Tube Questions

[carbonfold]

Ok ok.... again lets start with my Peavey VB-2

Let me explain my rig (in order from hands to wall) and how I'm set up and you let me know whatcha think about this issue.



American Fender Jazz Deluxe V

Furman Petal board (petals list in series)
Boss TU-2 tuner
Aphex Factory Punch Compressor
Radial A/B loop switch (loops listed below)
A Rat ProCo Keeley Mod looped with a Black Muff
B English Muff with Orange Drop Mod (12AX7 x2)
Aphex Bass Xciter

Peavey VB-2 (tubes listed below)
V1 - JJ ECC83S
V2 - GE JAN 5751 (NOS)
V3 - EHX (stock Phase Inverter tube)
Power - Ruby EL34BHT x6


As posted prior: VB-2 F2 Fuse Blew

So last night I'm rehearsing with my Peavey VB-2 and stomped on a few of my distortion/overdrive petals during the set with my EFX loop switch. The tone was fine at first then shifted very trebly, almost like a guitar amp, then the amp stopped producing sound ???


Had this repaired as a diode issue, however, one thing strikes me odd. Last night, while rehearsing, I ran across the same issue with my tone shifting very trebly while all my pedal were being used at once (I know I know, I love overdrive). I can be playing through half a set or so using these pedal all on (tone is fine and no tone shifting), but after it seems the amp is warming up, the sound (sometimes) go extremely trebly. It happened last night, but because of what I went through before, I shut everything down right on the spot. I waited a minute, and fired it back it. This issue did not replicate again last night. So I'm wondering what might ya'll think? To me, it sounds like I have a preamp tube going out, but do you think I might be sending too much signal to my preamp tubes? Does this sound like a microphonic issue? Could I be causing damage to my amp with this much OD (I am going through the padded input/low gain).

[Groover]

Not sure, but I do have a question... when all works, how would you compare the the 5751 vs the 12ax7 in the Phase Inverter slot?

It sounds to me that your problem may be a bad solder joint somewhere, but I'm sure someone can chime it in regards to the bad tube theory.

[SurferJoe46]

Old guy here - and possibly an old thought.....................make that "antique"

We had capacitors that acted just that way when they were dying. In TVs and old tube-radios they would start to cut tone or volume when they got loaded and they went downhill until you turned off the set and then restarted it. Good for a while anyway - but it would come back after a short time.

Some sets had a drain off in a resistor/capacitor network to ground the voltage that the caps stored. It was a very small drain and didn't affect the performance, but it would "reboot" if you will and drain the caps down so they didn't pop when you turned the set back on or had a (normal-happening in those days) power loss or surge.

Now I know there are huge caps in MY modern transistorized bass amp - I can see them through the cooling vents, so this might be an area to check.

[carbonfold]

Originally Posted by Groover

Not sure, but I do have a question... when all works, how would you compare the the 5751 vs the 12ax7 in the Phase Inverter slot?

It sounds to me that your problem may be a bad solder joint somewhere, but I'm sure someone can chime it in regards to the bad tube theory.

The difference between a 5751 and a 12AX7 is gain (something like the 5751 is approx 70% and the 12AX7 100%).

As a phase inverter, you will want something with a higher plate current. Both the 5751 and 12AX7 have a max 1.2 mA plate current. Instead of those, IMO, you will want to have something like a 12AU7. A 12AU7 has 10.5 mA plate current. It has a lower gain (I "think" it is something like 50% gain).

If you want maxium amount of current to your power tubes, you will want that 10.5mA plate current. If not, you will have to push your amp harder to attempt to achieve the same thing.

However, will it sound different? Depends on who you ask. If you ask me, it does. You ask someone who doesn't have that tube bug in their blood, they may look at you like you are some kinda OCD freak
Anyways, that's my 2 cents on the phase inverter.

[carbonfold]

All the tube info one can handle!


http://tubedata.milbert.com/sheets11.html