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Old 7th Feb 2020, 4:44 pm   #61
Luxman1050
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Default Re: Making an RF probe for VTVM

Yeah I'm not trying to spot the enemy in the sky with my VTVM ha.
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Old 7th Feb 2020, 4:52 pm   #62
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Default Re: Making an RF probe for VTVM

Changed caps in VTVM but still waiting for electrolytic replacement.
Someone put two 1000v 0.1uf caps in series where a 0.05uf cap goes makes sense except original is 3kv. So took it out and top cap taken brunt of load gone brown and slightly melted.
So 3kv in their now. Glad I looked.
Still trying to work out power supply for ea50 reading packard but seems maybe a link into the 12ax7 valve or 12au7 cant remember and still trying to get a decent can.
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Old 8th Feb 2020, 2:44 am   #63
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Default Re: Making an RF probe for VTVM

The power supply for a EA50 is simple. The socket, or more correctly the valve base isn't.

The two outside pins are the heater, the centre pin is the cathode, the single pin is the anode. So, one of the heater pins can connect to the cathode pin. Other heater pin requires its own wire from the power supply. The anode also requires a separate wire.

Try googling RF probes.

Joe
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Old 8th Feb 2020, 12:04 pm   #64
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Default Re: Making an RF probe for VTVM

Hi i used one of these https://www.ebay.co.uk/itm/BELLING-L...4AAOSwAzZbP0SD mounted in a metal tube 6.3 v for heater from the vtvm . 3 wires to vtvm signal. heater. and ground. Mick
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Old 8th Feb 2020, 1:49 pm   #65
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Default Re: Making an RF probe for VTVM

Cheers guys I have bought one of those funny enough bit coincidence!
I also found a bulkhead bnc kings kc 79-46 in one of my boxes brand new blimey the price of them around 25 quid. So I'll replace that in the unit.
Pics attached.
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Old 8th Feb 2020, 7:41 pm   #66
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Default Re: Making an RF probe for VTVM

Mick I was going to tap into the heater supply in my VTVM but Joe suggested that it's an extra 150mA strain on the transformer I take it you've had no problems in that department?
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Old 8th Feb 2020, 10:36 pm   #67
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Default Re: Making an RF probe for VTVM

Hi i am using a tech te65 vtvm the tx gets warm but no problem the te65 is a similar circuit to your vtvm manual says goes to 50mhz on ac range just checked with probe meter on dc and meter alown on ac gives the same reading this is at around 20mhz from sig gen. will send circuit and details if required but 9 out of 10 times for signal tracing in a faulty tx i just use a straight probe and the meter on ac , i find the rf probe to bullky to fit into new stuff its ok on things like kw2000s or the like but on pcb i find you can not get in to it as its two large
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Old 8th Feb 2020, 11:11 pm   #68
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Default Re: Making an RF probe for VTVM

That sounds promising.
Circuit and details be great Mike.
Many thanks Chris
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Old 8th Feb 2020, 11:11 pm   #69
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Default Re: Making an RF probe for VTVM

Sorry Mick
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Old 9th Feb 2020, 12:00 pm   #70
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Default Re: Making an RF probe for VTVM

Hi details as follows any thing you are not sure of i will try and help Mick
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Old 9th Feb 2020, 1:41 pm   #71
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Default Re: Making an RF probe for VTVM

What about the scale reading compared to the actual voltage being measured?

Lawrence.
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Old 9th Feb 2020, 2:32 pm   #72
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Default Re: Making an RF probe for VTVM

The output from probe is the peak rf converted to dc not rms or p/p. The rf is rectified by the ea50 to charge 0.01 cap to the peak voltage as its dc the screened cable can be stereo audio cable
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Old 9th Feb 2020, 3:33 pm   #73
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Default Re: Making an RF probe for VTVM

That's my point, so long as the OP is aware of this when measuring any voltages because the existing set up with his meter is based on it's diode circuit which in effect is a peak to peak job.

Lawrence.
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Old 9th Feb 2020, 3:35 pm   #74
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Default Re: Making an RF probe for VTVM

Horar cheers Mick that's great that's the setup I was using almost similar it was just finding the feed to the heaters. Nice one as I was gonna put a wander plug connector on side of unit connected to heater but was not sure which valve to use as initially I was gonna use the voltage straight off the tranny.
Cheers cant wait to get that up and running.
All best Chris
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Old 9th Feb 2020, 3:45 pm   #75
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Default Re: Making an RF probe for VTVM

Lawrence check posts 18# 20# circuit diagram and related info for use.
Cheers Chris
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Old 9th Feb 2020, 3:46 pm   #76
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Default Re: Making an RF probe for VTVM

Quote:
Originally Posted by cdm1christopher View Post
Horar cheers Mick that's great that's the setup I was using almost similar it was just finding the feed to the heaters. Nice one as I was gonna put a wander plug connector on side of unit connected to heater but was not sure which valve to use as initially I was gonna use the voltage straight off the tranny.
Cheers cant wait to get that up and running.
All best Chris
You need to be aware of the extra loading on the mains transformer that's presented by the EA50 valve heater...an extra 0.15 Amps....the transformer in yours looks minimal in that respect.

Lawrence.
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Old 9th Feb 2020, 4:09 pm   #77
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Default Re: Making an RF probe for VTVM

Quote:
Originally Posted by cdm1christopher View Post
Lawrence check posts 18# 20# circuit diagram and related info for use.
Cheers Chris
In the article photo's you referred to it says (Quote) "The result is an RMS reading"

It won't be....not with your meter.

Lawrence.
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Old 9th Feb 2020, 5:28 pm   #78
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Default Re: Making an RF probe for VTVM

Hi setting signal gen up for .5v pp using scope at 10mhz, the dc output from rf probe is .125v
straight into vtvm on ac range using the 1.5v setting and reading from the pp scale it reads .5vpp this is from 100khz to 32mhz manual says meter goes to 50 mhz checked to 32mhz the meter is a Tech TE65 Mick
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Old 9th Feb 2020, 5:43 pm   #79
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Default Re: Making an RF probe for VTVM

just reading other replys post 30 you say you cannot 0 ohms if your meter is a clone of the japanese Tech te?? then it maybe is like mine and 0 on ohms is in fact full scale full to the right hand side and not 0 as we know it just a thought Mick
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Old 9th Feb 2020, 7:24 pm   #80
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Default Re: Making an RF probe for VTVM

Seeing your comment and picture of Kings bnc (post 65) reminded me of a few twinax ?? 2 pole bnc lookalikes i used to have. viz Screen and TWO separate insulated inner conductors. I think used for datacomms years ago? Could be of use to you maybe?
eg https://www.ebay.co.uk/itm/Twin-Twin...IAAOSw53NY9Fza BTW,
The bnc you show I refer to as "panel mount". To me, bulkhead is a bnc cable mounting connector with a flange to suit fixing to a bulkhead.
A shame, but I think it was just over a year ago I offered a couple of rf probes on here. They were taken.
Rob
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