Testing EL34 valves - UK Vintage Radio Repair and Restoration Discussion Forum

crackle · 18th Feb 2014, 9:39 am

Hi
I am having problems testing EL34 valves on a valve tester I have built and wondered if these valves behave strangely on any of the commercial valve testers.
The problem is the tester does not return the expected value for the GM reading.

My other hope was to bring to the attention of others the problem that myself and others are having (going by the PM's I have received) with the Sussex valve tester. I wondered if that maybe the Thread in the "Homebrew" section was being over looked by someone with the experience to help resolve the issue.
If you feel you can help please see;
https://www.vintage-radio.net/forum/...=48853&page=53

Thanks
Mike

Jac · 18th Feb 2014, 8:33 pm

Mike,

I have tested a lot of EL34s on my AVO VCM163, and that went without any difficulties.
The result on the GM reading might be a bit dependent on the make.
Most of the valves I tested are Philips (/Mullard) and those always behave close to the published/specified values.

Jac

G6Tanuki · 18th Feb 2014, 9:06 pm

I've never had problems testing EL34s.

My only real interest is "do they still have adequate cathode-emission: what's the maximum current at zero grid-bias?".

[my usage of EL34s and such is in the likes of 'communications-quality' AM transmitter-modulators and public-address amplifiers where we focus much more on maximum-power-output and ICAS-ratings rather than audio-quality]

crackle · 19th Feb 2014, 11:45 am

When tested they went over 100mA but I have never taken the bias down as far as zero.

mark-jacobs · 22nd Feb 2014, 1:43 am

Tested a Philips NOS EL34 on a uTracer Curve Tracer using AVO specs at 250V on Anode and screen, grid -13.5. Spec is Ia=75mA Gm = 11 mA/V. Test results were Ia=94.09mA and Gm=12.04 mA/V, this was similar to others. The grid sweeps shown at anode volts of 200, 250 and 300 match the published Mullard specs. The uTracer max current is 200 mA and 300V, but even the published specs max out at an Ia of 300 mA. My AVO's give very close readings to my uTracer, but without the resolution and are a bit more finicky. At the indicated settings, you should see close to the AVO specs.

If your problem seems to be specific to the EL34 tubes, then as others mentioned it could be an issue with oscillation. I have wired my uTracer similar to the AVO testers which use a continuous wire loop from the switch selector to all the sockets and each pin connection at every socket has a ferrite bead as indicated. This is similar to the Amplitrex and Hickok 580 testers. Wire lead length needs to be kept to a minimum, and I recall lengths should be all more or less the same length between sockets. Many laboratory grade tube testers use plug in socket modules which minimize the lead length.
Mark

18th Feb 2014, 9:39 am	#1
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Testing EL34 valves Hi I am having problems testing EL34 valves on a valve tester I have built and wondered if these valves behave strangely on any of the commercial valve testers. The problem is the tester does not return the expected value for the GM reading. My other hope was to bring to the attention of others the problem that myself and others are having (going by the PM's I have received) with the Sussex valve tester. I wondered if that maybe the Thread in the "Homebrew" section was being over looked by someone with the experience to help resolve the issue. If you feel you can help please see; https://www.vintage-radio.net/forum/...=48853&page=53 Thanks Mike

18th Feb 2014, 8:33 pm	#2
Jac Heptode Join Date: Jun 2006 Location: Eindhoven, Netherlands. Posts: 642	Re: Testing EL34 valves Mike, I have tested a lot of EL34s on my AVO VCM163, and that went without any difficulties. The result on the GM reading might be a bit dependent on the make. Most of the valves I tested are Philips (/Mullard) and those always behave close to the published/specified values. Jac

18th Feb 2014, 9:06 pm	#3
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Testing EL34 valves I've never had problems testing EL34s. My only real interest is "do they still have adequate cathode-emission: what's the maximum current at zero grid-bias?". [my usage of EL34s and such is in the likes of 'communications-quality' AM transmitter-modulators and public-address amplifiers where we focus much more on maximum-power-output and ICAS-ratings rather than audio-quality]

19th Feb 2014, 11:45 am	#4
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Testing EL34 valves When tested they went over 100mA but I have never taken the bias down as far as zero.

22nd Feb 2014, 1:43 am	#5
mark-jacobs Triode Join Date: Dec 2009 Location: Tucson, Arizona, USA. Posts: 44	Re: Testing EL34 valves Tested a Philips NOS EL34 on a uTracer Curve Tracer using AVO specs at 250V on Anode and screen, grid -13.5. Spec is Ia=75mA Gm = 11 mA/V. Test results were Ia=94.09mA and Gm=12.04 mA/V, this was similar to others. The grid sweeps shown at anode volts of 200, 250 and 300 match the published Mullard specs. The uTracer max current is 200 mA and 300V, but even the published specs max out at an Ia of 300 mA. My AVO's give very close readings to my uTracer, but without the resolution and are a bit more finicky. At the indicated settings, you should see close to the AVO specs. If your problem seems to be specific to the EL34 tubes, then as others mentioned it could be an issue with oscillation. I have wired my uTracer similar to the AVO testers which use a continuous wire loop from the switch selector to all the sockets and each pin connection at every socket has a ferrite bead as indicated. This is similar to the Amplitrex and Hickok 580 testers. Wire lead length needs to be kept to a minimum, and I recall lengths should be all more or less the same length between sockets. Many laboratory grade tube testers use plug in socket modules which minimize the lead length. Mark Attached Thumbnails Last edited by mark-jacobs; 22nd Feb 2014 at 1:55 am.