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Post by Chris on Mar 28, 2016 11:30:22 GMT
Decided to have a wee crack at biasing my amp the other day. Looked out my multimeter and tried it against a 1.5v battery which showed 1v dc. I then tried it on the amp inners with the negative tucked into the chassis and the positive on the valve base as per instructions.
Nothing. Not a thing. No measurement at all. Tried the end around a light socket flex,nothing. Phone charger showed 1v. I've got a feeling the multi meters goosed but it shouldn't be - it's a good Fluke meter a T5 1000 electrical tester.
Any ideas?
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Post by pre65 on Mar 28, 2016 11:46:18 GMT
Is the bias voltage positive or negative ?
What is the valve you are trying to measure, and what pin are you measuring at ?
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Post by Chris on Mar 28, 2016 11:58:54 GMT
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Post by pre65 on Mar 28, 2016 12:16:26 GMT
Reading through those instructions it seems the bias is checked in a different manner to what I would have expected.
Are you using a mV (millivolt) setting on the meter ?
390mV = 0.39V = 39mA
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Post by Chris on Mar 28, 2016 19:02:21 GMT
Sorry pre65 got very busy. No,I'm using the V setting. There's no mV setting on it. There's V A or ohms.
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Post by pre65 on Mar 28, 2016 20:43:59 GMT
I tried to find information on your Fluke but I can't find what the resolution is at mV level.
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Post by MartinT on Mar 28, 2016 20:47:07 GMT
It sounds like it might need a new battery? Flukes are good meters.
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Post by Chris on Mar 28, 2016 21:05:49 GMT
Yeah tried new batteries as well MartinT. There are threads on the net about them getting knackered easily if dropped/abused and there's a fair chance that's happened. I don't know how to test it either but I will change the batteries again just in case. Tomorrow.
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Post by Chris on Mar 28, 2016 21:07:22 GMT
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Post by dsjr on Mar 28, 2016 22:53:05 GMT
I had a favourite cheapo digital meter that packed it in. Turned out to be an internal fuse, plus battery change. Couldn't afford a 'proper' meter...
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Post by MartinT on Mar 29, 2016 7:13:23 GMT
Flukes are brilliant but the Maplin Academy range are (were?) very good at half the price.
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Post by MartinT on Mar 29, 2016 8:01:39 GMT
It's been pointed out to me that the Fluke T5 1000 is not a standard DVM, it's a high voltage tester. Therefore the resolution is not good enough for audio electronics.
Sorry chris, you need to buy a low voltage DVM to get the results you need.
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Post by MartinT on Mar 29, 2016 8:03:55 GMT
Something like this for £14.99 (Maplin Precision Gold PG10B)  |
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Post by stanleyb on Mar 29, 2016 8:45:15 GMT
Something like this for £14.99 (Maplin Precision Gold PG10B) There is a story behind how Maplin ended up with those multi meters, and how I got involved in the whole process from day one nearly 17 years ago. All I can say is that the stuffed brown envelopes from the Far East at that time were in fact white  . |
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Post by MartinT on Mar 29, 2016 8:48:57 GMT
Really? Amazing, I've had one for a number of years and never knew. Those Chinese...
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Post by Chris on Mar 29, 2016 11:15:52 GMT
Thanks for that Martin. I will track one of those down come payday.
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Post by Mr Whippy on Mar 29, 2016 23:07:19 GMT
Why not check the battery with the continuity test and shorting the leads? Or try a resistance check on say a fuse?
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Post by Chris on Mar 30, 2016 6:55:48 GMT
No mate - it's the wrong thing entirely. Going to go for MartinTs recommendation and start again.
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Post by MartinT on Mar 30, 2016 7:37:23 GMT
I think at the price it's a no-brainer and should stand you in good stead for all sorts of testing.
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Post by Chris on Apr 1, 2016 16:07:35 GMT
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. 