Are your output valves matched for your amp?
Just because a set of valves says “matched” doesn’t mean it’s matched for your amp. Most valve suppliers put a sticker on the valve showing the anode current and the Gm.
But what were the test conditions?
So you might think they must be matched. Not necessarily the case. In the UK, a number of suppliers use and maintain venerable testers such as the AVO Mk4 that are limited to a maximum test voltage of 400 volts. This is fine for EL84s, but what about bigger valves that run at much higher voltages in amps?
If we take the example of the popular EL34, as used in Marshalls, Blackstar etc., the operating conditions can be 480 volts on the anode. The AVO test manual recommends testing at 250 volts, and the unit runs them at 75% power.
But to recreate the conditions they’ll experience in your amp, they need to be tested at 480-500 volts. Otherwise, there’s no guarantee they’ll still be matched in the real operating conditions in your amp. And if you’re pushing your valves hard, that 75% power may not be relevant either.
This is why every test certificate from VTGA for matched power output valves shows the test conditions. Because without that information, whatever’s marked on the box is just a bunch of numbers.
VTGA-200
Our custom built, state of the art power output valve tester can test at anode voltages up to 640 volts and run the valves up to 100% power. It also allows us to hear them and check for microphonics and noise. This tester operates as a class A output stage complete with output transformer, meaning it accurately recreates real conditions inside your amp.
Our other testers
Maxi-Matcher Tester
In early 2024 we introduced our Maxi-Matcher tester This bad boy tests not one, not two, but four output valves at once! Imagine the efficiency! It covers a wide range of valves, from the common octal base output valves to EL84s and 7189s. Basically, it’ll handle everything from a 6V6 up to a KT120. And being brand spanking new, it’s more reliable than our vintage AVO testers. This tester is the back up to our custom VTGA-200.
Our Custom-Built VTGA-100 Pre-Amp Valve Tester with audio check
Ah, the ECC83/12AX7 — the rockstar of valves!
We launched this tester in February 2024. It handles up to 16 ECC83 valves simultaneously. It’s a whopping three feet long (or just under a meter), weighs 20Kg (44lbs in old money), and tests each tube in a circuit typical of the V1 position in your amp. The VTGA-100 can also check most other preamp valve types and can even select balanced valves for the phase splitter position.
And that’s not all.
With this new gear, we can also listen to each valve to check for microphonics, noise, and hum. And even hook up an oscilloscope to look at the noise spectrum for detailed analysis.
The picture below shows 8 ECC83/12AX7 preamp valves being tested.
We teamed up with Chris at Vintage Amp Services to craft this beauty. Chris did an incredible job constructing the unit to our specifications, and put a ton of his own expertise into details of the design. And hey, if you’re in Swindon and need an amp repaired, give him a shout! He’s a veritable expert with vintage valve amps.
Element Engineering and Design Limited in Wiltshire, UK, used an NC machine to tool the strong steel chassis of this tube testing monster.
And as for those old AVO testers? Just hold your horses! We’re not bidding farewell to those faithful friends just yet. They’re still on duty, handling ‘oddball’ valves and rectifiers. We’ve just beefed up our testing game for the more common valves.
Our AVO Testers
We have two AVO testers. Our Mk 3 is now dedicated to testing rectifiers. Yes we test every tube rectifier before shipment.
Our AVO CT160 tester is used to test the much less common valves such as the EH 6973 and Tung Sol 7591. Okay, so we can’t listen to these valves as yet, but you can bet we’re working on it!
