GB Battery +/- polarity confusion

[SurreyNick]

I'm just making a replica Drydex H.1001 Grid Bias battery and have got myself into a state of confusion  

It would seem there is still a bit of juice in the original upon which the replica is based, but the polarity is the opposite of what I expected. As you can see from the attached picture I have the positive DMM probe in the + terminal socket and the negative probe in the 1.5 negative socket, the voltage reads (pos) +1.15. Surely, it should read (neg) -1.15?
Wouldn't this be putting a positive voltage on the valve grid?

Can someone help this dim-wit please?

Nick.
   

[tiv48]

from the point of view of the circuit + is connected to the chassis there for all the other battery connections will be negative with respect to the chassis
Rob T

[AlanBeckett]

Nick,

The Meter is doing what it should.
If you work your way down the Terminals they should read a progressively greater value - originally 1.5V for each 'Step'.
If you want it to be (possibly) more 'Logical put the Meter Negative in the + Terminal and measure the Sockets with the Positive Prod in the Terminals. They'll read Negative - I assume your Meter will do that.
That's how the Valves 'See' it when the GB Battery Positive is connected to Chassis/HT Negative ie the Grids will be Negative to the Filaments.

Alan

[Yorkie]

Yes, n a good battery, with the test leads connected as they are, you'd expect to see +1.5V, and if you move the negative prod to the other terminals, leaving the positive prod where it is, you'd expect to see progressively +3V, +4.5V, +6V, +7.5V and +9V. As rob says, because the + lead is connected to chassis, and the - lead to the grid, if you then checked the voltage between the grid and chassis, you'd see that the grid is negative relative to the chassis according to the amount of grid bias voltage you've selected on the GB battery.

See rough sketch attached.

Hope that helps.

Hmmm, I guess you might be in 'Melody Maker mode' Nick, in which case this might interest you, if you haven't already seen it:

https://cossor.com/how-to-make-a-grid-bias-battery/

[SurreyNick]

Thank you. I'm now a slightly brighter dim-wit. Probably getting up to dull-emitter

Thanks for the link David. I'm the radio colleague mentioned right at the bottom of the article who sent Stan the Pertirx. Cossor.com is his website. He's also the guy you provided with the nixie tube via me.

Nick

[Yorkie]

I half guessed as much Nick - I think it was you who sent me the link to Stan's site in the first instance.

As you know, the nixie tube did the trick and Stan dropped me a nice e-mail of appreciation.

If your grid bias battery looks as good as Stan's - and I'm sure it will do - it will look very bonny!

[Terry]

See rough sketch attached.

Hope that helps.

Sorry, Alan, it only adds confusion!

I can't  do a drawing on this phone but your error is in showing the negative terminal as the common one.

The postive terminal is common and should be connected to chassis, all the other terminals being progressively more negative.

In your example, the -6V terminal would feed the grid of the triode, leaving the other negative terminals free to feed various voltages to other parts of the set.

Don't forget that sets using such batteries would have multiple connections for this reason.

[AlanBeckett]

That wasn't me, it was David. I've only just caught up.
Indeed the Positive should go to Chassis and a Negative to the Grid.

Alan

[Old Sparky]

Possibly the confusion arises, as has been said, because we all treat the Negative line as common, usually chassis, which of course, it often is, whereas grids are biased Negative w.r.t (with respect to) chassis, which, to them is Positive, so, as Alan said, the meter is doing as it should. If you were to connect the Positive terminal of a DMM to chassis and measure, e'g. the HT line, the meter would show, say -200v when in fact the HT line is 200v. Positive WRT Chassis. IThis is because, unlike analogue meters, which must be connected the correct way round, most, if not all, DMMs aren't polarity sensitive, and indicate the polarity of the reading wrt whichever probe is connected to the (usually negative) chassis.

[Yorkie]

That wasn't me, it was David. I've only just caught up.
Indeed the Positive should go to Chassis and a Negative to the Grid.

Alan

I thought that's what I'd indicated in the sketch?

In the example I gave, if the positive prod of a DMM was applied to the grid and the negative prod attached to the chassis, the meter would read minus 6V.