I need some help on testing EL156 on AVO mk3. - UK Vintage Radio Repair and Restoration Discussion Forum

Jutonav · 7th Nov 2025, 9:20 am

Hi! First time poster here and I want to start of by thanking everyone here that posted a lot of helpful information as I've learned to use my AVO mk3!

I have some Telefunken EL156 tubes that I've been itching to test and I've done a lot of research on what settings to use. My plan is to to use 200/200V on anode and screen with -14V (maybe start with a higher negative voltage to be safe?). And expect a 60+Ia and around 8-10gm.

My main question is will this be safe for my AVO tester? As I understand it these tubes are high current and can be punishing for the tester to run.

Thanks in advance!

Stefan

vintage port · 7th Nov 2025, 11:49 am

Out and about so no data on el156 to hand but 200V and Ia of 60 isn't going to stress any tester in halfway functional condition, it's below a kt66! The AVO range goes up to 100mA and my Mk4 seems perfectly happy at that dissipation.

I do have the opinion that the higher Ia ranges are less congruent with results from static testing, but that's a different thing!

Richardgr · 7th Nov 2025, 12:06 pm

This operating point looks like it is testable:
https://frank.pocnet.net/other/docs/MK-RT.pdf

There is data for an EL150 in the AVO test data manual, that looks similar though I did not check the pinouts.

Jutonav · 7th Nov 2025, 9:28 pm

So starting with 200/200V and then go up in steps to get a reading closer to say 80-90mA Ia would be a smart way to go yea?

Also thanks for the input!

6AL5W-Martin · 8th Nov 2025, 12:45 pm

hello Richard,

please do not compare the small EL150 to a EL156.
EL150 is a better EL12, common radio tube. EL156 is a big one,
EL151 is again bigger then a EL156

EL156:

connect f to 6,3V~
set Fuse 200mA and connect Anode to +400V
set Fuse 100mA and connect the shield gate to +350V
cathode ground.

connect G1 to -16V and test anode current of 120mA to be 100%
connect G1 to -20V and test anode current of 75mA to be 100%

EL156 is tired to be replaced when the current is smaller then 60% of that.

greetings
Martin

CambridgeWorks · 8th Nov 2025, 4:00 pm

That is very useful test information Martin.
I have a few of these valves NOS and often wondered how to test them as I only have a CT160 and an old twin panel tester.

Unfortunately I can only achieve up to 500V at 100mA as I have two Solartron Vari-Pack psu model SRS153S that I can use and that is the maximum rating for each one.
However, one may be able to supply 120mA briefly for Ia?
I suppose I could also cut an octal base up to provide connections as I don't see the point of buying new bases just to test these valves.

This might be a job for winter time once I clear up the mess of part-full boxes all over the place that I have been sorting for transformers and chokes to offer on the forum!

Thanks, Rob

vintage port · 8th Nov 2025, 7:42 pm

Quote:

Originally Posted by Jutonav

So starting with 200/200V and then go up in steps to get a reading closer to say 80-90mA Ia would be a smart way to go yea?

Also thanks for the input!

Hi Jutonay. I'd say, looking at the datasheet that you have two options. One is to test in triode mode, so anode to say 250V, datasheet says Vg-12V gives about 87mA, you'd have to measure gm off the chart yourself. Second would be pentode with anode 300V, screen the same, Vg -16V, Ia looks around 63mA. No real need to wind the valve up further, these are achievable, you can tell if the valve meets spec, and won't stress anything.

Joe_Lorenz · 8th Nov 2025, 8:01 pm

Hello Jutonav,

please can you let us know why you desire to test them on the AVO? In what kind of application are they intended to be run? I've got a pair of EL156s in a Telefunken ELA V311/2 amplifier, and my way to test them has been in comparing cathode currents in situ. That will do for me.

Regards, Joe

vintage port · 9th Nov 2025, 5:02 pm

My guess is that he might not have the PSUs to deal with the kind of voltages and currents needed to goose up the valve near its limits? 500V, 150+mA supplies, with another supply for the screen and a third for the grid are not a regular feature on many peoples benches any more.

Richardgr · 10th Nov 2025, 8:00 am

This weekend I was helping a friend with the testing of an E130L. 100%, according to the datasheet, was 100mA at 250V anode and 150V screen, with grid at -15.5V. We recorded about 54mA at that exact operating point, but the curve is so steep for this tube that at -14.5V it was spot on. I could not trace the curves for the valve because my uTracer is only good for 150mA, but we did confirm the readings on an AVO mk4.

My point is that it is very inconclusive to test these high performance valves. What with tolerances, storage (getter not activated), testing requirements, and then the fact that most of the circuits they were designed for were tolerant to manufacturing differences, about the only thing you can conclusively test for is a serious loss of emission (and maybe heater cathode insulation or shorts).

Like Joe Lorenz says, in situ is the only effective solution.

Jutonav · 10th Nov 2025, 5:29 pm

Quote:

Originally Posted by Joe_Lorenz

Hello Jutonav,

please can you let us know why you desire to test them on the AVO? In what kind of application are they intended to be run? I've got a pair of EL156s in a Telefunken ELA V311/2 amplifier, and my way to test them has been in comparing cathode currents in situ. That will do for me.

Regards, Joe

I got seven of them and nothing to use them on besides testing them, thats pretty much it. I left them in the closet as I tried to learn more before doing something stupid.

I suspected that as Richardgr says it wont relly say to much about the tubes performance but It would be nice to atleast make sure they are somewhat ok before hoocking them upp propper system.

vintage port · 10th Nov 2025, 9:16 pm

Quote:

Originally Posted by Richardgr

This weekend I was helping a friend with the testing of an E130L. 100%, according to the datasheet, was 100mA at 250V anode and 150V screen, with grid at -15.5V. We recorded about 54mA at that exact operating point, but the curve is so steep for this tube that at -14.5V it was spot on. I could not trace the curves for the valve because my uTracer is only good for 150mA, but we did confirm the readings on an AVO mk4.
Like Joe Lorenz says, in situ is the only effective solution.

Yes, this is absolutely true for high gM valves where the difference between eg. 20 and 35 is within manufacturing tolerances and so taken into account by designers. But, in audio where I play, and I believe the EL156 is aimed, most popular valves are medium or even low gM and a tester has function here, even accepting the old Tektronix quip that if the valve is working in circuit it meets spec. Apropos of this, to my eye EL156 is medium gM when trioded, 11.6, albeit high powered?

Also, manufacturers specs are a good litmus for value if selling so, half a dozen new el156 that meet spec can be expected to achieve some frothy bidding on the famous 'bay.

Joe_Lorenz · 11th Nov 2025, 8:36 pm

I can say "I've had it for ages" when it comes to that Telefunken p-p amp with EL156s. It is nicely made and a real boat anchor at 20+ kgs, but I admit it has almost no practical use. Ua is 800V, so dust removal and checking electrolytics is a must before firing it up. It is a must that all base contacts are clean and free of oxide, as well as speaker connections (rated 100W) must be fine. So there is a lot that can possibly go wrong and destroy these valves. As I do not have many spares I have decided that it is a device which is better for display only. Yes, the EL156 ist beautiful, and good luck selling some, but ...

7th Nov 2025, 9:20 am	#1
Jutonav Diode Join Date: Nov 2025 Location: Sweden, Gothenburg Posts: 3	I need some help on testing EL156 on AVO mk3. Hi! First time poster here and I want to start of by thanking everyone here that posted a lot of helpful information as I've learned to use my AVO mk3! I have some Telefunken EL156 tubes that I've been itching to test and I've done a lot of research on what settings to use. My plan is to to use 200/200V on anode and screen with -14V (maybe start with a higher negative voltage to be safe?). And expect a 60+Ia and around 8-10gm. My main question is will this be safe for my AVO tester? As I understand it these tubes are high current and can be punishing for the tester to run. Thanks in advance! Stefan

7th Nov 2025, 11:49 am	#2
vintage port Tetrode Join Date: Dec 2010 Location: West London, UK. Posts: 58	Re: I need some help on testing EL156 on AVO mk3. Out and about so no data on el156 to hand but 200V and Ia of 60 isn't going to stress any tester in halfway functional condition, it's below a kt66! The AVO range goes up to 100mA and my Mk4 seems perfectly happy at that dissipation. I do have the opinion that the higher Ia ranges are less congruent with results from static testing, but that's a different thing!

7th Nov 2025, 12:06 pm	#3
Richardgr Octode Join Date: Oct 2019 Location: Täby, Sweden Posts: 1,110	Re: I need some help on testing EL156 on AVO mk3. This operating point looks like it is testable: https://frank.pocnet.net/other/docs/MK-RT.pdf There is data for an EL150 in the AVO test data manual, that looks similar though I did not check the pinouts. Attached Thumbnails

7th Nov 2025, 9:28 pm	#4
Jutonav Diode Join Date: Nov 2025 Location: Sweden, Gothenburg Posts: 3	Re: I need some help on testing EL156 on AVO mk3. So starting with 200/200V and then go up in steps to get a reading closer to say 80-90mA Ia would be a smart way to go yea? Also thanks for the input!

8th Nov 2025, 12:45 pm	#5
6AL5W-Martin Hexode Join Date: Nov 2006 Location: Biedenkopf, [Hessen], Germany. Posts: 497	Re: I need some help on testing EL156 on AVO mk3. hello Richard, please do not compare the small EL150 to a EL156. EL150 is a better EL12, common radio tube. EL156 is a big one, EL151 is again bigger then a EL156 EL156: connect f to 6,3V~ set Fuse 200mA and connect Anode to +400V set Fuse 100mA and connect the shield gate to +350V cathode ground. connect G1 to -16V and test anode current of 120mA to be 100% connect G1 to -20V and test anode current of 75mA to be 100% EL156 is tired to be replaced when the current is smaller then 60% of that. greetings Martin __________________ www.wellenkino.de Vintage Scope restorations

8th Nov 2025, 4:00 pm	#6
CambridgeWorks Dekatron Join Date: Jun 2010 Location: Spalding, Peterborough, Cambridgeshire, UK. Posts: 3,721	Re: I need some help on testing EL156 on AVO mk3. That is very useful test information Martin. I have a few of these valves NOS and often wondered how to test them as I only have a CT160 and an old twin panel tester. Unfortunately I can only achieve up to 500V at 100mA as I have two Solartron Vari-Pack psu model SRS153S that I can use and that is the maximum rating for each one. However, one may be able to supply 120mA briefly for Ia? I suppose I could also cut an octal base up to provide connections as I don't see the point of buying new bases just to test these valves. This might be a job for winter time once I clear up the mess of part-full boxes all over the place that I have been sorting for transformers and chokes to offer on the forum! Thanks, Rob __________________ Sorting my very large amount TTL & LINEAR ICs. Message any wants, you might be surprised!

8th Nov 2025, 8:01 pm	#8
Joe_Lorenz Heptode Join Date: Dec 2019 Location: Hohenroda, Eastern Hesse, Germany Posts: 721	Re: I need some help on testing EL156 on AVO mk3. Hello Jutonav, please can you let us know why you desire to test them on the AVO? In what kind of application are they intended to be run? I've got a pair of EL156s in a Telefunken ELA V311/2 amplifier, and my way to test them has been in comparing cathode currents in situ. That will do for me. Regards, Joe

9th Nov 2025, 5:02 pm	#9
vintage port Tetrode Join Date: Dec 2010 Location: West London, UK. Posts: 58	Re: I need some help on testing EL156 on AVO mk3. My guess is that he might not have the PSUs to deal with the kind of voltages and currents needed to goose up the valve near its limits? 500V, 150+mA supplies, with another supply for the screen and a third for the grid are not a regular feature on many peoples benches any more.

10th Nov 2025, 8:00 am	#10
Richardgr Octode Join Date: Oct 2019 Location: Täby, Sweden Posts: 1,110	Re: I need some help on testing EL156 on AVO mk3. This weekend I was helping a friend with the testing of an E130L. 100%, according to the datasheet, was 100mA at 250V anode and 150V screen, with grid at -15.5V. We recorded about 54mA at that exact operating point, but the curve is so steep for this tube that at -14.5V it was spot on. I could not trace the curves for the valve because my uTracer is only good for 150mA, but we did confirm the readings on an AVO mk4. My point is that it is very inconclusive to test these high performance valves. What with tolerances, storage (getter not activated), testing requirements, and then the fact that most of the circuits they were designed for were tolerant to manufacturing differences, about the only thing you can conclusively test for is a serious loss of emission (and maybe heater cathode insulation or shorts). Like Joe Lorenz says, in situ is the only effective solution.

11th Nov 2025, 8:36 pm	#13
Joe_Lorenz Heptode Join Date: Dec 2019 Location: Hohenroda, Eastern Hesse, Germany Posts: 721	Re: I need some help on testing EL156 on AVO mk3. I can say "I've had it for ages" when it comes to that Telefunken p-p amp with EL156s. It is nicely made and a real boat anchor at 20+ kgs, but I admit it has almost no practical use. Ua is 800V, so dust removal and checking electrolytics is a must before firing it up. It is a must that all base contacts are clean and free of oxide, as well as speaker connections (rated 100W) must be fine. So there is a lot that can possibly go wrong and destroy these valves. As I do not have many spares I have decided that it is a device which is better for display only. Yes, the EL156 ist beautiful, and good luck selling some, but ...