"That capacitor" in Mullard 3-3. - UK Vintage Radio Repair and Restoration Discussion Forum

terrykc · 3rd Dec 2010, 1:16 pm

The Mullard 3-3 was an exception to the 'general rule' as it had direct coupling from the anode of the EF86 and the grid of the EL84.

The only time I encountered this circuit in a domestic product was in a Grundig stereo adaptor, The EZ80 was replaced by the standard Grundig style contact cooled bridge rectifier but otherwise the circuit was absolutely identical, save for a change of the 390pF capacitor in the treble tone control to 400pF.

Does anyone know of any other examples of direct coupling like this?

Although Mullard/Philips modules of various types have been incorporated in other manufacturers designs from time to time, this is the only example I've ever come across of a paper design being used in this way - including Philips' products! - although the widely copied OC44/5 transistor radio circuit may well have come from a Mullard application note (but it's one I've never seen ...!)

Any others?

G8HQP Dave · 3rd Dec 2010, 2:20 pm

The Mullard 5-10 and 5-20 amplifier used direct coupling to the phase splitter, but a conventional capacitor to the output valves.

kalee20 · 3rd Dec 2010, 2:58 pm

Short superhets (eg Ferguson 208U) don't have a 'THAT' capacitor. (They may well have a coupling capacitor to O/P valve grid, but the voltage they block is low and negative. So no damage occurs due to failure).

Older radios with transformer coupling to output valve don't have a 'THAT' capacitor either. If the transformer is shunt fed, then there will be a coupling capacitor but failure does not lead to the same level of damage, so the capacitor isn't a 'THAT' capacitor.

Incidentally, I'd be inclined to say that the Mullard 3-3 sort of has a 'THAT' capacitor. If you look at the EF86 screen grid, it's decoupled to chassis with a fairly fat non-polarised capacitor. If this went really leaky, the EF86 would turn off, the anode voltage would rise, and coupling directly to the output valve it would start to fry the EL84. Of course, as the EL84 has a larger-than-usual cathode resistor, the consequences are not so calamitous - so is it a 'THAT' capacitor or not?

DangerMan · 3rd Dec 2010, 3:09 pm

Large chunks of many first generation colour sets look remarkably like the Mullard PAL colour set that was the subject of a booklet published in the mid-late 60's.
Decca's CTV25 springs to mind as almost a production version of that set, but Pye and GEC also used decoders and CDA's that are so similar to it that they are likely to have been derived from the same original source.
And perhaps typically, the Philips G6 was nothing like it !
Pete

roffe · 3rd Dec 2010, 7:10 pm

Long ago there were several other amplifiers that used direct coupling.A few:
http://www.bonavolta.ch/hobby/en/audio/el84_6.htm
http://www.bonavolta.ch/hobby/en/audio/el84_9.htm
http://www.bonavolta.ch/hobby/en/audio/el84_12.htm

and a very rare Thermionic Products TP100!
http://elektronikforumet.com/forum/v...hp?f=3&t=46528

Herald1360 · 4th Dec 2010, 8:24 pm

The third "bonavolta" schematic has the strangest way of depicting an ECC83 I've ever seen

glowinganode · 4th Dec 2010, 9:18 pm

Not as strange as the EZ81, with the heater between the cathode and anodes.
Rob.

3rd Dec 2010, 1:16 pm	#1
terrykc Rest in Peace Join Date: Nov 2010 Location: North Hykeham, Lincolnshire, UK. Posts: 515	"That capacitor" in Mullard 3-3. The Mullard 3-3 was an exception to the 'general rule' as it had direct coupling from the anode of the EF86 and the grid of the EL84. The only time I encountered this circuit in a domestic product was in a Grundig stereo adaptor, The EZ80 was replaced by the standard Grundig style contact cooled bridge rectifier but otherwise the circuit was absolutely identical, save for a change of the 390pF capacitor in the treble tone control to 400pF. Does anyone know of any other examples of direct coupling like this? Although Mullard/Philips modules of various types have been incorporated in other manufacturers designs from time to time, this is the only example I've ever come across of a paper design being used in this way - including Philips' products! - although the widely copied OC44/5 transistor radio circuit may well have come from a Mullard application note (but it's one I've never seen ...!) Any others? Last edited by Station X; 3rd Dec 2010 at 1:27 pm. Reason: Thread split.

3rd Dec 2010, 2:20 pm	#2
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: "That capacitor" in Mullard 3-3. The Mullard 5-10 and 5-20 amplifier used direct coupling to the phase splitter, but a conventional capacitor to the output valves.

3rd Dec 2010, 2:58 pm	#3
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: "That capacitor" in Mullard 3-3. Short superhets (eg Ferguson 208U) don't have a 'THAT' capacitor. (They may well have a coupling capacitor to O/P valve grid, but the voltage they block is low and negative. So no damage occurs due to failure). Older radios with transformer coupling to output valve don't have a 'THAT' capacitor either. If the transformer is shunt fed, then there will be a coupling capacitor but failure does not lead to the same level of damage, so the capacitor isn't a 'THAT' capacitor. Incidentally, I'd be inclined to say that the Mullard 3-3 sort of has a 'THAT' capacitor. If you look at the EF86 screen grid, it's decoupled to chassis with a fairly fat non-polarised capacitor. If this went really leaky, the EF86 would turn off, the anode voltage would rise, and coupling directly to the output valve it would start to fry the EL84. Of course, as the EL84 has a larger-than-usual cathode resistor, the consequences are not so calamitous - so is it a 'THAT' capacitor or not?

3rd Dec 2010, 3:09 pm	#4
DangerMan Heptode Join Date: Jul 2009 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 719	Re: "That capacitor" in Mullard 3-3. Large chunks of many first generation colour sets look remarkably like the Mullard PAL colour set that was the subject of a booklet published in the mid-late 60's. Decca's CTV25 springs to mind as almost a production version of that set, but Pye and GEC also used decoders and CDA's that are so similar to it that they are likely to have been derived from the same original source. And perhaps typically, the Philips G6 was nothing like it ! Pete

3rd Dec 2010, 7:10 pm	#5
roffe Hexode Join Date: Nov 2003 Location: Linkoping, Sweden Posts: 493	Re: "That capacitor" in Mullard 3-3. Long ago there were several other amplifiers that used direct coupling.A few: http://www.bonavolta.ch/hobby/en/audio/el84_6.htm http://www.bonavolta.ch/hobby/en/audio/el84_9.htm http://www.bonavolta.ch/hobby/en/audio/el84_12.htm and a very rare Thermionic Products TP100! http://elektronikforumet.com/forum/v...hp?f=3&t=46528

4th Dec 2010, 8:24 pm	#6
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: "That capacitor" in Mullard 3-3. The third "bonavolta" schematic has the strangest way of depicting an ECC83 I've ever seen __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

4th Dec 2010, 9:18 pm	#7
glowinganode Octode Join Date: Apr 2009 Location: Aylesbury, Buckinghamshire, UK. Posts: 1,522	Re: "That capacitor" in Mullard 3-3. Not as strange as the EZ81, with the heater between the cathode and anodes. Rob. __________________ We have done so much, for so long, with so little, we are now qualified to do anything with nothing.