Deminishing Output?

[nashvillebill]

Aw, I miss the old PBG, rants and all. But welcome to the "new" PBG.

 

[BassmanPaul]

Aw, I miss the old PBG, rants and all. But welcome to the "new" PBG.

As do I. He could, and did, get his knickers in a twist at times but I think his heart was in the right place.

 

[BassmanPaul]

deminishing is not a word, diminishing is.

Didn't your spel cheqer let you know??

 

[hodgy]

I'd check the bias. The 5 pro only has the one 12AX7 for the drive circuit, not the 3 preamp tubes like the 4pro. If it was a 4 pro I'd say check the pre tubes first, then the bias. In this case, check the bias first.

 

[Psychobassguy]

I would definitely check the bias after a year. If any of the tubes has drifted differently from the other it's time for a new set.

There are no power tubes in this amp. Preamp tubes are cathode biased, "self-biasing." The amount of voltage output to drive the power section from them is fixed.

 

[B-string]

But to be clear, tube (output) amps are not alone in needing proper bias. Many SS amps are stable their entire life, others may need the output bias "touched up". The SVT 3/3 Pro seems to be the most common for bias drift and the most touchy to do properly.

 

[Psychobassguy]

That's exactly the answer I was hoping to get, although I don't think I'm equipt to perform the test as you described. I do have one more question though, wouldn't the output voltage be effected by the output of the preamp section? You said to pump in a 40 hz sine wave, but at what amplitude, and where should the gain control be set? Or, is that a dumb question?

Your question is a very intelligent question, and pertainant to the measurement. A power measurement should be made by a qualified technician, who will check the amp's output at drive voltage specifications in various parts of the circuitry. Your amp may need an adjustment to its output transistor bias, which is what the representative from Ampeg alludes to-

I'd check the bias. The 5 pro only has the one 12AX7 for the drive circuit, not the 3 preamp tubes like the 4pro. If it was a 4 pro I'd say check the pre tubes first, then the bias. In this case, check the bias first.

 

[Psychobassguy]

I suspect not! The post was too "nice' for PBG.

Bear in mind that many of the "original" PBG's comments are not present on this board in their entirety or context. He's a friend of mine, and his reputation on this board for being a curmudgeon has been largely shaped by others, often at the expense of the truth. That said, I do doubt that he would have been as dry as I am. He is a character.

 

[nashvillebill]

Bear in mind that many of the "original" PBG's comments are not present on this board in their entirety or context. He's a friend of mine, and his reputation on this board for being a curmudgeon has been largely shaped by others, often at the expense of the truth. That said, I do doubt that he would have been as dry as I am. He is a character.

If you see the "original" PBG anytime soon, tell him that we hope he's doing well!

 

[georgestrings]

If you see the "original" PBG anytime soon, tell him that we hope he's doing well!

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- georgestrings