Velleman K7000 - UK Vintage Radio Repair and Restoration Discussion Forum

longneck90 · 8th May 2019, 12:33 pm

Hello to everyone. This query may be in the wrong place, so, to the Moderator's, feel free to move it. I feel a bit silly airing this particular enquiry, as really, I should know the answer myself. I have constructed this Vellerman Signal Tracer/Injector Kit. That's easy. My dilemma is; How to safely connect it to a valve radio, when most valve radios have voltages up to 300 Volts, and the 'Vellerman ' is powered by 9 Volts. All advice gratefully received. Thanks in advance. All the best. John.

Kentode · 8th May 2019, 12:50 pm

Not silly at all John, we all start at the beginning!

If you have a circuit diagram of a particular radio, post it here and you'll get specific advice.

In general terms you loosely couple the signal at the aerial, then transfer it forward to the grid of the first valve, then to the next valve and so on.

The 300 volts DC are on the anode of the output valve, with lower voltages on the preceding valves.

The grid of each valve should be seeing millivolts of AC signal.

Hope that helps.

Herald1360 · 8th May 2019, 6:21 pm

The input and output of the kit have series capacitors already (C4 and C5). If you change these for some 400V rated ones (if they're not already) that should provide adequate protection for the unit provided it's running on its own floating (battery?) supply. If you use it on a live chassis set, simply treat it as a part of the set (ie just as potentially dangerous) and proceed with the same caution.

https://www.velleman.eu/downloads/0/...nual_k7000.pdf

info on the device.

longneck90 · 8th May 2019, 6:28 pm

Hello to all. Thanks to Kentode for your advice, and reassuring reply. I am now able to proceed, but cautiously. I am actually intending to use it to try and track down why the FM on a Murphy A674 isn't working. (ECC85 OK) Thanks, and all the best. John.

David G4EBT · 8th May 2019, 6:59 pm

As has been said and can be seen on the circuit, C4, 0.1uF (100nF) cap protects the input to the tracer, so if you apply it to say the anode of an IF valve, rather than the signal grid input of the audio valve, the K7000 is protected from harm. Likewise, C5 (also a 0.1uF cap) is on the output of the injector, so protects that part of the K7000 from harm. As I recall, both caps are rated at 400V. They're the red ones on the PCB next to the pots at the pic below.

A point worth mentioning is that because both the injector and tracer amp are on the same compact PCB and aren't independently switched, you will get some 'breakthrough' on the amplifier from the injector, so when you hear that, it isn't faulty - it's just a limitation of the kit and doesn't detract from its usefulness.

Precautions on live chassis radios has been mentioned. Remember not to connect the ground lead directly to the chassis of such radios, but via a 0.1 uF cap. As the K7000 is battery powered, connecting the ground wouldn't be as catastrophic as connecting the ground of an earthed piece of test gear such as a scope or signal generator, but even so...

There's an excellent interactive article at this link on signal tracing in radios, which I've mentioned before:

http://www.nostalgiaair.org/Referenc...ost/post01.htm

If you click on this link and go to the circuit of a valve receiver, you'll see various points on the circuit marked with capital letters in brackets EG (A) etc. If you put your cursor over those points in turn, it will tell you what to expect in a working radfio, and what should be happening. For example, it explains that you should not hear any signals at points C, F, K & V - the Screen Grids. If you hover your cursor over point B and it will tell you that a signal should be heard there. It explains that he function of the "coupling condenser" is fundamentally that of keeping the plate voltage (at B) off the grid of the following tube (at D).

Hope that helps a bit.

Good luck in sorting the set John.

electronwilly · 8th May 2019, 7:42 pm

The k7000 injector is a AC audio waveform with no harmonics so cant be coupled into the antenna, Billy.

Herald1360 · 9th May 2019, 1:11 am

So it is- a phase shift oscillator, no less. I wonder why? The usual suspect is a multivibrator which generates loads of harmonics up into the RF range.

Easy enough to knock a separate one up, though.

longneck90 · 9th May 2019, 7:44 pm

Hello to everyone. Thank you all for your helpful advice, and David for your extended and descriptive piece of information, as well as links to other sources. The output from the Vellerman K7000 is very clear, and extremely loud when volume is turned up. SWMBO is wondering could I not find some more relaxing form of entertainment. All the best. John.

8th May 2019, 12:33 pm	#1
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Velleman K7000 Hello to everyone. This query may be in the wrong place, so, to the Moderator's, feel free to move it. I feel a bit silly airing this particular enquiry, as really, I should know the answer myself. I have constructed this Vellerman Signal Tracer/Injector Kit. That's easy. My dilemma is; How to safely connect it to a valve radio, when most valve radios have voltages up to 300 Volts, and the 'Vellerman ' is powered by 9 Volts. All advice gratefully received. Thanks in advance. All the best. John.

8th May 2019, 12:50 pm	#2
Kentode Octode Join Date: Mar 2015 Location: Yorkshire, England. Posts: 1,301	Re: Velleman K7000 Not silly at all John, we all start at the beginning! If you have a circuit diagram of a particular radio, post it here and you'll get specific advice. In general terms you loosely couple the signal at the aerial, then transfer it forward to the grid of the first valve, then to the next valve and so on. The 300 volts DC are on the anode of the output valve, with lower voltages on the preceding valves. The grid of each valve should be seeing millivolts of AC signal. Hope that helps. __________________ Regards, Ken. BVWS member

8th May 2019, 6:21 pm	#3
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Velleman K7000 The input and output of the kit have series capacitors already (C4 and C5). If you change these for some 400V rated ones (if they're not already) that should provide adequate protection for the unit provided it's running on its own floating (battery?) supply. If you use it on a live chassis set, simply treat it as a part of the set (ie just as potentially dangerous) and proceed with the same caution. https://www.velleman.eu/downloads/0/...nual_k7000.pdf info on the device. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

8th May 2019, 6:28 pm	#4
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Re: Velleman K7000 Hello to all. Thanks to Kentode for your advice, and reassuring reply. I am now able to proceed, but cautiously. I am actually intending to use it to try and track down why the FM on a Murphy A674 isn't working. (ECC85 OK) Thanks, and all the best. John.

8th May 2019, 6:59 pm	#5
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,761	Re: Velleman K7000 As has been said and can be seen on the circuit, C4, 0.1uF (100nF) cap protects the input to the tracer, so if you apply it to say the anode of an IF valve, rather than the signal grid input of the audio valve, the K7000 is protected from harm. Likewise, C5 (also a 0.1uF cap) is on the output of the injector, so protects that part of the K7000 from harm. As I recall, both caps are rated at 400V. They're the red ones on the PCB next to the pots at the pic below. A point worth mentioning is that because both the injector and tracer amp are on the same compact PCB and aren't independently switched, you will get some 'breakthrough' on the amplifier from the injector, so when you hear that, it isn't faulty - it's just a limitation of the kit and doesn't detract from its usefulness. Precautions on live chassis radios has been mentioned. Remember not to connect the ground lead directly to the chassis of such radios, but via a 0.1 uF cap. As the K7000 is battery powered, connecting the ground wouldn't be as catastrophic as connecting the ground of an earthed piece of test gear such as a scope or signal generator, but even so... There's an excellent interactive article at this link on signal tracing in radios, which I've mentioned before: http://www.nostalgiaair.org/Referenc...ost/post01.htm If you click on this link and go to the circuit of a valve receiver, you'll see various points on the circuit marked with capital letters in brackets EG (A) etc. If you put your cursor over those points in turn, it will tell you what to expect in a working radfio, and what should be happening. For example, it explains that you should not hear any signals at points C, F, K & V - the Screen Grids. If you hover your cursor over point B and it will tell you that a signal should be heard there. It explains that he function of the "coupling condenser" is fundamentally that of keeping the plate voltage (at B) off the grid of the following tube (at D). Hope that helps a bit. Good luck in sorting the set John. Attached Thumbnails __________________ David. BVWS Member. G-QRP Club member 1339.

8th May 2019, 7:42 pm	#6
electronwilly Hexode Join Date: Jan 2011 Location: Westerhope, Newcastle Upon Tyne, Tyne and Wear, UK. Posts: 408	Re: Velleman K7000 The k7000 injector is a AC audio waveform with no harmonics so cant be coupled into the antenna, Billy.

9th May 2019, 1:11 am	#7
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Velleman K7000 So it is- a phase shift oscillator, no less. I wonder why? The usual suspect is a multivibrator which generates loads of harmonics up into the RF range. Easy enough to knock a separate one up, though. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

9th May 2019, 7:44 pm	#8
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Re: Velleman K7000 Hello to everyone. Thank you all for your helpful advice, and David for your extended and descriptive piece of information, as well as links to other sources. The output from the Vellerman K7000 is very clear, and extremely loud when volume is turned up. SWMBO is wondering could I not find some more relaxing form of entertainment. All the best. John.