Where can I buy an el34 bias probe in the UK?

rawk100

I'm after the type of probe that sits between the valve base and the valve so that the current can be measured via some flying leads. I think they have a 1 ohm resister built in. I've got a multimeter already so I'm just after the probe. They only place I can see them for sale is at Hotrox (the TAD ones), and it looks like I can buy them from China on eBay. Is there anywhere else in the uk that sells them?...

RiftAmps

Mac Electronics make a good one, although you need to phone them up to order - http://www.mac-electronics.co.uk

John_A

I have some China Ebay ones that were far cheaper than anything I could find in the UK, came with a dedicated meter too and have been working for years:

One of these:

http://www.ebay.co.uk/itm/Tube-Amplifier-EL34-KT88-6L6-6V6-KT66-Tube-Amp-Bias-Tester-Suzier-SZ-99-/281863726806?hash=item41a06326d6:g:w4UAAOSwf-VWURiO

rawk100

John_A said:

I have some China Ebay ones that were far cheaper than anything I could find in the UK, came with a dedicated meter too and have been working for years:

One of these:

http://www.ebay.co.uk/itm/Tube-Amplifier-EL34-KT88-6L6-6V6-KT66-Tube-Amp-Bias-Tester-Suzier-SZ-99-/281863726806?hash=item41a06326d6:g:w4UAAOSwf-VWURiO

I did look at buying one from China but was unsure of the quality, so it's good to hear that it's worked ok for you.

Did you have to pay any additional import charges when they delivered it?

John_A

No additional import duty, I think they put a value of $5 on the package, came in about 5 days too

martinw

John_A said:

I have some China Ebay ones that were far cheaper than anything I could find in the UK, came with a dedicated meter too and have been working for years:

One of these:

http://www.ebay.co.uk/itm/Tube-Amplifier-EL34-KT88-6L6-6V6-KT66-Tube-Amp-Bias-Tester-Suzier-SZ-99-/281863726806?hash=item41a06326d6:g:w4UAAOSwf-VWURiO

Hmm.

I bought one of these a couple of months back. Put in a lowish offer, haggled to about £30 delivered.

Seemed ok when I got it, apart from the US power supply, but still works ok on batteries for now and I have a few 5V PSUs around.

Anyway, whilst using it, I noticed that the anode and screen voltages were higher than previously on that amp, and on further checking I found that this device has a design flaw of sorts.

You'd expect there to be a 1 ohm resistor in each valve base/plug assembly, and the 4-way switch then just switches from one set of sense wires to the next. Wrong. The 1 ohm resistor is in the meter assembly, and the 4-way switch switches each valve in turn through the same 1 ohm resistor, leaving the other 3 open circuit. The other 3 valves are therefore 'off' and not drawing current, meaning that the supply voltages are artificially high, and the bias may be incorrectly set.

I pointed this out to the manufacturer (with great difficulty as their English is poor and my Mandarin covers counting to 10, ordering a beer and saying 'Hello pretty girl') and initially they were happy to give me half of my money back rather than waste both our time returning the item through Ebay. Unfortunately, when I mentioned that I could modify the tester to work correctly, they then withdrew this offer until I supplied them with pictures of how I'd modded it!

Not wanting to do a couple of hours of consultancy work for £15, I've declined and will cut my losses. I should have known better really, you get what you pay for.

Avoid.

rawk100

martinw said:

John_A said:

I have some China Ebay ones that were far cheaper than anything I could find in the UK, came with a dedicated meter too and have been working for years:

One of these:

http://www.ebay.co.uk/itm/Tube-Amplifier-EL34-KT88-6L6-6V6-KT66-Tube-Amp-Bias-Tester-Suzier-SZ-99-/281863726806?hash=item41a06326d6:g:w4UAAOSwf-VWURiO

Hmm.

I bought one of these a couple of months back. Put in a lowish offer, haggled to about £30 delivered.

Seemed ok when I got it, apart from the US power supply, but still works ok on batteries for now and I have a few 5V PSUs around.

Anyway, whilst using it, I noticed that the anode and screen voltages were higher than previously on that amp, and on further checking I found that this device has a design flaw of sorts.

You'd expect there to be a 1 ohm resistor in each valve base/plug assembly, and the 4-way switch then just switches from one set of sense wires to the next. Wrong. The 1 ohm resistor is in the meter assembly, and the 4-way switch switches each valve in turn through the same 1 ohm resistor, leaving the other 3 open circuit. The other 3 valves are therefore 'off' and not drawing current, meaning that the supply voltages are artificially high, and the bias may be incorrectly set.

I pointed this out to the manufacturer (with great difficulty as their English is poor and my Mandarin covers counting to 10, ordering a beer and saying 'Hello pretty girl') and initially they were happy to give me half of my money back rather than waste both our time returning the item through Ebay. Unfortunately, when I mentioned that I could modify the tester to work correctly, they then withdrew this offer until I supplied them with pictures of how I'd modded it!

Not wanting to do a couple of hours of consultancy work for £15, I've declined and will cut my losses. I should have known better really, you get what you pay for.

Avoid.

A very timely post as I've just worked this out this morning, it seems that the probe I got from China doesn't have a 1ohm resistor in it. One wire is connected to the socket side of the probe (where the valve goes) on pin 8 and the other wire is connected to the pin of the probe (that pushes into the valve base) on pin 8. The pin and socket on pin 8 of the probe aren't connected. So all it does is divert the volts off pin 8 through your meter. My meter doesn't have an internal resistor so the probe isn't much good!....

uncledick

rawk100 said:

martinw said:

John_A said:

I have some China Ebay ones that were far cheaper than anything I could find in the UK, came with a dedicated meter too and have been working for years:

One of these:

http://www.ebay.co.uk/itm/Tube-Amplifier-EL34-KT88-6L6-6V6-KT66-Tube-Amp-Bias-Tester-Suzier-SZ-99-/281863726806?hash=item41a06326d6:g:w4UAAOSwf-VWURiO

Hmm.

I bought one of these a couple of months back. Put in a lowish offer, haggled to about £30 delivered.

Seemed ok when I got it, apart from the US power supply, but still works ok on batteries for now and I have a few 5V PSUs around.

Anyway, whilst using it, I noticed that the anode and screen voltages were higher than previously on that amp, and on further checking I found that this device has a design flaw of sorts.

You'd expect there to be a 1 ohm resistor in each valve base/plug assembly, and the 4-way switch then just switches from one set of sense wires to the next. Wrong. The 1 ohm resistor is in the meter assembly, and the 4-way switch switches each valve in turn through the same 1 ohm resistor, leaving the other 3 open circuit. The other 3 valves are therefore 'off' and not drawing current, meaning that the supply voltages are artificially high, and the bias may be incorrectly set.

I pointed this out to the manufacturer (with great difficulty as their English is poor and my Mandarin covers counting to 10, ordering a beer and saying 'Hello pretty girl') and initially they were happy to give me half of my money back rather than waste both our time returning the item through Ebay. Unfortunately, when I mentioned that I could modify the tester to work correctly, they then withdrew this offer until I supplied them with pictures of how I'd modded it!

Not wanting to do a couple of hours of consultancy work for £15, I've declined and will cut my losses. I should have known better really, you get what you pay for.

Avoid.

A very timely post as I've just worked this out this morning, it seems that the probe I got from China doesn't have a 1ohm resistor in it. One wire is connected to the socket side of the probe (where the valve goes) on pin 8 and the other wire is connected to the pin of the probe (that pushes into the valve base) on pin 8. The pin and socket on pin 8 of the probe aren't connected. So all it does is divert the volts off pin 8 through your meter. My meter doesn't have an internal resistor so the probe isn't much good!....

In your original post you said you had a multimeter.  Every multimeter I've owned has had a DC current facility so why don't you want to use it on yours?

martinw

Here's their latest reply:

Hello!
I have had tell you.
Your idea is good.But i can't finish that like your idea.
If you can finish your idea.That's good,You can change T1 you received.
You just tell me you have a good idea.No other.Just a word.
How to believe you.
My tester is working good.I don't think have something wrong with it.
You said it's not good.Just need more time to show number on LED.
You idea can show number is fast then my tester.
You can finish it.I would like to pay you GBP15.

:-S

rawk100

I think that translates into "here's 15 quid.....now fuck off"......!

ICBM

I think it translates more like "actually I don't have a clue what you've told me because I don't really know how this stuff works, I'm just following something I read on the internet and decided to make a commercial product to do it, so here's £15 to cover my embarrassment".

At least one of the early US-made commercial bias probes did feed the full valve current out through the meter too, but it's still the wrong way of doing it.

martinw

I'd like the £15 to f*** off, but they will only pay me that if I mod the tester, then send them pics etc as to how I did it!

Originally they were happy to do it as a partial refund, but then they later added strings to it.

ICBM said:

I think it translates more like "actually I don't have a clue what you've told me because I don't really know how this stuff works, I'm just following something I read on the internet and decided to make a commercial product to do it, so here's £15 to cover my embarrassment".

It's become pretty clear through my conversations with them that they have no idea about valve amps, and little about electronics.

welshboyo

So, the TAD one I have, does that have the same design flaw?

Happy to offer mine up for testing/dissecting if needs be!!

alseic

bump for the old thread
is there anything ok?
I had Biascom II but it is not available, and spending 125GBP or so for TAD version is just ridiculous, imo.

ICBM

It isn't too hard to make your own - I've done it with the base from a dead valve (break the glass carefully, remove all the innards and unsolder the wires) and a valve socket, with all pins wired straight through apart from pin 8 which is done with a 1-ohm resistor, which is then also connected at the top end to an eyelet tab bolted to the socket flange, then the whole lot assembled with resin or hot-melt glue so the high-voltage pins are safely enclosed inside the valve base.



Then with it in place you simply measure the voltage between the chassis and the flange of the socket using a standard multimeter, with croc clips if you prefer to keep the meter on while you adjust the bias. OK, if you want to do more than one valve at the same time you need to make more than one so it starts to get a bit more of a faff...

alseic

Thanks for the info

Well in the worst case I will make my own bias probes as you suggested, I can afford expensive meter I just don't like to spend/support such overpriced products with my money.

Some shop in Poland (I am from Poland) was selling such probes for ~6 GBP each, so it was like 45GBP for meter + 4 probes - quite ok, but it wasnt same thing as sold in China. Unfortunately I have no idea where my bias probes are lol.

Stevepage

I bought mine from eurotubes.Com 

Arrived in just under a week and I just used it to bias my Jsx. Costs about £35 if I remember right