[FredMan]

Hallo,
Nach einem Röhentausch in ein Fender HotRod DeVille tritten Probleme auf mit der Phase Inverter (V3).

Der originale rohre (Sovtek 12AX7) gibt keine probleme aber wenn ich ein JJ ECC83S darin steck und die Amp afgewärmt ist, fängt denn Amp an sehr laut zu Brummen wenn sie laut bespielt wird. Die Endstuferöhren werden dabei sehr heiss und das Anodeblech fängt an zu gluhen!. Mit ein "dummy load" tritt dass problem nur auf (scoop!), wenn ich vorsichtig(!) mit ein Holzstick auf der Rohre klopf. Auch ein andere JJ Rohre gibt das Problem. Es sieht so aus das die JJ's empfindlich sind fur die starke Vibrationen in der Amp.

Weiss jemand was hier los ist? Soll ich andere Röhre probieren?

Grusse (und entschuldige fur mein schlechtes Deutsch ;-)
FredMan

[sjhusting]

Hello FredMan

I didn't want to answer this, because I don't really know the answer, but since no one else is replying, I'll do it anyway.

This shouldn't happen. I've used JJs in various positions in my 2x12 deville without this happening, including, I think, the ECC83S. At the moment I have one in V2 (I think).

The definitive site for Hot Rods is http://studentweb.eku.edu/justin_holton/
I couldn't find anything like your problem (see "miscellaneous problems").
Seem to be a lot of problems with the screen resistors, though, which could cause glowing plates..

If you are comfortable working on a live amp, check your bias. If you are not comfortable working on a live amp, take it to a good tech. If you aren't sure if you are comfortable, take it to a tech. There are lethal voltages in there (485V) and you have to get close to them to check the bias.


 steven

[FredMan]

Hi Steven!

I checked the bias and it's ok. The plates only start glowing when the phase inverter becomes unstable. I was aware of the link you posted but the only problem that was mentioned there that comes close to my problem is the sloppy 82k resistor on the PI. But "unfortunately" this one is fine. I just changed the output tubes and rebiased them and started over testing but the problem still stays. If anything else comes into your mind: let me know! It could just be a bad production badge of the JJ's...

Thanx for your answer!

FredMan

[sjhusting]

The problem is when you put the JJ in V3 (PI), right? Have you tried a different tube there, or swapped v2 and v3?

[bluesfreak]

Hi,

when reading thru this I get a bit puzzled as you mention that you checked Bias (on PreAmp or PowerAmp Tubes?) and that your plates go cherry (again, Pre or Power Amp?).
Some how it seems that either one of your Tubes is microphonic and/or your Amp goes into something like Oscillation pulling to much current.
I would first ensure that your PreAmp Tubes are in perfect shape and then check the PowerAmp Tubes.
Also check the Contacts in the sockets, the JJs have somewhat thinner pins then the Russion Tubes so you might have to tighten the contact sockets up to prevent a loss of contact.
While doing that I would also check for any broken or burnt resistor on the Grids or Plates (broken resistors might give you good contact in idle but will vary when exposed to vibrations)...

just my 2c
bluesfreak