PY 81 as power rectifiers?

[Amie]

Done the transformer thing, the best orientation for lowest coupling is with the normal mounting surface of the mains transformer at 90° to the output one..

I'm just going to mount the output transformer far enough away....possibly, next to the speaker off the chassis completely if its electrically stable that is....

[Kalee20]

Sounds good progress. It made a noticeable difference then?

(I tried to reply to your PM's but they are turned off for you).

[Amie]

Sorry, mums been doing her thing, I'll ask and turn them on again, its her way of letting me know she cares.
I am interested in that pm answer.

Noticeable difference? Just done as you suggested at the moment, it makes a big difference just on that alone, well worth knowing.

Thanks,
Amie

[Kalee20]

It could be the reason why many radios had the transformer mounted actually ON the loudspeaker - to maximise the distance from the mains transformer.

Years ago I made an amplifier on a small chassis, first power-up (with O/P transformer not yet mounted) I didn't think it was working, there wasn't a squeak from the speaker. Until I applied an input! It blew me away, I just wasn't used to not hearing a faint hum or hiss. I named the chassis 'Humphrey" because it was hum-free...

Later, I mounted the output transformer, drilled holes in my lovely painted chassis, screwed it in place, switched it on, to my dismay I got a hum. Pulling the valves (EL41 and ECC82) the hum was still there. Worked out it was magnetic coupling between the mains and output transformers. Spoiled the project

It's called 'learning the hard way.'

[Terry]

Done the transformer thing, the best orientation for lowest coupling is with the normal mounting surface of the mains transformer at 90° to the output one..

Yes, the magnetic field is at its minimum at 90°.

Even better is to mount them at 90° in two planes. This achieved by using a 'drop through' method of mounting the mains transformer by cutting a rectangular hole in the chassis for the bobbin and mounting the transformer so that the laminations are flat against the chassis and at 90° to those of the output transformer mounted upright in the conventional manner.

An alternative, if transformer and chassis sizes are suitable, mount the mains transformer on the top of the chassis as normal and mount the smaller output transformer horizontally under the chassis on the front or back.

You can probably think of other ways of achieving the same objective.

[Amie]

Thanks Terry.

Any pitfalls to watch for if the audio transformer is mounted away from the chassis completely? it would mean quite long primary connection wires to the anode (10 or 15 cm). Hum is hardly noticeable where it is, but it is noticeable.

But, on the other hand I don't want to mount it remotely, then find it needs to be mounted back on the chassis when its been wired and ruin it!

I don't think it would be possible to mount like you suggested as I've already blunderd into committing to a chassis design and hadn't considered magnetically coupled hum

[pwdrive]

Any pitfalls to watch for if the audio transformer is mounted away from the chassis completely? it would mean quite long primary connection wires to the anode (10 or 15 cm). Hum is hardly noticeable where it is, but it is noticeable.

Not in an electrical sense, I had approx. 2 metres of twin cable to connect HT and OP anode to an output transformer in some of the loudspeaker cabinets I had, eg: HRO receiver to loudspeaker, never had any problems.....The standard HRO receiver never had an output transformer fitted on/in the receiver.

Picture of my old HRO receiver(s) and loudspeaker unit, the one in the background is my original HRO Senior, the one under the loudspeaker is a later version, the Reception Set R106 MKII...aka a HRO-5t, both most excellent receivers.

Lawrence.

[Amie]

Nice radios

What about if I'm using a little NFB? (Two more wires....)

Thanks,
Amie.

[pwdrive]

For NFB try as is, if any problem use screened conductor(s) for the NFB.

Lawrence.

[Amie]

Thanks Lawrence,

I'll give it a go....