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Old 26th Oct 2018, 8:39 pm   #1501
G4WYZ MikeyP
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Default Re: The "Sussex" Homebrew Valve Tester.

Some more photographs show the wiring.
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Old 29th Oct 2018, 9:12 pm   #1502
G4WYZ MikeyP
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Default Re: The "Sussex" Homebrew Valve Tester.

I've been asked by Martin "G8UWM-MildMartin" to add some notes to the 'Bill of Material', it's now at version 12.

The reason for the updating the ‘Bill of Material’ was the original design by the late Mike Rowe, there was update (see the last paragraph). Lets call the original Version One, there are two further design versions a Four and a Nine, these updates are thanks to Martin “Dekatron”.

The original consisted of three boards, Main, Daughter and Low Voltage Heater.

Version Four only one PCB board was used and two Power MOSFETs are used to supply voltage to the Anode and Screen grid switches. Also linear voltage regulators are used to obtain the low heater voltages.

Version Nine, a daughter board (LR8 board) is mounted on main PCB which removes the series Zener Diodes, ie ZD1...ZD7 arrangement and uses a high-voltage, low-output current adjustable linear regulator (U1). to control two Power MOSFETs (TR2 & TR4) for the Anode and Screen grid voltages.

The schematic diagram has TR2 & 4 as IRF830, but the BOM (Post #974) captured by “Herald1360” on a post #104 before it disappeared has them listed as BUZ80, theses are not available at Farnell but STP3NK80Z are. Which are rated at 800 volts at 2.5A, this explains why they run cool, requiring no heat sink.

Mike G4WYZ
29/10/2018

NB
The picture is competed Sussex.
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Old 5th Nov 2018, 4:50 pm   #1503
Chris55000
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi!

For those who want or need to test series–operated valves in TVs or universal radios, etc., the traditional method of catering for these on valve–testers has always been to use multitudes of selecor switches and transformer secondary taps, etc., etc., which, in the 40s/50s was the only reasonable way of dealing with these types of valve, but as other Members have pounted out, rapidly makes expanding the "Sussex" to deal with series–operated valves a no–go in the traditional methods!

Now that economical semiconductors/modules are available it's time fo look at this problem afresh!

If you consider these valves again, the maker always stated "SÓeries Supply" for the heaters in their data, so instead of having to try and guess myriads of heater–voltages that might range from 3.6V to over 60V (leaving out such gems as the 117L7/117N7 for now!), we provide a simple high–voltage current controlled supply, with a simple selector switch in the current regulator giving currents of 100, 150, 200 and 300mA, with a simple Asian High Voltage Boost Voltage Converter Module, feeding a floating 7805 connected in Constant–Current Mode, with four resistors to select the current output.

A fourth 0–200V meter can then be added across the heater terminals to monitor the valve's heater voltage, and this test is also suitable for testing for partial s/c's across CRT heaters!

Circuit Information and parts list to follow when I've bought the module and tested it!

Chris Williams
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Old 5th Nov 2018, 5:21 pm   #1504
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by G4WYZ MikeyP View Post
The early construction phase, this version incorporating an IEE mains socket.
Hi Mike, where did you get the housing/case from? Do you have a part number to hand?

Thanks.
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Old 5th Nov 2018, 6:31 pm   #1505
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi!

Further to my above post earlier today I have now chosen two inexpensive modules, currently about £10 total, that will (hopefully!) provide a simple economical series-heaters valve expansion for the Sussex Valve Tester suitable for 100mA, 150mA, 200mA, and 300mA valves.

Only one simple 12V isolated supply is needed, I'll provide exact details, drawings and specs when I've tested the circuit - the modules have to come from China!

(I know you've got "X" and 'L' series valves if you really do want to push the boat out but the number of times I've come across a 450mA or a 600mA valve in my lifetime is nil!)

Chris Williams
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Old 5th Nov 2018, 11:12 pm   #1506
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi!

The Sussex Construction & Operating Manual states "Ed Dinning can manufacture transformers with an additional 6V winding for a fourth meter on request" and I ordered mine with this in mind, but for any Mamber who only had a standard three–meter transformer made, then a 3W dc–dc isolated converter module rated for 9 or 12V dc output can be connected to the Sussex's positive LT supply for the control circuits or rectified (W01 bridge and 1000u 25V) from one of the low voltage heater supply windings to power a fourth meter – these converters are rated 1kV isolation so the meter module's supply requirements are correctly catered for!

Chris Williams
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Old 6th Nov 2018, 6:00 am   #1507
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi!

Just a quickie update to say if any Member finds the short bit of wire supplied with the connectors on the Sussex's specified LCD Meter Modules is too short to be of any use, you can find these in cheapie Far Eastern audio products or old VCRs, or, if you don't have any of these items, IS possible to purchase the connector contacts and housings separately or in small bags of kits from Far East/Chinese online vendors – they're called 'XH' series connectors, and you can buy them from 2–way to 8–way!

Chris Williams
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Old 7th Nov 2018, 4:07 pm   #1508
G4WYZ MikeyP
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by Sinewave View Post
Hi Mike, where did you get the housing/case from? Do you have a part number to hand?
Hello Sinewave.

I brought mine from Farnell and their part no is 722431

73's

Mike
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Old 7th Nov 2018, 6:29 pm   #1509
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Default Re: The "Sussex" Homebrew Valve Tester.

Hello Mike G4WYZ,

When you were suggesting an alternative MOSFET you wrote - 'Which are rated at 800 volts at 2.5A, this explains why they run cool, requiring no heat sink.'

They will only run cool if they are passing a small current or dropping a small voltage.
If you test an EF86 at 4mA at 250V they will run cool.

If someone tries to test a power valve at low voltage and high current, the MOSFET in the anode regulated supply will get hot. It will need a heatsink.
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Old 14th Nov 2018, 4:18 pm   #1510
G4WYZ MikeyP
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Default Re: The "Sussex" Homebrew Valve Tester.

Thank you for pointing this out, the only valves I've tested is small signal types and 7360's as I only built mine for that application.
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