The Rude Tube

[bernbrue]

congrats my friend!

thanks a lot, Volker! Happy new year!
regards
Bernd

 

[mikeyB]

There are anoying plops when switching through the different modes (Triode, Pentode, Peak 1-4). Is there a solution for this? Enjoy it!
regards
Bernd

For s1b try 4M7 resistor across each pair of contacts - this ensure all the caps are charged up to the same dc level.

Cheers

Ian

Trying to implement this on a mic stage EF86 on a lomo pre but still got the plops!
Does this depend on the switch type - should it be a MBB (make before break) shorting type?
I`m using toggle so this will be BBM - this wil mean the pole will momenterally float -so should i go 4m7 from pole to each way? will this work or should i use rotary MBB?

thanks

mikeyb

 

[bernbrue]

Hi,
I used MBB (make before break) lorlins and with these I only get a slight plop when switching between Triode & Pentode Modes. With all other modes there is no noise at all. I think there is a pcb on it´s way ...
regards
Bernd

 

[Hank Dussen]

Hi,
I used MBB (make before break) lorlins and with these I only get a slight plop when switching between Triode & Pentode Modes. With all other modes there is no noise at all. I think there is a pcb on it´s way ...
regards
Bernd

Great!

 

[mikeyB]

Hi,
I used MBB (make before break) lorlins and with these I only get a slight plop when switching between Triode & Pentode Modes. With all other modes there is no noise at all. I think there is a pcb on it´s way ...
regards
Bernd

Thanks Bernd - i will investigate!

MikeyB

 

[ChrioN]

I've never gotten distortion by fiddeling with the bias resistor in a couple of other circuits. All with triodes.
Is there anything unique or special about the 6as6 tube or it suroundings?
One more question!  Whats the guesstimate max db gain coming from the redd to the 6as6?

 

[bernbrue]

Hi,
the bias pot changes both, gain in normal mode and colour of distortion in overdrive mode. With almost no bias applied there is a gentle, kind of starving distortion which is very rich in pentode mode with lots of drive. Especially in peak mode the EQ effect is more pronounced the more bias is set (the more current is flowing through the cathode). In these modes the bias pot functions as a kind of Q control.

Distortion is mainly achieved by overdriving the 6AS6. It´s an ordinary miniature pentode like a few other quite similar tubes, the 6AU6 and 6AK5  for example, that I´m going to test in this environment. E80F as substitute for the EF86 and also the E188CC as sub for the E88CC are going to be tested soon as well. I also found a solution to implement the Squish mode, though we need another toggle switch for this. It would also be quite nice to provide a relais switching the 6AS6 in and out of the circuit (aka dirty/clean switch), because even without overdriving the 6AS6 the total harmonic distortion is quite high. I wouldn´t call it "clean".

My guess is that the overall gain is around 20dB or so. All in all it´s a really amazing and versatile tube DI, tubalizer, crunch & distortion box for all kind of audio sources. A nice toy for all audio engineers to play with 
regards
Bernd 

 

[leadbreath]

i think the 6as6 bypass switch is a good idea.
i cant wait to knock one of these together!!

thanks for the good work bernd
mick

 

[bernbrue]

Here we go

http://www.groupdiy.com/index.php?topic=47485.0



regards
Bernd

 

[bernbrue]

Hi,
I´ve updated the 1st post: schematic redrawn for pcb design (pdf)
stay tuned
regards
Bernd

 

[bernbrue]

Hah, I´ve never thought that this could happen to me. Well, I took the Rude boy out of the rack again and did some measurements. I had always very high THD figures and knew there must be something wrong. It was the input transformer that wasn´t hooked up correctly. I had neither any data of the Sowter nor any colour code to correctly identify primary/secondary side of the transformer. So I measured it out and finally made it work correctly. Now I´ve got very accurate frequency response and for a distortion box quite good THD figures. So for line level operation we don´t need a pad in front of the input transformer. Anyway, Drask put it on his "to do list" for the pcb. In case someone wants to use a microphone input transformer, we´re going to provide an optional, switchable input pad on the pcb.
regards
Bernd

 

[drask]

First pics on the new prototype

​

 

[bernbrue]

Hi Jerome,
that looks fine. Well done!
regards
Bernd

 

[alexc]

Very interesting project indeed!

Looking forward to hearing the results of all of Bernnbrue's and now Drask's hard work 
And building on Guavatone's fab orange86 implementation too.

Thanks guys for these fine developments.
We are lucky to have such contributions to the group.

Here's a pic of my messy proto :

- a red47 style eq/gain stage with a baxandall-ish style 3band eq (Anglefire actually) and 6as6 tube instead of the ef86 - stuck i the middle of this channel strip

Still foolin' 'bout with this part - sort of works with eq controls basically doing what's expected and some (un!) controlled distortion from the 6as6 gain make up stage.

Regulated, variable screen voltage variation and  variable regulated CV to the 3rd leg of this interesting and (if I may say) cantankerous tube.

A long way from being ready! but very instructive on pentodes, which I knew very little about..

The big box around it is all working fine and very quiet - an Guavatone Orange 86 pre with DI  then an Analag/Silent Arts poorman 660 limiter.  This guy has 10 transformers.

Because I can! Don;t need a reason. :

Wot a mess! But will eventually be great (or near approximation)

So these guys's work will be a godsend for the other, *tidier* seperate units I'm doin

Cheers

 

[bernbrue]

Hi Alexc,
thats insane, I´ve seen a few of your monster channelstrip builts, this one is the most impressive, whow. Yes, indeed, the 6as6 is a very interesting tube. What is your impression concerning grid 3? I didn´t really know what to do with it and connected it to cathode since I couldn´t hear any difference when connecting elsewhere. Would you explain what exactly you did with grid3, please, and what  the sonic differences are? I´m going to tinker around with this tube once again to see what else it can do.
regards
Bernd

 

[alexc]

Thanks and yes it is! Another pic of the innards where it will sit is attached.

My proto is a little different - having 3 band eq which sit in a feedback loop of the 6as6 tube fed by a  traffo (a cheaper 600:600 which will get a little fur being driven with quite high level, by the output of the orange86 pre module)

After the eq are some controls (hopefully!) driving the 6as6 tube's triode/pentode mode, cathode bias voltage, additional control voltage and output level to another AU7 driver stage and edcor 15K:600 output traffo.

Finally that's connected to the poorman 660 with edcors and on to the outside world ???
The orange86 input module has switchable HiZ DI, line and mic inputs with utc 08 and a haufe as well. The eq and limiter each have relay bypassing.

The Analag/Silent Arts  PSU with Edcor traffo powers up the whole thing perfectly (this is one of my fav all purpose tube box PSUs) with a pair of seperate regulated +HV rails with quite healthy currents!, +/- LV rails good for up to 500mA or so each and a high current dc filtered unregulated heater supply.

The Orange 86 has it's own regulated HV which also is available to the 'eq+drive' proto as well.

I'm tweaking the PSU to give variable HVs, which can also used for the 6as6 screen and plate supplies. The bipolar supply ( among other things) is set to a voltage divider with pot to give a variable CV from -10V to +10V dc at very low current.

Also have a pot as the 6as6 kathode resistance, with a wired in/out bypass cap.

---

First off, the EQ consumes a lot of the 6as6 gain as makeup, so I don't get any really crazy gains over that pentode (so far). I haven't really achieved very high gains yet, still learning about them.

I've been testing such that I can easily remove the eq feedback around the pentode and see the effect it has.

So, first issue is my eq curves are little weird and second issue is the pentode stage gain is not high enough yet.

I have found so far (as expected!), the screen voltage makes a lot of difference to the pentode setup, as does the cathode bias as well as the input signal voltage and the plate resistor value.

So - all quite standard and yet with issues there.

The triode/pentode mode doesn't do so much yet, but I haven't really found good bias settings yet
so hard to tell while already playing with plate and screen volts etc.

So far, CV -10V to -4V causes no output, CV > -4V thru 0V and to + 4 and beyond volts increases amplitude to a point then no further effect

I seem to end up with around 2.7V on the kathode, +2.5V on the CV, with plate and screens around 120V.

So - quite early on in the fun there - together with playing around with EQ makes for a very interesting and challenging circuit. I may well change it a great deal. I've been subbing the 6as6 with another ef86 just to get a handle on the whole thing!

Not much help as yet on how this pentode works much less sounds! Without even thinking yet of some of the neat twists that Bernbrue is doing  8) 8)

But I'm working on it 

Will post on my progress.
This guy is my current focus while I do the metal work for some other stuff.

One thing I will say - the orange 86 is very nice and the poorman works very well with it.
If I can get this 'eq + drive' module going, it will be another fine addition to my line up of crazy, modular  channel strips. Funnily enough, I end up using these ones the most.

Cheers

 

[alexc]

Here's a link to the Angelfire '3 band eq you can love'  (towards the bottom of the page)

http://www.angelfire.com/electronic/funwithtubes/Amp-Tone-A.html

and a pic of my front panel (so far!)

PS The Angelfire site is pretty awesome. Lots to be learnt there. Thanks Mr Angelfire 8)

 

[alexc]

Another EQ I like very much could also be adapted - from the fender pa100 mixer amp
(silver face tube). It has +/- Bass and Treble knobs and is surprisingly effective.

In fact that whole input mixer is pretty great sounding.
I wouldn't at all mind a version of it in rack.

I did a mashup of the relevent circuit section which I've attached.

 

[drask]

Thank's for all Alexc.
It's a very interesting project. I hope to ear sound early

Great monster =D

 

[bernbrue]

Alexc,
I played around with the ampegs mid range eq section in my prototype right after the 6as6. Holy moly, that´s gonna be implied in the Rude Tube II built. The bright switches and the rest of the EQ section is also very interesting. It might be good to investigate about the 12DW7 , since it is used in the ampeg amp and the "vulture solo" as well. To be continued.
regards
Bernd