Question on Tube Types and Brands

[Outlier22]

So this isn't related to PRS amps per se but to tube amps in general. I hope that is okay.

I just bought a Fender Supersonic 22 combo used for a pretty good price but I found that once I was able to test it out at volume it gets dirty way earlier that I would expect. (on the clean channel) Seemingly much earlier than my Blues Jr. I didn't test out my strat, only my CE24. I know the 85/15 pickups are pretty hot but still, I'm talking about the amp breaking up at volume level 3 which I don't think is even loud enough to play with my band. The Blues jr can stay clean with volume level on 3 or 4 and master cranked up less than half way and be clean AND loud enough for our band (at least in our practice space). My DSL 15's clean channel has even more headroom. Now, I love the sound of my other amps as they start to break up, but I thought this was a bit "flubby". (not sure how else to describe it. It's not what I expected for "Fender Clean Sound") I was hoping to have a mostly clean sound at 3-4 volume and push the amp for breakup with my OD pedal(s).

...I did also crank the amp to 5 or a little over 5 and that completely changed the sound. Although still broken up, I found the amp had a really nice sounding break up at this volume. Possibly more of the frequency (bass maybe) was starting to compress at this volume. Or possibly the speaker was really moving at this volume. I thought, I can definitely live with this sound! Except that it was too loud for the band in our small practice space.

First does anyone have experience with this amp? (or with the Deluxe Reverb as the SS22 clean channel is more or less like a DR.) Is it supposed to get dirty so early? If so, maybe my answer is crank it up past 5 and to get an attenuator.

Doing some quick internet searches regarding tubes and biasing, I found from a few sources that if the tubes are biased to hot, you will have extra headroom and if they are biased too cold you will have less headroom. (I might have that backward). Being a used amp, I think it is very probable that the early break up issue could indicate that the power tubes need to be biased so i'm planning to bring it to my amp tech.

But my next question is, can you change power tube types or brands to alter the amount of headroom available? I want to get a handle on that before I bring it to my amp tech so I can let him know what kind of tubes I would like. No sense in paying for the service twice right? What tubes are recommended? (I think the amp uses 6v6's, but some supersonics may have come with 6l6's. so I'm not totally sure. Are these tubes interchangeable?

As far as pre-amp tubes go, I'll definitely change these while I'm at it. I think it comes with 3 12ax7's and 2 AT7's. I was thinking JJ tubes based on a youtube video comparison but any suggestions there? (it's hard to really tell listing to a youtube video) I have not really experimented with my other tube amps, so I could do that, but that's gonna be a lot of tubes to buy so hoping for some suggestions first.

 

[RickP]

Setting the bias hotter will lower headroom and put you into overdrive sooner. There are many methods of getting voltages for bias setting, but the safest I know of is to use something like the Bias Probe from Eurotubes. (Eurotubes.com) This device keeps you from poking around inside where dangerous, even deadly, voltages exist. Safety first... tones really are not “to die for.”

With the ability to re-bias, you can change tubes of the same type as your amp came with (6V6 for 6V6 etc), as different tubes do respond differently. You should not swap in other types of tubes, even through some will fit in the socket. The entire circuit is built to work together, so swapping parts requires an in-depth knowledge of the interactions so you don’t smoke something in the process.

Just so you know, some amps are made to switch tube types and have that capability built in. Some even use more than one type of power tube simultaneously, Mesa/Boogie being one who does this regularly. This is generally marked on the amp, near the power tubes, and may have switches to accomplish it.

Preamp tubes allow a little more flexibility. 12AX7 is the standard preamp tube, though some parts of the Fender circuit use a lower power tube, the 12AT7, and I have heard of people using them in place of a 12AX7 to lower power and clean up the amp. I don’t know if this is possible with your amp, but I’d suggest looking for a 12AX7 with a cleaner response. Also, make sure that a previous owner has not put a 12AX7 where a 12AT7 is supposed to be, as that will certainly take some headroom from the amp.

A 22 watt Fender show be able to get decently loud and clean, without significant breakup in the lower half of the dial. Another thing you can do is roll your guitar volume back a touch, to 6 or 7 let’s say, as a way to clean up the input from less distortion.

Just remember that every part of your signal path, from fingers to speaker, has some influence on how that tone sounds. Tubes are an important part, but just a part, of the sound.

 

[Outlier22]

Fantastic reply Rick and you confirmed my suspicion that the amp should not be breaking up so early. But I’m definitely not willing to try the bias prob and bias it myself. It’s going to my tech for that . I didn’t spend months in lockdown to get kill by my amp lol.

I didn’t check to see what tubes were in thenpre-amp. I was assuming they were all then recommended tubes. But the previous owner could have changed tubes and put the wrong ones in the preamp?? I may just have my tech look at that as well.

Oh and I did roll back the guitar volume and that did clean up the amp some but the volume was too low to play w the band.

thanks for all this info again. I’ll bring the amp in to have the tubes checked / replaced the and get it biased and see where that lands me. I agree w you that it should stay clean in the lower part of the volume. And w everything you said, I’m now wondering about those preamp tubes. It seems to break up quick when the volume isn’t even that high. And then when you really turn it up it starts to sound better - as if the power amp tubes are just getting going. AND when I turned back the guitar volume the amp volume definitely drops. If it was the power section compressing early, the volume would not necessarily increase w more guitar volume it would just compress more. So turning it down wouldn’t drop the volume so much as it would reduce compression right?

well anyway, thanks for the feedback!

 

[László]

Rick knows his stuff!

As to tube brands, I prefer NOS (new, old stock), usually made before 1980, BUT they're expensive. Worth it if you're into getting that last ounce of tone, not a big deal if you're happy with new tubes.

 

[RickP]

Fantastic reply Rick and you confirmed my suspicion that the amp should not be breaking up so early. But I’m definitely not willing to try the bias prob and bias it myself. It’s going to my tech for that . I didn’t spend months in lockdown to get kill by my amp lol.

I didn’t check to see what tubes were in thenpre-amp. I was assuming they were all then recommended tubes. But the previous owner could have changed tubes and put the wrong ones in the preamp?? I may just have my tech look at that as well.

Oh and I did roll back the guitar volume and that did clean up the amp some but the volume was too low to play w the band.

thanks for all this info again. I’ll bring the amp in to have the tubes checked / replaced the and get it biased and see where that lands me. I agree w you that it should stay clean in the lower part of the volume. And w everything you said, I’m now wondering about those preamp tubes. It seems to break up quick when the volume isn’t even that high. And then when you really turn it up it starts to sound better - as if the power amp tubes are just getting going. AND when I turned back the guitar volume the amp volume definitely drops. If it was the power section compressing early, the volume would not necessarily increase w more guitar volume it would just compress more. So turning it down wouldn’t drop the volume so much as it would reduce compression right?

well anyway, thanks for the feedback!

Certainly worth having your tech look at it. I went over and took a look at the SS, and it is indeed similar to the DR, except it is solid state rectified, which is a good thing for headroom. Another thing it has that the DR doesn't is a master volume and two gains. That Master is another place to add headroom. Turn the master up first, maybe 75% or higher, then start bringing up the channel gains. Turning up the Master frees the power section to provide cleaner power, then you can dial in the amount of grit you want with the Gains. Give that a shot.

 

[Outlier22]

Certainly worth having your tech look at it. I went over and took a look at the SS, and it is indeed similar to the DR, except it is solid state rectified, which is a good thing for headroom. Another thing it has that the DR doesn't is a master volume and two gains. That Master is another place to add headroom. Turn the master up first, maybe 75% or higher, then start bringing up the channel gains. Turning up the Master frees the power section to provide cleaner power, then you can dial in the amount of grit you want with the Gains. Give that a shot.

yeah but the master is for the “burn” channel only. The clean channel ONLY has one volume - and bass and treble knobs. I didn’t try to get clean sounds on that burn channel. I guess it’s possible.

But yeah, the Supersonic has that added channel w a master volume which is cool and different than the deluxe. But it’s missing the tremolo. Otherwise is based on a deluxe. ...and I did hear about the solid state rectifier which I wasn’t sure if it was good or not.

 

[Outlier22]

Ok I dropped of the amp with my local amp tech so we’ll see. But as I was dropping it off I took a look at the pre-amp tubes and I could access all but 1 of them while he was writing up a slip and I found 3 of them were 12ax7s and one was indeed a 12at7. I looked up the schematic and it looks like the correct tubes were in the right slots so I’m guessing that last tube WAS an At7. But the tech said (referring to power tubes) that they look a bit beat up. I think he means old / discolored as they weren’t actually damaged. So we will probably replace them all and see where that lands is. ...His initial thought was that it was simply a tube issue.

in the meantime I was playing a strat through my blues Jr at really low “bedroom levels” master volume down near 1 and preamp volume on 4 and now that amp is starting to get distorted at that volume where it didn’t before. So I’m guessing it’s a tube issue on that amp now as well. Lol!

 

[RickP]

Ok I dropped of the amp with my local amp tech so we’ll see. But as I was dropping it off I took a look at the pre-amp tubes and I could access all but 1 of them while he was writing up a slip and I found 3 of them were 12ax7s and one was indeed a 12at7. I looked up the schematic and it looks like the correct tubes were in the right slots so I’m guessing that last tube WAS an At7. But the tech said (referring to power tubes) that they look a bit beat up. I think he means old / discolored as they weren’t actually damaged. So we will probably replace them all and see where that lands is. ...His initial thought was that it was simply a tube issue.

in the meantime I was playing a strat through my blues Jr at really low “bedroom levels” master volume down near 1 and preamp volume on 4 and now that amp is starting to get distorted at that volume where it didn’t before. So I’m guessing it’s a tube issue on that amp now as well. Lol!

Tubes do wear out. Getting a less full, or more distorted, tone is a sign they’ve seen better days. Preamp tubes generally live a more comfy life and last a long time, but power tubes played regularly can degrade significantly in a year or so, and less in some circuits/uses. It might be a good idea to swap in some new power tubes on the Blues Jr, and keep the old ones as spares.

 

[Outlier22]

Ok, looks like he replaced 3 pre-amp tubes. (there are 4, which makes me think he didn't just replace them all to start over but 3 needed replacing) and both output (power amp) tubes. I haven't picked it up yet and won't get a chance to crank it till the weekend anyway but I expect this will resolve my issue. Thanks again for the advice all. I'll check in to confirm when I get to play it.

 

[Outlier22]

Okay thanks again Rick and Les. I got the amp back and tested it out around 4 and 5 volume and the amp is super loud now and super clean at that volume. The amp tech just replaced both power tubes and 3 of the 4 preamp tubes. (And biased the power tubes of course). He offered to swap a 12at7 w a 12ax7 to provide more clean headroom but I told him I’d test it out as is first. It’s definitely not needed and perfect as is for the volume my band plays at to stay clean when I need it.

...Maybe it too clean now lol. Hoping I can drive it to overdrive w a boost but I have a feeling it’s just gonna get louder. If so I’ll have to use the “burn channel and/or my OD pedals for edge of breakup sound.??? But that is more or less what I expected when I bought it and it’s basically how I’ve been using the Marshall. anyway thanks again!

 

[Deleted member 5962]

He offered to swap a 12at7 w a 12ax7 to provide more clean headroom

Your tech really said that too you??????

 

[Tone-y]

Your tech really said that too you??????

Other way around surely

 

[Outlier22]

Your tech really said that too you??????

That’s what he said. I forgot what he said that particular tube was for. I think he said it was a crossover???? Could be something to do with the trasnformers.??? Crap I don’t remember. I could call him and ask. I could point it out to you though. It was the one right in the front row left of the power amp tubes. I’m 90% sure he said
He could put in a 12ax7 in the spot and get more headroom.

I’m not home right now otherwise I could double check what is in the spot right now.

 

[RickP]

That’s what he said. I forgot what he said that particular tube was for. I think he said it was a crossover???? Could be something to do with the trasnformers.??? Crap I don’t remember. I could call him and ask. I could point it out to you though. It was the one right in the front row left of the power amp tubes. I’m 90% sure he said
He could put in a 12ax7 in the spot and get more headroom.

I’m not home right now otherwise I could double check what is in the spot right now.

Phase Inverter, probably.

The idea of swapping a lower gain preamp tube is an old trick used for many years to tame overly aggressive amps. This can also be done in some reverb circuits, though I don’t know as much about the new amps as the old black faced ones. Some tubes can even be removed entirely if their part of the circuit isn’t in use.

You just have to know the circuit and interactions to know where you can swap, and where you can’t. Best leave that to a qualified technician if you’ve any doubts.

 

[Deleted member 5962]

Ok, perhaps I misread your comment. You said swap an AT7 for an AX7... I thought you meant it had an AX7 and he was replacing it with an AT7. If it has an AT7 and he’s offering to swap an AX7, then he is correct that it will have more headroom.

The opposite (what I thought you were saying) is a commonly quoted mistake. People say that all the time, that switching to a lower gain preamp tube gives more clean headroom. That is not correct. What it gives you is less gain in that gain stage. Your amp will get NO louder cleanly (headroom) with a lower gain tube. The opposite is true. The higher gain tube you can put in any position without overdriving it, the more clean headroom you’ll have.

 

[Outlier22]

Phase Inverter, probably.

Yes I think that is what he said. Lol. Didn’t know what he was talking about really so promptly forgot what he said. Haha

You just have to know the circuit and interactions to know where you can swap, and where you can’t. Best leave that to a qualified technician if you’ve any doubts.

yes! 100% agree. I just dont have the time of spare brain power to learn tube circuit technology. So 100% leaving this to the professionals.

 

[Deleted member 5962]

I just dont have the time of spare brain power to learn tube circuit technology. So 100% leaving this to the professionals.

Oh no! I've been replying and you thought you were leaving it to the professionals??? I better stop talking!

I will say one thing though, that may help. One of the biggest reasons for many misconceptions about how this stuff works, is loosely used terminology. Example: When most guitar players think "more gain" they are thinking "more overdrive." But when you talk about two tubes, more gain actually is the opposite... it means more clean headroom in that gain stage. More "output." If tube A has a gain factor of 100 and tube B has a gain factor of 70, that means that tube A will put out much more signal before it overdrives or clips. IF you were to say push both tubes to 80, tube B is clipping/overdriving by the last 10 of the factor. Meanwhile, Tube A is still clean and still has room.... headroom.

Where people get confused, is that lets say you have 3 of tube A in the circuit, before long you've built up enough gain in the circuit to overdrive the tubes. While 3 of tube B in the same circuit may not overdrive. But, a lower gain tube never equals "more clean headroom" like so many say. What it does, is lower the gain, make your amp stay cleaner higher up on the dial, but ONLY at less overall output than tube A would provide. It might widen the clean range on your gain control. But that whole thing is at a lower level since it's not pushed as hard, and that is NOT added headroom.

Also, since it was brought up in this thread, what many people think is "power tube saturation" is very often (probably "most" often) the PI stage being overdriven. This varies in degree from design to design, but there's a reason PI is so important in amps that push the back end, the JCM 800 being perhaps the most classic example. The old "it has to be loud" to sound great thing from the JCM800 is not the power tubes being overdriven, it's the PI stage. PI tubes are huge in that amp for this reason. Pushed power tubes react differently than pushed PI stage. Some push them hard enough to do both, but many many times the sound people love is the PI stage more than the power stage, being pushed into clipping.

What Rick mentioned about lower gain PI tubes does two things, PI tube overdrives easier, but pushes the power stage less hard (lower output tube). Both of these things can be desirable when trying to get a bit more drive at lower volumes on certain amps like he mentioned. But it will take away clean headroom as it will overdrive the PI earlier, and not send as much level of signal to the power tubes.

 

[Outlier22]

No no. This is all great info. I was asking for this info so thank you! ..I just mean I’m not going to be doing any of the work. .

I totally agree. Guitar players often think “overdrive” or “distortion “ when they hear gain. I guess because amps sometimes use the word gain instead of volume on amps w master volumes. So turned up the “gain” will increase the Overdrive. But yeah, Gain really just means volume so what your saying about high gain tubes makes sense.