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01-03-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 141
Post ID: 25221
Reply to: 25219
Tube change simplicity
 Paul S wrote:
Anthony, congratulations on getting your project to this point!  I mention without referring back to your schematics, I think you will be glad to have test points, along with variable resistors (trim pots) to re-set operating points, as needed, if only for normal drift. This can help avoid insanity down the road, and it also give you the chance to "dial in" your operating points by ear, when you are ready to do this. Again, I am not sure what's called out. In any case, ESR changes with X/O changes would make VRs useful there, as well.

Best regards,
Paul S


Thanks for your words Paul.  I am very tempted to make the tube change experience as simple as possible, without mucking up the look to the whole amplifier.  We will see what I can come up with.

Cheers,

Anthony
01-03-2019 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,624
Joined on 05-27-2004

Post #: 142
Post ID: 25222
Reply to: 25218
So far so good...

 anthony wrote:
Thanks for your thoughts Romy.  Last night I roughly wired in some random crossovers….
I wrote a loooong replay to you after that post but my 2.5 yo son turned off my computer while I was posting it. Hate to rewrite it….Your chasses design look spectacular by the way. In many year what your will dive back to that amps you will not believe you did it.
 
 anthony wrote:
So, six channels are now operational in the first DSET.  By up I mean the anode voltages on all tubes is about right and the currents are in the ballpark of where they need to be.  I am yet to check the DC Offset so hopefully that goes ok.
Congratulations. Do not be too anal about the anode voltages. For both stages anything above 175 will go, do care about plate current, particularly on the driver stage and at DHT stage.

 anthony wrote:
The Channel B is still an issue of sorts.  I have reduced R5 from 12k to 5k to get down to 200v at the anode of the 6e5p.  For the life of me I can't figure out why because all components in the bias string are the correct value and the cap is polarity correct.  Channels A & D also operate from the same arrangement for the positive bias and they hit their targets first time, so to my thinking it must be an issue in the negative bias string, however that string is correctly installed.  So, I have a decision to make.  In Channel B, assuming that I use a similar first order  RRC Low Pass filter at the start, do I reduce the 30k resistor by 7k, or do I reduce the 12.1k resistor that sits closer to the grid by 7k?  I am leaning toward changing the crossover resistor, and am not even sure either will make an audible difference.  
I am not sure what you have in there, I would keep the R5 as is. You should have -150V at point #06 that should burn in the 1K and 420K resistor, arriving at driver tube grid at ~-4V. You need to short the chela B input and to measure the -4V at grid. At that time of you have 200V on plate the tube will be completely operational. Then you apply positive bias on the left side of the filter (resistor 30K). The voltage on the left side will be different and you need to turn you positive supply trimmer to set it to 0mv. The p[point is that positive supply need ONLY to get rid of current flow over the filters, the amp should work fine of you short the inputs.  Make sure that you .043uF cap to ground is not shorted. From what you describe it might be the case.

 anthony wrote:
One thing has become very clear to me while sorting out this first DSET...the crossovers in Channels A-D affect the operation of the bias, so when changing filters I may have to re-tune the bias for that channel. 
Yes and no. Your bias is your 12.1K resistor, pretend it as a virtual buttery. Or you can pretend it a firewall for you bias voltage. Now, when you calculate a filter you do it considering the load impedance, in my case it is 12.1K and I intentionally too keep it the same in all channels. There are too many variables to equate if you begin to change the bias rector. The key point is that if you change filter resistors AND bias resistors then the amount of voltage you have available in positive bios supply will not be enough for you to set 0V at input. So, you would need to assure R11 resistor to make sure that you VR1 will be able to set 0V in the middle of own operation. To me it is too many changes and I prefer to keep my bias resistor at 12.1K and if I want to change the crossover point then I just adjust the series resistor and the cap to ground. There are two things you need to recognize. First, in the channel B the first restore 30K and shunt 12.1K are not a filter but voltage divider that mitigate the volume of the channel output. The filter is a combination of 30K resistor and cap to the ground. Second, is that when you change you filter make sure that in your circulation you use ONLY Bessel curve, it is important.
 
Generally speaking I would be interested to know how you like to change the crossovers. I feel that sine you have the same configuration as I do I know that result you should be getting and there is a HUGE amount of time invested into this thing to do experimentation, listening, testing, measuring etc and there is not a lot known to me room for improvements. Trust me it has  nothing to do with ego  and I will LOVE to learn if you fine any better way to organize what has been organized, unless you use other compression driver…


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
01-03-2019 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,624
Joined on 05-27-2004

Post #: 143
Post ID: 25223
Reply to: 25220
Keep dong what you do...
 anthony wrote:
Looks like I spoke too early.  When I made that statement I'd only tested the voltages in the DHT Channel and they were pretty close to correct...but when I put a tube in there it glowed a little too hot so I quickly shut it down.   Bugger!

What tube do you use? I hope you did not experimented with 4V tubes! When you have the things in test state then get any cheap tubes (45,2a3 etc..) and to experiment on them

 anthony wrote:
Romy, without any DHT tube in place, I have 403V coming out of the big filter cap for the DHT Channel (separate power supply) and 147V/8.3mA at the anode of the 6e5p which is a little higher/lower than the 140V/10mA on your schematic.  I am wondering if this lower current could be the problem?  I added some more resistance to drop the anode voltage and although I thought it was going to drop it 9V it only dropped it 3V, and the anode current remained at 8.3mA.  Tomorrow I will drop the anode voltage further so see if that raises the current.
The DHT channel is direct coupled, so you need to be very careful with it as the plate on the driver tube acts as bias of the DHT. The 147V/8.3mA you got is OK if would not make the DHT to flash. Make sure that when DHT get high voltage the pate voltage of the driver tribe has been stabilized.

 anthony wrote:
It would be great if you could remember some of your time with the DHT Channel.  I've only just got my head partially around your IDHT Channels and this circuit is almost entirely different again. 
Well, the DHT and IDHT are different animals for sure, the driver state look very different for them in my amp and here is the reason. I wanted to use the same driver tube for sure and I want it to be direct coupled. The problem that the 5E6P has too much gain to drive my IDHT directly, so I need to reduce the 5E6P gain. I went to a classic cathode bias. The cathode bias has been wonderful but it has a major problem: the cap on cathode. The cap is need there to get the nominal tube gain but in my care I need to gain. So I left the cathode cap out and get my IDHT the lower voltage it needed. I do not remember the numbers now, you need to look in the thread where I experimented with it. I can post a link if you want me.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
01-03-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 144
Post ID: 25224
Reply to: 25223
In my dreams
I woke up this morning to have the brightest thought that my DHT issues are probably caused by how I have wired up the filament transformers.  When I ordered all the transformers for this project I gave Lucas of Black Art Automation the design brief 'build the best you can'...that's kind of like signing a blank cheque...but we talked about building tight regulation transformers on big cores with minimal heat gain et cetera, and one of the things that he did was make individual 2.5V and 4V transformers for the DHT filaments.

There's nothing wrong with that of course but they are also centre-tapped, which I was not expecting.  I have brought the centre-tap into the amplifier chassis and bonded it to the chassis ground, which I am thinking is not allowing it to float to make the 184V reading at the DHT Cathode: it stays firmly planted at 0V when the DHT is getting too hot.  

I hope that is the issue because I would also like a couple of extra wires in the filament cable so that the 12.6V filament supply can be parallel wired to offset a larger than expected voltage drop.
01-04-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 145
Post ID: 25225
Reply to: 25224
Aaarrggghhhhh
 anthony wrote:
I woke up this morning to have the brightest thought that my DHT issues are probably caused by how I have wired up the filament transformers. 


After rewiring the filament transformers this morning, I have spent all day trying to figure out why there is next to no current flowing across the cathode resistor of the DHT tube.  Wiring was checked every which way, measurements were taken, exasperation mounted, everything was ruled out, I even rewired half of the circuit just in case I had a broken wire somewhere...India is thrashing us in the cricket...nothing was going to plan.  I was miserable.

Then I swapped the used YO186 I purchased just for this testing stage and put in a NOS 1939 vintage tube and the circuit worked straight away with all voltage and current targets just perfect.  Put in a 45 and it was just as perfect.

Good to have it working though...just wish it had been 8 hours earlier!  So all 6 channel of the first DSET are now operating.

The DC Offset would not trim to zero and 0.1mV was as low as it would go before running out of trimpot.  The pot from one end to the other would only adjust the DC Offset by 0.7mV, which is much less than I thought it would.  My 0A2 are quite closely matched for voltage and are within 0.3V of each other.  Swapping the tubes had no effect on the DC Offset so I might have to play with another tube to cancel that offset to zero.

With the input shorted I made some quick noise measurements at the output of each channel:
A - 0.2mVAC
B - 0.2mVAC
C - 0.3mVAC
D - 0.25mVAC
E - 6.7mVAC - I assume this is hum and it was a little dangerous to reach around to the hum pot to try to eliminate it so I did not - should be able to do better than this
F - Held the Lazy Ribbon to my ear and could hear not a thing.


The noise numbers are quite good so I don't think there will be any major wiring changes required for the second DSET, although I will reposition the amplifier so that I am able to try out the hum pot for the DHT Channel.  Next up I will make it safe and get a mate to help me lift it upstairs and into position.  Once there I will see if I can figure out the audio analyser and make some more checks and measurements.  I really want to make a detailed input impedance graph and I have the software here to do it...I think you would be interested in that plot Romy.


Woohoo!
01-04-2019 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,624
Joined on 05-27-2004

Post #: 146
Post ID: 25226
Reply to: 25225
Very good.
 anthony wrote:
I woke up this morning ….
It was funny that you named it “In my dreams”. Whan I was “designing” and building the Milq I had a lot of dreams about the problem I had. I am not am amplifier designer or some kind of DIY evangelist. In fact I had no truly DIY audio experience before it. I did my phonostage and the power amps because I did not had around me somebody who would do it for me at the level I want to do it. So, when I start to do the damn soldering I was learned a lot and for some period of time it become a very much become full time labor, not time wise but mind-wise. There was a period when Milq took so much time in my life that stopped do anything, literally anything but making Milq to sound right. In the epicenter of that period there was six months when I stopped working, stopped dating, stopped socializing with other people. I woke up 7 AM and went to beg at midnight, all time working on the amplifier and having 100% of time dedicated to thinking about the amplifier. My mind was so saturated at the time by the applier need that I have dream about Milq circuitry, Milq’s problem, Milq’s need… It was a lot of Kafka like dreams…. very certifiable. I am not sorry about that time and I even then had very defined feeling that after I do it I am not planning to do it anymore. So, nowadays if I need to dive into Milq to make some changes then I feel that I am rereading the dairies of my life… very interesting…
 
 anthony wrote:
Then I swapped the used YO186 I purchased just for this testing stage and put in a NOS 1939 vintage tube and the circuit worked straight away with all voltage and current targets just perfect.  Put in a 45 and it was just as perfect.

Congratulations… the old DHT are very finicky…

 anthony wrote:

The DC Offset would not trim to zero and 0.1mV was as low as it would go before running out of trimpot.  The pot from one end to the other would only adjust the DC Offset by 0.7mV, which is much less than I thought it would.  My 0A2 are quite closely matched for voltage and are within 0.3V of each other.  Swapping the tubes had no effect on the DC Offset so I might have to play with another tube to cancel that offset to zero.

 
Yes, I also was not able to make 0mv at DHT. This is fine. The best that I was able to do is 0.4 at one and 0.6 at another amp. That all are very fine numbers. Anything below ~10mV are perfectly fine. If you stick you head to the MH hosts and to correlate the auditable buzz with DC offset on DHT then you will not hear anything under 10—15mV. So, whatever you have: if you do not hear from the speaker then you are fine. Mind you that as the amp juts start you might have a minor HF noise and some glassy sound from speaker – this is from aging 5E6P that will go away as the tube worm up.  The DC offset at the amp input is more friendly and you should be able to make it 0mV



"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
01-04-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 147
Post ID: 25227
Reply to: 25226
Distressingly familiar
 Romy the Cat wrote:
 anthony wrote:
I woke up this morning ….
It was funny that you named it “In my dreams”. Whan I was “designing” and building the Milq I had a lot of dreams about the problem I had. I am not am amplifier designer or some kind of DIY evangelist. In fact I had no truly DIY audio experience before it. I did my phonostage and the power amps because I did not had around me somebody who would do it for me at the level I want to do it. So, when I start to do the damn soldering I was learned a lot and for some period of time it become a very much become full time labor, not time wise but mind-wise. There was a period when Milq took so much time in my life that stopped do anything, literally anything but making Milq to sound right. In the epicenter of that period there was six months when I stopped working, stopped dating, stopped socializing with other people. I woke up 7 AM and went to beg at midnight, all time working on the amplifier and having 100% of time dedicated to thinking about the amplifier. My mind was so saturated at the time by the applier need that I have dream about Milq circuitry, Milq’s problem, Milq’s need… It was a lot of Kafka like dreams…. very certifiable. I am not sorry about that time and I even then had very defined feeling that after I do it I am not planning to do it anymore. So, nowadays if I need to dive into Milq to make some changes then I feel that I am rereading the dairies of my life… very interesting…
  


To mirror your obsession, but not as the instigator of the project, rather as the duplicator, it has been my plan for some time to take off all of January to get my Melquiades/Macondo installed in my room.  Being self-employed with too many clients to keep satisfied that is not really going to happen but I do plan to be able to operate with the emphasis towards leisure rather than work for the next couple of months as a compromise, perhaps something like week-on week-off, but something at least very flexiblle.  My wife is with me completely in the desire to have this project finished, but I suspect for slightly different reasons than I. 


A sign of my obsession is that I have been too transfixed to respond to some of your earlier posts and comment....


 Romy the Cat wrote:
 
Your chasses design look spectacular by the way. In many year what your will dive back to that amps you will not believe you did it. 
 


Thanks Romy.  In the back of my mind I always thought that was the kind of self-reaffirming effect that I would like to have...to be able to look back and go "wow, I did THAT".  Even to have my son or daughter keep the system when I am gone and for them to have the same "wow, dad did THAT, and I remember him doing it when I was just a kid"
  


 Romy the Cat wrote:
 
Generally speaking I would be interested to know how you like to change the crossovers. I feel that sine you have the same configuration as I do I know that result you should be getting and there is a HUGE amount of time invested into this thing to do experimentation, listening, testing, measuring etc and there is not a lot known to me room for improvements. Trust me it has  nothing to do with ego  and I will LOVE to learn if you fine any better way to organize what has been organized, unless you use other compression driver…


Other than the obvious exact crossover points needing to be tweaked for my room, I remember reading somewhere on your site some time ago about perhaps a second order on the Upperbass might be more appropriate for rock music and perhaps a 4th order low pass on the ribbon may improve the results.  Of course I am leaving myself open to these things, and I still listen to most kinds of music.  It was Willie Nelson and some European jazz yesterday but in the press to get stuff finished for Christmas I think I listened exclusively to Bruckner symphonies for almost 6 days straight (I discovered Celibidache and was transfixed by the slow phrasing in particular of the 8th).

Your effort and experimentation and work to fine-tune your system are exactly what attracted me to this project in the first place, and please believe me when I say that the closer I come to a realisation of my efforts the more I understand and appreciate just how colossal yours has been.        
   
01-04-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 148
Post ID: 25228
Reply to: 25227
DSET Power draw
This morning I logged the mains power draw so that I can properly size the fuses.


DSET Power Draw.jpg




Mains power here is 240VAC.



It's a 4 minute startup protocol.  It briefly draws an amp when plugged into the wall and the Services LPS fills its capacitors, then settles down to virtually nothing, less than 20w.  Then I hit the power foot pedal and the AC filaments/heaters are all lit up and being direct AC there are no caps or other electronics so not much of a spike.  The bias and 1st Stages are powered 45 seconds later (just past 1m on the graph) and there is a 5A spike as the power supply caps are filled.  That sits at about 150w until three minutes later the DHT, 2nd Stages and Single Stages power supplies are energized.  The DMM logs once a second and managed to capture about 11A, which is as much as the mains supply is rated, maybe a little more...perhaps I should put in a soft start.  Anyway, after that the amp sits on a pretty neat 400W power draw at idle.  Being Class A that should be where it stays even when playing music.


 

So, 400 watts power draw to light up a combined total of 30w-33w of output power.






01-04-2019 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,624
Joined on 05-27-2004

Post #: 149
Post ID: 25229
Reply to: 25228
It would be fun to visit you but I never in AU....
 anthony wrote:
To mirror your obsession, but not as the instigator of the project, rather as the duplicator, it has been my plan for some time to take off all of January to get my Melquiades/Macondo installed in my room.  Being self-employed with too many clients to keep satisfied that is not really going to happen but I do plan to be able to operate with the emphasis towards leisure rather than work for the next couple of months as a compromise, perhaps something like week-on week-off, but something at least very flexiblle.  My wife is with me completely in the desire to have this project finished, but I suspect for slightly different reasons than I. 
I was also self-employed, running consulting s-corporation and taking 6 month off I once calculated how much money I lost turning down some lucrative contracts. It was a lot! Well, it was juts money… Saying that I need to admit that if I were married that time I do not think I would be able to pull it off. My compliments to you wife patience
 anthony wrote:
I listened exclusively to Bruckner symphonies for almost 6 days straight (I discovered Celibidache and was transfixed by the slow phrasing in particular of the 8th).    
Now we are taking!!! Celibidache certainly would do it. A few years back I caught live performance of the 8th in London with Vienna and late Mazel. They did a very nice slow version of adagio, not as slow as Celibidache did during his slower concerts but still quite slow but Mazel did some absolutely mind boggling poses and some amassing prolonging phrases that went against all rules of physics. That all make the performance absolutely beyond believe. If you like very slow interpretation, like I do, then you might start to listen some Barbirolli Mahler…
 anthony wrote:
..the closer I come to a realisation of my efforts the more I understand and appreciate just how colossal yours has been. 
Yep, tell it to my wife… :-)
 Anthony wrote:
It's a 4 minute startup protocol.  It briefly draws an amp when plugged into the wall and the Services LPS fills its capacitors, then settles down to virtually nothing, less than 20w.  Then I hit the power foot pedal and the AC filaments/heaters are all lit up and being direct AC there are no caps or other electronics so not much of a spike.  The bias and 1st Stages are powered 45 seconds later (just past 1m on the graph) and there is a 5A spike as the power supply caps are filled.  That sits at about 150w until three minutes later the DHT, 2nd Stages and Single Stages power supplies are energized.  The DMM logs once a second and managed to capture about 11A, which is as much as the mains supply is rated, maybe a little more...perhaps I should put in a soft start.  Anyway, after that the amp sits on a pretty neat 400W power draw at idle.  Being Class A that should be where it stays even when playing music. So, 400 watts power draw to light up a combined total of 30w-33w of output power.
It is not the numbers that I got. I had if I member correctly 330W draw after the amp hit the cruse temperature, the I initial inrush of current was I think about 10A and I use 8A slow blow fuse for the whole amp. The 4 minute startup protocol is kind of slow but it for sure protect the amp's parts well. 
 


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
01-05-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 150
Post ID: 25230
Reply to: 25229
You would be most welcome...
...to call in if you ever did get to Aus.  There is plenty to see and experience here, and the weather is great just about all the time.  A critical ear applied to my efforts would be most welcome.

 Romy the Cat wrote:

I was also self-employed, running consulting s-corporation and taking 6 month off I once calculated how much money I lost turning down some lucrative contracts. It was a lot! Well, it was juts money… Saying that I need to admit that if I were married that time I do not think I would be able to pull it off. My compliments to you wife patience
 


Life is so much more than earning a living.  My slow month or two to start this year will be followed by a hectic ten, so I am not too concerned about lost income.  Doing something because you are passionate about it is so much more rewarding that grinding out the $$$ just because you want more.


 Romy the Cat wrote:

Now we are taking!!! Celibidache certainly would do it. A few years back I caught live performance of the 8th in London with Vienna and late Mazel. They did a very nice slow version of adagio, not as slow as Celibidache did during his slower concerts but still quite slow but Mazel did some absolutely mind boggling poses and some amassing prolonging phrases that went against all rules of physics. That all make the performance absolutely beyond believe. If you like very slow interpretation, like I do, then you might start to listen some Barbirolli Mahler…  


I was working away in my office with youtube in the background pumping out a version of Bruckner 8 that I cannot even remember (Barenboim/Berlin I think), then a Celibadache video of the same symphony came on and I thought it was the rapture.  Oh my!  I got straight on Discogs and bought the DVD set and I don't even have a DVD player, but I will get one (I should have got an Oppo 205 before they sold out).  I will certainly look up the Barbirolli Mahler...   


 Romy the Cat wrote:

It is not the numbers that I got. I had if I member correctly 330W draw after the amp hit the cruse temperature, the I initial inrush of current was I think about 10A and I use 8A slow blow fuse for the whole amp. The 4 minute startup protocol is kind of slow but it for sure protect the amp's parts well. 
 


Our builds are a little different.  Yours uses all toroids, or mostly so, which are more efficient than the EI that I use.  Your Services power supply (SMPS?) may be more efficient than my 5A linear power supply plus I have a whole extra power supply for the DHT channel that would incur extra losses because of the extra iron.

At the moment I have a fuse for the Service LPS, one for the filaments/heaters and one for the remainder.  3A works fine for all the power supplies (just tested it) but I was now thinking about removing the fuse for the filaments altogether.


01-07-2019 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 459
Joined on 01-07-2006

Post #: 151
Post ID: 25231
Reply to: 25230
EI vs toroids
Congratulations on the build!

 anthony wrote:
  Yours uses all toroids, or mostly so, which are more efficient than the EI that I use.

Why have you chosen EI vs toroids? The latter emit less.

Cheers, Jarek



Cheers,
Jarek
01-08-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 152
Post ID: 25232
Reply to: 25231
Its about noise
 N-set wrote:
Congratulations on the build!

 anthony wrote:
  Yours uses all toroids, or mostly so, which are more efficient than the EI that I use.

Why have you chosen EI vs toroids? The latter emit less.

Cheers, Jarek

Hi Jarek,

Yes, toroids can leak less magnetic flux than EI if they are wound such that the entire core is covered, but is flux leakage a problem if you are able to keep the transformers away from sensitive circuits?  Toroids come into their own when you are forced to mount the transformer near the circuits, but otherwise EI have them covered on most fronts.

Toiroids
  • are smaller for the same power rating
  • are more efficient transformers of power than EI
  • if carefully made can have low flux leakage
  • are high bandwidth devices so more noise on the power line is transferred into the circuit
  • have no gap and will hum when there is DC on the mains


EI
  • are larger for the same power rating
  • have a gap and do not hum when you have DC on your mains (unless there is so much that the core becomes saturated)
  • are lower bandwidth devices so act as a low pass filter for mains noise (we really only need to pass 50/60Hz - the rest is unwanted)
  • leak some flux so they should be kept further separated from the sensitive circuits


Personally, I would use EI in just about every situation for audio...unless I had no option but to tuck the transformer in tight to a sensitive circuit.


Cheers,

Anthony
01-08-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 153
Post ID: 25233
Reply to: 25232
The pin 8 question
Hi Romy,

I've been reading the 6e6p-dr datasheet and it seems as though pin 8 (a shield) is recommended to be tied to a lower negative voltage than the tube cathode.  Have you bothered or experimented with this?  This is no problem in the DHT Channel because of the cathode resistor, but in Channel D the cathode pin is connected directly to ground and I don't know how to get a potential lower than ground.
Regards.
Anthony
01-08-2019 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 459
Joined on 01-07-2006

Post #: 154
Post ID: 25234
Reply to: 25232
Cont'ed
Anthony, thank you for the explanations. For some reasons you mention, I use C-cores. Loose coupling (pri and sec on the different legs), controlled gap and low emission. BTW toroids do have some "distributed gap" but it's small and uncontrollable.

Cheers, Jarek



Cheers,
Jarek
01-09-2019 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,624
Joined on 05-27-2004

Post #: 155
Post ID: 25235
Reply to: 25233
A good question.
Anthony, I grounded in my amp it in order the shield was not hanging there free. You certainly must NOT leave it disconnected and you do need to tie to something. Generally biasing of these electrostatic fields shields is very murky territory. There is a community of people out there who insist that it makes difference and I have seen even some gizmos that introduce bias to external shields. The shields in 6E6P is much closer to anything, so a positive or negative bias might be effective. I did not experiment with it and I have no way to predict how it might impact sound. Do not take it too far as I can see you running an active feedback loop over the 6E6P shield… :-) 
 
Let me know if you do experiment with it and what you find. I would be looking for noise and sound impact. Do not forget to burn a used tube at least 1Hr before you make any judgments. It might be hard for you as you do not have 6E6P in a full bandwidth channel and to make any concussion within a narrow bandwidth channel you need the whole system to be setup, calibrated and it sound to matured in your own perception.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
01-22-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 156
Post ID: 25239
Reply to: 25229
Barbirolli Mahler
 Romy the Cat wrote:

If you like very slow interpretation, like I do, then you might start to listen some Barbirolli Mahler… 
 


I've found Barbirolli Mahler 6 & 9 by New Philharmonia Orchestra and Berlin Philharmonic respectively.  I'll give the records a spin when they turn up.  Also grabbed Mahler 7, Bernstein NY Philharmonic.
01-22-2019 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,624
Joined on 05-27-2004

Post #: 157
Post ID: 25241
Reply to: 25239
Yep, Barbirolli would do it...
When I was making a sarcastic joke about you begin to enjoy slow interpretations (something that any VERY good playback should do to a system owner) and referred you to the Barbirolli’s Mahler of cause I mean the exquisite  performance of 1967 of Sir Barbirolli with New Philharmonia. The “Allegro” movement is so much out of this would that I hardly believe anybody would listen any other version of Mahler 6 after listening to what Barbirolli did with it. It was told that Rostropovich pull out all his own recordings of Elgar cello concerto and never recorded it again after he heard the Jacqueline du Pre’s  take on the concerto in August 1965, ironically with the same Barbirolli… I have no idea why people keep recording the M6 after Barbirolli 1967. Whatever was possible to be expressed in that music was done by maestro Barbirolli.  




"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
01-31-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 158
Post ID: 25254
Reply to: 25241
First music testing
So, the first DSET is still downstairs on the electronics bench and I am back to work for a while, but not too hard and not for too long (I hope).  I've added all the filters and checked and tested and changed some more things and decided that it was time to see if I could get any music to play.  Several crappy drivers and speakers that I had scrounged for just this purpose were wired up and I pressed the go button to stream some Tidal.


First Music Testing.jpg


It works!  I have sound.  Kind of a weird sound with the mix and match driver selection but at least it is comprehensible.

This is the front of the amplifier where it wraps around the chassis pillar for the horn stack...

Amp Front.jpg


Plenty of thought has gone into the speaker cables largely because there are plenty of them and I would prefer for them to be hidden completely from view.  Five of the six channels exit the amplifier in the well that fits around the horn stack pillar where they are nicely hidden, and the bass channel exits from the side closest to the Bass Cannons.  I've thought about different types of speaker wire from exotic to simple and in the end I have gone with simple Duelund 16GA tinned copper wire.  I've used this before with fullrange speakers and it is fine.  The big benefit for me is that it is black and the individual wires are tinned:  black to hide it and the tinning because these speaker wires will not be terminated in any way, no spades, bananas or whatever, just crushed in the binding posts of the driver one end and directly soldered to the output transformer on the other end.  Inductance and capacitance should not be an issue for such band limited amplifier channels, and even the Injection Channel that runs fullrange will run 14dB or so down.  Terminations seem to be the major issue in speaker cables, and these Duelund wires when used this way will eliminate a joint/termination each side of each binding post while proving resilient to oxidation in a tight crush joint at the transducer.

As discussed earlier I have gone for ammeters instead of voltmeters.  I can hit the mA target on all but one channel (F), but with exception of E (DHT Channel) they sure do wander about a bit, particularly the 6C33C channels.  Romy, is this normal?  I set them at about 240mA/150mA/150mA and they will go down over time and then they will come back up and past their original settings then they may wander down again.  Makes setting a stable current draw like herding cats. 
Targets 1.jpg



Here is Channel F.  It won't come over about 20-25mA.  Plus the DC Offset won't trim out less than about 0.27V (yes volts).  I have a feeling that the two problems are linked and will check to see where I have wired up the input filters for each channel.

Targets 2.jpg



Anyway, music has been playing downstairs for a couple of hours now and the only temperatures that I am concerned about are the 3 final anode resistors (15k 12W) for the first stages of A/B/C.  The hottest of those according to my thermal camera is about 140C (280F) so it might pay in the long run to parallel a pair of 30k 12W resistors even though the datasheet specifies 350C maximum and there should be decent airflow from the chassis fans at that part of the case.

The next DSET is also taking shape...

Next One.jpg



Getting closer!


01-31-2019 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,624
Joined on 05-27-2004

Post #: 159
Post ID: 25256
Reply to: 25254
So far so good.
 anthony wrote:
Plenty of thought has gone into the speaker cables largely because there are plenty of them and I would prefer for them to be hidden completely from view.  Five of the six channels exit the amplifier in the well that fits around the horn stack pillar where they are nicely hidden, and the bass channel exits from the side closest to the Bass Cannons.  I've thought about different types of speaker wire from exotic to simple and in the end I have gone with simple Duelund 16GA tinned copper wire.  I've used this before with fullrange speakers and it is fine. 

Be careful with the speaker cables. The knowledge about the cables that you developed running a full range systems is not applicable running DSET. You do not need cable that run overall well. With DSET and very limited bandwidth you might go away with very cheap wires. You will find eventually the some of the speaker cables might be better but it would need a well matured system where sound will be observed in context of the given channel loading

 anthony wrote:
As discussed earlier I have gone for ammeters instead of voltmeters.  I can hit the mA target on all but one channel (F), but with exception of E (DHT Channel) they sure do wander about a bit, particularly the 6C33C channels.  Romy, is this normal?  I set them at about 240mA/150mA/150mA and they will go down over time and then they will come back up and past their original settings then they may wander down again.  Makes setting a stable current draw like herding cats. 

Sorry, I do not understand you. The 240mA/150mA/150mA is fine. As the tubes new they will run off a lot of current but after 20-30 hour of burn they will stabilize. Read my 6C33C Survival Guide.

 anthony wrote:
Here is Channel F.  It won't come over about 20-25mA.  Plus the DC Offset won't trim out less than about 0.27V (yes volts).  I have a feeling that the two problems are linked and will check to see where I have wired up the input filters for each channel.

You will find the bug, it is there. If you need to get extra 10mA then you might change the value of bias resistors.



"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
02-02-2019 Post does not mapped to Knowledge Tree
anthony
Posts 236
Joined on 08-18-2014

Post #: 160
Post ID: 25274
Reply to: 25256
All fixed?
So, my two problems have been fixed, I think.

First was the issue with the 6e6p  for the HF Channel not being able to draw enough current.  I checked the bias and it was fine and the potentiometer allowed plenty of adjustment so I changed nothing in the circuit.  A new tube was swapped in and bingo! the current is back and all is good.  All that I can think is that all the time that I ran that tube without pin 8 grounded has worn it out and it may be near failure.  When I first left the amp on for several hours a couple of weeks ago now the current from that rube was fine and it slowly dropped over time.  However, the three 6c33c channels were varying as well so I did not think too much of it.  The new tube pulls the required current with the pot somewhere near the middle of its range and I will leave the amp going all day today with the hope that the current will not fall as it did with the previous tube.

My second problem was not being able to set the DC Offset to zero.  It sat at about a minimum of 230mV plus or minus 15mV regardless of the gas tubes I randomly swapped in there.  I tried half a dozen all up and decided that the issue was elsewhere.  What I did in the end was replace a 1k resistor that leads into the 100k potentiometer for trimming DC on the positive side with a 100k resistor, so 100 times larger.  The offset now trims to zero with the pot close to halfway through its travel.  Romy, I don't know if that is an error on the schematic or if I have some other issue, but the offset seems stable.
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