12 volt HT valves... Are they?? - UK Vintage Radio Repair and Restoration Discussion Forum

Hunts smoothing bomb · 13th Apr 2011, 4:55 pm

Hi All,

I was surprised to read in the spring 2011 BVWS bulletin that it was stated that there was no difference between the mullard valve EBF83 with 12v HT and the mains set version EBF89, also the same was said about the 12v HT ECH83 and mains set version ECH81.

I found this hard to believe so I went and rummaged for a couple of ECH81's and an EBF89 and put them in a philips car radio I have which should use 2 x ECH83's and 1 x EBF83, the result?........... It works perfectly so are they really the same valve with different numbering? I haven't tried the ECH83 or EBF83 in a mains set yet and don't think I will either

Cheers

murphyv310 · 13th Apr 2011, 5:03 pm

Indeed it is thought that the '83's are specially selected versions of their 81 & 89 brothers.
I have been using an ECH83 in my B40 for the past 10 years.

Leon Crampin · 13th Apr 2011, 6:06 pm

They're the same - but selected to give reasonable gain at low HT voltages. Using the '83s in a mains set is no problem- I've done it.

The give-away is that the interelectrode capacitances are the same for each pair of valves, in all respects. If these valves were really different, the capacitances would differ.

I wonder where Philips got the 50V max HT rating from for the '83 series?

Leon.

G8HQP Dave · 13th Apr 2011, 9:01 pm

That part of the data sheet was written by Marketing instead of Engineering?

BTW there was a long discussion about this on another forum - I'm sure Google will find it for you.

Alan Stepney · 13th Apr 2011, 9:33 pm

In fact you can run a lot of valves with ht far below what the data sheets state.

I have just built a simple audio oscillator using an EF91, with SIX volts "ht", for a demonstration I am giving.

The ECH81/83 is particularly forgiving and will do lots of things that it isnt supposed to.

Peter.N. · 13th Apr 2011, 11:54 pm

That's interesting, I didn't knowm that. The 0C16 works very well on 12 volts.

Peter

paulsherwin · 14th Apr 2011, 1:14 am

I've always suspected that this was purely a matter of marketing. I can't tell the difference between an ECH81 and an ECH83 by looking at them and the ECH83 seems to work fine with standard HT voltage. I've never tried a bog standard ECH81 in an old car radio, but my guess would be that it would work without problems.

Bill · 14th Apr 2011, 12:23 pm

How difficult would it be to modify a mains radio with ECH81/EBF89 + others to 12V operation? Is there an output valve that would drive a speaker with 12vHT? Possibly 12A6, EL32 or use an EF80/91 ? What about a small inverter to supply 200v just for the O/p valve? My experiments using a 12v/mains inverter to supply an unmodified mains set were not satisfactory, it worked but lots of noise from the inverter.
Bill

kalee20 · 14th Apr 2011, 12:37 pm

Quote:

Originally Posted by Alan Stepney

I have just built a simple audio oscillator using an EF91, with SIX volts "ht", for a demonstration I am giving.

That's nothing Alan - I once built a push-pull LC oscillator (25kHz) using an ECC82, it continued to run with 50mV HT.

ricard · 15th Apr 2011, 8:55 am

Quote:

Originally Posted by Bill

How difficult would it be to modify a mains radio with ECH81/EBF89 + others to 12V operation? Is there an output valve that would drive a speaker with 12vHT? Possibly 12A6, EL32 or use an EF80/91 ? What about a small inverter to supply 200v just for the O/p valve? My experiments using a 12v/mains inverter to supply an unmodified mains set were not satisfactory, it worked but lots of noise from the inverter.
Bill

Well, these 12V valves were intended for car radios so there must have been output valves capable at operating at these voltages too.

/Ricard

John M0GLN · 15th Apr 2011, 9:30 am

The only one I can find in the Radio Valve Data Book 7th edition (output valve section) is a 12K5 tetrode, which has the heater, anode and screen grid at 12.6V, but it won't be very loud, 35mW is the output, and it has a cathode, which wouldn't be needed for DC operation, but would it have to have one to give mechanical support to a filament when designed for a bumpy car journey?

John

Peter.N. · 15th Apr 2011, 9:52 am

The radios that used these valves, or at least the ones I was familier with used an 0C16 transistor for output because you couldn't get enough power from a valve. As far as I know this was the first transistor to be used in a car radio and for a single ended output it worked very well, most importantly it did away with the need for a vibrator HT pack, or rotary converter as some early ones had, thus considerably reducing the power consumption. - I had one in my Vauxhall Cresta, the quality was much better than the early all transistor portables with push pull outputs. I think my radio was a Pye TRC 1000.

Peter

murphyv310 · 15th Apr 2011, 10:14 am

Hi.
My Dad had I believe although I could be wrong an Ekco hybrid set in his Rover P4 (1956, 75) which was much better than the all valve set (vibrator HT) in his 1951 V8 Pilot!

G8HQP Dave · 15th Apr 2011, 10:49 am

Quote:

Originally Posted by jcaines

it has a cathode, which wouldn't be needed for DC operation

A directly-heated valve mixes up bias and heating, which can be a problem when the heater voltage is half the 'HT' voltage. 1.5V battery valves could cope, because of the relatively large HT. Having a separate cathode separates the two issues.

neon indicator · 15th Apr 2011, 1:30 pm

If you have no separate Cathode at 0V approx, what incentive do the electrons have to visit Anode, and create current flow (thus raising the cathode voltage slightly till grid is low enough volts to limit current?

And indeed some valves might not have much current with Grid at 0V and cathode at +12V. So for low HT a indirectly heated cathode is a great idea.

I have wondered though even with indirect cathode is current from LV heater to higher voltage cathode (as an anode) possible or is heater coated with ceramic that resists electron flow in a vacuum? Could damaged heater insulation, but no DC electrical short be cause of "apparent" heater / cathode shorts due to vacuum emission when valve hot and cathode at higher volts (e.g. CRT or TX PA at 400V to 5000V)?

kalee20 · 15th Apr 2011, 1:38 pm

Quote:

Originally Posted by Peter.N.

The radios that used these valves, or at least the ones I was familier with used an 0C16 transistor for output...

Mine does (or even an OC16, not 0C16 - Mullard list these before 'P' in their data book index).

Getting significant amounts of power out of low-voltage valves might be a big challenge - at 12V, you would need 0.5A anode current. And to get this level of emission would need a seriously big cathode needing serious heater power. With 0.45A at 6.3V for a 6V6 (which is often operated around 40mA average Ia), you would scale up to 5A needed to heat a cathode with 500mA emission capability.

neon indicator · 15th Apr 2011, 2:04 pm

That's the best explanation I've read of why higher and higher power Valves use more HT and not more current.

i.e. 40W per 6146 is about 450V
500W per valve is nearly 5000V PSU.

I presume a nano-spikey cathode would have higher emission than a smooth surface for same temperature? Didn't someone invent cold cathode "spikes"?

John M0GLN · 15th Apr 2011, 3:12 pm

Quote:

Originally Posted by G8HQP Dave

Quote:

Originally Posted by jcaines

it has a cathode, which wouldn't be needed for DC operation

A directly-heated valve mixes up bias and heating, which can be a problem when the heater voltage is half the 'HT' voltage. 1.5V battery valves could cope, because of the relatively large HT. Having a separate cathode separates the two issues.

Its something I hadn't thought of, but obvious when pointed out by both yourself and neon indicator.

John

Synchrodyne · 16th Apr 2011, 6:39 am

Quote:

Originally Posted by Bill

How difficult would it be to modify a mains radio with ECH81/EBF89 + others to 12V operation? Is there an output valve that would drive a speaker with 12vHT? Possibly 12A6, EL32 or use an EF80/91 ? What about a small inverter to supply 200v just for the O/p valve? My experiments using a 12v/mains inverter to supply an unmodified mains set were not satisfactory, it worked but lots of noise from the inverter.

The starting point for the original Mullard work with 12V HT valves was the Radiomobile 200X car receiver, so in a sense, that was modification of a conventional receiver, albeit vibrator-powered rather than mains-powered. The Mullard papers are available in this thread: https://www.vintage-radio.net/forum/...ullard+outlook.

As to other “regular” valves that might operate with 12V HT, I’d say the EF89 is a good candidate, as it is essentially the same as the pentode in the EBF89 (EBF83). Strange, though that in the Mullard car radio series the EF97 was the vari-µ pentode. Whether the EF97 is a rebrand of another B7G pentode I don’t know, but its pinouts differ from the prime suspect, the EF93 (6BA6). It could be that it was purpose-designed, and basis the above-mentioned Mullard papers, seems to have had a somewhat higher slope than the EBF83.

Then if the triode section of the ECH81 (ECH83) operates well enough as an AF voltage amplifier at 12 V HT, so might the trode sections of the EBC81 and EABC80. And if they work, then maybe an ECC83 would too. Still, if a double-triode is needed, there is the ECC86. Evidently this was a 12 V HT valve designed for FM car radio, I would imagine as a combined RF amplifier and self-oscillating mixer, though possibly as a shunt cascode RF amplifier. But it could well be satisfactory at AF.

Transistor inverters became available commercially about the same time as hybrid car radios, may be a little before – some mention in: https://www.vintage-radio.net/forum/...ullard+outlook. Somewhere else in this forum is recorded the existence of car radios that used transistor inverters in place of vibrators, but evidently they were very much in the minority as compared with the hybrid type. Probably they were more used to power mobile radiotelephone equipment where 12V HT valves may not have been suitable for all functions, particularly on the transmit side. Conceivably someone combined an inverter-powered AF output valve with a 12V HT RF/IF section. That might have been done for bus and coach units, where the tuner unit was sometimes separate from the power amplifier, see: https://www.vintage-radio.net/forum/...ht=coach+radio. But I imagine that for car radio receivers, once the inverter was included, it was just as easy to power the whole unit from it.

The output valve question has already been addressed by others. That said, the valve line-up for the Marconi Monitor marine watch receiver, quoted as being suitable for 24 and 220 V DC operation. Most valves are of the low HT type, the count being 1 x EF97, 1 x EF98, 4 x ECH83, 1 x EBF83, 1 x D77, and 2 x PL84. One wonders were the PL84s operated on 24 V DC, perhaps in Class B, and were they able to drive the apparent built-in speaker?

Cheers,

Heatercathodeshort · 16th Apr 2011, 9:37 am

This is very interesting and I have always suspected that the car radio range of valves were just selected versions of their AC mains counterparts. They were produced long before the frame grid valve was developed for domestic applications.
Standard valves are certainly able to operate at very low anode voltages. A typical example is the octal EBC33 that amplifies extremely well when it's anode load resistor goes all but O/C resulting in around 5 volts on it's anode! My guess is the EF39 may well have similar qualities. I built a single valve receiver that is quite happy to oscillate with only 18v on it's anode. J.

13th Apr 2011, 4:55 pm	#1
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	12 volt HT valves... Are they?? Hi All, I was surprised to read in the spring 2011 BVWS bulletin that it was stated that there was no difference between the mullard valve EBF83 with 12v HT and the mains set version EBF89, also the same was said about the 12v HT ECH83 and mains set version ECH81. I found this hard to believe so I went and rummaged for a couple of ECH81's and an EBF89 and put them in a philips car radio I have which should use 2 x ECH83's and 1 x EBF83, the result?........... It works perfectly so are they really the same valve with different numbering? I haven't tried the ECH83 or EBF83 in a mains set yet and don't think I will either Cheers __________________ Lee

13th Apr 2011, 5:03 pm	#2
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: 12 volt HT valves... Are they?? Indeed it is thought that the '83's are specially selected versions of their 81 & 89 brothers. I have been using an ECH83 in my B40 for the past 10 years. __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

13th Apr 2011, 6:06 pm	#3
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,873	Re: 12 volt HT valves... Are they?? They're the same - but selected to give reasonable gain at low HT voltages. Using the '83s in a mains set is no problem- I've done it. The give-away is that the interelectrode capacitances are the same for each pair of valves, in all respects. If these valves were really different, the capacitances would differ. I wonder where Philips got the 50V max HT rating from for the '83 series? Leon.

13th Apr 2011, 9:01 pm	#4
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: 12 volt HT valves... Are they?? That part of the data sheet was written by Marketing instead of Engineering? BTW there was a long discussion about this on another forum - I'm sure Google will find it for you.

13th Apr 2011, 9:33 pm	#5
Alan Stepney Rest in Peace Join Date: Feb 2008 Location: Dorset, UK. Posts: 947	Re: 12 volt HT valves... Are they?? In fact you can run a lot of valves with ht far below what the data sheets state. I have just built a simple audio oscillator using an EF91, with SIX volts "ht", for a demonstration I am giving. The ECH81/83 is particularly forgiving and will do lots of things that it isnt supposed to.

13th Apr 2011, 11:54 pm	#6
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: 12 volt HT valves... Are they?? That's interesting, I didn't knowm that. The 0C16 works very well on 12 volts. Peter

14th Apr 2011, 1:14 am	#7
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,957	Re: 12 volt HT valves... Are they?? I've always suspected that this was purely a matter of marketing. I can't tell the difference between an ECH81 and an ECH83 by looking at them and the ECH83 seems to work fine with standard HT voltage. I've never tried a bog standard ECH81 in an old car radio, but my guess would be that it would work without problems.

14th Apr 2011, 12:23 pm	#8
Bill Pentode Join Date: Dec 2005 Location: Denton, Manchester, UK. Posts: 188	Re: 12 volt HT valves... Are they?? How difficult would it be to modify a mains radio with ECH81/EBF89 + others to 12V operation? Is there an output valve that would drive a speaker with 12vHT? Possibly 12A6, EL32 or use an EF80/91 ? What about a small inverter to supply 200v just for the O/p valve? My experiments using a 12v/mains inverter to supply an unmodified mains set were not satisfactory, it worked but lots of noise from the inverter. Bill

15th Apr 2011, 9:30 am	#11
John M0GLN Octode Join Date: Jan 2004 Location: Southport, Merseyside, UK. Posts: 1,156	Re: 12 volt HT valves... Are they?? The only one I can find in the Radio Valve Data Book 7th edition (output valve section) is a 12K5 tetrode, which has the heater, anode and screen grid at 12.6V, but it won't be very loud, 35mW is the output, and it has a cathode, which wouldn't be needed for DC operation, but would it have to have one to give mechanical support to a filament when designed for a bumpy car journey? John Last edited by Brian R Pateman; 15th Apr 2011 at 12:19 pm. Reason: Nested quotes removed.

15th Apr 2011, 9:52 am	#12
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: 12 volt HT valves... Are they?? The radios that used these valves, or at least the ones I was familier with used an 0C16 transistor for output because you couldn't get enough power from a valve. As far as I know this was the first transistor to be used in a car radio and for a single ended output it worked very well, most importantly it did away with the need for a vibrator HT pack, or rotary converter as some early ones had, thus considerably reducing the power consumption. - I had one in my Vauxhall Cresta, the quality was much better than the early all transistor portables with push pull outputs. I think my radio was a Pye TRC 1000. Peter

15th Apr 2011, 10:14 am	#13
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: 12 volt HT valves... Are they?? Hi. My Dad had I believe although I could be wrong an Ekco hybrid set in his Rover P4 (1956, 75) which was much better than the all valve set (vibrator HT) in his 1951 V8 Pilot! __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

15th Apr 2011, 1:30 pm	#15
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: 12 volt HT valves... Are they?? If you have no separate Cathode at 0V approx, what incentive do the electrons have to visit Anode, and create current flow (thus raising the cathode voltage slightly till grid is low enough volts to limit current? And indeed some valves might not have much current with Grid at 0V and cathode at +12V. So for low HT a indirectly heated cathode is a great idea. I have wondered though even with indirect cathode is current from LV heater to higher voltage cathode (as an anode) possible or is heater coated with ceramic that resists electron flow in a vacuum? Could damaged heater insulation, but no DC electrical short be cause of "apparent" heater / cathode shorts due to vacuum emission when valve hot and cathode at higher volts (e.g. CRT or TX PA at 400V to 5000V)?

15th Apr 2011, 2:04 pm	#17
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: 12 volt HT valves... Are they?? That's the best explanation I've read of why higher and higher power Valves use more HT and not more current. i.e. 40W per 6146 is about 450V 500W per valve is nearly 5000V PSU. I presume a nano-spikey cathode would have higher emission than a smooth surface for same temperature? Didn't someone invent cold cathode "spikes"?

16th Apr 2011, 9:37 am	#20
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: 12 volt HT valves... Are they?? This is very interesting and I have always suspected that the car radio range of valves were just selected versions of their AC mains counterparts. They were produced long before the frame grid valve was developed for domestic applications. Standard valves are certainly able to operate at very low anode voltages. A typical example is the octal EBC33 that amplifies extremely well when it's anode load resistor goes all but O/C resulting in around 5 volts on it's anode! My guess is the EF39 may well have similar qualities. I built a single valve receiver that is quite happy to oscillate with only 18v on it's anode. J.