Preamp Tube Options - Baby Will 18-Watt Build

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Traitor Joe
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Preamp Tube Options - Baby Will 18-Watt Build

Post by Traitor Joe »

Hello everyone,

I can't find an answer for this that's unequivocal enough for me to understand so here goes.

What preamp tube options are there for my Baby Will 18-Watt clone?

A part of me is uncomfortable with using different types of tubes in the preamp stage so I've been hesitant to use one tube type in V1 (12ax7 let's say) and another in V2 (12at7 say). However, I don't really know anything about how the circuit actually works so please let me know if my fear is misguided.

I currently have these old "Nec" brand 12at7's that I took out of an old reel-to-reel tape machine in both preamp slots because whenever I put 12ax7's in I end up with a very, very small range of usable volume before I start loosening floorboards and peeling paint.

I *always* mic my amp for every gig just to help combat the directionality of guitar speakers so the at7's have been useful in getting a reasonable stage volume and I've never had too little volume or headroom. However, the at7's give the amp a bit less "oomph" than I'd like; they're a little thinner-sounding compared to when I put the ax7's in there (and I'm not just talking about volume, there's like a "girth" to the sound that's lacking with the old at7's. The amp is less "powerful.")

What tube "mismatches," if any, are acceptable in this circuit? If I have a 12ax7 in V1, can I safely use an at7 in V2? Would that even help solve my problem? Would the opposite? I've read than 5751's are more like an ax7 than an at7 is; would I need one or two of those? What different preamp tube configurations would work without causing damage?

Thanks for your time, everyone!
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by JMPGuitars »

Traitor Joe wrote:
Fri 08/16/19 2:32 pm
What preamp tube options are there for my Baby Will 18-Watt clone?
If you want it to sound as intended, 12AX7 and equivalent tubes. ECC83, ECC803, 12AX7, 7025, CV4004, are all essentially the same with some minor differences.

5751 is supposedly similar in all aspects to a 12AX7, except it's 70% amplification factor instead of 100% like the 12AX7s.

What tube "mismatches," if any, are acceptable in this circuit? If I have a 12ax7 in V1, can I safely use an at7 in V2? Would that even help solve my problem? Would the opposite? I've read than 5751's are more like an ax7 than an at7 is; would I need one or two of those? What different preamp tube configurations would work without causing damage?
12AT7, 12AU7, etc... though their pin grid is the same, they are not equivalent of 12AX7. They will have lower amplification, and affect your voltages. They'll also change the tone of your amp. That said, it should be safe enough to try them out. If you prefer the way they sound in some combination, I would test your voltages and make sure you're in spec compared to the datasheet for the given tube you're testing.

If you want to learn more about individual tubes, you can search for tube + datasheet. For example, if you search for "12ax7 datasheet" on google you'll get a list of sheets with useful information. They'll show MAXIMUM ratings, as well as typical operation.

It's quite possible you may not like the sound of the amp with anything but 12ax7 equivalent tubes. If that's the case, you should consider an attenuator instead of messing with the tubes.

Thanks,
Josh

PS. Mismatching tubes is not relevant to this conversation. Power tubes (besides single power tube amps) are generally installed in pairs, or quads, etc... Those pairs are matched to each other (within certain margins of error) to perform and bias well together. This is a whole other topic, with an array of opinions. ;)
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Traitor Joe
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by Traitor Joe »

First off, thank you so much JMP. Really appreciate the depth of your answer.
JMPGuitars wrote:
Fri 08/16/19 3:08 pm

It's quite possible you may not like the sound of the amp with anything but 12ax7 equivalent tubes. If that's the case, you should consider an attenuator instead of messing with the tubes.
This brings up a great point that I've tried but perhaps not implemented ideally; I constructed an attenuator using (only) an L-Pad and built it right into the front of the amp. It certainly "works" but it makes the amp sound really lifeless and just... bad.

I remember reading something somewhere about putting a lightbulb "in-line" with the L-Pad so as to not "slam your transients into a wall."

Would this make the attenuator work better? How would I go about wiring it up?

A bit off topic but hopefully useful to someone else that stumbles upon this thread...

Thanks again!
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by JMPGuitars »

Traitor Joe wrote:
Fri 08/16/19 3:37 pm
This brings up a great point that I've tried but perhaps not implemented ideally; I constructed an attenuator using (only) an L-Pad and built it right into the front of the amp. It certainly "works" but it makes the amp sound really lifeless and just... bad.

I remember reading something somewhere about putting a lightbulb "in-line" with the L-Pad so as to not "slam your transients into a wall."

Would this make the attenuator work better? How would I go about wiring it up?

A bit off topic but hopefully useful to someone else that stumbles upon this thread...

Thanks again!
I wouldn't go that route. There's a little bit of info on a DIY attenuator here: viewtopic.php?f=25&t=24414

Personally, I bought a different one. I think mine was about $100, and uses a speaker motor, and doesn't kill the tone. It also has a treble boost switch if needed. There are other versions with EQ type stuff on them. You want at least double the wattage of your amp as far as the attenuator is concerned.

You can find the schematic for it on google if you really want to make your own. I won't mention the brand though, you'll have to figure that part out. ;)
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by Traitor Joe »

JMPGuitars wrote:
Fri 08/16/19 3:47 pm
I wouldn't go that route. There's a little bit of info on a DIY attenuator here: viewtopic.php?f=25&t=24414

Personally, I bought a different one. I think mine was about $100, and uses a speaker motor, and doesn't kill the tone. It also has a treble boost switch if needed. There are other versions with EQ type stuff on them. You want at least double the wattage of your amp as far as the attenuator is concerned.

You can find the schematic for it on google if you really want to make your own. I won't mention the brand though, you'll have to figure that part out. ;)
Awesome, thank you sir!
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by crgfrench »

12AX7, 12AX7A, 12AX7R, 12AY7, 12AT7, 12AU7, 12AV7, 5751,
6072, 7025, 7025WA, CK5751, CV455, CV492, CV2650, CV3650, CV4004,
CV4017, CV8154, CV8312, CV9859, CV10175, CV10319, CV10662,
ECC803, ECC803S, ECC81, ECC83, ECC83S, M8137, QB339.

You can mix and match in the Baby Will. i.e., 12AY7 followed by CV4004 etc.

Fear not -- roll 'em!
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by crgfrench »

Weber Mass and the Rivera Rock Crusher are nice attenuators.
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by Daviedawg »

There is another option which works well on the 18 watt variants, VVR on the PI and power stages. It leaves full voltage on the preamp stage. I have used that on my 19 watt virtually since I built it. I also have an attenuator but have hardly used it because I felt it had more effect on the tone than VVR. Full VVR over the whole amp is easy to install but has much more detriment to the tone.

It is a while since it was discussed but I am sure there are schematics in the downloads with this shown.

Dd

Edit. Look in the mods and circuit ideas for Lite 2 with VVR. The same principle will apply to modifying the power supply stages on most 18 watt variants. You can get a small pcb and components to make installation simple.
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by Traitor Joe »

[/quote]
crgfrench wrote:
Fri 08/16/19 9:28 pm
12AX7, 12AX7A, 12AX7R, 12AY7, 12AT7, 12AU7, 12AV7, 5751,
6072, 7025, 7025WA, CK5751, CV455, CV492, CV2650, CV3650, CV4004,
CV4017, CV8154, CV8312, CV9859, CV10175, CV10319, CV10662,
ECC803, ECC803S, ECC81, ECC83, ECC83S, M8137, QB339.

You can mix and match in the Baby Will. i.e., 12AY7 followed by CV4004 etc.

Fear not -- roll 'em!
Daviedawg wrote:
Sat 08/17/19 1:02 am
There is another option which works well on the 18 watt variants, VVR on the PI and power stages. It leaves full voltage on the preamp stage. I have used that on my 19 watt virtually since I built it. I also have an attenuator but have hardly used it because I felt it had more effect on the tone than VVR. Full VVR over the whole amp is easy to install but has much more detriment to the tone.

It is a while since it was discussed but I am sure there are schematics in the downloads with this shown.

Dd

Edit. Look in the mods and circuit ideas for Lite 2 with VVR. The same principle will apply to modifying the power supply stages on most 18 watt variants. You can get a small pcb and components to make installation simple.
Thanks a bunch for the advice! VVR looks very interesting.
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by Traitor Joe »

JMPGuitars wrote:
Fri 08/16/19 3:08 pm

If you want it to sound as intended, 12AX7 and equivalent tubes. ECC83, ECC803, 12AX7, 7025, CV4004, are all essentially the same with some minor differences.

5751 is supposedly similar in all aspects to a 12AX7, except it's 70% amplification factor instead of 100% like the 12AX7s.

12AT7, 12AU7, etc... though their pin grid is the same, they are not equivalent of 12AX7. They will have lower amplification, and affect your voltages. They'll also change the tone of your amp. That said, it should be safe enough to try them out. If you prefer the way they sound in some combination, I would test your voltages and make sure you're in spec compared to the datasheet for the given tube you're testing.

If you want to learn more about individual tubes, you can search for tube + datasheet. For example, if you search for "12ax7 datasheet" on google you'll get a list of sheets with useful information. They'll show MAXIMUM ratings, as well as typical operation.

It's quite possible you may not like the sound of the amp with anything but 12ax7 equivalent tubes. If that's the case, you should consider an attenuator instead of messing with the tubes.
If I could please pick your brain again JMP...

I've looked up the datasheets but if I'm honest I have no idea what I'm looking for. (I've done things like recap my Peavey Encore 65 and I built the Baby Will myself but the instructions were lego-simple and I'm decent at soldering but I don't understand the circuit *at all.*)

For example...

The JJ 5751 Datasheet lists the following under "Typical Characteristics"

Typical Characteristics:
Ua = 100 V
Ug = -1 V
Ia = 0,8 mA
S = 1,2 mA/V
Ri = 58 kΩ
µ = 70

(https://www.jj-electronic.com/images/st ... f/5751.pdf)

Which seems to indicate to my uninformed mind that they're not quite compatible with 12ax7's because so many of the numbers don't match the Typical Characteristics on the JJ ECC83s Datasheet:

Typical Characteristics:
Ua = 250 V
Ug = -2 V
Ia = 1,2 mA
S = 1,6 mA/V
Ri = 62,5 kΩ
µ = 100

(https://www.jj-electronic.com/images/st ... ecc83s.pdf)

Am I comparing the wrong data points? Or are the figures above within acceptable tolerances?

Thanks again!

Edited to properly quote JMP
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by JMPGuitars »

Traitor Joe wrote:
Mon 08/19/19 12:51 pm
Am I comparing the wrong data points? Or are the figures above within acceptable tolerances?
Compare them, and their max values, to the target voltages of the circuit you want to put them in. The baby will is like a lite 2, right? I forget.

Look at the voltage test sheets I added here: viewtopic.php?f=25&t=24418

For example, the Lite 2/Superlite TMB voltages: files/JMPGuitars_18_Watt_Lite_2b_Voltage_Test_Chart.pdf

The plate voltages for V1 are 150. It's neither tube's typical voltage, but well beneath the 300V maximum for either tube's plates. You'll notice that the limiting values are generally the same between those two tubes.

In the PI, the plates are at 225. Either tube would be within their limits, but I don't know how this would sound with a 5751 without trying it out.

When you look at the typical operation, you can compare them and see that the tubes don't behave quite the same. For example, the amplification factor, and currents are different. So while they'll work interchangeably, they will impact the way the circuit sounds, and potentially affect other areas as well. You can swap a tube and fill out that full voltage chart to get a clearer picture of the full story. Then, you know, play the amp and see how it sounds.

If you look at the bottom of those two datasheets you linked, you can see two graphs called curve traces. Those show how the tube behaves under specific changes in voltage. For example, look at the top line, on the right graph. That represents grid voltage at 0V. With the anode (plate) voltage at 150, the 5751 is at 5mA. The ecc83 looks like it's at 3.2mA with the same anode voltage.

If you want to learn more about this and how it pertains to amp circuits, read this chapter from Merlin's book: http://www.valvewizard.co.uk/Common_Gain_Stage.pdf

Just keep in mind that Merlin is a master of theory, but practice and theory don't always 100% agree.

Thanks,
Josh
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by Traitor Joe »

JMPGuitars wrote:
Mon 08/19/19 2:11 pm
Traitor Joe wrote:
Mon 08/19/19 12:51 pm

Am I comparing the wrong data points? Or are the figures above within acceptable tolerances?
Compare them, and their max values, to the target voltages of the circuit you want to put them in. The baby will is like a lite 2, right? I forget.

Just keep in mind that Merlin is a master of theory, but practice and theory don't always 100% agree.

Thanks,
Josh
Thanks again for such an in-depth answer. I'll have a lot of fun with that PDF you shared.

I get the impression that the Lite 2 is similar to my Baby Will except the Baby Will is diode-rectified as opposed to tube-rectified. Also, mine has only Volume & Tone. No TMB or tremolo or anything. Single channel, one input.

I built it into the Valve Junior Chassis; check out the layout:

(http://www.rh-tech.org/public/z_stingra ... t%20v2.pdf)

Here's the (brilliant) build instructions I followed:

(http://legacy.guitaramplifierpcbs.com/D ... l%20v4.pdf)

Going over the last few pages is jogging my memory a bit; I think I skipped several of the final voltage tests out of impatience (don't try that at home kids, a mistake on my part.)

I think I'll get some 5751's, actually test the voltages this time, and report back if I need to. I'm hoping I can figure it out with the information you already shared and a little more patience.

Thanks again Josh, really appreciate you taking the time.
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by Traitor Joe »

Traitor Joe wrote:
Mon 08/19/19 3:31 pm

I get the impression that the Lite 2 is similar to my Baby Will except the Baby Will is diode-rectified as opposed to tube-rectified. Also, mine has only Volume & Tone. No TMB or tremolo or anything. Single channel, one input.

I built it into the Valve Junior Chassis; check out the layout:

(http://www.rh-tech.org/public/z_stingra ... t%20v2.pdf)
Correction to the above, mine differs from the layout I shared in that it only has one input and no standby switch.
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Re: Preamp Tube Options - Baby Will 18-Watt Build

Post by JMPGuitars »

Traitor Joe wrote:
Mon 08/19/19 3:31 pm
I get the impression that the Lite 2 is similar to my Baby Will except the Baby Will is diode-rectified as opposed to tube-rectified. Also, mine has only Volume & Tone. No TMB or tremolo or anything. Single channel, one input.
They are basically the same except for the rectifier. I just looked over the schematic here: http://www.rh-tech.org/public/z_stingra ... c%20v5.pdf

If you compare that to my schematic in the downloads section for the "Lite 2b(ish)" - you'll see it's very similar to yours except the rectifier.

The Lite 2 series doesn't have TMB, only tone knobs. Only the classic has tremolo. The Superlite TMB is another version that's single channel, but with TMB control.

Good luck with your experiments, let us know how it works out.

Thanks,
Josh
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