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Hi i buy 4 nos brimar tube 6bq5 after 5minute(v5) 1 turn red and the amps less sound .I change the tube v5 and after 15 min v4 turn red (iron plate in tube.
1 What the probleme with the tube?
2 It's dangereous for my amp?
3 The tube sound great before turning red .I think put my jj el84 i dont want to my amps burn.Tank

This is not good for the amp and especially the tube!! It's called "red-plating" on the tube.

Does the problem follow the tube? What I mean is when you switch the tubes between V4 and V5, does the same tube socket get red plating or does the probelm stay with the tube?

If the problem stays with the socket, it is probably an amp problem with something wired wrong (solder joint, value of a resistor or capacitor or incorrectly wired) with that socket.
If the problem stays with the tube, it is probably a tube problem (bad tube). Try another one of the tubes and see if it red-plates.

Hope this helps.

When a vacuum tube circuit malfunctions and draws excessive current, the anode ("plate") may overheat, sometimes causing a visible red or orange glow. This is universally indicative that the tube is experiencing an overload condition.


If the tube is overloaded, not only can the plate warp, causing a short to outer grids or beam-shaping elements, but the emissive layer on the cathode will be consumed very quickly. The equipment's power supply and the tube's load (output transformer) are likely to be damaged by a sustained overload condition, so power should be immediately disconnected when a glowing plate is found.

Audio output tubes in guitar amplifiers are usually due to a bad coupling capacitor upsetting the bias or a shorted load.

If any tube presents a glowing plate, the equipment should be shut down immediately to avoid further damage.

Possible causes are:

Failing/shorted output tube - this can overheat the output transformer and/or power tranformer.
Improperly biased output tube.
Failing cathode resistor bypass capacitor.
Failing output transformer

If the amp worked with other tubes, it sounds like a bad tube.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

The tech check the valve 1 is bad (the first turning red)3 are good 2 brimar 1 valvo i test in my amp turning red a little bit after 8 min.

I put jj el 34 no problemo i continu with the jj.

The brimar and the valvo glas is tinny compar to the jj and fit a little less fit and the socket. It possible this tube not support the voltage?

Somebody try a good vintage el84

Brimar and Valvo are good, and will not normally have problems with the voltages. I also use Mullards. Don't try mixing two different kinds of EL84s - eg Valvo + Brimar, as they will probably be very unbalanced, and you could get more hum, or even one of the pair red-plating. For good vintage tube suggestions and prices I recommend going to Terry Kilgore (aka Tube Tramp aka Sgt Overdrive) - http://mhuss.com/sgtoverdrive/ BTW he used be Dave Lee Roth's guitarist.

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Great tones come in small glass jars!

Today i reicieve a lesson 101 to check the voltage and some check in my amps .The tech say to me after check the voltage. THis amp have to high voltage for old 6bq5 i have .In the book the limite voltage of old 6bq5 not fit in my amp .THat ok jj fit and the old 12ax7 modified my sound .Tonight change some capacitor orientation im happy with that.