AVO CT446 Transistor Analyser.

[Chris G0EYO]

I have just picked up one of these and wondered if anyone can help with any user instructions or a circuit.

Regards

Chris G0EYO

[ukcol]

Hello Chris

I have a manual for one of these kindly supplied by Jeremy (Pamphonica).

If you PM me with your email address I will send it to you as a pdf file.

Colin M

[RogerWalker]

I have a CT446 and have always been put off restoring it by the need for 14 batteries either U7 or U10. The small Battery company can supply something similar for a fiver a piece, but seventy quid seems a lot. Has anyone ever devised a mains PSU for this beast please? Six of the batteries are in series to make 9V; the other eight are also arranged in series but 'tapped' at 1.5V intervals a bit like an old grid bias battery. The meter used in these is similar/identical to that of the CT160 valve tester so I suspect a lot have had the meter ripped out and the rest of the unit just binned. Pity because they are beautifully built. I bought a [very bad] copy of the data manual a while back - very faint and badly copied - which I was intending to clean up. But as I lost interest in the restoration for the reason stated, it never got done. I'd be happy to share the data stuff with the group as and when I can make it readable.

I am embarking on a project to build a base panel for an Avo 2-panel tester just now and restoring the CT446 could well be next if I can find a way to resolve the battery problem.
Regards
Roger

[davidgem1406]

Hello Paul,

I have a Taylor 44 Transistor tester that I have restored to the point of needing power. I don't fancy using batteries in it as it takes a 15V AVO style battery and the old grid bias battery.

I have designed a power supply for it using 1 x +15V regulator and variable -V regulators for each of the minus supply lines that would have been the GB battery.

Not built it as yet but it should work OK.

Dave

[ukcol]

Originally Posted by RogerWalker

I have a CT446 and have always been put off restoring it by the need for 14 batteries either U7 or U10.

Hi Roger

Have a look at this thread:

https://www.vintage-radio.net/forum/...ad.php?t=78716

Colin M

[David Simpson]

Chris & Roger,
I have completely stopped using the internal battery supply. Instead - a fixed 9V sourced from a DC PSU for the analyser's amplifier & oscillator,(HT). And then just use the existing External Volts connections for chosing your Collector volts. I actually use a two channel DC PSU for most functions, but a simple homebrew battery pack would suffice. Normally there are 14 cells, 6 for the fixed amp & osc supply, and the remaining 8 are switched to give a max of 12V.
Apologies for poor focus on pictures. If you have a pdf copy of the circuit diagram, its easy enough to see where to take the 9V connections from.

Regards, David

[RogerWalker]

Thanks to all for responses. I think I'll go for David's solution for the restoration and consider Chris's for future use.

I have had too many disappointments with equipment using meters [that fail five minutes after 6 months of restoration is completed] to invest too much time and money in building a custom PSU until the finished unit has worked reliably for a while!

The link to the battery replacement thread was a revelation - and just goes to prove the amazing value of this site as a knowledge base. Thank you.
Roger

[Analogman]

Hello,

I know this thread is old, but I recently aquired a CT446, and I decided to use just normal AA batteries instead of the U10's. This should be OK, no?
The height is about the same and to get around the fact that the AAs are too thin, I am using some rubber garden hose and some small gaskets as spacers to center them. The only thing I am not sure about is the polarity, but I am assuming that the pos. goes in first and the spring holder pushes against the neg. side. Hope this works.

[Jeffreyabb]

Hi
I got a 446 a while ago without its meter. I wanted to see if the rest of it was working. Not wanting to pay high prices for batteries I might only use for a few minutes, I also decided to use (cheap) AA batteries & whatever I had to hand. The outside diameter of the battery was the same diameter as some plastic water overflow pipe I had. To centralise the AA battery I used short lengths of toilet roll centres. Pretty basic, but it worked. Pity the 446 had too many problems to bother with at the time.
Jeff

[David Simpson]

Folks, Just a reminder since my post on 3/3 last year :-
Replacement meters can be obtained from Benchmark Instruments.
sales@benchmark-bpl.com Tel. 01582 668305

Meter Type 175L 90MC 30uA
Back in 2008 it cost £79.31 inc. VAT & Carriage.

Batteries - Forget them ! Out of the total of 14, Six are just used for powering the Osc & Amp. This is the HT(9V) which the meter initially displays.
Looking on the underside of the Battery Compartment - they're the 6 holders in a straight line. +ve on the left, -ve on the right. Just run two wee leads to a pair of wee sockets for an external supply. That leaves two lots of 4 holders, either side, giving a max of 12V. Bottom left of the l/h/s group of 4 is +ve, and top right of the r/h/s group is -ve. But we only needs to use the 3 External Volts sockets & the selection switch, anyway.
A decent modern two channel DC PSU will provide near enough transient free supplies.
Hopefully my two pictures are not too out of focus.
Please make the effort to keep these lovely old testers working. They were s.o.t.a. when I first started repairing them back in the 60's.

Regards, David

[Analogman]

Hi David,
Thanks for your reply, and your tip about benchmark meters. I will certainly look in to that should I need a meter. I just powered up my CT446 with the AA batteries and doing an initial power test noticed that the meter reads too high (around 14V), when I turn it off the needle rests around 3V and does not go back to zero. Do you know anything about calibrating these or how to zero the meter?
Thanks.
Lucas

[David Simpson]

Hello Lucas,
To eliminate a fault in the Battery Compartment - use the meter display as you would an AVO 8 Multimeter(the 446 has the same O/V of 20Kohms). ie. Use the Meter HP & LP sockets, applying a known voltage or current, to correspond with the range on the Meter Switch. Best start with a low voltage of a couple of volts, or just a single 1.5V battery.
Let us know how you get on.

Regards, David

[Analogman]

Hi David,
I tried out what you suggested and got no readings what so ever. It could be that i am a completely ignorant fool, or that i did not use the right settings, i am not sure. Also i do not have the right kind of plugs for these sockets, i will have to try and find some. However using a 1.5v battery and setting the meter gauge to 1-5volts i tried to measure the battery with some alligator clips stuck into the Hp and Lp sockets. No movement.
As stated before the meter is always at three, but is not stuck and moves freely.
When i do the normal battery test it goes up to 13,5-14v. I did an internal measurment of the batteries and measured 9,65v on one side (the right plug i think). I could not get any measurements from the other plug.
Obviously I will have to spend some more time on this machine
Thanks,
Lucas

[threeseven]

I have a CT537 tester, mains powered version. Powers up but won't calibrate, probably a cap, will have to sort it out.

[David Simpson]

Hello again Lucas,
I'll attatch a copy of the relavent page for using the CT446 as a Multimeter.
For checking the current ranges, a 1Mohm pot( or a resistance box) in series with an external mA Meter placed across the C and E NPN transistor connectors, can be used. Start off with the Pot set at its highest resistance & the Meter Switch at 1A, just as a precaution. Current can be controled by an external adjustable DC voltage PSU, between 0 & 12V.
For example, on the 0.1mA range, with 144Kohms, a voltage of 15V gives FSD. Well, on mine anyway.
I banged on earlier about me fitting a Benchmark meter. Not having used my 446 for a couple of years, and trying to remember if R41 or R42 were used for calibration, removed my B/M meter & fannied about a bit.(Actually, an AVO8/6, used in its place for FSD, shows 2/3 FSD on it's 50uA range). Anyway, the outcome is - the damn B/M meter doesn't like being moved in & out of a 446, or moved around one's workbench - now sticking !
Will have to check it out, and if its phooked, will just use the bigger AVO 8/6. I've plenty of AVO8's, so sod forking out for a new meter. Actually, I did mention some time ago, in relation to a long winded CT160 discussion, that an AVO8 on its 50uA range - with a print of a CT160's meter's red & green etc scale sellotaped over the first 2/3's scale - makes an excellent & reasonably accurate substitution. This will work just as well for a 446. Considering the horrendous cost of original AVO 30uA CT160 or CT446 meters, a decent working AVO8 can be picked up for just 20 or 30 quid! And is a lot more robust & protected.
Incidently, if one does use an AVO8 as a substitute in a 160 - by pressing REV MC - the full extent of reverse "Whanging" can be seen.

Regards, David

[David Simpson]

Folks, With a wee bit of copying/ printing size adjustment & jiggery pokery with sellotape - the CT446's scale can be temp transposed onto an AVO8's scale. With time, the AVO8's scale plate could be removed & covered over with an ascetate copy.
Anyway, with a copy just lying on top of the glass, & with 0.1mA selected on the CT446, an Ic of 49.6uA is easily read off the AVO8 as 50uA. Not bad eh ?
To digress again, similar accuracy was observed with a AVO8/CT160 set-up(as reported last year).

Regards, David

ps. Regarding pictures :- Yes I know, David Simpson needs to improve his Macro usage of his digital Camera. Jiggered if I can get focus spot on, Sorry.

[Analogman]

Hi David,
Well as always, the old "it helps to read the manual" saying turns out to be true! After reading about which settings to use and how to set the polarity on the Hp and LP sockets, i was indeed able to get a reading. Using a 1.5v AAA battery and setting the meter switch to 1-5v, the meter jumped all the way up to 15 and then settled at around 14v? Setting the meter switch to 15v, the meter barely moved from around 3 to about 4v. Setting the meter switch to 1A i got a reading of about 65mA or 10v? As always the meter settles back to about 3 when turned off or not in use. What do you think??
I will try to do the current range check soon, but how do I zero that meter?
Thanks, lucas

[David Simpson]

Lucas,
If your meter is permantly stuck at 3 on the 0 - 15V range, even with the Function Switch = Off. Then there is a mechanical problem with the movement. Something is stopping the armature from returning to rest.Prahaps the mechanical zero is badly bent inside.
You'll need to remove 8 4BA retaining bolts from the casing & the whole set comes out. The meter is secured with two long 2BA bolts into the rear 1/4" thick paxolin board. These bolts are also the connections for the meter movement. The meter should then be released from the set, but take care - the rubber neoprene gasket might need gently prising away if its been stuck there for nigh on 50 years. The meter can be split apart(gently again) by removing the 4 8BA wee bolts. The meter's faceplate is retained by two even smaller wee bolts, 10BA I think. Slide it off parallel to the meter casing - dont lift it - it'll damage the delicate pointer. Never poke anything metalic near the phosphor bronze springs. Gentle tapping of the case or a wee puff down a straw might help dislodge any foreign matter. If it still sticks - you'll need to get it repaired by a professional meter repairer.

Regards, David

[diyHans]

Originally Posted by ukcol

Hello Chris
I have a manual for one of these kindly supplied by Jeremy (Pamphonica).
If you PM me with your email address I will send it to you as a pdf file.
Colin M

Dear Colin,
Could I have a copy of this manual too ?
I have been searching for this manual for a long time. Hopefully you can help me !
Thanks
Hans

[mark-jacobs]

The manual for the CT446 was posted previously: https://www.vintage-radio.net/forum/...993#post467993

The problem is finding the associated transistor manuals that give all the test parameters for this unit. I have two of these units, both have a mains unit and no batteries.

A common problem with these meters (AVO 30ua variant) is that they either go open easily, therefore use a meter protection diodes, or the meter becomes sticky. I have worked on a half dozen of these meters, and everyone seemed to have some type of problem. The sticky meter can be because the bearing is too tight, a bent needle hitting the face plate, an iron flake/rust between winding and magnet, or very common is the paint applied to the back of the meter flakes off and jams the meters/hairspring coil.

If they fail to zero, then the back hairspring coil may be out of adjustment.

Mark