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Old 28th Mar 2021, 11:12 am   #1621
Steve Gibson
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi there

The other 2 valves are NOS (as are the Russian valves).

Yes I have ferrite breads on the connectors, and the valves don't seem to be overheating, just that the specs are no where near the datasheet and the Russian varices show leak 2 on the way down from test, but not on the way up to test.

Want to check that this isn't a issue with the tester and that I have set the switches right for the valve.

Regards

Steve
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Old 29th Mar 2021, 6:32 am   #1622
Diabolical Artificer
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Default Re: The "Sussex" Homebrew Valve Tester.

Looking at the EL84 curves with Va & Vg2 @ 250v & Vg1 @ -7v you should have about 55mA emission, see attached. Better to set it to Vg1 -8v .... Ia = 40mA. As long as the result is in that ballpark your valve is ok. Re your leakage question,not sure how this leakage tester works in this tester, but it's possible if a valve is still warm that there will still be a few electrons floating about and you might be reading that charge.

Andy.
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Old 29th Mar 2021, 10:15 am   #1623
Steve Gibson
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by Diabolical Artificer View Post
Looking at the EL84 curves with Va & Vg2 @ 250v & Vg1 @ -7v you should have about 55mA emission, see attached. Better to set it to Vg1 -8v .... Ia = 40mA. As long as the result is in that ballpark your valve is ok. Re your leakage question,not sure how this leakage tester works in this tester, but it's possible if a valve is still warm that there will still be a few electrons floating about and you might be reading that charge.

Andy.
Yeah that's what I thought, but the valves I have are at 20mA and 30mA and both seem to work ok in the amplifier, so until I get a known good tube I am uncertain if the results are down to bad tubes, problems with the tester or optimistic specifications.
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Old 29th Mar 2021, 12:16 pm   #1624
Joe_Schober
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Default Re: The "Sussex" Homebrew Valve Tester.

Alternative Transformer and Heater Supplies

Hi, I'm also on the way to build this Valve Tester.
Since it's hard to find a transformer, I want to take several standard transformers and DC/DC converters for the heater supply.
See attached drawing.

Does anyone think that causes problems?

Second question: For the selector switches I want to take from "LORLIN"
https://www.reichelt.de/stufen-drehs...ct=pos_1&nbc=1
I'm not sure if they are durable!?

Best Regards from Germany, Joe
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Old 29th Mar 2021, 3:28 pm   #1625
chriswood1900
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Default Re: The "Sussex" Homebrew Valve Tester.

Joe
The original design was based on using several transformers so as long as each transformer has a sufficient rating that should be fine.
As regard the Lorlin switches they would be quite close to their rating on some combination of valves, however, if you HT does not exceed the 300V max and you don't switch them while the circuits are powered my view is they also should be OK. The heater circuit is likely to be the one which is closest to the max limit.
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Old 29th Mar 2021, 3:59 pm   #1626
vidjoman
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Default Re: The "Sussex" Homebrew Valve Tester.

When I built my 'Sussex' I used a separate 12 volt transformer supply to power 12 volt automotive relays with contacts rated at 10 amps to switch the heater volts so the heater switch only has to switch the relay current.
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Old 29th Mar 2021, 11:04 pm   #1627
Steve Gibson
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by Joe_Schober View Post
Alternative Transformer and Heater Supplies

Hi, I'm also on the way to build this Valve Tester.
Since it's hard to find a transformer, I want to take several standard transformers and DC/DC converters for the heater supply.
See attached drawing.

Does anyone think that causes problems?

Second question: For the selector switches I want to take from "LORLIN"
https://www.reichelt.de/stufen-drehs...ct=pos_1&nbc=1
I'm not sure if they are durable!?

Best Regards from Germany, Joe

I just purchased the transformer made for this project from Ed (see earlier in the Post). It reduced the space and wiring requirement and works very well.

For the switches, I would compare the part number on the BOM from Rapid Online, and the check the data sheets to get the correct match
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Old 30th Mar 2021, 9:18 am   #1628
Joe_Schober
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Default Re: The "Sussex" Homebrew Valve Tester.

@Chris,
Didn't know about the original design. So transformers should work.
For the DC/DC converters I will have a look for modules with higher current output.

@vidjoman
Relays which can switch 300 VDC are not common and therefore expensive.

@Steve
If I compare the "Taiwan Alpha" from the original BOM with the "Lorlin", they are looking quite equal.
Since I don't plan to switch while in operation, I will give it a try.


Cheers, Joe
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Old 30th Mar 2021, 10:21 am   #1629
vidjoman
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Default Re: The "Sussex" Homebrew Valve Tester.

I didn’t say anything about switching 300 volts, just the heaters that require a higher current than the Lorlin switch ratings.
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Old 30th Mar 2021, 10:58 am   #1630
Joe_Schober
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by vidjoman View Post
I didn’t say anything about switching 300 volts, just the heaters that require a higher current than the Lorlin switch ratings.
Ups, my fault. Mixed question and answer here.

Anyhow, the manual say that you should first set heater, plate, screen voltage
and THEN plug the tube into its base.

If I understand everything right, then you will never have to operate the switches while under power (current)!?

-Joe
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Old 30th Mar 2021, 12:44 pm   #1631
KeithsTV
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Default Re: The "Sussex" Homebrew Valve Tester.

Many years ago I had a problem with relays switching high voltages, up to 600v. The relays that we were using were only rated at 150v but on contacting the manufacturers I was told that provided the connection was made before any voltage was applied and the voltage was removed before the connection was disconnected there was no problem with using the specified relays. In the application, automatic test equipment, it was possible to set up all the relays before any voltage was applied and remove the voltage before the the relay connections were broken. Actually switching a high voltage, especially dc, the relay contacts will not last long.

Keith
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Old 31st Mar 2021, 6:54 am   #1632
Diabolical Artificer
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by Steve Gibson View Post
Yeah that's what I thought, but the valves I have are at 20mA and 30mA and both seem to work ok in the amplifier, so until I get a known good tube I am uncertain if the results are down to bad tubes, problems with the tester or optimistic specifications.
The valve's will work ok, they just won't deliver full power. Buy a new EL84 from RS and check your tester, that or find a big 5k resistor (15w or 10w at a pinch and be quick) and bodge it in place of the valve, that's the only way you will know what the craic is.

Andy.
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Last edited by Station X; 31st Mar 2021 at 8:27 am. Reason: Quote attributed.
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Old 30th Sep 2021, 11:19 pm   #1633
Richardgr
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Default Re: The "Sussex" Homebrew Valve Tester.

Is it possible to use too many ferrite beads on the valve bases?

I have a small bead on every pin, and each pin number is a seperate loop. (NB I am using mini-banana plugs and not switches to configure the tube for testing).

Sometimes the tester works fine, but sometimes it gives odd results with a tube that had tested fine in the past. It seems to be the small signal tubes that are affected the most.
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Old 1st Oct 2021, 8:13 am   #1634
Electronpusher0
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Default Re: The "Sussex" Homebrew Valve Tester.

I have used a bead on every valve pin like you and never had any problems. I have used this system on an AVO 2 panel, a curve tracer and the sussex.

Peter
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Old 1st Oct 2021, 9:00 am   #1635
vidjoman
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Default Re: The "Sussex" Homebrew Valve Tester.

I also put a ferrite bead on every valve pin and also every switch pin. Never had a problem with any oscillation.
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Old 6th Oct 2021, 11:47 am   #1636
vidjoman
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Default Re: The "Sussex" Homebrew Valve Tester.

The only problem that I had when I started to use it was that sometimes the oscillator failed to start but a minor tweek of the preset cured that.
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Old 11th Nov 2021, 11:15 pm   #1637
unitelex
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Default Re: The "Sussex" Homebrew Valve Tester.

See post 1503 by Chris55000.

I have also been considering how best to incorporate provision for series heater valve variants, 100mA, 300mA etc

The existing design currently brings the heater connections out to allow an external supply to be connected, this is fine but not always convenient when travelling onsite for example.

I have put together this circuit which covers both regulated current settings for series heaters but also DC regulated voltage as an option for those preferring DC fed heaters, or if like me you don't have the multiple tappings on your transformer - this could be an option.

Notes:
The simulation is using regular LT317A as I don't have the higher voltage 317HVT model yet. So bear in mind if you run the simulation to use heater loads below 30V

The voltage regulator output is intentionally connected to the switch wiper A, this keeps the range switching simple, avoiding the need for a double pole switch etc. The side effect of this puts 1.25V on the output when none of the ranges are selected, but I believe this is OK as RL2 disconnects the heater until invoking Test mode anyway, by which time the operator should have selected an appropriate heater setting.

These regulators are dissipating a fair amount particularly in the 300mA setting with low voltage heaters such as PCC84, PC95 etc so physical implementation would require a substantial heat sink and good thermal pad/paste.

It is best not to change the heater select switch while in test mode so as to minimise arcing at the selector switch contacts. This is where the AC scheme does better as the arc is quenched every half cycle of the waveform.

I would be interested in form members comments on this circuit idea.

Best Regards
Chris
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Old 12th Nov 2021, 1:15 pm   #1638
unitelex
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Default Re: The "Sussex" Homebrew Valve Tester.

Re my last post,
The current regulator is working with correct currents initially however the current is falling by 10% as the heater warms up and the voltage across the heater rises. It seems 10% of the current is passing back through the voltage regulator so my idea to connect the VR to the switch moving contact is not going to work out.

The voltage regulator is only working on 4V, 5V and 6.3V, basically I am varying the wrong resistor in the output divider, it only works with values around 200 Ohms or thereabouts for the upper resistor.
So looks like I will need to go back to the conventional setup for the VR and add another switch or relay.

Chris
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Old 12th Nov 2021, 3:39 pm   #1639
G8UWM-MildMartin
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Default Re: The "Sussex" Homebrew Valve Tester.

Is it possible that one of the modules that comes up on a Google search for "DC Buck Boost Converter CC CV 0.5-30V 4A Power Module Adjustable" would be any use?
They have a display showing current and voltage and an adjustment knob.
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Old 12th Nov 2021, 7:44 pm   #1640
unitelex
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by G8UWM-MildMartin View Post
Is it possible that one of the modules that comes up on a Google search for "DC Buck Boost Converter CC CV 0.5-30V 4A Power Module Adjustable" would be any use?
They have a display showing current and voltage and an adjustment knob.
Yes that would probably work for many valve types and being switch-mode would not be expected to have thermal dissipation concerns. We do need 45V requirement on some series heater valves such as UL84 etc.

Best Regards
Chris
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