How to identify an unknown transformer. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Mullard_Nut_74 · 6th Jun 2020, 1:46 am

Watching youtube rebuilds I have seen some pretty intense looking power supply setups for things as simple as an 807 push pull amplifier.
I remember a friend of ours had the same 807 Amp in the 80s and while it had a large transformer on board, it didnt have a whole separate power supply board to build up tge power.
So I guess I am lucky being into this hoby in Australia with 240V.
Sorry I seem to have got this thread well off topic.
Its a gift of mine.
I will report back when I have some readings and hard evidence from the transformer.
Was going to do it today but found out my family is coming round for the weekend.
Shoving stuff in boxes and putting tubes and electronics away out of reach of little fingers now like crazy.

Radio Wrangler · 6th Jun 2020, 2:54 am

Quote:

Originally Posted by Lucien Nunes

AFAIK the standard configuration is a 120-0-120 supply with the centre-tap grounded, serving all single-phase consumers.

That's what all single (well, two, really) phase customers think they get, but other single phase customers will get supplies from other phases of a three phase system.

The utility companies want to keep loading reasonably well balanced on their three phase generators and distribution systems.

So a neighbourhood will have a three-phase transformer, but unlike ours, the three secondaries are not star or delta connected. The ends are isolated and each of the three windings has a grounded/neutral centre tap. So there are six live phases. A given home gets two live phases from the same winding, so they are 180 degrees out of phase. Homes are distributed amongst the three secondaries, so there can be 120 degree phase shifts between the mains supplied to different premises.

So there are only two phases within a home, but there are six phases within the distribution system.

The UK system has three phases within the distribution system, and single phase within a home. We don't have the American's easy access to a lower voltage for low power appliance, but they don't have the easy integration of single and three phase for industry that we have.

David

petervk2mlg · 6th Jun 2020, 2:56 am

Use your meter to identify all the various windings. They'll show continuity. It sounds like you have identified the 6.3 winding on the transformer. What I do is just put 6.3 volts into the winding I've identified as the filament winding and measure the AC voltages on the other windings I've identified as continuous. It's quite safe as long as you keep your fingers clear of the suspected primary and the HT secondary (ies).
Once you have cleared up which is the primary, you can put the appropriate AC into it and check your suspicions.

Radio Wrangler · 6th Jun 2020, 8:02 am

While doing that, once you've identified the primary/primaries, if it is in two parts, connect them in series, measure the total voltage from the pair, then reverse the connection to one winding if they didn't add. It's important to get the phasing right if two windings are used in series or parallel (a common method of covering 120 and 240v ranges that makes best use of copper)

David

llama · 8th Jun 2020, 10:02 am

I notice one of the valves is a 5Y3 so expect one of the windings to be an isolated 5 Volts.
Graham

6th Jun 2020, 1:46 am	#21
Mullard_Nut_74 Tetrode Join Date: Mar 2020 Location: Sydney, New South Wales, Australia. Posts: 65	Re: How to identify an unknown transformer. Watching youtube rebuilds I have seen some pretty intense looking power supply setups for things as simple as an 807 push pull amplifier. I remember a friend of ours had the same 807 Amp in the 80s and while it had a large transformer on board, it didnt have a whole separate power supply board to build up tge power. So I guess I am lucky being into this hoby in Australia with 240V. Sorry I seem to have got this thread well off topic. Its a gift of mine. I will report back when I have some readings and hard evidence from the transformer. Was going to do it today but found out my family is coming round for the weekend. Shoving stuff in boxes and putting tubes and electronics away out of reach of little fingers now like crazy. __________________ If only he could have used his evil genius for niceness instead of evil. Max Smart 18 Sept 1965

6th Jun 2020, 2:56 am	#23
petervk2mlg Heptode Join Date: Jan 2007 Location: Parkes, NSW Australia Posts: 877	Re: How to identify an unknown transformer. Use your meter to identify all the various windings. They'll show continuity. It sounds like you have identified the 6.3 winding on the transformer. What I do is just put 6.3 volts into the winding I've identified as the filament winding and measure the AC voltages on the other windings I've identified as continuous. It's quite safe as long as you keep your fingers clear of the suspected primary and the HT secondary (ies). Once you have cleared up which is the primary, you can put the appropriate AC into it and check your suspicions.

6th Jun 2020, 8:02 am	#24
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,874	Re: How to identify an unknown transformer. While doing that, once you've identified the primary/primaries, if it is in two parts, connect them in series, measure the total voltage from the pair, then reverse the connection to one winding if they didn't add. It's important to get the phasing right if two windings are used in series or parallel (a common method of covering 120 and 240v ranges that makes best use of copper) David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

8th Jun 2020, 10:02 am	#25
llama Octode Join Date: Jun 2006 Location: St Osyth, Nr Clacton, Essex, UK. Posts: 1,482	Re: How to identify an unknown transformer. I notice one of the valves is a 5Y3 so expect one of the windings to be an isolated 5 Volts. Graham __________________ Half my stuff is junk - trouble is, I don't know which half!