The Rude Tube

[Kingston]

I guess I was just too enamored with this:
http://www.youtube.com/watch?v=-D9UwfcivsY&feature=related

Surely you realise there is some damn impressive mix and bus compressors happening before it was sent to the culture vulture?

That's a great sound, but the only thing I hear from the culture is the usual tube fart people these days are mostly trying to avoid. If that raw mix was sent to tape instead and distorted equally it would actually sound good.

 

[baadc0de]

I guess I was just too enamored with this:
http://www.youtube.com/watch?v=-D9UwfcivsY&feature=related

Surely you realise there is some damn impressive mix and bus compressors happening before it was sent to the culture vulture?

That's a great sound, but the only thing I hear from the culture is the usual tube fart people these days are mostly trying to avoid. If that raw mix was sent to tape instead and distorted equally it would actually sound good.

What I read from the youtube description seems to imply that the vulture was first and phoenix for buss compression later. Could be the way you described it too, I haven't had time to play with CV, just heard it once at another studio. Btw, would you care to draw any comparisons of CV against Drive-1?

 

[Kingston]

What I read from the youtube description seems to imply that the vulture was first and phoenix for buss compression later. Could be the way you described it too, I haven't had time to play with CV, just heard it once at another studio. Btw, would you care to draw any comparisons of CV against Drive-1?

Seems to me there were some crucial steps missing from that youtube description, like how the entire drum mix was carefully crafted. And that compression is unlike any phoenix I've ever heard. What other 2-3 compressors did he not mention? That bass on the other hand is culture vulture exactly as I know it, as are the many demos by drask and bernbrue. I wouldn't put it on a drum bus just like I wouldn't drive drum bus through a guitar preamp either.

As for Drive-1, it's a more subtle thing, and bass is much better controlled (since there's an active EQ stage in it). Something that was designed for bus duties and not so much an obvious "tube effect" unit like the CV. At the most extreme setting it doesn't so much "fart out" like CV, but clips in a strange high gain guitar amp style. That part I don't like so much, but for screaming vocals and hard leads there's probably no equal. Not really my style though, and that's why I'm still (forever?) searching for that golden tube distortion.

I'm actually planning another overkill unit that puts other overkill units to shame. I will steal a trick or two from the CV as well.

 

[bernbrue]

I´ve never heard or seen a CV in real life, but as far as the Rude Tube is concerned, it compresses in a really nice way. Distortion is different from this typical Marshall/Fender distortion. You may find it nice on synths, bass or even guitar, but it doesn´t sound like a guitar amp.  Clean pentode or triode mode is great for adding 3rd/2nd harmonics, the effect is subtle but clearly audible. I tested the Rude Tube on a drum bus with these settings and I really liked it. Rude Tube II is an attempt to get closer to a guitar amp sound. Cap values play an important role as well. I´ll have to experiment with different values and tubes as well.
regards
Bernd

 

[alexc]

Well I got back to this and finally am stitching up my version of a eq+preamp with a 6SA6 switchable pentode/triode mode gain stage, variable dc control voltage and variable cathode bias voltage.

So I've settled on cathode bias range of 1V to 5Vdc  and CV range of -7V to +10Vdc and running the pentode mode at a gain of x90 with typical cathode bias of +2.0Vdc and CV of +2.0Vdc. Around 130Vdc on plate and 75Vdc on screen from a 258V B+ regulated.

In triode mode, the gain drops to x21.

It's driving a 100K 'post' pot then into a 6N5P (ac coupled) white cathode follower to 15K:600 output traffo.

It's fed by a balanced input to small 600:600 input transformer followed by a feedback 3band
baxandall style EQ using a 6N2P configured as a grounded cathode amp + cathode follower and 100K 'pre' pot.

The gca+cf has a gain of x60 (quite a cold bias) and the eq feedback is around -32db, meaning the whole eq+preamp can easily take input signals from around 4Vpp to 80Vpp. I will adjust the bias of the gca again when I integrate this into it's channel strip. B+ is 285Vdc regulated.

The whole thing is nice and stable and noise is in line with what I expect. I'll focus on that when I integrate this into it's channel strip  (Red47 -> EQ with drive -> Poorman 660).

The frequency response is totally flat 20-20KHz when being driven by my Motu and output to the Motu audio interface.

To Do :

Tweak the pentode/triode biasing of the 6AS6 with a variable mode thingy.

The CV dc voltage could probably use some 'smoothing' if possible to mellow out the transition of the 6AS6 from 'starved plate' kind of sound at negative CV to the 'turbo boost' kind of thing at positive CV. That could include some 'Bernbrue Rude Tube' style filtering around the pentode.

Elevate the heater or add a step-network (more likely) between the gca and cf so as not to exceed the cathode/heater max voltage of the 6N2P tube

-----------  How's it sound? 

GROOT! Very happy right now.

Playing my guitar thru a clean active DI to around 4vpp into the eq+drive module sounds very nice indeed. Clean to unmistakably crunchy to heavy distortions. Sounds more 'interesting' than my previous 'overdriving of a gca with voltage divider' style of distortion. Much more  crunch more easily achieved without 'fizzyness' using the 'CV' knob and 'pre' knob. Lots of gain adjustment further available on the 'cathode bias' knob. 'Level' knob provides overall gain control.

The EQ is quite subtle, being a 'hi fi' style baxandall with dBs+15/-15 150Hz, +5/-5 700Hz and +10/-10 1KHz and flat with all bands centred. Makes a nice change from my previous tone stack or pultec styles.

So - very happy indeed. Tubes and transformers with pentode drive. Just fab.

Now to tweak, integrate and cleanup.


Cheers

 

[bernbrue]

Hi Alex,
interesting stuff. I´ve would like to ask a few questions. The CV for G3, is it changing the sound substantially that it is worth to make a bipolar PSU? What would be the ideal fixed voltage to feed G3 for distortion? How are you going to implement this, with a dedicated pot on frontpanel? Would it be possible to combine the adjustable voltage with a dual bias pot? I have a "ready to experiment" setup on my bench right now and start to breadboard the distortion stage shown above. It will be switchable with relays. I´m thinking of combining it with a mono LA2a as a kind of channel strip with mic/line/DI preamp, switchable "flair"or "distortion" tube stage and compressor for guitars, basses and vocals or whatever suits. For smoothing the CV to G3 it might be good to put a cap between G3 and ground.
kind regards
Bernd

 

[alexc]

Well I'm in the home stretch now!

Got the EQ working as it should, as well as having tamed the  6as6 pentode/triode switching nicely and finally, balanced up the WCF output section.

Noise floor is pretty good considering all that is going on gain wise here

Today I did some rearranging of a few things in order to nail down the Orange 86 I am using as the front end.
Noise is really good as stable. Able to switch my mic, line and HiZ inputs and use all of the gain available with an acceptable noise floor.

On the line input which uses a 600:600 haufe input transformer and no additonal pad  (so far), I am getting noise floors of -82dBu (measured as an spl 20-20KHz) for loopback, -80dbu for maximum nfb and -60dBu at min nfb

Thats for max 35dB of gain (using 6N1P paralleled to Edcor  15K:600  x5 stepdown traffo on the orange86 output).

So firstly I have to say that the Orange86 is really, really good  8) Well done to Charlie Guavatone!

Now I have theOrange 86 working right, I can say that is is just amazing on an electric guitar - a jazzmaster in this case.  No messing around - turn it up and what a harmonically rich, slightly compressed and authoritative sound it is.
Easily the best clean electricguitar preamp I have built. Awesome harmonic content I've not yet achieved with triodes
(this is my first pentode pre attempt). This into my Motu audio interface input mixer, rounted back out and to a stereo monitor amp - and old hifi with push-pull EL84s  ;D

So - thats *just* the preamp!  I still have to fine tune the ef86 operating point for higher gain than the x64 I seem to be getting right now, but basically its rocking very majorly.


-----

Now the eq with drive section is good - totally flat response at the end of the nfb eq+GCA+CF and into the Rude Tube pentode.

Very nice curves, quite subtle shelving centre flat. Hifi style.

The gain across that eq+GCA+CF is more or less unity and can take very hot input signals from the Orange86. Easily up to 38Vpp that it can put out. The nfb part of the eq reduces this way down at the grid of the GCA. I have a 'Pre' pot on the end of the GCA+CF.

This EQ section picks up some nice GCA+CF warmth along the way too!  That feeds the pentode like in Bernd's Rude Tube. And all is still well and quiet noise wize

On the 6as6, I have my operating point pretty much sorted, the CV works fine, the pentode mode gain is x90 or so and the triode mode is around 22 or so. I am adding the variable morph to my mode switch : a lorlin switch (Mode) and a pot (Morph).

The CV is done like this : I have a regulated +12/-17V from the Poorman PSU board I'm using in this channel strip.
I feed them to the ends of a 100K pot and take the centre as my CV. I add resistors on each end to match the travel of the pot at the extremes to  around  -7Vdc to +10vdc. I feed that CV into g3 of the pentode.
So this is the 'Drive' knob.

Have a 2K pot on the pentode cathode with a resistor in series to allow me to vary the cathode bias from +6Vdc to +0.5Vdc. So this is the 'Bias' knob.

Now the pentode output is ac coupled to a WCF. I may need to change that because I need some control before the wcf. Can't really put a pot to ground there. Don't want to use global nfb as it would defeat the purpose.

In fact I may not need a 'post' pot, as this is what the bias+drive basically does. Kind of.
Still to finalise that bit.

I like the step down with the 6n5p wcf with 15K:600 edcor output of the  eq+drive module. Using 220V B+ with 1.5K on the plate, 220R on the kathode and in between tubes. Have 100V in between tubes and +2V or so on the lower kathode. Should be balanced pp for a 15k load. More or less.

Still have the option to elevate heaters (all the heaters are dc floating and not referenced to ground)

Right - my first problem is I'm seeing some low-freq rollof in triode mode, and additional hifreq roll off in pentode mode of the 6as6. It's independant of level and occurs at the output of the pentode and before the wcf. Taking just the pentode out of circuit and all is flat as.

Still to figure that out too. I thought pentodes didn't have a lot of miller capacitance so it should be something else?


---

And so making great progress. Should be buttoning it up in a week or two. Just need to sort out those things and do the remaining integration and testing.

-----

The rude tube part is really interesting. The CV acts like a 'gain moodulator'. It only does something when the 6as6 is set up for high gain.

In triode mode is does very little (to level - not neccessarily to harmonic structure : still to check that out).
In pentode mode, if the tube is biased for strong gain, the CV is just like a volume control.
It varies the harmonic structure a lot - obviously, as it is varying the degree of drive going on in the tube.

Still making observations, but in sound it is like a volume control or as a distortion control if you are pushing it already.

So in use, one has the mode to fool with and then the degree of drive. The 6as6 can be fed with anything from 0 to 40Vpp.

Using the 'Pre' knob starts the drive ball rolling and the 'Post' knob is just a master volume.
The crunchiness is dialled in using the bias and drive controls. And maybe the 'morph' too!  ;D

----

Now the CV knob can be somewhat irregular in control depending on where it is. There's a kink around -3Vdc or so.
Before that, the pentode is kind of starved and bedraggled. Very distorty and kind of thin. It goes down all the way to shutting off the tube practically. Above the kink, it's pretty smooth to +2V or so. On to 10V and it increases the gain, but less so as you get closer to +10Vdc. So the action is kind of -3V to +2V but is usable all the way to +10V for the max gain condition.

So the CV probably needs some smoothing. Could be some kind of r-c or evn r-l-c like Bernd!
Not sure yet. Right now it does what I expect from the data sheets more or less.

What Bernd seems to be doing is linking it to the kathode bias with interesting filtering.
And that's where I'll be soon. Trying some things out and seeing what it's like.

I'm also planning on some simple hpf and lpf at the end of the pentode.

Have to say, this monster has been a fine learning experience. I went from  never a pentode to listening to the subtlties of pentode screen, suppressor and plate biasing! Not to mention baxandall eq'ing all on top of a Poorman 660.

This has combined at least four of my favourite things!

Cheers and thanks for reading  that rambling lot.

 

[alexc]

> The CV for G3, is it changing the sound substantially that it is worth to make a bipolar PSU? What would be the ideal fixed voltage to feed G3 for distortion? How are you going to implement this, with a dedicated pot on frontpanel?

Probably not. Could get most of the benefit with just 0Vdc to +10Vdc.
I'm using 'Pre Level' knob -> 'Pentode/Morph/Triode' switch + knob -> 'Drive' -> 'Bias' -> 'Level'  knobs.

>Would it be possible to combine the adjustable voltage with a dual bias pot? I have a "ready to experiment" setup on my bench right now and start to breadboard the distortion stage shown above. It will be switchable with relays.

Sure.

The way I understand it, 'advancing' bias knob increases + bias voltage and so decreases gain.
                                    'advancing' CV on a knob increases CV voltage (from -ve -> =+ve) and increases gain.

But  both the bias and the CV do similar things
ie. allowing more current to flow so really, any linking scheme could have merit.
Opposing each other or adding to each other or any which way is fine as long as it works.

> I´m thinking of combining it with a mono LA2a as a kind of channel strip with mic/line/DI preamp, switchable "flair"or "distortion" tube stage and compressor for guitars, basses and vocals or whatever suits.

I would!  My first tube strip is triode pre+fender tone stack+LA2A. It is really good, but I'm thinking I may retweek the input pre. After this experience I think I can do better than the standard 2x AX7 setup.
The hard part is putting in the EQ!

>For smoothing the CV to G3 it might be good to put a cap between G3 and ground.
That's what I'm hoping. Just to make it a little less twitchy in the -ve  voltage region.

Somehow I think I'll leave the really fancy CV filtering to your design and drask's pcb!
I want to button this puppy up and get it to my lounge room.

Thanks for the rude tube Bernd - tis a lot of fun. (now the crap part of this build is done!)

 

[alexc]

Another good day of diy 

Spent it checking the pm660 module - all working perfectly and fully integrated with a relay bypass.

Worsened noise floor by about 2dB when engaged with no GR and unity gain.
Which is very good.

Adding the rest of the lights and VU long leads worsened again by around 1.5dBu.
Not too bad - I think I can reclaim this when I reference the heaters.
I see up to 3dB or sensitivity to noise with the floating dc heaters.
I have a VU buffer module, so I may use that if it improves distortion and maybe noise.

So far, the Orange86+PM660 and all relays, meters and light shows, gives a noise floor of around -75dBu
(vs -82dBu for loopback  ('spl' style of measurement, 20Hz to 20Khz) with both at unity,  for line input and outputs connected to my Motu - which is around 7dB worse than loopback.

Tomorrow I do the integration with the eq+drive block and the eq relay bypass.
Hopefully that won't cost too many dBs in noise.

I've reinforced the grounds with heavier guage solid wire to get the dc to ground resistance at all the interconnect ground points as low as I can and it's looking quite good and very stable.

-------------------------

So during my freq sweeps of the orange86, I can see a little low freq roll off - maybe 1dB at 20Hz with a little resonant bump just before. Pretty good.

But I think I have too much hf roll off - about 5dB at 20KHz, starting at around 2.5KHz and 3dB down at 10KHz or so. That's not too good ???  So I need to resolve that too.

It appears to be very similar to what I get with the eq+drive's 6as6 pentode - I think it is screen bias/bypassing which is the culprit in both cases. I know the operating point on each of the pentodes is not quite right.
So I will focus on that shortly.

The PM660 is pretty much completely flat with no GR. It has around 16dB of total gain available with 6N5P signal tubes. Am easily getting 14dB GR here using 5687 side chain tubes.

Under strong GR, all holding together nicely - a tad less hifi than just the orange alone with very nice spongy GR.
I did the usual time constant mods so I have slow to vfast settings.

Apart from my Orange roll off it all works very well. Sounds  bloody great. With moderate GR, say 8dB, and moderately fast release, I don't really hear any additional distortion, so quite happy with that.
More GR at fast settings gets a little more crunch.

Noise is well below audible even with quite strong levels through out. With around 12dBu of overall gain (making up around 12dB of GR) with no signal, the noise floor is worsened by around a further 5dB to probably -70dBu.

I think I have another 18dB of gain to go before the noise becomes too audible at -60dBu or so.
Beyond that is noise gate required territory.

This is by far the most challenging part of stringing together a bunch of modules in one box. It takes methodical step by step additive checking until finally the whole stack of plates holds up ;D

All sounding good with electric guitar, with the poorman limiting taking just a little away from the Orange86's full fidelity.

--------------

Tomorrow will be interesting : first time I'll have heard the whole strip together!

Then I can tweak some more rude tube configs before 'finalizing' and printing my front panel label.

Regardz

 

[bernbrue]

Hi Alex,
your progress report is very educative. I´m going to try a few of your ideas soon. I´ve got a new prototype running on my bench now. At the moment I´m testing the 6ak5 (EF95) (G3 interally connected to cathode) as distortion tube, which is very interesting and less harsh in sound in comparison to the 6AS6. I´m trying to find an alternative to the bias setup and different pk modes. I had some hf roll off with the redd preamp as well, which was mainly caused by the missing overall feedback loop and placement of the output pot. I tried it after the ECC88 tube and realized a hf rolloff when decreasing the output volume. I´ll report back soon.
regards
Bernd

 

[alexc]

Sounds very interesting Bernd.

I would like to get to the place where I can audition some of those filtering networks you use. Maybe soon.

I've gone a little pentode mad myself.  ;D  Adding the EF85 to my reading list  ;D

I have my plan for the next tube box - again with the orange 86 then to RuffRecords Helios eq board when it is available,  going to a 6BC5 pentode and onto a single ended 6S4A triode to gapped Carnhill 9600:600.

That will be the front end for my in-progress standalone Poorman MKII, using PM660 PSU as well as inductor PSU.
8x pentode GR tubes. And 10W of PP 6V6 - pure, 'primitive design' brute force cap charging current.

I also am using some of the small power pentodes in SE and  PP amp configs - EF95 and 6AQ5 so far.

---

Just today I slayed the noise dragon in the integration of my Orange86/Baxandall/RudeTube/Poorman strip.
Took a while! Lots of learning regarding grounding schemes, heater schemes and so on.

So far  I have unity gain noise floor losses of 1dB for the Orange, 5dB for the EQ+Rude Tube and 2dB for the Poorman Limiter. I think I can improve the EQ+Rude Tube maybe another 2dB or so.

That just leaves me to figure out the freq response issue on the Orange (high freq rolloff) and the same thing in the 6AS6 pentode mode. Hopefully I can do so soon - I think it is the choice of screen operating points, which I will refine some.

With luck, tomorrow I will implement the mode morph switch/pot and the CV end points (-7V and +10V).

Next day will be the listening where I decide which 6as6 controls to retain from the set of bias, CV, pre, post and morph. Maybe I keep them all!

So happy - I spent days and days 'integrating' the noise out this monster, but the gods have been kind to me.

I'm nearly there.

What I have heard so far is a BIG step forward from my previous attempts at triode gain stages in terms of complexity and (dare I say it) 'maturity' of the egtr sound.

I now have a dual AX7 Mesa Blues Rocket distortion box to sell!

And I would never have even tried except for your original Rude Tube work!

Thanks kindly  8)

 

[bernbrue]

Hi Alex,
I just fiddled around with my new prototype. What a pleasure! Concerning G3 of the 6AS6 I tried almost all possible connections and must say that connecting to cathode sounds the best for me. Yes, there is some kind of extra gain and distortion flavour when feeding G3 with 0-10V, but for my taste it´s a little bit to harsh sounding. I tested some cathode bypass caps and I think that I´m going to built it with no cap at all as standard setting and add some switchable bypass caps with inductor in series to ground. I didn´t try a 1M pot for blending between triode and pentode. I simply replaced the pot with a 1M resistor and switched between screen and ground. The triode mode sounds a bit strange (dull). I have to check that. There is also no attenuation in front of the drive pot. Just the drive pot and thats it. A relay simply switches the 6AS6 stage in and out. The REDD Amp is fantastic for DI.  A clean guitar or bass sounds really round and fat. Enjoy the time with listening to your "Frankenstein Channel".
regards
Bernd

 

[tardishead]

are there still going to be PCBs for this project?

 

[bernbrue]

Hi,
Drask has designed a pcb for this. I don´t know when he is going to let it fab. But yes, there will be a pcb of my 1st prototype.
regards
Bernd

 

[Zachery]

Read through this thread, very interesting actually might be my next build. Quick question I read earlier you didn't use the redd psu, and you used a version of the daoc as the power supply. I notice the daoc operates at approx 235v and your unit runs around 290v. I was just wondering if you could point me in the direction of how to make the psu or update the daoc psu? Not asking for a direct answer or anything, if you want that would help, but Im all about reading and learning so even a point in the right direction would be helpful.
Thank you.

 

[bernbrue]

Read through this thread, very interesting actually might be my next build. Quick question I read earlier you didn't use the redd psu, and you used a version of the daoc as the power supply. I notice the daoc operates at approx 235v and your unit runs around 290v. I was just wondering if you could point me in the direction of how to make the psu or update the daoc psu? Not asking for a direct answer or anything, if you want that would help, but Im all about reading and learning so even a point in the right direction would be helpful.
Thank you.

Hi,
the high voltage rail is the same as the D-AOC PSU. You´ll see about 290V when measuring before R128 (470R). Look up the schematic and you´ll see what I mean.
regards
Bernd
regard

 

[alexc]

Bit more on my Rude Tube travails ...

After I had integrated my eq+drive module into my Orange86+PM660 channel strip, I found that with the high pentode gain, the noise floor became too high.

So I began to chase down the cause - I was seeing very high noise increase with the CV and kathode bias set for pentode gain of 33dB, CV at +2V and kathode bias at +2V. Input signal at around 4Vpp.

Firstly I found I had a very high ripple on the rectified, cap filtered heater supply. The standard circuit had 4700uF before a 0.5R dropping resistor and 4700uF after, supplying 4.65A of current. The circuit is referenced to common ground.

I was seeing around 50mV of hash on heater ground with respect to chassis ground and several volts ! on heater +ve wrt chassis ground. A sawtooth wave shape, 100Hz.

So I added some more capacitance, for a total of 20,000uF at the rectifier +ve and that dropped the noise floor quite a bit. (several dB).

Some (Duncan PSU) simulations shows that I need more like 50,000uF or 10,000 x current rule of thumb. And placed at the rectifier +ve terminal, before the dropping resistor.

While I wait for more 4700uF caps to arrive, I continued to re-inforce grounds with some small improvement there.

But still no cigar 

I rebuilt my prototype block by block starting with loopback noise floor -> -83dBu (spl 20-20KHz BW)

- WCF ecxtremely quiet - as expected for something with -14dB gain to output  -> -83dBu

- With 30dB gain pentode mode, no variable CV, no pre or post gain pots -> -60dBu
  Not too bad, given I have still quite a bit of heater/PSU hash floating about, maybe 20mV at the grid of the pentode

- added pre and post pentode gain pots with no real difference -> -60dBu
  Pre pot rotation, no effect on noise floor. Post pot improves noise floor as gain is reduced (as expected)

- CV added (+15V connected to -17V thru 100K pot, tap is CV)  -> -48dBu with pentode set for 30dB gain!

So there it is - the CV circuit I have used is adding some huge 50Hz/100Hz spikes.

OK - so I removed the CV and connected 6as6 G3 suppressor to kathode.
Noise is reduced as before to -60dB. So thats 20dB of noise for a gain of 30dB or so.
I think the additional heater caps should improve that 5dB or so. Maybe 8dB if I am really lucky.

The problem then is :

Kathode bias turns out to be  around 0.5V to get that 30dB gain.
Biasing colder to 6V or so kills the gain very rapidly.

So if I want lots of gain on the pentode, I need the bias very hot and so it distorts quite ugly-ly!
If I bias cold then tone improves as distortion disappears.

Before, when I could vary the G3 from -4V to +10V and the kathode from 0V to 6V independantly, the distortion was much more contollable and nicer in character.

Connecting the bias and G3 together is basically killing the G3 'gain modulation/multiplication' effect I was seeing.

The guitar now sounds quite 'ring modulation' like with the CV and kathode connected and hot biased (0.5V)  or quite undriven with bias cold (6V). No real useful middle ground.

---------

I need to check some more but that seems to be happening.

I subded the 6as6 for a standard pentode 6bc5 (G3 to kathode) and found the same sort of effect. Harsh distortion at hot bias or none at cold bias.

Phew! As always, just then you think you have a result, an understanding .... reality pops up and bites your ass :

Cheers

 

[alexc]

I figured out part of my issues - the reason why I have no useful distortion in my eq+drive module is :

When I last wrote that I had achieved some 'grout sound', I had a wiring error in my white cathode follower (wcf) output stage  :

Turns out that the wcf lower tube was turned off due to incorrect wiring, making the top tube function as a sort of grounded cathode amp (GCA) biased very hot (0.5V). It was being fed the huge pentode output, via a 1M 'post' pot and so was distorting this non-WCF GCA stage strongly but controllably.

Which sounded really good 

When I rebuilt that section after calculating the correct biasing, I ended up with a wonderful sounding WCF with no distortion even when fed with very high amplitude signals.

So what I was now hearing was essentially the pentode gain stage alone - because that is being fed by a unity gain eq block (unlike the Rude Tube, with a high gain GCA), it is not easy to distort, occurring only when essentially biasing it at 0V. And the the distortion is is not real nice!

I will now use a parallel GCA , same as Bernd's Rude Tube. For kicks, I will also try a GCA+CF combo as well.

I still haven't resolved my variable CV supply noise issue - I'm using the G3 to kathode connection for now.
But I hope to sort that out before making a decision about which way is best.


Life's a learning experience!

 

[glbaudio]

for who interested, i've putted a case production request in the DIY-Racked.com site, here the link:
http://www.diy-racked.com/diy-talk/viewtopic.php?f=7&t=212
pls add any clue to let him do it! ;-)

 

[bernbrue]

for who interested, i've putted a case production request in the DIY-Racked.com site, here the link:
http://www.diy-racked.com/diy-talk/viewtopic.php?f=7&t=212
pls add any clue to let him do it! ;-)

No,
please don´t do that. I mentioned it in the Rude Tube pcb thread. For personal reason I don´t want to see my project in any of Purushas case. I don´t want that Purusha makes money with my project. I would really appreciate if you respect my opinion. Further details in the pcb thread.
regards
Bernd