rolling tubes on pre-amps: needs a burn in time ?

[Funky40]

Thank you very much @Wasnex and @friend33

"Phase Inverter" was another term i stumbled across.
If i see a tube rated as phase invertor, can i still use it in my one tube Bass preamps ?
i mean, the point here, i would nit damage anything ?
(just trying to understand and to get the picture complete)

 

[Wasnex]

Thank you very much @Wasnex and @friend33

"Phase Inverter" was another term i stumbled across.
If i see a tube rated as phase invertor, can i still use it in my one tube Bass preamps ?
i mean, the point here, i would nit damage anything ?
(just trying to understand and to get the picture complete)

The Bottom Line:
You can use a tube with balanced sections anywhere but it won't make a significant difference in most circuits.


Background Info:
A phase inverter (PI) is used in push pull output sections. The PI takes the signal and breaks it into two signal paths that are out of phase with each other. One signal feeds the push side of the output section, and the other signal feeds the pull side of the output section.

A transformer can also be used as the PI, but it tends to be pretty rare.

For max clean power you want the push and pull sides of the output section to have the same voltage swing. So, AFAIK, a tube specifically selected for phase inverter duty will have balanced sections.

Some Considerations:
1. With guitar amps, asymmetric distortion can be desirable, so you might not actually want a tube with balanced sections in the PI.
2. There are several different types of PI circuits, and some do not benefit from a tube with balanced sections.
3. In order for the balanced section tube to really be beneficial, the entire output section must actually be balanced (which is unlikely). In some instances I will pay the extra few dollars for a balanced sections, but it may be a waste of money.
4. Some PI circuits include a balance control so a tube with balanced sections is not necessary.

Images from How to design valve guitar amplifiers (valvewizard.co.uk) See Phase Inverter links in the frames in the left column.

Long Tailed Pair (PI)

This circuit may benefit from a balanced sections tube.

Cathodyne (PI)

Only one triode is used, so a balanced section tube is not needed.

You might also see some HiFi applications where a balanced section tube is desire because one triode is in the left channel, and the other is in the right channel.

 

[friend33]

@Wasnex ’s last couple of posts are spot-on and thorough.

If I may paraphrase/simplify some of the key points, not sure if some of it might go over your head:

1. V1 is generally considered the most “important” tube in tube rolling (as in “if you’re just able to put some dollars into one…”). Part of this is due to the fact that it is first in the chain. Each gain stage in the amp is ramping up your relatively weak guitar signal significantly, so the characteristics of that first tube will be amplified by each successive stage, including character, noise, etc.

2. That “rule”, while broadly true, may not apply to any specific amp or circuit, try tubes in different positions and use your ears.

3. Preamp tubes are “dual triodes” - actually two tubes inside the glass, often casually referred to as the two “sides” of the tube. A circuit may utilize both “sides” of the tube, or just one, or one side for one purpose and the other for another.

4. A phase inverter/PI uses both “sides” - each assigned to one of a pair of power tubes. The tubes operate like the pistons in your car. One is pressing down and firing, while the other is pulling up, then they reverse. (Note: this is the common “push-pull”, Class AB circuit - there are other types.)

5. Because of the way a PI operates, it is considered beneficial to have both sides “balanced” - that is, they are very close in relative strength. You generally will pay more for this, and tolerances can be had that are as close as 1%, 5%, or 10% (more for closer).

6. That “rule”, while broadly true, may not apply to any specific amp or circuit, try different tubes and use your ears.

If somebody is marketing a tube as good for use as a PI, it generally just means that the triodes are balanced. It’s fine to use this tube anywhere that the tube type (12ax, 12at, etc.) is appropriate for.

 

[Funky40]

If somebody is marketing a tube as good for use as a PI, it generally just means that the triodes are balanced. It’s fine to use this tube anywhere that the tube type (12ax, 12at, etc.) is appropriate for.

ok, i see clear now.

3. In order for the balanced section tube to really be beneficial, the entire output section must actually be balanced (which is unlikely). In some instances I will pay the extra few dollars for a balanced sections, but it may be a waste of money.

ok, what i take out "for my simple uses with simple tube pre amps" is:
A Tube advertised as beeing good as a "Phase Invertor", will just cost more !
But won´t have any advantages on sayed use*, much likely. *(single tube pre amps)

Much Thanks to You both, @Wasnex and @friend33

What a good and dense resource of information this thread is !
Awesome. Much appreciated

 

[Fuzzbass]

Just saw that Mike at KCANOS has the Mullard CV4024 on sale this month at $70/pair (usually $40 each). Those K-labeled tubes in the plain white boxes that I’ve had always tested to full NOS spec and are a great sounding at7. (No affiliation, but any tubes I’ve sourced there over the years have been spot-on, he’s a highly reputable dealer.)

Also, I've done a bunch of gigs with Mike and he plays a mean slide guitar!

I'll go back to lurking now...

 

[Phaidrus]

ok, i see clear now.


ok, what i take out "for my simple uses with simple tube pre amps" is:
A Tube advertised as beeing good as a "Phase Invertor", will just cost more !
But won´t have any advantages on sayed use*, much likely. *(single tube pre amps)

Much Thanks to You both, @Wasnex and @friend33

What a good and dense resource of information this thread is !
Awesome. Much appreciated

So how do you like the A-Bass and O-Bass preamps for bass guitar?

 

[Funky40]

So how do you like the A-Bass and O-Bass preamps for bass guitar?

you should take your question over into one of the pre-Amp threads !
i don´t run any of the two AMTs alone, they are in front of a "Oracle",
so i had to put anyway anything i say into a context vs. all three pres, since they build one chain. Lets focus here on tube rolling, please.

i´ve rolled on all three the tubes btw. !
and settled for now with the Genalex Gold Lion (reissue) on the A-Bass, and also for the Oracle.
I have now another ECC83 for the A-Bass that i have to check. ( a TAD RT010)
I´m just interested to see if it sounds different

O-Bass has a ECC81 in, which brings down the gain, which makes, that the possible useful range **bevore** OD kicks in, is way way bigger.
Setup this way, is the O-Bass quite similar to the A-Bass vs. its gain range.
And my Basses have high output Gain, so i can easily run the A-Bass also into OD.

tryed different ECC81 tubes on the O-Bass, and the one i liked the most was one from ebay (noname), ( the seller is out of them), but i run now nevertheless another ECC81, cause it gives the sound a very mid-frequenzy focus. (TAD RT003) Thats so a nice addition to the A-Bass.

as sayed: i rolled the tubes in the meantime in all three Pres, also the Oracle,
and that *definitly* adds alots to the equation, especially in this "3 tube Pres in a row" context.
A-Bass and O-Bass definitly wants to see another tube than the stock.

A-Bass is a good value for the money ! ......and probably a bit more flexible then the O-Bass,
aslong we talk Basses with a good output.
Oracle is another league. Its subtle, but its there.......and its EQ section is different.
In my opinion the best EQ section of any of the Pres.
A- and O- Bass is perfect to go in front of it.
For overdriven sounds, would i not want to have the oracle alone. (but i´m not necessarily a OD guy with Bass)
The Oracle is perfect for saturation effects and some subtle drive in the bass, ....adding some OD from the A-Bass makes it sound different. For me, its a perfect match.
O-Bass on top of it, mostly to have more options when its about way haevier drive ( like it with my E-Piano (VST) )


my guess: .....seems a general thing, that one tube would not deliver the same as several tubes in a row, since each tube can act as a slight compression and/or "limiting" unit.
Thus changing how the next tube stage would "react" to your playing.
Several tubes in a row gives so way more control over the sound, ...in several different aspects.
.....ahhhh wait: "thats how "they" build Amps, haha. Got it !"

I´m VERY happy that i rolled the tubes !
......seems to be a nessecity !

Genalex Gold Lion (reissue) seems for us here in europe a good starting point,
for a good sounding 12AX7 / ECC83 (available at thomann for us here for example)

 

[Phaidrus]

my guess: .....seems a general thing, that one tube would not deliver the same as several tubes in a row, since each tube can act as a slight compression and/or "limiting" unit.
Thus changing how the next tube stage would "react" to your playing.
Several tubes in a row gives so way more control over the sound, ...in several different aspects.
.....ahhhh wait: "thats how "they" build Amps, haha. Got it !"

Well, exactly. I'm thinking of using the A-Bass in front of my Little Mark Vintage amp head, which already has a tube in the preamp section. For a fuller, thicker tone (no OD).