ENGL Savage 120 mk1 troubleshooting [ENG]

Hi, first off, this post is in English as I don't speak French very well, but I've seen a lot of good knowledge on this forum, so I thought I give this a shot. Should this not be allowed, please do remove this post. Please feel free to respond in French if you want to.

So, I have this ENGL Savage 120 mk1 and ever since I bought new back in 2009 it is eating outputtubes for breakfast. I have to replace them every few months or so because one starts red plating, no matter how meticulous the bias is set (by me or by a tech).

In my search for a solution I came across a label on the powertransfo with the values of the sec windings printed on it. To my surprise it doesn't have the 6.3VAC (2x3.15) tap to feed the heaters, instead it has a 7.2VAC output. As far as I know ecc83's and 6550's are designed for 6.3VAC on the filaments. I measured this unloaded (no tubes) and get 7.54VAC on the heaters and loaded (tubes in place) gives me 7.01VAC. This seems way too high.

Is it normal for Engl to use these higher voltage transfo's and could this be a cause of red plating in the long term?

I did contact Engl directly, but didn't receive any reply to this day.

Cheers,
Erik

Don't know if higher voltage on heaters could cause red plating.. Can the hum pot adjust voltage on heaters ?

Thanks,

No the hum pot is a voltage divider to balance between the center tap and the output but the total voltage remains 7.2VAC.

I did get note from Engl though just now stating values are depending on the load and should measure 6.8VAC in normal conditions (which is within the +/-10% tolerance). They suggest installing a high wattage resistor in case it remains too high.

Bonsoir,

Aucune inquiétude avec le 6,3 Volts des tubes.

Si l'ampli mange des tubes c'est un problème de bias.

Vérifier -30 Volts environ sur la tension de bias.
Facile : C'est la seule qui est négative.
Réglage selon données ENGL ou fiche technique des tubes.

Méthode Quick and dirty) regarder les tubes dans le noir comme l'explique Lord Valve.

KT88, KT90, KT100 can be treated as 6550s, although all three of these tubes are supposed to be able to take more current. The ultimate test is to view the tubes' plates IN THE DARK, after they have been powered up for 15-20 minutes. If you see any red spots, back the current off a bit. One exception to this is the NOS 6V6; some of these will show a slight red "stripe" down the center of the plates even when they're set fairly cold. I've seen them run for years in this condition. *Large* red blotches, or even the entire plates turning red, is what you want to watch out for.
Lord Valve (LORD_VALVE@prodigy.net)
TX