Headroom- tubes, speaker, or inherent in the amp.

**Doc Music** · 05-07-2013, 10:20 AM

I have a Pro Junior (stock.) I love the tube sound compared to my Crate or SS DEC Junior, but it lacks headroom and breaks up too much at low volumes. Discussions here talk about new speakers- I now have the stock 10 inch. If I want more head room what do you suggest. I do not have much $$ to spend. Thanks for your input.

**SamBooka** · 05-07-2013, 10:36 AM

Always start with cheapest/easiest first.
Try a 5751 in the pre.

That said.. you CAN improve the headroom of a Pro Jr. but part of their charm is that the scream RAWK.. that is why I use mine as a cute bookend. Since you happy with yours a 15$ mod yhou can do yourself in 30 seconds would be the first step.

**Bebop Tom** · 05-07-2013, 10:40 AM

I have a pro jr and changed the speaker to a Weber that they said would be better for jazz. No difference. It is inherent in the amp. 15 watts, designed to distort, one little ten inch speaker. You could spend hundreds of dollars on upgrades or a separate larger cabinet, but why waste your money. Use it for quiet practice, or sell it and move to a hot rod deluxe, a Deluxe Reverb, or a solid state amp.

**Doc Music** · 05-07-2013, 11:10 AM

Thanks

**SamBooka** · 05-07-2013, 12:30 PM

Just curious.. what Weber did you put in yours PJr Tom?

**2bornot2bop** · 05-07-2013, 02:29 PM

Originally Posted by Jabberwocky

What you are looking for is to reduce the sensitivity, in other words, gain of your preamp.

Which is why it's important to select preamp tubes designed with lower gain...so I've been told. As an experiment I recently installed 7025's exclusively, reported to possess lower gain than average 12AX7's, and all I can say is I've never experienced a more positive change in a guitar amp.

**Double 07** · 05-07-2013, 05:38 PM

Power tubes!!! Power tubes come in different "grades" some of which will break up earlier and some will break up later.
So you can order EL84's (or any power tube) that will break up at low volume or not until you get to very high volume
on your amp. "Grades" not meaning "good or bad" just some are designed to provide early breakup and some are designed
to stay clean at higher volume (still the same great tube sound).A lot of rock guys like the tubes that break up early for
the power tube distortion and of course jazz guys generally prefer the tubes that break up waaaay later for headroom / clean volume. Call your tube vendor and tell him you
want some EL84's for more headroom in your amp. That should increase headroom more than the speaker change.
I seriously doubt your 15 watt Pro Junior is causing your speaker to distort unless you got a really low wattage
handling speaker. Yes, think of it like speakers. Some speakers will break up at lower volume while some won't
break up until the amp is totally cranked (some will handle more clean wattage than others). Great sounding speakers are available for either taste just like tubes.

Usually Fender amps will ship with tubes that are somewhere in the middle of that power tube "breakup spectrum".
Although I have seen some Fenders that shipped with power tubes that break up really early. Which I don't understand
since Fenders are generally known for having great warm tube cleans.

After getting power tubes that won't break up so quickly, if you want even more headroom, then try some
preamp tubes with lower gain like a 5751, 12AY7, 12AT7, or even a 12AU7. That should provide some
more clean headroom.

**cosmic gumbo** · 05-07-2013, 05:59 PM

Loud and clean is not in the realm of many 15w tube amps.

**ruger9** · 05-07-2013, 07:07 PM

It is inherent to the amp circuit BUT- a lower-gian V1 tube could give you enough headroom to be happy.

The different ratings on power tubes (breakup: early, middle, late) is MINOR compared to swapping out that V1 tube. Ditto speakers. I'd say, in order, what has the most effect on headroom:

1) amp circuit
2) V1 tube
3) speaker
4) power tube rating

**barrymclark** · 05-07-2013, 07:12 PM

Originally Posted by ruger9

It is inherent to the amp circuit BUT- a lower-gian V1 tube could give you enough headroom to be happy.

The different ratings on power tubes (breakup: early, middle, late) is MINOR compared to swapping out that V1 tube. Ditto speakers. I'd say, in order, what has the most effect on headroom:

1) amp circuit
2) V1 tube
3) speaker
4) power tube rating

Agree with this. It has been my experience that even amps built to overdrive can be greatly tamed by the V1 and speaker. Some amps though....5150... Just overdrive. Ha ha

**Bebop Tom** · 05-07-2013, 07:49 PM

Originally Posted by SamBooka

Just curious.. what Weber did you put in yours PJr Tom?

10A125 30 watt, as per their suggestion.

**SamBooka** · 05-07-2013, 08:59 PM

I looked at the schematic.... 10k input resistor... no bypass cap on the first stage cathode... I got as far as the .01 coupling cap and said "yeah... this is a gainy amp"

If you are talking about NOS tubes, 7025s are not lower gain than 12ax7s. Back in the 50s and 60s they were built to tighter tolerances and might have had a quieter filiament design (but I could be wrong). By the 70s there wasn't much difference between them. New prod 12ax7s vs 7025s is really just marketing since there is sooooo much variation from maker to maker.

**Double 07** · 05-07-2013, 09:13 PM

Originally Posted by ruger9

It is inherent to the amp circuit BUT- a lower-gian V1 tube could give you enough headroom to be happy.

The different ratings on power tubes (breakup: early, middle, late) is MINOR compared to swapping out that V1 tube. Ditto speakers. I'd say, in order, what has the most effect on headroom:

1) amp circuit
2) V1 tube
3) speaker
4) power tube rating

You guys in here are such jerks sometimes. Get real

**SamBooka** · 05-07-2013, 09:22 PM

Originally Posted by Double 07

You guys in here are such jerks sometimes. Get real

Remind me in September and I will put a scope on my pro jr and see where the clipping starts first.
I am sure that if you posted this on TDPRI BillM would chime in within a couple of hours. I would (exceptionally) take his word on anthing pertaining to PJr and BJr.

**Double 07** · 05-07-2013, 10:22 PM

Power tubes that idle at a lower current are usually prone to "breaking up" or going into distortion at lower than the proper volume (for that kind of tube). Because they idle at LOW current compared to the average tube.

So they have LOWER HEADROOM. For some musical-instrument applications, the user may want this effect. It is usually seen as undesirable for high-end audio, because lower idle current means higher distortion, which most people dislike hearing in their music playback.

Power tubes in the MIDDLE range fit the average profile for that tube type. They are most commonly recommended for the average amplifier user, especially for high-end audio amplifiers. These tubes will give the "PROPER" amount of headroom for their operating point. So the amplifier will perform as the manufacturer intended.

Power tubes that idle at a higher than average current will give more HEADROOM than the amplifier designer intended. With these tubes, your amplifier volume / gain will need to be turned up much higher to achieve "break up". Some instrument amplifier users might wish for this sound effect.

**SamBooka** · 05-07-2013, 10:29 PM

Did you write that yourself? I'm very impressed you must be an expert!

**ruger9** · 05-08-2013, 05:35 AM

Originally Posted by Double 07

Power tubes that idle at a lower current are usually prone to "breaking up" or going into distortion at lower than the proper volume (for that kind of tube). Because they idle at LOW current compared to the average tube.

So they have LOWER HEADROOM. For some musical-instrument applications, the user may want this effect. It is usually seen as undesirable for high-end audio, because lower idle current means higher distortion, which most people dislike hearing in their music playback.

Power tubes in the MIDDLE range fit the average profile for that tube type. They are most commonly recommended for the average amplifier user, especially for high-end audio amplifiers. These tubes will give the "PROPER" amount of headroom for their operating point. So the amplifier will perform as the manufacturer intended.

Power tubes that idle at a higher than average current will give more HEADROOM than the amplifier designer intended. With these tubes, your amplifier volume / gain will need to be turned up much higher to achieve "break up". Some instrument amplifier users might wish for this sound effect.

All true. As is the fact the power tubes will have the LEAST EFFECT on overall breakup when compared to the amp circuit, V1 tube, and speaker. Note how I am able to have intelligent discourse without calling you a "jerk."

**SamBooka** · 05-08-2013, 11:48 AM

OH!!! CARVIN BOY!

You have to admit.. best thread of 2013 so far!!!

**AlsoRan** · 05-08-2013, 12:01 PM

Originally Posted by Jabberwocky

He has to at least give attribution to the source of the article instead of presenting it as his own. That is called plagiarism: What is the Bias Point .

And it isn't as simple as choosing tubes with higher bias current for more headroom. This article explains it well: Biasing .

No, I don't think Double 007 knows what he is talking about either. Merely pulling things out of cyberspace. But what do you expect from some guy who thinks that Carvin owes him a free axe because he sent in some suggestions and then goes to town about it when he does not get what he thinks he deserves?

"Beware the Jabberwock, my son! The Jaws that bite!..."

(From the poem by Lewis Carroll, 1871)