Valve heaters and dial lamps - UK Vintage Radio Repair and Restoration Discussion Forum

short wave · 13th Dec 2015, 11:43 am

After watching a youtube video I learned something quite new to me.
Most radio and TV forum members will be familiar with the idea of running valve heaters in series in particular the TV people (“U” series at 100mA and “P” series at 300mA) . The dial lamp can also be designed into the series circuit , being of the same current value as the valve heaters.

The video talks of tap in the 35Z5 rectifier diode. This is not a centre tap as you would think (for example used in 3S4 , 3V4 , 12AH8 , 12AU7 , 12AX7 to name a few ) but is a special one that you can add a suitable lamp (or resistor) in PARALLEL with it and not burn out the “other half” (or
valves in the rest of the string)... all new to me! (also,you?)

I will raise the following questions…

1) Has it been used in the UK or an American thing (“all American five”)
2) Has it been used in any other applications other than in TV /radio
3) Any other valves with an “off” centre tap ( found 35W4 also)
4) Is it just limited to diode/ rectifiers

link to video
https://www.youtube.com/watch?v=Xbgs_BhNxXY
(jump in at 7-40)

link to valve data
35Z5
http://www.r-type.org/exhib/aaa0889.htm
35W4
http://www.r-type.org/exhib/aaa0908.htm

Other info here
http://www.philcorepairbench.com/tips/svctip40.htm

regards S-W

Nuvistor · 13th Dec 2015, 1:50 pm

A nice write up of the PSU in the All American Five years radios. I think it was standard to put the lamp across that heater section, according to the write up earlier sets had a resistor as well as the lamp so that if/when the lamp burned out the rectifier did not take too much strain, Later sets did away with the resistor and damage to the rectifier woukd occur a short while after.
Frank
http://www.angelfire.com/electronic/...bes/AA5-1.html

turretslug · 13th Dec 2015, 4:08 pm

Depending on your standpoint, an awful and cynical piece of penny-pinching and cheese-paring, or an effective and ingenious way of minimising component count. Personally, it offends the purist in me to stress an expensive component like a rectifier valve by over-running part of a filament when a known short-lived bulb inevitably failed, but it would have been to valve-makers' satisfaction....

Certainly, it keeps the radio going when the bulb fails, but an appropriate compensating NTC thermistor in parallel with the bulb to even things up would have been laughed (or budgeted) out of court.

Nuvistor · 13th Dec 2015, 5:56 pm

My felling is penny pinching, cheese pairing, but we don't know how cut throat the USA market was then and if a set cost a dollar more in the shop they would have lost sales.

Frank

13th Dec 2015, 7:37 pm

Yes, the American market was a lot cheaper (no BVA etc.) and much larger, so the odd penny (the same word on both sides of the pond) saved was worth it. The valve makers thought so too.

G6Tanuki · 13th Dec 2015, 8:57 pm

I don't see the 'split' heater in "all-american five" radios as at all wrong: given the expected lifetime of valves (and radios) compared with the spending-power of the consumers-of-the-day it made *perfect* sense!

Some people get worryingly bogged-down in issues of designing-for-longevity; I rather focus on "how to bring the best technology to the most people at the lowest cost". The various "AA5" radios from the 1930s through to the 1960s met a market-need in a sensible way. Why design your radio to last ten years if the purchaser wants a new-style one in five?

From memory, in "The Setmakers" someone from the UK whose business was selling extension-loudspeakers who travelled to the US in the 1930s came back saying "there's no market for extension-loudspeakers in the US; they just buy another radio".

And for that I truly commend the US approach!

julie_m · 14th Dec 2015, 12:45 am

The whole "All American Five" idea was certainly ingenious. Whether it was for good or for evil depends on your point of view, I suppose. And the number of sets that have outlasted their design lifetime surely speaks for itself.

Mr Moose · 14th Dec 2015, 2:51 am

Hello,
Some American sets used tapped barretters (current regulator tubes) to supply the dial lamps.
One example is the 140R8 http://www.radiomuseum.org/tubes/tube_140r8.html and part of a circuit (schematic) showing its use here http://www.radiomuseum.org/images/sc...het_631440.png. (The 140R8 barretter is shown as a resistor.)
Yours, Richard

FrankB · 15th Dec 2015, 6:58 am

Here in the US, they were only used in radios and some "El Cheapo" amps here.
I have never seen one used in a TV set, (Excepting the combo sets, of course) at least in my 45+ years of repairing.(But they did tend to throw the odd designed set in once in a while too).
Since the filaments were series, in the AA5's, and cost was a concern, the bean counters wanted to save every where they could. So the 35Z5 and 35W4 were used as the most common rectifiers in the AA5 sets. Adding a power TX for safety and a fil. winding were out of the question, production cost wise, for most Mfgr's.

IIRC, there may have been other rectifiers also that used the split fil. , but none spring to mind immediately.
When the fil. in the pilot lamp died, an excessive amount of current flowed through the rectifier's remaining fil, and greatly shortened the life of the tube.
In fact I remember some tube mfgr's refused to accept defective new rectifiers of those types, unless you replaced the pilot lamp at the same time as the rect. tube!

13th Dec 2015, 11:43 am	#1
short wave Pentode Join Date: Mar 2013 Location: Leeds, West Yorkshire, UK. Posts: 246	Valve heaters and dial lamps After watching a youtube video I learned something quite new to me. Most radio and TV forum members will be familiar with the idea of running valve heaters in series in particular the TV people (“U” series at 100mA and “P” series at 300mA) . The dial lamp can also be designed into the series circuit , being of the same current value as the valve heaters. The video talks of tap in the 35Z5 rectifier diode. This is not a centre tap as you would think (for example used in 3S4 , 3V4 , 12AH8 , 12AU7 , 12AX7 to name a few ) but is a special one that you can add a suitable lamp (or resistor) in PARALLEL with it and not burn out the “other half” (or valves in the rest of the string)... all new to me! (also,you?) I will raise the following questions… 1) Has it been used in the UK or an American thing (“all American five”) 2) Has it been used in any other applications other than in TV /radio 3) Any other valves with an “off” centre tap ( found 35W4 also) 4) Is it just limited to diode/ rectifiers link to video https://www.youtube.com/watch?v=Xbgs_BhNxXY (jump in at 7-40) link to valve data 35Z5 http://www.r-type.org/exhib/aaa0889.htm 35W4 http://www.r-type.org/exhib/aaa0908.htm Other info here http://www.philcorepairbench.com/tips/svctip40.htm regards S-W

13th Dec 2015, 1:50 pm	#2
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Valve heaters and dial lamps A nice write up of the PSU in the All American Five years radios. I think it was standard to put the lamp across that heater section, according to the write up earlier sets had a resistor as well as the lamp so that if/when the lamp burned out the rectifier did not take too much strain, Later sets did away with the resistor and damage to the rectifier woukd occur a short while after. Frank http://www.angelfire.com/electronic/...bes/AA5-1.html

13th Dec 2015, 4:08 pm	#3
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,396	Re: Valve heaters and dial lamps Depending on your standpoint, an awful and cynical piece of penny-pinching and cheese-paring, or an effective and ingenious way of minimising component count. Personally, it offends the purist in me to stress an expensive component like a rectifier valve by over-running part of a filament when a known short-lived bulb inevitably failed, but it would have been to valve-makers' satisfaction.... Certainly, it keeps the radio going when the bulb fails, but an appropriate compensating NTC thermistor in parallel with the bulb to even things up would have been laughed (or budgeted) out of court.

13th Dec 2015, 5:56 pm	#4
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Valve heaters and dial lamps My felling is penny pinching, cheese pairing, but we don't know how cut throat the USA market was then and if a set cost a dollar more in the shop they would have lost sales. Frank

13th Dec 2015, 7:37 pm	#5
Guest Guest Posts: n/a	Re: Valve heaters and dial lamps Yes, the American market was a lot cheaper (no BVA etc.) and much larger, so the odd penny (the same word on both sides of the pond) saved was worth it. The valve makers thought so too.

13th Dec 2015, 8:57 pm	#6
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Valve heaters and dial lamps I don't see the 'split' heater in "all-american five" radios as at all wrong: given the expected lifetime of valves (and radios) compared with the spending-power of the consumers-of-the-day it made perfect sense! Some people get worryingly bogged-down in issues of designing-for-longevity; I rather focus on "how to bring the best technology to the most people at the lowest cost". The various "AA5" radios from the 1930s through to the 1960s met a market-need in a sensible way. Why design your radio to last ten years if the purchaser wants a new-style one in five? From memory, in "The Setmakers" someone from the UK whose business was selling extension-loudspeakers who travelled to the US in the 1930s came back saying "there's no market for extension-loudspeakers in the US; they just buy another radio". And for that I truly commend the US approach!

14th Dec 2015, 12:45 am	#7
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Valve heaters and dial lamps The whole "All American Five" idea was certainly ingenious. Whether it was for good or for evil depends on your point of view, I suppose. And the number of sets that have outlasted their design lifetime surely speaks for itself. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

14th Dec 2015, 2:51 am	#8
Mr Moose Octode Join Date: Jul 2008 Location: Gloucestershire, UK. Posts: 1,043	Re: Valve heaters and dial lamps Hello, Some American sets used tapped barretters (current regulator tubes) to supply the dial lamps. One example is the 140R8 http://www.radiomuseum.org/tubes/tube_140r8.html and part of a circuit (schematic) showing its use here http://www.radiomuseum.org/images/sc...het_631440.png. (The 140R8 barretter is shown as a resistor.) Yours, Richard

15th Dec 2015, 6:58 am	#9
FrankB Heptode Join Date: Oct 2005 Location: Olympia, Washington, USA. Posts: 664	Re: Valve heaters and dial lamps Here in the US, they were only used in radios and some "El Cheapo" amps here. I have never seen one used in a TV set, (Excepting the combo sets, of course) at least in my 45+ years of repairing.(But they did tend to throw the odd designed set in once in a while too). Since the filaments were series, in the AA5's, and cost was a concern, the bean counters wanted to save every where they could. So the 35Z5 and 35W4 were used as the most common rectifiers in the AA5 sets. Adding a power TX for safety and a fil. winding were out of the question, production cost wise, for most Mfgr's. IIRC, there may have been other rectifiers also that used the split fil. , but none spring to mind immediately. When the fil. in the pilot lamp died, an excessive amount of current flowed through the rectifier's remaining fil, and greatly shortened the life of the tube. In fact I remember some tube mfgr's refused to accept defective new rectifiers of those types, unless you replaced the pilot lamp at the same time as the rect. tube!