Wanted Bias Meter for valve amplifier

[Arkless Electronics]

I've got one I bought for £3.99 from Netto's and it works perfectly well. Obviously I use quality ones in my day to day work but it's handy to have one that can be considered disposable to take if you're eg helping a mate with his car electrics and there is a risk of it getting stood on or having a pipe wrench dropped on it.
The OP is only wanting to measure the bias on his valve amp and this usually means about a volt or so (up to 60V if measuring the actual bias rather than the voltage at the bias test points). I haven't personally ever heard of one blowing up when used to test the mains. I don't doubt that it has been known to happen but this would likely be a particular make and model and not a common issue. I have used my £3.99 one to measure the mains on several occasions with no problems.

The safety issue is worth considering if one intends to use it for high voltages yes but I have trouble in believing such incidents as Marco mentions are more than rare isolated incidents. Caveat emptor though...

[Marco]

Some further comments, posted on behalf of the same qualified EE...

"As for £3.99, for a test instrument, well what can you say to that! The problem is that these things do explode. One major issue (apart from measuring voltage at 240V), is the instrument reliability when someone goes from testing resistance, to measuring voltage, even down to 60-70 volts.

They short out in an impressive manner, and valve amps can easily produce these voltages with a decent bit of current (amps) behind it!!"

Marco.

[JohnJo]

For measuring mains voltages you should be using a category II or better to give protection against arc flash if the multimeter inadvertently presents a short circuit due to wrong range selection, voltage spike, damage etc.

Here's a useful guide from the experts, Fluke: https://assets.tequipment.net/assets...ter-safety.PDF

[Arkless Electronics]

People will have to make up their own minds on this...

One often sees these at Lidl and other such German stores and despite being cheap and made in China they often have German "VDE" and/or EU safety markings on the outer cardboard packaging. These will have been purchased in huge quantities and the tale above (I can guess who the EE is) is the only such tale I've ever heard of. If Lidl/Aldi/Halfords/Maplins etc £5 meters were regularly exploding I reckon it would have made the press and there would have been product recalls etc.

Yer pays yer money and takes yer choice but I don't have any problem with them personally. It is probably best to avoid ones from ebay or car boot sales as they won't have undergone Lidl/Aldi/Halfords/Maplins own in house safety checks.

The single biggest risk is from user error by having the meter switched to measure current and then putting it across the mains. Most meters (all that I've seen) have a fuse inside for protection against this. Most meters have a separate input socket for this and you have to unplug the positive probe from its normal position and replace it in the "Amps" socket. Some cheap ones allow the normal socket to be used for mA readings though and a quick look at my Netto one reveals this to be the case here. This IS something to at least be aware of.

To put all this in perspective though, the OP is wanting a meter to measure bias and in most cases there are bias test points, accessible without removing covers etc, for just this purpose and we are usually talking a Volt or so...

[Marco]

(I can guess who the EE is)

I seriously doubt it. The one you think it is would've said what he had to say here, so no gold star!

Marco.

[RothwellAudio]

Looking for a Bias meter for a valve amplifier to adjust and set when required

Does the valve amp in question have test points easily accessible from the outside of the case? How many volts (or millivolts) are expected?
If you're expecting, say, 100mV I can't see how even the cheapest/crapest meter could injure you. It will be measuring the voltage across a small value resistor in series with the cathode and even if the meter went short circuit it wouldn't damage anything.

Of course, it might be cathode biased design, which would be a bit different. We don't know until you tell us.

[Eaton Mess]

Thank you all for your comments!
I didn't realise a simple request would simulate such a discussion

@Marco I have been warned off using the cheap Chinese meters by other professionals for the reasons you stated. Although many are not intrinsically dangerous in the wrong hands or through lack of experience (ME) they can be lethal because of their design, lack of proper protection or mixing DC and AC through the same inputs

@Rothwell Audio Well it all depends - I have more then one amplifier to bias as I have SET's and Push Pull and they range from simple easily accessible external bias points with adjustable pots to the need to be a circus contortionist with the amplifier upside down and messing around within the internals.

Its been suggested to me that an ex MOD meter would be the best option called the Fluke 25 (re badged Fluke 27) whilst more expensive and older than the Maplin, Lidl, EbAY Chinese meters it is better quality, safe to use and would have lasting value?

There is an interesting appraisal here