WOW, what a difference

I believe you need to remove the screws at the top of the tube shroud/cage and lift off the top piece. Then you can swap the tubes. If you have no inquisitive young children or pets around then you might consider leaving that piece "off".

You're lucky. With those 12AX7s you ran a risk, apparently, of overloading some components (the coupling caps, maybe). Some things sound best just before the stress blows a hole in your personal ozone layer.
That center driver tube is the crucial volt-amp for both channels (dual triad). It is the single most variable sound-enabler in the ST-120, by most accounts. As deepee says, keep trying. You can't have enough variability here. PM me should you care to hear my own history. It's long.

mcgyver74 wrote:
The amp still sounds amazing, not as "crisp" as it did with the 12ax7 but it's a noticeable improvement over the 12au7 in the center socket (I swapped back and forth to see...well after a few minute cool down anyway )  the 12bh7 was def a good improvement.

Give it time ... once your ears (and brain) adjust to what they're hearing now, you may find that it's just right.

not only are the tubes sunk way down inside the chassis they have a heatsink on them that is the exact size of the holes they go in, so I cannot figure out for the life of me how to get these puppies out....

You talking shields?



Normally, those are twist lock, and you need to turn them a bit, then kinda rock them out of the socket. And yes, they can be a bit of a PITA to remove. The compression types shown in the pic (the ones with the ridges) can usually be pulled apart a bit at the seam so you can get them off the tubes.

Not shields.  The Tube Box DS has those somewhat silly metal thingies that seem to be intended as visual bling, and maybe to keep some fingers away from the tubes...

Actually those are not the shields I am talking about, those come off with 4 screws easily, if you look down in the holes there is a heat sink glued to the tube itself (A thing with fins) I can get the tube to rise a bit in the hole (so it's not locked in) but since the heatsink is the same size as the hole and the tubes are sunk so far, I cannot get a strong enough grip to pull them up past a point

They put a finned heatsink on a 12AX7 in a phono pre-amp? That's... odd. Sounds like you might need to remove the outer metal cover of the pre-amp.

Unfortunately you cant, the chassis slides out the front and the tubes poke up so you cannot do that

Hey, saw someone had exactly the same question over on Vinyl Engine ...

(oh, wait ... that was you!)

And ya ... looks like the tubes just pull out once you remove the top shields, but your problem is getting enough of a grip to do that. I'd suggest putting on a clean nitryl or vinyl glove and give it another go. That should give you better traction on the glass. You could also try a damp rag with windex or some such on the glass first. If you do need to rock the tube a bit, that's kewl, long as you take it easy and re-tension the sockets after.

Once you get the tubes out, THEN you should be able to pop the case and adjust the sockets for a decent but not killer tight. Also seems to be common practice just to leave the heat sinks off the tubes when done. You may find they won't fit the STRs anyway, as I believe those have thicker glass than most - I do know the shields on my Eico were a tight fit, but they had vertical splits so I was able to open them up a bit. The STRs should be able to fend off any stray RF that might otherwise be a problem. I'd also dampen the tube pins with D5 before putting them back in ... that should prevent them oxidizing in place and causing more problems down the road.

Last step would be to maybe drop a line to Project and ask them what da hey they was thinking when they designed the friggin case ...

Oh. You'd probably be doing yourself a favor to check the new tubes for microphonics and such prior to buttoning things up and calling it done. Just fire up some music and tap them lightly a few times with a stick to see if there's any weirdness.

Thanks, yeah that's me, I figured ask in a few places..


I'll try the rubber glove thing (man that does NOT sound good LOL) to get the tubes out (phrasing LOL)


What are microphonics?

mcgyver74 wrote:Thanks, yeah that's me, I figured ask in a few places..


I'll try the rubber glove thing (man that does NOT sound good LOL) to get the tubes out (phrasing LOL)


What are microphonics?

If you tap a warm tube gently but sharply with a wooden pencil or the light-weight wood or plastic screwdriver you use to crank the bias pots, you'll hear a "tink" sound out of one or both speakers. No need for a crow-bar or a torque wrench for this task.
You'll likely notice the presence of a microphonic tube first if you hear a slight metallic "tink" whilst flipping a front-panel switch or tapping the surface of the component. Then it's a matter of isolating which tube is acting up with the pencil-tapping routine. No need to thwack it hard -- you'll know right away just with a very gentle tap after everything is good and warmed up, and it's just as common among $200 NOS super-duper signal tubes as it is with their modern-day $20 re-issues.
I suppose in extremis that a highly microphonic tube will reverberate with music coming out of the speakers, generating feedback distortion, but often as not it's just a minor annoyance and no need to round-file the thing. Also, make sure you've identified the right tube. Thwacking a perfectly innocent neighbour can mechanically transfer the vibration to the errant tube next to it, so in a four-tube layout it will be the loudest "tink" that's your culprit.
I had a '64 Pontiac with a "reverb" switch that attempted to extract a "concert hall" sound on the radio from a mono signal. It was a factory option. Maybe that's where all them military-rejected microphonic tubes ended up. . .
Generally, in my experience, the high-gain signal tubes in preamps and drivers are the most susceptible to this defect. I've never encountered microphonics develop in a tube that ran quietly after its first good warm-up,nor conversely, seen one that got better over time, or anything "under the hood" that can be tweaked to fix it. Correct me if I'm wrong but I deduce it's a manufacturing / QC matter. The best of the tube-sellers, such as Andy Bowman and Jim McShane, test for this as a matter of course. Intermittent noise or badly mismatched dual triodes are a far larger blight on sound than minor microphonics.

mcgyver74 wrote:

What are microphonics?

After buying new dual triodes is not the ideal time to ask this question! Microphonics refers to vacuum tubes' tendencies to act as mechanical to electrical energy transducers. When you order tubes you might consider requesting "low microphonics". I suggest you give your microphonic tubes to your guitar amp buddies. They sometimes view microphonics as a desirable feature.

FYI: capacitors can be microphonic as well.

Testing: In the absence of a proper tube hammer, you could use a dry bamboo chopstick (safer but less effective than the eraser end of a Ticonderoga #2 pencil) to gently tap the envelopes of your tubes. Do this test while your device is powered on and set for low volume. Most every tube will exhibit some degree of microphonics but this simple test will let you know if you have any particularly sensitive tubes. You might hear clicking, thumping, or metallic rattling from your speakers when you perform this check. If the perturbation is pronounced or sustained you may have a microphonics issue. In the worst case your amplifier will become unstable, go into regenerative feedback and let the smoke out of your tweeters--just as you locate the power switch.

...j

j beede wrote:

mcgyver74 wrote:

What are microphonics?

After buying new dual triodes is not the ideal time to ask this question! Microphonics refers to vacuum tubes' tendencies to act as mechanical to electrical energy transducers. When you order tubes you might consider requesting "low microphonics". I suggest you give your microphonic tubes to your guitar amp buddies. They sometimes view microphonics as a desirable feature.

FYI: capacitors can be microphonic as well.

Testing: In the absence of a proper tube hammer, you could use a dry bamboo chopstick (safer but less effective than the eraser end of a Ticonderoga #2 pencil) to gently tap the envelopes of your tubes. Do this test while your device is powered on and set for low volume. Most every tube will exhibit some degree of microphonics but this simple test will let you know if you have any particularly sensitive tubes. You might hear clicking, thumping, or metallic rattling from your speakers when you perform this check. If the perturbation is pronounced or sustained you may have a microphonics issue. In the worst case your amplifier will become unstable, go into regenerative feedback and let the smoke out of your tweeters--just as you locate the power switch.

...j

@j beede, thanks for that additional info. Wasn't aware that caps were susceptible as well. In the case of capacitors, can the problem be addressed by longer leads or some other way of physically isolating the condenser from chassis/speaker vibes?

For the most part after the testing I've done of the various preamps I own or have owned I'm of the belief a lot of the justification for high priced preamps is pure marketing hype since all the preamp is supposed to do is direct music from the source to the amp without coloring it in any way. The preamp is also there to allow you to control volume. Some preamps add gain, some necessary like phono preamps. The gain that they add seems to be perceived as adding 3D space or openness. But in reality you can duplicate that by turning up the volume. i understand that a tube preamp gives you an additional layer of coloring the sound both by tube rolling and also by tone controls and if that's what one wants then that's fine. But if a preamp causes hum as it did in my case with a VTA SP-10 and SP-12 then it's something very undesirable.

In actuality I've considered passive preamps. And hopefully I will have the chance to give one a try. I think that may be the best option for me.

I'm really kind of curious about the claim that a VTA preamp 'sounds' as good as a commercially available preamp costing 5X the price since the goal of a preamp is to not color sound. In what way does it sound like that preamp costing 5X the price?

An amp I once owned had tubes that, like yours were not offering any way to grab them.
I used two pieces of masking tape. slide one piece down along the side of the tube and used a machinist scale to push the tape to the side of the tube and made sure it was adhered to the tube itself.
Placed the other piece of tape on the opposite side of the tube and was easily able to pull the tube out. Did this several times during the time I owned it.
Worked well for me....

Ah ... the handy man's secret weapon ... duct tape!



PS .. try to avoid taping over the labeling, as sometimes just looking at that cross-eyed can make it go away.

sKiZo wrote:Ah ... the handy man's secret weapon ... duct tape!  



PS .. try to avoid taping over the labeling, as sometimes just looking at that cross-eyed can make it go away.

If you can't be handsome, be handy.

sKiZo wrote:
Ah ... the handy man's secret weapon ... duct tape!  



PS .. try to avoid taping over the labeling, as sometimes just looking at that cross-eyed can make it go away.
If you can't be handsome, be handy.

deepee99 wrote:
If you can't be handsome, be handy.