Subminiature tube amp with only line out

[Bionic_Bigfoot]

Hi,

I'm wondering if it would be possible to make a subminiature copy of a full sized amp,for instance a Marshall JMP bass,with subminiature tubes,and only a line level out, not a speaker out.This way I could run the amp either to a computer interface for use with IRs, or to a solid state power amp,then to a cab with a driver. If possible,would it be easy to adjust the various values of components to the subminiature tubes? Thanks.

[JMPGuitars]

Hi, welcome to the site!

It sounds like you're more interested in making a tube preamp than an amp.

There's a few different submini tubes that are dual triodes that you could theoretically replace 12AX7s with, but you'll need to adjust the components (as you mentioned) to support them. The other thing to consider is that there will be variations in current and amplification factor, that will change the way the circuit sounds/works.

If your intent is to use it for bass, lower amplification factor might be a good thing. 6021 tubes are only around 35 mu, so that might be a good starting point.

If you put in the effort for the R&D, you could definitely come up with something cool. On the other hand it would be way less effort to buy or build a preexisting tube preamp. Maybe not as satisfying though.

Thanks,
Josh

[Bionic_Bigfoot]

Thanks for the reply.
Yes, you're right in that I am inquiring about a preamp.
However, I want something that will capture the power section distortion of a full sized amp, not just preamp distortion.
If I were to build a full amp out of subminiature tubes,
and then somehow have output low enough to be at line level, this would be a preamp that sounded like a full amp. I don't know if this is possible, though.

[crgfrench]

Oh it is possible all right.

http://www.garnetamps.com/herzog.htm

http://www.stephensonamps.com/stage-hog.htm

http://beavisaudio.com/projects/valvecaster/

https://londonpower.com/electronics/bass-preamp/

The ones above use regular size tubes. Here's one with submini tubes:

https://jjs.at/electronic/class_ab_subminiature.html

[zuceno]

You should be made aware that in a lot of cases there is no real advantage to using subminiature tubes.

The types used for hearing aids are for battery applications only, they do not work well with power supplies. While there might be reasons for using some of the industrial types in hifi applications, they are generally designed for clean sounds.

The Russian 6n16b and 6n17b are probably the most useful subminis for guitar amps. You can treat those as being like 12AU7 and 6SL7 electronically, but the heater current is much higher than their standard counterparts, and they do not like a high B+.

[JMPGuitars]

Thanks for the reply.
Yes, you're right in that I am inquiring about a preamp.
However, I want something that will capture the power section distortion of a full sized amp, not just preamp distortion.
If I were to build a full amp out of subminiature tubes,
and then somehow have output low enough to be at line level, this would be a preamp that sounded like a full amp. I don't know if this is possible, though.

What Zuceno said is correct. You have to be aware of how they handle the B+, and if the B+ is too low for the tone you want, it's not going to sound good.

If you want the full output tube distortion sound, then you're actually talking about amp slaving. However, you obviously can't run the preamp amp at output dissipation levels. At least not directly. You could run Amp 1 into an attenuator with a line out into Amp 2. With this method the types of tubes you use won't matter. It won't necessarily sound good either, you would need to experiment.

You also need to keep in mind that power tube overdrive also incorporates output transformer overdrive/saturation. So either way, you need to run from the speaker out to get that tone. Using the method above with an attenuator, you have a good chance. You'll need to make sure the attenuator is at least double the wattage of the amp you want to use it with.

Thanks,
Josh

[Bionic_Bigfoot]

What Zuceno said is correct. You have to be aware of how they handle the B+, and if the B+ is too low for the tone you want, it's not going to sound good.

If you want the full output tube distortion sound, then you're actually talking about amp slaving. However, you obviously can't run the preamp amp at output dissipation levels. At least not directly. You could run Amp 1 into an attenuator with a line out into Amp 2. With this method the types of tubes you use won't matter. It won't necessarily sound good either, you would need to experiment.

You also need to keep in mind that power tube overdrive also incorporates output transformer overdrive/saturation. So either way, you need to run from the speaker out to get that tone. Using the method above with an attenuator, you have a good chance. You'll need to make sure the attenuator is at least double the wattage of the amp you want to use it with.

Thanks,
Josh

Got it. This thread was very helpful. I realize that I'm looking for a regular amp, not a submini. Thanks.

[Bionic_Bigfoot]

You should be made aware that in a lot of cases there is no real advantage to using subminiature tubes.

The types used for hearing aids are for battery applications only, they do not work well with power supplies. While there might be reasons for using some of the industrial types in hifi applications, they are generally designed for clean sounds.

The Russian 6n16b and 6n17b are probably the most useful subminis for guitar amps. You can treat those as being like 12AU7 and 6SL7 electronically, but the heater current is much higher than their standard counterparts, and they do not like a high B+.

Before I bag this idea entirely, what about the Korg Nutube? Would the design that I'm proposing work with it?

Specs:
http://korgnutube.com/pdf/Nutube_DatasheetV1E.pdf

[katopan]

I made a subminiature version of the Superlite TMB almost 10 years ago.
viewtopic.php?t=22236
Pics & clips that were lost in that post are here:
https://sites.google.com/site/chosenaud ... otscreamer

Running something like this into a dummy load (resistive if you want easy, reactive if you want better) will give you a line out only amp. The main advantage of submini valves is real pentode output overdrive at low output power, meaning smaller transformers and smaller dummy load. You can get other low power real pentodes these days (like Russki 6F4P and equiv) but I haven't yet been able to get a pair of them in push-pull to sound right for a 4W 18 Watt variant.

[zuceno]

Before I bag this idea entirely, what about the Korg Nutube? Would the design that I'm proposing work with it?

As I see things, the Nutube is a step on the way to a future amplifier which may be a real world beater. It doesn't have advantages right now.

Something we don't talk about much is immediacy, but that is a factor in the appeal of small simple valve amps.
You pick a note on your guitar, the signal goes down the cable into the amp and comes out of the speaker. That takes time - only about 130mS for an 18Watt. As an electric guitarist, you accommodate for that delay in your playing, and get used to that.

Organists have to learn to cope with much larger delays - you press a key on a pipe organ and in many cases you have to wait perhaps 350mS or more for the sound to reach your ears - so the electric guitar is not the only instrument which has a delay.

A lot of the circuitry in solid state amps causes signal delays. Each stage delay is tiny, but they add up. If you meet a big SS amp from the early 70s you will notice a big delay - or rather, you just "won't like the feel", because you will not realize that the delay is what you don't like.

The valve amp scored better for immediacy than the SS amps of the past - you played a note on a valve amp, it came out quicker than from a SS amp, which is why valve guitar amps didn't die when everything else in the world moved over to using transistors. Yes, the tonal qualities were also important, but a large valve amp still only has 4 or 5 stages of amplification, whereas most SS amps had many more in the old days.

Now we are 50 years on from those days of yore, the SS amps are competing with the valve amps' immediacy. The Output Transformer of a valve amp is the limiting factor. That delays the signal by 110-120mS and there is no easy way around it. The hifi people occasionally turn out transformerless output stages, but they don't sound right for guitar and you could roast a turkey by holding it over the heaters - it takes a lot of output valves to make things like that work to give a high output.

What Korg are apparently aiming for, or working towards, is an amp that has the low number of gain stages in a traditional valve amp, the sonic advantages of using valves, but which loses the delay of the valve amp OT.

In other words, a valve guitar amp which has the best immediacy ever.

But that is in the possible future.
For now, it is difficult to see an advantage to using a Nutube, over using conventional tubes.


You haven't expressed much about what you really really want. As things stand you could go with any of a range of bedroom amp designs, using a big resistor as a dummy load and a take-off from the output.

or do you want something like this?

https://www.youtube.com/watch?v=D10mXHfJJAQ

[Bionic_Bigfoot]

Before I bag this idea entirely, what about the Korg Nutube? Would the design that I'm proposing work with it?

You haven't expressed much about what you really really want. As things stand you could go with any of a range of bedroom amp designs, using a big resistor as a dummy load and a take-off from the output.

https://www.youtube.com/watch?v=D10mXHfJJAQ

First and foremost, I want a JMPsound.
Secondly, I want to do it quietely. If doing it quietly isn't an option, I'll probably build either an 18watt, or something single ended with an el34. I really haven't decided yet.

[geoff 1965]

have a look at the "18W plexi" in the download section,it has the JMP type preamp with the 18W power section.if you used VVR or a PPIMV you could get lower volume and hopefully the JMP sound your looking for.

[katopan]

First and foremost, I want a JMPsound.
Secondly, I want to do it quietely. If doing it quietly isn't an option, I'll probably build either an 18watt, or something single ended with an el34. I really haven't decided yet.

How about a Mark Huss 6V6Plexi for much lower power than the full size?
https://mhuss.com/Plexi6V6/

I've had huge success with a reactive dummy load, re-amping the signal and running it at below TV volume through a real guitar speaker.

[crgfrench]

Here is a load box you can build, this is from TubeDepot's 5E3 kit plans. Values are for speaker impedance of 8 Ohms and an amp with max 20W output. I used Arcol HS75 resistors for this in my Denim Deluxe.

Screen Shot 2019-07-21 at 10.48.52 PM.png

[crgfrench]

It has no tubes. I've never tried one. But could you possibly be looking for a Spamp?
https://www.etsy.com/listing/477969731/ ... lifier-and

[zuceno]

could you possibly be looking for a Spamp?

I doubt that is what the OP wants - it will not be clean enough in one direction and too dirty in the other. OTOH thank you for making me aware of this device, it may be something I like.

[crgfrench]

Maybe an Atomic Amplifire would work?
https://youtu.be/4dxgUIMQw2c