Engl Thunder 50 Tube Replacement Problem

Franco_S

Hi,

I own an Engl Thunder 50 and need to replace the Power Tubes. The current ones in there are Engl's own 5881. I was sent a matched pair of Svetlana 6L6GC power tubes from Duckson and Pinker (where I purchased the amp and it is under warranty). However, one of these is smaller than the other. One is marked 05 07 (big one) and the other 04 08 (small one).

I have a few questions.

Firstly, are these tubes ok to be used within the amp, and if so which way round do they go? I do not want to have the wrong tubes in the amp as it will affect performance and also life of the tubes.

Secondly, in the case of the Engl Thunder 50, does replacing power amp tubes require biasing, or is it simply a case of plugging them in?

Finally, if they do require biasing, does anyone know of a place in or near Gloucester that will do this for me? Going to Duckson and Pinker in Bath is difficult for me at this moment in time and I would rather have it done locally. I have already tried aroundabout sound in cheltenham, but they do not do this. I have also tried ringing GTV in cheltenham but they have never answered the phone.

Thanks for your time,

Franco

Eoin Madsen

The valves will only fit in one way, so it shouldn't be possible to insert them incorrectly. Both valves should be identical - even if you could get two 6L6s that were noticably different in size or shape, I don't think they could be matched. Contact the seller and ask them what's going on.

As far as I'm aware all ENGL amps are fixed bias, so it would be a bit of a job to alter the bias. It should work okay without adjustment, but I would recommend contacting ENGL and asking them about it - specifically mentioning that you intend to change from 5881s to 6L6GCs.

Eoin

Franco_S

Thanks for your reply.

The bar code says that they are a matched pair, although I am also dubious about this. The only difference apart from the size is the marking 04 08 and 05 07. As for getting them the right way round, I was referring to if the larger tube had to be closer to the power supply than the smaller tube (as opposed to plugging the tubes in).

I thought that if they are different sizes, the position of them within the circuit would affect the performance of the amp depending on which way round they were and was wondering if there is a correct way round?

I am currently waiting for a call back from Duckson and Pinker in Bath to see if they know anything about the tubes being different sizes.

Any information is greatly appreciated, cheers for the help

Franco

Eoin Madsen

Both valves perform exactly the same function out of phase with each other - this is the reason why they have to be matched (and, by extension, interchangeable).

Paladin

A valves characteristics are heavily dependant on its size. A matched pair should be identical.

Karl Hungus

Hmm, can you take a picture of the valves for us at all?

Franco_S

They both read:

Svetlana Electron Devices
6L6GC
Made in Russia

OTK2

The one on the left also reads:
05 07

The one on the right also reads:
04 08

As you can see the one on the right is smaller, as is its base.

Karl Hungus

Hmm, that looks very odd indeed, can't say I've ever seen something like that before. I'd say your best bet is to return them from where you bought them.

Eoin Madsen

Unfortunately, not all companies "match" valves by the same set of characteristics. It's possible that by whatever (I guessing low) standards this company use, both of those valves give the same reading. Personally, I'd enquire about a refund and then shop somewhere reputable, like Watford Valves.

How much did those two cost you?