Two heater windings? - UK Vintage Radio Repair and Restoration Discussion Forum

BigClick · 8th Feb 2016, 7:44 pm

Hi folks,

Circuit diagram attached shows three heater windings.

One is for the rectifier, another one; "Y" feeds all valves with the exception of the Tuning Indicator EM80 which is fed from "X"

Can anyone advise why there is a seperate heater winding (X)?

Further, could I rectify and regulate a feed from X and use it to power a low voltage low current module addedd to the chassis?

'LIVEWIRE?' · 8th Feb 2016, 8:50 pm

Other members may know why this is either desirable or neccesary, because I'm not sure. Were all sets equipped with 'magic eye' tuning indicators wired this way? As a matter of interest of which radio is the diagram a part? As to using that winding to power a low voltage, low current module, this will depend on the current rating of heater winding 'X', the exact current to be drawn by the added module, and the supply voltage it needs. Presumably you intend to keep the EM80 in use? If so bear in mind that manufacturers often rated components, including transformer windings to be adequate for the job they were designed to do, with little spare 'capacity' for want of a better word. Check the heater current rating of the EM80 (I don't have it's data to hand)

vinrads · 8th Feb 2016, 8:55 pm

Different heater voltages what are the other valves?

Ed_Dinning · 8th Feb 2016, 9:04 pm

Hi, possibly 6.3v for TI, 4 or 5 v, which must be isolated for rect.
Then 4v for the rest of the valves.

Any advance?

Ed

turretslug · 8th Feb 2016, 9:45 pm

That was my thought, as was the case in a few late 'thirties sets- but then the rectifier is indirectly heated, which smacks of post-war (ish), when not many 4V valves would have been employed. EM80 is early 'fifties? Then, I thought directly-heated output valves- but the non-rectifier heaters both have one side to chassis. So, still getting splinters in the finger-tips....

Lucien Nunes · 8th Feb 2016, 9:49 pm

Quote:

could I rectify and regulate a feed from X

One side of winding X is currently grounded, therefore if your module connects to the existing circuit or the outside world, to enable the DC rails to share the ground you would only be able to use half-wave rectification. Whether this is acceptable probably depends on your load current. The alternative would be to float the AC side and use a bridge rec, causing half-wave 'camel humps' to appear across the TI h-k insulation.

Tractorfan · 8th Feb 2016, 9:50 pm

Hi,
The EM80 has a 6.3volt 300mA heater.
Cheers, Pete.

BigClick · 8th Feb 2016, 10:42 pm

Quote:

Originally Posted by vinrads

Different heater voltages what are the other valves?

Sorry I thought I had replied earlier.

The valve lineup is ECC85, ECH81, EF85, EABC80 EL84 and the EM80

The rectifier is an EZ80

According to the sheet all the valves are 6.3 other than the rectifier which I dont know but that hs its own winding.

Lucien Nunes · 8th Feb 2016, 11:03 pm

Quote:

the rectifier which I dont know

The first letter of European 'pro-electron' valve codes indicates the voltage, E being 6.3V.

Perhaps the transformer was also used in a different chassis that required the two windings, and having been re-purposed for this model it was simply convenient wire all the chassis-mounted valves to one winding and the EM to the other?

ukcol · 8th Feb 2016, 11:14 pm

No doubt "BigClick" is refering to the Regentone A155 he is working on. See the thread here.

I can't think of any technical reason for have a separate heater winding for the tuning indicator. I suspect the reason will be something similar to that sugested by Lucien.

turretslug · 9th Feb 2016, 1:02 am

With just the TI fed from the second heater winding, this implies a low current rating- perhaps the transformer was intended for a design that, say, used an EB91 as FM demodulator and they wished to float the winding to a positive voltage to reduce the risk of hum in this vulnerable stage? Then, the EABC80 was incorporated instead and separation was unecessary, the TI using this winding for wiring convenience rather than technical reasons.

BigClick · 9th Feb 2016, 1:09 am

You might be on to something, I read on this forum that the chassis was used in other variations of this design and there were two additional EL84s. So maybe the extra windings would have also heated the additional valves?

turretslug · 9th Feb 2016, 1:29 am

Aha- a push-pull output might have used a phase-splitter driver circuit whose valve had a highly-elevated cathode, making a separate heater supply prudent.

AC/HL · 9th Feb 2016, 1:33 am

The ECC85 and dial light are also supplied by the X winding.

BigClick · 9th Feb 2016, 10:39 am

Yep, I missed those, so thats sorted the XY mystery, I must redouble my checks before posting.

On the subject of transformers, the OPT from the same set has two grey wires that are soldered to an isolated tag. Is this because the OPT may have had other configurations? See pic.

turretslug · 9th Feb 2016, 2:02 pm

Oh well, maybe splitting the feeds just saved the transformer maker from having to wind too thick and stiff a gauge of wire round the bobbin. Still, it gave the grey matter a bit of a stretch trying to cook up possible reasons.

Maybe the empty tag was simply used as a junction point? I've been working on a pre-war GEC set whose OPT had lots of tags on a similar strip, but many of them proved to be unconnected and used for parking stuff.

BigClick · 9th Feb 2016, 2:51 pm

Thanks that is reassuring

I also have a transformer from a Mullard amp kit that I think is shot!

Is there anyway to trace its orign from the number (see pic)?

I think its shot because there was wax all over the bottom and its bubbled out of the LAMs, plus there is no logic to any readings across the wires.

8th Feb 2016, 7:44 pm	#1
BigClick Hexode Join Date: Dec 2015 Location: Walsall, West Midlands, UK. Posts: 327	Two heater windings? Hi folks, Circuit diagram attached shows three heater windings. One is for the rectifier, another one; "Y" feeds all valves with the exception of the Tuning Indicator EM80 which is fed from "X" Can anyone advise why there is a seperate heater winding (X)? Further, could I rectify and regulate a feed from X and use it to power a low voltage low current module addedd to the chassis? Attached Thumbnails

8th Feb 2016, 8:50 pm	#2
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: two heater windings Other members may know why this is either desirable or neccesary, because I'm not sure. Were all sets equipped with 'magic eye' tuning indicators wired this way? As a matter of interest of which radio is the diagram a part? As to using that winding to power a low voltage, low current module, this will depend on the current rating of heater winding 'X', the exact current to be drawn by the added module, and the supply voltage it needs. Presumably you intend to keep the EM80 in use? If so bear in mind that manufacturers often rated components, including transformer windings to be adequate for the job they were designed to do, with little spare 'capacity' for want of a better word. Check the heater current rating of the EM80 (I don't have it's data to hand) Last edited by 'LIVEWIRE?'; 8th Feb 2016 at 8:58 pm.

8th Feb 2016, 8:55 pm	#3
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,762	Re: two heater windings Different heater voltages what are the other valves?

8th Feb 2016, 9:04 pm	#4
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: two heater windings Hi, possibly 6.3v for TI, 4 or 5 v, which must be isolated for rect. Then 4v for the rest of the valves. Any advance? Ed

8th Feb 2016, 9:45 pm	#5
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,396	Re: two heater windings That was my thought, as was the case in a few late 'thirties sets- but then the rectifier is indirectly heated, which smacks of post-war (ish), when not many 4V valves would have been employed. EM80 is early 'fifties? Then, I thought directly-heated output valves- but the non-rectifier heaters both have one side to chassis. So, still getting splinters in the finger-tips....

8th Feb 2016, 9:50 pm	#7
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Re: two heater windings Hi, The EM80 has a 6.3volt 300mA heater. Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

8th Feb 2016, 11:14 pm	#10
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: two heater windings No doubt "BigClick" is refering to the Regentone A155 he is working on. See the thread here. I can't think of any technical reason for have a separate heater winding for the tuning indicator. I suspect the reason will be something similar to that sugested by Lucien.

9th Feb 2016, 1:02 am	#11
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,396	Re: two heater windings With just the TI fed from the second heater winding, this implies a low current rating- perhaps the transformer was intended for a design that, say, used an EB91 as FM demodulator and they wished to float the winding to a positive voltage to reduce the risk of hum in this vulnerable stage? Then, the EABC80 was incorporated instead and separation was unecessary, the TI using this winding for wiring convenience rather than technical reasons.

9th Feb 2016, 1:09 am	#12
BigClick Hexode Join Date: Dec 2015 Location: Walsall, West Midlands, UK. Posts: 327	Re: two heater windings You might be on to something, I read on this forum that the chassis was used in other variations of this design and there were two additional EL84s. So maybe the extra windings would have also heated the additional valves?

9th Feb 2016, 1:29 am	#13
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,396	Re: two heater windings Aha- a push-pull output might have used a phase-splitter driver circuit whose valve had a highly-elevated cathode, making a separate heater supply prudent.

9th Feb 2016, 1:33 am	#14
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: two heater windings The ECC85 and dial light are also supplied by the X winding.

9th Feb 2016, 10:39 am	#15
BigClick Hexode Join Date: Dec 2015 Location: Walsall, West Midlands, UK. Posts: 327	Re: two heater windings Yep, I missed those, so thats sorted the XY mystery, I must redouble my checks before posting. On the subject of transformers, the OPT from the same set has two grey wires that are soldered to an isolated tag. Is this because the OPT may have had other configurations? See pic. Attached Thumbnails

9th Feb 2016, 2:02 pm	#16
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,396	Re: Two heater windings? Oh well, maybe splitting the feeds just saved the transformer maker from having to wind too thick and stiff a gauge of wire round the bobbin. Still, it gave the grey matter a bit of a stretch trying to cook up possible reasons. Maybe the empty tag was simply used as a junction point? I've been working on a pre-war GEC set whose OPT had lots of tags on a similar strip, but many of them proved to be unconnected and used for parking stuff.

9th Feb 2016, 2:51 pm	#17
BigClick Hexode Join Date: Dec 2015 Location: Walsall, West Midlands, UK. Posts: 327	Re: Two heater windings? Thanks that is reassuring I also have a transformer from a Mullard amp kit that I think is shot! Is there anyway to trace its orign from the number (see pic)? I think its shot because there was wax all over the bottom and its bubbled out of the LAMs, plus there is no logic to any readings across the wires. Attached Thumbnails