A @6.3V - to reduce local heating I'm pondering replacing this with a 12AT7 and only powering one filament - 0.15A @6.3V - so reducing the heating effect and - hopefully - reducing drift too]

Croozer · 27th Jan 2018, 8:46 pm

Many thanks. I'll run both heaters.

Diabolical Artificer · 28th Jan 2018, 9:10 am

I thought leaving a heater running on a valve without HT applied was a big no no, resulting in a damaged cathode. It's also wateful. If your running one section only at 12.6v as you say you'd have to drop the other 6.3v across a resistor. Better to tap off 6.3v from your 12v supply using a potential divider or use a CCS or 7805 and red LED.

Here's some good info - http://www.valvewizard.co.uk/heater.html

Heater filaments arn't linear like resistors and have a different resistance cold as compared to hot.

Andy.

Boater Sam · 28th Jan 2018, 9:21 am

Your maths are correct, but I can't see why you would only want to run half the valve.
If you are concerned about the unused half suffering cathode poisoning even though you are not using it, presumably so that the valve remains viable in use elsewhere, then wire that half as a diode and put a few volts on the anode so it ticks over.
Even 5v or 10v will keep it going for negligible HT current. Then its only one high value resistor extra.

Sideband · 28th Jan 2018, 11:32 am

It is possible to light only one half of the ECC83 if you connect to pin 4 or 5 (depending on which half you want) and pin 9.

TrevorG3VLF · 28th Jan 2018, 12:49 pm

Why not connect both halves of the valve in parallel?
What is the application?

barrymagrec · 28th Jan 2018, 1:04 pm

Quote:

Originally Posted by Sideband

It is possible to light only one half of the ECC83 if you connect to pin 4 or 5 (depending on which half you want) and pin 9.

Indeed - but is there data on which heater connection is for which half? There is no mention in my Mullard Maintenance Manual (price 10/6)

Station X · 28th Jan 2018, 1:09 pm

Easy enough to find out by experiment I'd have thought. Personally I'd just connect the heaters in series or parallel to suit the supply voltage.

ms660 · 28th Jan 2018, 1:19 pm

It's easy, pins 1 to 4 is one half, pins 5 to 8 is the other half, pin 9 is the heater common:

Second page: www.r-type.org/pdfs/ecc83.pdf

Lawrence.

G8HQP Dave · 28th Jan 2018, 2:16 pm

Heat the side you are using. Leave the other cathode cold, and ground the electrodes.

A hot cathode but no current means cathode interface layer. A warm cathode with current means cathode bombardment. A valve lasts longest when it is either off or on, not something in between.

Croozer · 28th Jan 2018, 2:21 pm

Many thanks for all the replies.

I've never used only half a valve before, and I don't know what best practice is; my thought was to use only what I needed (cathode poisoning etc. ) but the other valve in circuit has 12 V heater.
Cathode poisoning isn't really an issue, because the other half of the valve is redundant, but as a 'good practice' measure, eg. in case I ever want more gain, the cost of a resistor in the heater circuit seemed a low price to pay. The application is af amplification in a pantry TX.

Biggles · 28th Jan 2018, 2:47 pm

You could always connect a 6.3 Volt 0.3 Amp lamp in series with the heater to drop from 12V to 6V and use this as a dial lamp or power indicator. I would personally just use the heaters in series as intended and risk damaging the other half of the twin triode. Is it of any great consequence?
Alan.

27th Jan 2018, 6:01 pm	#1
Croozer Pentode Join Date: Jul 2016 Location: Edinburgh, Scotland, UK. Posts: 110	A stupid question -heaters in series I have a stupid question whose answer I can't see. I wanted to use half an ECC83 and only one of its two heaters. 12.6v at .15A in series, 6.3V .3A in parallel, for use in a 12v parallel heater chain. 1.CONSIDER RESISTANCE OF HEATERS: I needed the resistance to balance using one heater. So what is the resistance of the heater in one half of the valve 6.3V/0.3 = 21R But back-checking, 12.6/0.15= 84R If the two resistances are connected in series, then the two individual heaters' resistances should sum to the total. (84R) 2.CONSIDER WHAT I NEED FOR CIRCUIT: I have 0.15A traveling through a circuit which needs to drop 6.3V I therefore need a resistor of 6.3V/0.15 A = 42R (Which is also half of the 84R total heater resistance) My brain is tired. It's been a hard week for work, and my mind is stuck in press officer mode, not technical mode. I'm not seeing something very basic about the difference between the two. Could someone please explain the discrepancy between 1 & 2 above? What is the resistance of half a heater? Many thanks Croozer Last edited by Croozer; 27th Jan 2018 at 6:13 pm. Reason: Error in circuit topography

27th Jan 2018, 6:10 pm	#2
Croozer Pentode Join Date: Jul 2016 Location: Edinburgh, Scotland, UK. Posts: 110	Re: A stupid question -heaters in series Mistake in context if circuit topography

27th Jan 2018, 6:12 pm	#4
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: A stupid question -heaters in series ECC83 has its heater in two sections, you're right. Each section is 6.3V 0.15A (or 42Ω). So if you put in parallel, you draw 0.15A + 0.15A = 0.3A, obviously all at 6.3V. Effective resistance is half 42Ω, or 21Ω, which is exactly what you get by considering 6.3V and 0.3A. But if you put in series, you have 6.3V + 6.3V = 12.6V. And the resistance is 42Ω + 42Ω = 84Ω (resistances in series add), which is exactly what you get by considering the 12.6V at 0.15A. If you're just using one section, then it'll behave like a 42Ω resistor.

27th Jan 2018, 6:14 pm	#5
Croozer Pentode Join Date: Jul 2016 Location: Edinburgh, Scotland, UK. Posts: 110	Re: A stupid question -heaters in series Mistaken blank post above

27th Jan 2018, 6:15 pm	#6
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,561	Re: A stupid question -heaters in series The valve has two heaters, one for each half. Each is rated at 6.3 volts 0.15A. They can be connected in series or parallel.. Why do you want to connect only one half of the heaters and then add a resistor?, why not just connect them as intended?

27th Jan 2018, 6:32 pm	#7
Croozer Pentode Join Date: Jul 2016 Location: Edinburgh, Scotland, UK. Posts: 110	Re: A stupid question -heaters in series All, Many thanks for your quick response. I needed someone from the outside to point out a mistake so obvious I couldn't see it. I was intending to strap all unused electrodes together and thence to earth, in that context it didn't seem sensible to light the heater. But I don't know the correct procedure for using half a valve. Recommendations welcome

27th Jan 2018, 6:38 pm	#8
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,561	Re: A stupid question -heaters in series I see no problem with running the heater on the unused half. Unless others have better data info than I have I am not sure that which heater connection runs which half of the valve - if it is unspecified it may change for different makes of valve or different manufacturing plants.

27th Jan 2018, 6:45 pm	#9
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: A stupid question -heaters in series The only downside I can see for running the heater on the 'unused' half is that it introduces additional heat which - if the valve's being used in something like a VFO - could cause additional thermal drift. Using an external resistor located well away from any temperature-sensitive parts of the VFO reduces this problem. [I'm currently trying to reduce the thermal-drift of the VFO in a Trio 9R-59 communications-receiver which uses an ECC85 double-triode but only one triode is actually needed. The non-centre-tapped heater takes 0.45A @6.3V - to reduce local heating I'm pondering replacing this with a 12AT7 and only powering one filament - 0.15A @6.3V - so reducing the heating effect and - hopefully - reducing drift too]

27th Jan 2018, 8:46 pm	#10
Croozer Pentode Join Date: Jul 2016 Location: Edinburgh, Scotland, UK. Posts: 110	Re: A stupid question -heaters in series Many thanks. I'll run both heaters.

28th Jan 2018, 9:10 am	#11
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,670	Re: A stupid question -heaters in series I thought leaving a heater running on a valve without HT applied was a big no no, resulting in a damaged cathode. It's also wateful. If your running one section only at 12.6v as you say you'd have to drop the other 6.3v across a resistor. Better to tap off 6.3v from your 12v supply using a potential divider or use a CCS or 7805 and red LED. Here's some good info - http://www.valvewizard.co.uk/heater.html Heater filaments arn't linear like resistors and have a different resistance cold as compared to hot. Andy. __________________ Curiosity hasn't killed this cat...so far.

28th Jan 2018, 9:21 am	#12
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: A stupid question -heaters in series Your maths are correct, but I can't see why you would only want to run half the valve. If you are concerned about the unused half suffering cathode poisoning even though you are not using it, presumably so that the valve remains viable in use elsewhere, then wire that half as a diode and put a few volts on the anode so it ticks over. Even 5v or 10v will keep it going for negligible HT current. Then its only one high value resistor extra.

28th Jan 2018, 11:32 am	#13
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: A stupid question -heaters in series It is possible to light only one half of the ECC83 if you connect to pin 4 or 5 (depending on which half you want) and pin 9. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

28th Jan 2018, 12:49 pm	#14
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: A stupid question -heaters in series Why not connect both halves of the valve in parallel? What is the application?

28th Jan 2018, 1:09 pm	#16
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: A stupid question -heaters in series Easy enough to find out by experiment I'd have thought. Personally I'd just connect the heaters in series or parallel to suit the supply voltage. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

28th Jan 2018, 1:19 pm	#17
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: A stupid question -heaters in series It's easy, pins 1 to 4 is one half, pins 5 to 8 is the other half, pin 9 is the heater common: Second page: www.r-type.org/pdfs/ecc83.pdf Lawrence.

28th Jan 2018, 2:16 pm	#18
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: A stupid question -heaters in series Heat the side you are using. Leave the other cathode cold, and ground the electrodes. A hot cathode but no current means cathode interface layer. A warm cathode with current means cathode bombardment. A valve lasts longest when it is either off or on, not something in between.

28th Jan 2018, 2:21 pm	#19
Croozer Pentode Join Date: Jul 2016 Location: Edinburgh, Scotland, UK. Posts: 110	Re: A stupid question -heaters in series Many thanks for all the replies. I've never used only half a valve before, and I don't know what best practice is; my thought was to use only what I needed (cathode poisoning etc. ) but the other valve in circuit has 12 V heater. Cathode poisoning isn't really an issue, because the other half of the valve is redundant, but as a 'good practice' measure, eg. in case I ever want more gain, the cost of a resistor in the heater circuit seemed a low price to pay. The application is af amplification in a pantry TX.

28th Jan 2018, 2:47 pm	#20
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: A stupid question -heaters in series You could always connect a 6.3 Volt 0.3 Amp lamp in series with the heater to drop from 12V to 6V and use this as a dial lamp or power indicator. I would personally just use the heaters in series as intended and risk damaging the other half of the twin triode. Is it of any great consequence? Alan.