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Old 28th Nov 2017, 5:24 pm   #1
SeanMcK
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Default AVO wattage and powerfactor unit for 7's & 40's

Does anyone know the specified values for the three fixed resistors in these units?
I have one for the Avo 40 and in that two of these resistors have the same 4 band colour code, the 3rd one appears to have only 3 colours. See photos.

As I understand the code the 4 banded resistors are meant to be 4.7k 5%, they measure approx 5.4k. I am stumped over interpreting the colour code for the third fixed resistor but from memory it measures approx 10.6k. The variable resistor is marked 35k.
I have seen somewhere, probably in here, a photo of the insides of the Model 7 version of this unit and the variable resistor was marked 100k so I am presuming the fixed resistors also have values which differ from those in my one.
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Old 28th Nov 2017, 5:28 pm   #2
TonyDuell
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Default Re: Avo wattage and powerfactor unit for 7's & 40's

The right hand photograph shows a 4.7k 5% resistor. You read the bands in the order left to right, yellow = 4, violet = 7, red = 2 (2 zeros in the position) so 4700 ohms or 4.7k. The gold band is the 5% tolerance.

The left hand photograph shows a resistor using the old body-tip-spot code. The body is grey, which is 8. The tip (right hand tip in your photo) is red, which is 2. The spot is also red, so 2 more zeros. That's 8200 ohms or 8.2k. The left tip, being gold, again indicates 5% tolerance.
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Old 28th Nov 2017, 5:43 pm   #3
SeanMcK
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Default Re: Avo wattage and powerfactor unit for 7's & 40's

Brilliant thanks.
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Old 29th Nov 2017, 5:50 pm   #4
AndyGilham
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Default Re: Avo wattage and powerfactor unit for 7's & 40's

A little further information on the Avo Power factor units

Both the Model 1 (1951) and Model 2 (1958) used the following resistor values

The Model 7 voltage ranges used 15kohm, 15kohm and 24kohm
The Model 7 Start/Adjust pot used 100Kohm

The Model 40 voltage ranges used 4.7kohm, 4.7kohm, 8.2kohm
The Model 40 Start/Adjust pot used 35Kohm

See attached drawing.

I have the schematic as well, but can't upload it for some reason.
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Old 29th Nov 2017, 6:56 pm   #5
SeanMcK
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Default Re: Avo wattage and powerfactor unit for 7's & 40's

Ta Andy that's great, I have a very rough and scribbled on simplified hand drawn schematic from what I found, perhaps you would compare it to yours and, ignoring values, let me know if it is correct?
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Old 30th Nov 2017, 9:40 am   #6
AndyGilham
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Default Re: AVO wattage and powerfactor unit for 7's & 40's

Here is the schematic diagram from the original drawing, i have managed to upload it.
Probably not been seen since the 1960's!
Hope this helps.
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Old 30th Nov 2017, 2:28 pm   #7
SeanMcK
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Default Re: AVO wattage and powerfactor unit for 7's & 40's

That's great, ta!
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Old 1st Dec 2017, 1:46 pm   #8
AndyGilham
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Default Re: AVO wattage and powerfactor unit for 7's & 40's

By the way SeanMcK, do you have a Mark 1 or Mark 2?
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Old 1st Dec 2017, 4:10 pm   #9
SeanMcK
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Default Re: AVO wattage and powerfactor unit for 7's & 40's

Both, in both model 40's & 7's.
Is the significant difference between the Mk1's & Mk2's not the addition of the PF circuits in the latter?



PS
Ah, just seen your AVO/Megger thread, all becomes clear lol.

Last edited by SeanMcK; 1st Dec 2017 at 4:32 pm.
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Old 2nd Dec 2017, 11:20 pm   #10
Phil G4SPZ
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Default Re: AVO wattage and powerfactor unit for 7's & 40's

Quote:
Originally Posted by SeanMcK View Post
Is the significant difference between the Mk1's & Mk2's not the addition of the PF circuits in the latter?
I have a couple of Model 7 Mk Is dating from 1950 and 1952 which have the P.F. sockets fitted, but all my Mk II examples of both the Model 7 and Model 40 have the P.F. sockets. I have read that P.F. sockets were available to special order for a time, presumably before Avo incorporated them as standard.

I also have some Model 7 Mk IIs which have black Bakelite screw-down terminals, rather than the red and black 4mm/screw down terminals which became standard later.

I have a wattage/power factor unit for the Model 7 but have never had cause to use it. Thanks to Andy Gilham for posting the circuit. My example looks pristine, and I don't think anyone else has ever used it either! This thread is encouraging me to try it out in anger...
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Old 5th Dec 2017, 4:37 pm   #11
AndyGilham
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Default Re: AVO wattage and powerfactor unit for 7's & 40's

SeanMck
I was speaking mainly of the power factor units themselves. The Mark 1 had an aluminium front panel, whereas the Mark 2 they went to a moulded panel. In fact it was Ferguson C2/150/56 F13 moulding powder.

Not sure if the attached helps, but it shows the set-up guide. This is from the original drawing set for the Mark 1

Regards
Andy Gilham
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Old 6th Dec 2017, 12:54 pm   #12
SeanMcK
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Default Re: AVO wattage and powerfactor unit for 7's & 40's

Ta Phil, could you post full sized images of
1) the "power factor" plate (the graph thing) and
2) the circular wattage thing which I presume is in the unit's lid.
Since the circuit is so simple I am thinking of a DIY version for my Avo7 and, if those images show them to be the same as those for a Model 40, then I can probably scan, and then print, the ones on my unit.
Andy, ah ok, the one I have has an aluminum plate/sheet as a facia but under that is a sheet of Bakelite-like or resin impregnated material which is about 1/4" thick.
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