Valve testers

[murphyv310]

Hi.
There is a lot of threads about various different valve testers, the AVO CT160 seems to be a firm favourite and is often seen for sale for a lot of money. What I have found out over the last few weeks from many different sources is the the CT160 actually is not as accurate as the immensely simple AVO MK1.
The Mullard tester with the cards is also grossly over rated with no clear indication of the parameters of the valve under test.
I recently acquired an AVO MK1 tester in totally original condition and it was tested against a Hickock tester that had just been calibrated, the result was impressive with results being within 1%.
I wonder why then the MK1 isn't so popular?

[MichaelR]

Hi Trevor,

I think the biggest disadvantage would be the fact that with the Mk1 you cannot set any grid bias for the valve under test so no control of the grid current.Any current flowing would load the grid supply differently with differing valve types.

The mullard tester I had was a fully working sytem with all cards and was really a pass/fail tester. I had a ct160 which I thought was very good , I currently have a Taylor 45C which I have found to be excellent for my needs.

Mike

[Mike Phelan]

My take on the Mullard "one arm bandit" tester is that a few places where I worked, they were used in the shop, and customers could bring in valves to test to supplement our brew money.
The added advantages were:

• We sold them valve(s)
• They often brought in the equipment for us to repair because the fault was not due to a valve
• They mixed them up and put them in the wrong holders.

[ms660]

The Mullard high speed was a good w/shop sevice machine in it's day we mainly used them for go no go emission tests. I use a Hickok based 177 for my old valves, basic but very good, does grid current & gm ok, with a tagged tube extender you can monitor actual grid bias etc very simple circuit appart from the switching. There is a lot of waffle about valve testers these days, I suppose it's wether or not it is classed as a tester or characteristic meter, if it's RF then substitution is the only real test in my experience.

Lawrence

[PJL]

Although the Mullard tester is designed as a go/nogo tester, I developed some software to calculate the test conditions. The CRT is pretty linear so it is possible to get a reading of sorts from it.

It does do a few things that other testers do not for example, it uses regulated DC test conditions, it has many more LT taps as it runs the valves at the minimum LT voltage recommended by the manufacturer.

I keep meaning to add gm to it's capability by injecting AC onto the grid using a small transformer with another transformer in the anode I can use to inject some of the source signal to create a null.

[bodge99]

Hello All,

Just a quick question if I may.

PJL said, regarding the Mullard tester, "It does do a few things that other testers do not for example, it uses regulated DC test conditions, it has many more LT taps as it runs the valves at the minimum LT voltage recommended by the manufacturer."

Regarding the number of LT taps, is this significantly different to the way AVO's or the Sussex handle this aspect? I'm still building the Sussex and am at the stage where I could easily make changes (e.g. transformers not wound yet..)

Regards,

Bodge99

[Leon Crampin]

My view is that the Mullard tester is a very poor substitute for any of the AVO testers. This arose from the patents which AVO held which relate to their system of measurement in which unregulated AC is (generally) applied to the valve under test which then acts as a rectifier whilst testing takes place. Without writing a treatise on valve testing, the AVO system is extremely elegant in that it determines ratios, thus obviating the need for regulated supplies.

Mullard/Philips made valves and CRTs - but not meters. This is why their tester rather stupidly incorporates a tube for a function which would be far better performed with a meter. The punched card system is inflexible and requires a nightmare arrangement of contacts to read it.

As you may have guessed, I'm not a fan.

The AVO Mk1 tester is an elegantly simple device - admittedly with limitations such as parasitic oscillation with high slope valves and the running of devices under test at zero bias - but it's really versatile. I use mine frequently and if you know its limitations, it will test most things to a fair degree of accuracy.

Try testing a Russian valve for which you have the data on a Mullard tester...

Leon.

[theoldtrout]

Having a few months ago acquired and restored a Mullard HSVT - and still trying to complete my set of cards, I agree with the above criticism. I only got one because I have amassed about 5000 valves over the years and need to sell a lot them on, so a quick go/no go tester like the HSVT is ideal. Any of AVO valve testers would be nice to own, but the prices!

[jay_oldstuff]

I have the best of both worlds, in my cellar where I keep my valve stock 1000+ valves, I have a HSVT I find it invaluable. Most of my valves are unboxed pulls i buy in job lots cheaply. With the HSVT i can take a untested valve from stock and quickly check it's condition. I also have an AVO mk1 which sits on my workbench and gets used more when I'm playing with stuff or for testing if a valve is faulty before delving into my stocks.

Jay

[murphyv310]

Interesting answers guys!
Up to recently I didn't have a valve tester. The last one I had was a Mullard and it went in 2007, I didn't like it as it had no proper calibration, drifted continuously and took up far too much room, in it's defence sold for a good amount on ebay!
With well over 10,000 valves between myself and Bob the need for another tester was irrelevant.
When this one turned up I kept it as it was in mint condition, working perfectly, accurate and free!
So far it has been a quick way of testing the valves I have been recently been given, so no complaints so far.

[Lucien Nunes]

Outside of vintage radio circles the modern-day rules about valves and testers seem to be written by people with a limited range of interests in valves, primarily esoteric hifi and musical instrument amps. For many such enthusiasts, knowing whether a valve 'works' or not is insufficient, hence the zero-bias conditions of the Mk.1 or the non-numerical results of the HSVT are of scant interest. The Mk.1 is also unsuited to testing some of the most prized audiophile bottles.

For my part, the only reason I don't use the Mk.1 in earnest is that there is a good Mk.4 on the bench and I know many of the popular settings and results, so I stick with what I know. Repeatedly using two testers that give different results for the same valve would be confusing. I also sometimes like to play with those naughty valves that the Mk.1 can't test or gives strange results for!

Lucien

[ms660]

Originally Posted by Leon Crampin

My view is that the Mullard tester is a very poor substitute for any of the AVO testers. This arose from the patents which AVO held which relate to their system of measurement in which unregulated AC is (generally) applied to the valve under test which then acts as a rectifier whilst testing takes place. Without writing a treatise on valve testing, the AVO system is extremely elegant in that it determines ratios, thus obviating the need for regulated supplies. Mullard/Philips made valves and CRTs - but not meters. This is why their tester rather stupidly incorporates a tube for a function which would be far better performed with a meter. The punched card system is inflexible and requires a nightmare arrangement of contacts to read it. As you may have guessed, I'm not a fan. The AVO Mk1 tester is an elegantly simple device - admittedly with limitations such as parasitic oscillation with high slope valves and the running of devices under test at zero bias - but it's really versatile. I use mine frequently and if you know its limitations, it will test most things to a fair degree of accuracy. Try testing a Russian valve for which you have the data on a Mullard tester... Leon.

Hello Leon, Hickok originally held a similar patent, I am not sure which came first, the Hickok method is also elegantly simple.

See:

http://www.grc9.nl/Overige/I177B/Bes...-177MANUAL.PDF

Lawrence.

[David Simpson]

Folks, Just to clarify AVO's early description of their range of testers, for the un-initiated, according to their list & pictures in the yellow 1950's/60's Valve Data Manuals :-
There is the "AVO VALVE TESTER" = The original 1940's "2 Panel Tester"(Which some folk call the "Mk1").
Then there is the "Valve Characteristic Meter" - big bulky upright cabinets - Mk 's 1,2,3 &4. Which started out in the 1950's.
Then there is the CT160, which AVO call "Valve Tester Type 160". Produced from the mid-50's through to late 60's.(Mainly for military use).
Just thought I'd mention it. So as to avoid confusion between the original Valve Tester(Best call it "Two Panel"), and the VCM Mk1 which is more versatile & sophisticated.
The 2 Panel just uses fully sinusidal AC applied to all valve connections. It also has a lovely big meter which is extremely robust & can put up with frequently being whanged hard against the fsd stop. A good Go - No Go tester.


Regards, David

[murphyv310]

Thanks for the clarification David. Indeed mine is a Two Panel Tester. It certainly has been well used during my days off!

[ms660]

For those interested the original Hickok patent can be found here:

http://books.google.co.uk/books?id=F...patent&f=false

Also contains info on AVO and other manufactures.

Lawrence.

[MichaelR]

Originally Posted by murphyv310

Thanks for the clarification David. Indeed mine is a Two Panel Tester. It certainly has been well used during my days off!

My comments earlier were referrring to the VCM mk1 not the 2 panel tester, never had one of those

Mike

[Bazz4CQJ]

Some years ago, I worked for a company which had been created by being privatised out of another agency. One day after the separation, I got a call from an old colleague who was still with the agency and who desperately needed a small job doing for which they no longer had the kit. However, he had no money, no authorisation and no time - but I got it done for him anyway.

A while later, I bumped in to him at his location and after a few minutes, he took me to a stockroom where there was a vast array of old and unwanted scientific test equipment, and as a thanks for my earlier help, he told me I could have any one item that was there. And that is how I got my AVO VCM163 !

[Craig Sawyers]

That is quite an impressive way to get a VCM163! Like gold dust.

I started off with a 2-panel AVO, but it was really only suitable for small signal valves. So I sold it, and bought a Taylor 45C, which I still have.

Then I got a 160, with known broken meter movement. A bit later I was picking up a job lot of stuff, and saw an AVO heavy duty voltmeter with clearly the same design of movement. I got that free, transplanted the movement into the 160 meter case, and then added an op-amp driver to match the movement to the 160. Works a dream.

I then got given a Mk1 and a Mk3. The Mk1's meter has no innards, so that needs some thought. The Mk3's grid voltage pot was totally stuffed, so I replaced it with a 10k, 3W wirewound from the spares box, replaced the diode vavles with 1N4007's and it works a real treat.

So just need to fix the Mk1, and I'll have enough valve testers to keep me happy for a while. Well, until I find a way to pick up a Mk4 and a 163 cheap, that is ;-)

Craig

[Philips210]

Hi

I was lucky enough to acquire an Avo VCM Mk3 about twenty years ago. It had apparently been dropped into a skip at the local college and rescued by one of the lecturers. He kindly donated it to me for various repair jobs.

After about twelve years of occasional use, I had to replace the o/c meter movement with a Sifam type movement together with an op amp circuit and is now working well.
Also, the little top cap lead was missing but it was a simple task to make one.
The accompanying valve data manual suggests it is for the Mk1 to Mk4 range so the extra data will be useful for testing later valves.

The Mk3 lacks a B9D valve base which I am contemplating fitting to my tester as it will be useful to check say PL508, PY500A etc valves.

I also wondered about fitting a B10B base for PFL200 and PCF200 valves, although there won't be a great demand for testing these. As these have ten pins and the thumbwheel has switching for a maximum of nine pins, additional switching would be required so complicating matters further.

I certainly like the flexibility of the Avo thumbwheel switch design compared to Mullard's requiring a dedicated punched card for each valve. I would however like to own a Mullard HSVT and maybe an Avo VCM163 as well.

Symon

[Craig Sawyers]

Since the B10B valves involve at least one pentode section, and the AVO manual connects the supressor grid to cathode, that connection could be made hard wired in the valve base.

There are only about 20 valves that ever used that base anyway.

Or am I missing something?

Craig