Tube DI Box

[ruffrecords]

DL94 looks to be an intersting tube because it has two filaments and, if muy reading of the datasheet is correct, you can use just one of the filaments for simple class A circuits whjch halves the heater current to 50mA. I am now looking for a spice model of this tube.

Cheers

Ian

 

[rock soderstrom]

DL94 looks to be an intersting tube because it has two filaments and, if muy reading of the datasheet is correct, you can use just one of the filaments for simple class A circuits whjch halves the heater current to 50mA. I am now looking for a spice model of this tube.

Cheers

Ian

I experimented with battery tubes years ago. I thought they sounded modest...just my 0.02$

 

[heatwalk]

A 12Vac wallwart plus the Gyraf style transformer in reverse seems like a nice simple solution for small package. 12:230 or 12:120 with a doubler? But i understand not liking the wallwart in general. Just coming from the perspective of if this isnt sitting in a rack but closer to pedal platform size/ working within some limitations. Im also thinking of it from a DIY machining perspective - a 2mm jack is a lot easier to drill out than an IEC.

If level control is desired would a dual triode be a better choice? Something like a 12BH7 with innerstage volume control? Gain stage into vol into CF into XFMR.

 

[Wavelength]

Whats the resistance of that 150H choke?

3700 ohms, just did the calculation and maybe the 60H @ 2750 would be better for this. I am biasing the grid at 1.65v directly off the dac output pin.

 

[Wavelength]

The idea for using a 12Vac input and then boosting that was used by EHX on some of their tube pedals. They ran into the problem in the field with the wall warts going dead and the musician stranded.
Battery and Tube is not a good idea unless your using something like the 6418 with 10ma filament. Microphonic if you don't use them right, plus impossible to use in a cathode follower setup.
I looked at a number of DI today, I know this is suppose to be simple but most have an effects loop and some kind of EQ. Everything changes the character of the sound. Designed 12 different transistor and tubes ones since yesterday

 

[Wavelength]

I have 1200 of the 6418 here and use them in pedals. The big problem people have with them is that they are directly heated. That means the bias point is mid point of the filament. Second this tube can be very microphonic, plus you can't use it as a cathode follower. So this is how I use it in a pedal. First triode wired with a 0.3ma current source diode in the plate and a 10T pot in the cathode leg. I use a LM317L as a current source @ 10ma to power the filament. Since the plate and output Z of that tube is so high I use a LSK189 source follower directly coupled to the plate and a 1ma current source from ground to the source. That gives me a gain of ~8 and a pretty low output impedance. Not great but good enough. I also put the 6418 on 1/2" of foam and use a quiet relay for switching. I run the B+ regulated at 33V with a series LTC1144 cap charge pump. For low microphonics you need to adjust the bias to low grid current.

 

[ruffrecords]

The 6418 is an interesting tube, mainly because of its incredibly low heater power consumption. Unfortunately this comes with an exceptionally low power output which will not be sufficient for this application. Where it is used in audio applications, it always appears to need support of several semiconductor devices in the audio path which is something I prefer to avoid. Thanks for the suggestions though. The DL94 i mentions consumes 10 times the heater power but is more than capable for providing the output drive capability needed. It may also be possible to run it at onl y 50mA and still have sufficient power so tubes of this type are by no means rules out. All suggestions gratefully received.

Cheers

Ian

 

[Wavelength]

Ian,
The DL94 is directly heated as well and therefore using one half of the filament is not a good idea. Better to use them in series since the G3/Fct is the center tap and therefore the direct connection to the mid point. Also not finding a good data sheet with curves for that tube. If you have one please send it this way.

 

[moamps]

https://tubedata.altanatubes.com.br/sheets/030/d/DL94.pdf

 

[ruffrecords]

Ian,
The DL94 is directly heated as well and therefore using one half of the filament is not a good idea. Better to use them in series since the G3/Fct is the center tap and therefore the direct connection to the mid point. Also not finding a good data sheet with curves for that tube. If you have one please send it this way.

I find this confusing because the data sheet page 2 definitely appears to show operating characteristics for a single heater (see data sheet in post above this one.)

Cheers

Ian

 

[pvision]

I'd say go battery or go 110 / 220 Volt. Wallwarts are evil things - always low quality, don't like being left on, plugs fall out, etc

For battery, what about a power drill battery? 18 Volt Li-ON battery from Milwaukee, etc. I bet someone has 3D-printed a receptacle for one, or there is one available from AliExpress. Slap on a fully-charged battery and you're good to go

Or go for a very shallow 2U box and put eight DIs with a common internal PSU with mains power

 

[Wavelength]

Ian,
Sure thing if you want to bias the grid negative it appears that will work. For someone who has been helping design 300B and various other directly heated triodes this evades me. Without a cathode and using half the filament and drawing to the center tap it doesn't seem to make much sense. I guess you could ignore the G3 reference and use say two 22 ohm resistors from the CT and F+ and join them to create a virtual center tap and bias from there.

 

[pvision]

I'd say go battery or go 110 / 220 Volt. Wallwarts are evil things - always low quality, don't like being left on, plugs fall out, etc

For battery, what about a power drill battery? 18 Volt Li-ON battery from Milwaukee, etc. I bet someone has 3D-printed a receptacle for one, or there is one available from AliExpress. Slap on a fully-charged battery and you're good to go

Or go for a very shallow 2U box and put eight DIs with a common internal PSU with mains power

And here it is:

https://www.aliexpress.com/item/1005004014247222.html

or

https://www.ebay.co.uk/itm/176191652737

You can get a couple of amp hours from one battery so you could probably power an 8-channel version with one

 

[Wavelength]

FYI Heyboer makes a nice 115/230 small power transformer I use in the amp in my moniker. Using a 6ZY5G rect and drawing 30ma (3.9uF via 30h/40ma 100uF) I get 200V clean, 1.2A 6.3V CT supply. This was a Classic Transformer design since they went under Heyboer bought them out. I think Tube Depot sells them in the US or contact Heyboer direct. Use to be 18111 model number. https://www.tubedepot.com/

 

[ccaudle]

I know I'm coming in kind of late to this discussion, but @ruffrecords did you read any of Thor's thread about the low voltage tube circuit (~48V HT)?
reflected plate amplifier thread

 

[ruffrecords]

FYI Heyboer makes a nice 115/230 small power transformer I use in the amp in my moniker. Using a 6ZY5G rect and drawing 30ma (3.9uF via 30h/40ma 100uF) I get 200V clean, 1.2A 6.3V CT supply. This was a Classic Transformer design since they went under Heyboer bought them out. I think Tube Depot sells them in the US or contact Heyboer direct. Use to be 18111 model number. https://www.tubedepot.com/

I could not find any at tube depot. There were a few at mojo tone but not the one you mentioned. I didn't see any toroids though.

Cheers

Ian

 

[ruffrecords]

I know I'm coming in kind of late to this discussion, but @ruffrecords did you read any of Thor's thread about the low voltage tube circuit (~48V HT)?
reflected plate amplifier thread

I rememeber that thread but not visited it in relation to this topic. Thanks for the reminder.


Cheers

ian

 

[ruffrecords]

So, I am guessing that in order to achieve your goal/intent of this DI circuit being only a tube/valve design, the circuit will require some type of an output transformer for it to have enough gain.

The transformer is there to provide a balanced and floating output. In this application it does not have gain but actually drops the signal level.

Below is a part of the phono-preamp circuit mentioned above that takes a magnetic phono-cartridge level signal as its input and outputs a "Line-Level" signal to drive a power-amplifier. YES.....I do recognize that there are some transistors involved here, but.....come on!!!

I guess I am a bit of a purist when it comes to tube circuits. There are very many so called tube circuits (even professional mixers) with lots of semiconductors in the signal path. Marketing people make a huge thing about it been a tube product when in fact it is largely a semiconductor one. To my mind they are, at best. hybrid designs and do not deserve to be called tube.

Cheers


Ian

 

[Rob Flinn]

I'm not really understanding the need for the box to require particularly low power consumption. From the discussion so far it seems like the whole project is geared around using the least amount of power possible. Surely the emphasis should be placed on what is going to sound the best. I would be looking at some of the R core transformers available on ebay or Aliexpress. I have used them before & they work well & are cheap. For me I would much rather do this than mess around with voltage doublers etc even if the box needs to be bigger.

 

[merlin]

I'm not really understanding the need for the box to require particularly low power consumption.

+1, inevitably design by committee has resulted in the thread deviating far from Ian's OP.