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Old 12th Feb 2014, 10:24 pm   #1061
vidjoman
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Default Re: The "Sussex" Homebrew Valve Tester.

The ferrite beads are listed in the parts list and available from Rapid Electronics. Buy 100 and fit to every valve holder pin and most switch tags.
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Old 12th Feb 2014, 11:01 pm   #1062
crackle
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Default Re: The "Sussex" Homebrew Valve Tester.

Do you just thread the wire through once or twice, or more.
Just had a look and they don't seem to be mentioned in the parts list in the original manual.
Have you got the details of the ferrite beads which you can let me have.

Where the wiring to the valve sockets is concerned is it best to bunch them into a cable form or leave loose and separate them?

Thanks, Mike.
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Old 13th Feb 2014, 10:36 am   #1063
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Default Re: The "Sussex" Homebrew Valve Tester.

"Just had a look and they don't seem to be mentioned in the parts list in the original manual."

It's listed in the BOM in post #1. Item 99.

Last edited by vidjoman; 13th Feb 2014 at 10:36 am. Reason: added info
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Old 13th Feb 2014, 11:16 am   #1064
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Default Re: The "Sussex" Homebrew Valve Tester.

Thanks, but what size wire did you use, I will need 1.7mm hole at least.
Did you strip the last 6mm or so of insulation?

Last edited by crackle; 13th Feb 2014 at 11:35 am.
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Old 13th Feb 2014, 6:28 pm   #1065
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by crackle View Post
Could you also please confirm if the type of problems I have been experiencing with EL34 valves is caused by a lack of ferrite beads.
If so what beads should I use, where would I get them, and how are they fitted.
Mine has a couple of large (10mm dia) ferrite rings around the bunched wires to the valveholders. Mine came from surplus gear I was stripping.

I got a few beads and added them to the individual wires later, my beads came from some old SMPS I was saving for parts.....

The grid wire is screened cable, just ordinary microphone stuff.

Richard
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Old 13th Feb 2014, 9:39 pm   #1066
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Default Re: The "Sussex" Homebrew Valve Tester.

I have some ferrite rings somewhere I will fit them and get some beads from Farnell.

But I still think it would be useful to know if the 4.5 volts worth of sawtooth AC interference on the HT line is normal operation for this type of HT and current regulation circuit.
Please can anyone help and explain.

Thanks
Mike
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Old 13th Feb 2014, 11:49 pm   #1067
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Default Re: The "Sussex" Homebrew Valve Tester.

I assume the scope is in reasonable calibration. It shows the sawtooth at 10ms which is 100Hz and the sort of waveform you would get from a poorly smoothed full wave rectifier.
Can you try fitting a suitable resistor across the HT supplies i.e. no valve fitted, the resistor imitating the current drawn by a typical valve. Then check to see if you still have the sawtooth waveform? At least you should be able to ascertain whether it is power supply problem or something happening when a valve is in circuit under test.
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Old 14th Feb 2014, 12:13 am   #1068
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Top cap
In another photo in post nr. 1047, the scope is set to 5ms per div and it is the best part of 4 divisions between peaks, surely that is 20ms or 50Hz, I had not noticed it had changed.
That sounds like a good idea to test with resistors and eliminate the valve from causing the problems.

I have been experimenting with changing the settings of the grid volts and HT/screen supplies.
With the bias increased to about -19v the current reduces and the GM goes from 2 to 7.
A similar thing happens if I keep the bias at -13.5v and reduce the HT and screen to 175v, the gm rises from 2 to 7.5.
I realised today I did not have the earth connected to the ground and thought, ah, I hope that is the cause of the problem, but it has made no difference connecting it.

Mike
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Old 14th Feb 2014, 11:14 am   #1069
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi
I have performed various tests with just a resistor as a load and photographed the results.
Please note the scope setting as these may have been changed for different photos.

Photo --- scope probes--- Function sw--- load
Photo1 the resistors I used both about 6k ohms each
Photo2 --- anode-cathode, switch on test, 6k load,
Photo3 --- anode-cathode, switch on test, 3k load,
Photo4 --- anode-cathode, switch on leak1 or 2, 6k load,
Photo5 --- anode-cathode, switch on htr, 6k load,

continued in next post.
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Old 14th Feb 2014, 11:15 am   #1070
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Default Re: The "Sussex" Homebrew Valve Tester.

Photo6 --- anode-cathode, switch on leak1 or 2, no load,
Photo7 --- anode-cathode, switch on htr, no load,
Photo8 --- HT fuse-cathode , switch on htr, 6k & no load,
Photo9 --- HT fuse-cathode , switch on test, 6k load,
Photo10 --- HT fuse-cathode , switch on test, no load,

I hope this will help in the analysis of the problem that is causing the spurious readings with EL34 valves.
I do appreciate any suggestions to help me resolve this. I am happy to carry out any specified tests and measurement.

Thanks
Mike
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Last edited by crackle; 14th Feb 2014 at 11:22 am.
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Old 14th Feb 2014, 1:56 pm   #1071
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Default Re: The "Sussex" Homebrew Valve Tester.

Sorry forgot to mention Scope Probe is x 10.
Mike
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Old 14th Feb 2014, 6:47 pm   #1072
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Default Re: The "Sussex" Homebrew Valve Tester.

Mike, I cannot help thinking that the problems exist in the power supplies somehow.
It may be worth carefully checking over the wiring of all supplies and making sure the pre-regulator has sufficient headroom on its input. If this supply is not right it will affect the Anode and Screen test voltages. Also check that all 0V Ground connections are all linked up, the presence of a 50Hz waveform is strange and seems to suggest a missing ground somewhere.
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Old 14th Feb 2014, 11:21 pm   #1073
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Mike, note that if you do not have sufficient PSU headroom it is possible to adjust the mains tappings in 10v increments to closely match the actual mains voltage at your location.

Ed
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Old 14th Feb 2014, 11:30 pm   #1074
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Default Re: The "Sussex" Homebrew Valve Tester.

I have 345 volts at the fuse.
I checked the HT diodes and they tested OK but I changed them anyway.
The Grid supply diodes also checked OK.
I have been all over the wiring and can find no errors.
I am really in need of some test by test guidance on how to resolve this.
Thanks
mike

Last edited by crackle; 14th Feb 2014 at 11:40 pm.
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Old 15th Feb 2014, 4:16 am   #1075
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Default Re: The "Sussex" Homebrew Valve Tester.

Mike, just for interest, what Mosfets are you using, are they BUZ80's?
I ask because I had some problems with this type which were cured when I fitted IFR830's.
Your problem is probably not related but I am curious
Les
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Old 15th Feb 2014, 7:49 am   #1076
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Les
The mosfets I used are BUZ80A's, the control seems to be good with the voltage very close to the the planned voltage steps. It also seems quite good under load of 45 mA the 250 volt setting is 245v.
There are some IFR830B mosfets on ebay, Pk of 2 1.20, one of them is actually sold as Fairchild, would you recommend going for the named one, they are a good bit more expensive. 2.5 each.

I wonder if the fact that I have twisted pairs of wires together, e.g. the wires to the current limit switch, I did this just to help identify them and keep together, could this cause any issues with capacitance etc, is there any particular wires which would be best NOT to twist together.

thanks
Mike
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Old 15th Feb 2014, 8:27 am   #1077
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi gents, a further thought on checking regulation.
Connect a power resistor across the anode supply to draw say 40mA. Note voltage regulation.
Connect a resistor to draw the same current across the diode bridge and note regulation, then repeat this across the transformer winding, noting regulation figures. The regulation across the anode supply should be better (less volts) than the other two if the reg is working correctly, provided the voltage does not drop too far at the rectifier/winding, this is a test for headroom.
You could also repeat at a current of about 50mA for a period of a minute of so and look for droop. This could be due to a poor soldered joint. Switch off, discharge all caps and check joints for temp.

Ed
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Old 15th Feb 2014, 6:00 pm   #1078
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Guys
I have done some load tests as Ed sugested, results are below.

With load connected on anode and voltage readings taken from anode and HT fuse (pre-regulation)
-----------no load-----42mA----82mA
Anode---- 251---------250------249
Fuse------363---------346------336

With load moved onto HT fuse and then later onto TX output voltage readings taken at same point as load.
-----------no load----42mA----82mA
HT fuse--- 358------- 340------328
TX op----- 260------- 257------254

Note;
Although my mains voltage is 230v the mains is connected to the TX 250v tap. There seemed plenty of volts on the OP windings, all were a little high, so I felt it best to use the 250v tap rather than the 230v tap.
e.g. even set like this the 6.3v heater winding gives 7.06v open circuit, 6.99v with a EL84 (.76A), and 6.9v with a EL34 (1.5A)

Thanks
Mike

Last edited by crackle; 15th Feb 2014 at 6:07 pm.
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Old 15th Feb 2014, 6:12 pm   #1079
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Default Re: The "Sussex" Homebrew Valve Tester.

Looking at your 'scope images, I'm reminded of some similarity between those and my Sussex when I was having similar problems with EL34 valves.

The symptoms are similar, the gm reading is always low and variable, the Anode current tends to vary a lot but is always much lower than it should be. In fact, the anode supply voltage will be seen to vary by a hundred volts or so in a cyclic manner. In my experience this was caused by spurious oscillation in the EL34 valve, cured by soldering a 150k resistor to pin 5 of the octal valveholder and connecting the grid wire to that.

I suggested, a few posts ago, that you might try putting your hand around an EL34 under test and see what, if any, difference the hand makes to the readings on the Ia and gm meters. I might have missed the answer, but that was, for me, the clue to the final solution of this very perplexing problem! Caution, though, because if the valve heater has been switched on for a while, the valve will be uncomfortably hot to touch.
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Old 16th Feb 2014, 4:28 pm   #1080
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Default Re: The "Sussex" Homebrew Valve Tester.

I have read through this thread a couple of times and am now getting the parts together to build a version of the 'Sussex VT1'.

With reference to post #647 by Dekatron, I have knocked up a PDF Chart which relates to the Red, White, Green sections of the original Valve Tester meter.

The columns represent the upper and or lower values of each section.

To use:

Look down the middle column of the Green section (100%) to find the relevant mA/V figure for the valve under test, then scan across that line to find where the mA/V reading from the valve tester falls, Bad, Fair or Good.
Job done.

I hope this may be useful,

Andy
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