The "Sussex" Homebrew Valve Tester.

[Steve Gibson]

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

[Diabolical Artificer]

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.

[Steve Gibson]

Originally Posted by Diabolical Artificer

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.

[Joe_Schober]

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

[chriswood1900]

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.

[vidjoman]

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.

[Steve Gibson]

Originally Posted by Joe_Schober

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

[Joe_Schober]

@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

[vidjoman]

I didn’t say anything about switching 300 volts, just the heaters that require a higher current than the Lorlin switch ratings.

[Joe_Schober]

Originally Posted by vidjoman

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

[KeithsTV]

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

[Diabolical Artificer]

Originally Posted by Steve Gibson

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.

[Richardgr]

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.

[Electronpusher0]

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

[vidjoman]

I also put a ferrite bead on every valve pin and also every switch pin. Never had a problem with any oscillation.

[vidjoman]

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.

[unitelex]

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

[unitelex]

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

[G8UWM-MildMartin]

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.

[unitelex]

Originally Posted by G8UWM-MildMartin

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