Hi Romy

I have a mono completed full range Melquiades and another only with the bias circuit hooked-up.

The bias voltage I get on the 6e5p is around minus 4.4v on both the circuits. This is with the inputs shorted. With the inputs connected to adjust voltage to 0.0mvdc, I get a reading of plus 0.4vdc. This is with VR1 set at maximum (20kohm). This is the “lowest” reading I can get without increasing R9, VR1 or R4. I can’t figure out why i am getting these readings.

To get around minus 3.4v on the 6e5p bias and 0.0mVdc on the input, I tried 510kohm resistors in R4 and R6 and increased R5 to 10kohm. This seems to work.

On the melquiades circuit revision 3.6 the C5 (10uF 250v) is wired up +ve to ground and in revision 4.0 C5 is wired –ve to ground. Revision 3.6 works for me, with revision 4.0, I get around -130v on OA2 and -0.75v on the 6e5p bias. Which is the right way?

cb wrote:

The bias voltage I get on the 6e5p is around minus 4.4v on both the circuits. This is with the inputs shorted. With the inputs connected to adjust voltage to 0.0mvdc, I get a reading of plus 0.4vdc. This is with VR1 set at maximum (20kohm). This is the “lowest” reading I can get without increasing R9, VR1 or R4. I can’t figure out why i am getting these readings. To get around minus 3.4v on the 6e5p bias and 0.0mVdc on the input, I tried 510kohm resistors in R4 and R6 and increased R5 to 10kohm. This seems to work.

OK, you made some mistakes and I am sure that it is imposable to have + 0.4V on the grid, 0.0V at input, with R5 resistor in place and the gas tubes outputting +150V and -150V.

Let do it step by step:

1)    Disconnect R4 and R6 and put the C4 and C5 in the right polarity

 2)    Confirm that your gas tubes are 150V (144-151 is fine, depending of the brand of the tube). If you pull them out they should have ~200V (>190V) in bias lines.

 3)    Measure current that fallow to the gas tubes. I should be between 10mA and 15mA. The lover current the longer the gas tube will live but still stay above 10mA and below 20mA. Use R11 and R12 to set the current for the gas tubes. It wills all depends from how many volts your PS outputs. You just burn the spare voltage on those power resistors.

 4)    Check the R9 and R10. The R9 should be a little smaller as the R9 + VR1 in the middle of its range should be approximately equal to R10.

 5)    Put identical R4 and R6, it does not matter the values, let keep it ~400K

 6)    Confirm the value of your R5 and connect the R4 and R6. You do not need to apply B+.

 7)    Short the input and set minus from minus 3.2V to minus 4.2V on grids. If you have different voltage then modifies your R6 to set the correct voltage on the grid.

8)    Apply B+ on the first tube.

9)    Measure the plate voltage in a point “A”

10) Now you need to adjust the amount if bias on the tube in order to have 200V on plate. You understand that amount of bios is irrelevant and it would depend from the given tube of yours.  Averagely the minus 3.4V-3.5V will give you 200V and 15-17mA of plate current. Do not be too finicky about it – the current in the driver tube in THIS application is not really critical. Set plate voltage between 170V and 200V with whatever bias voltage it will be (let presume -3.4V+/.5V)

11) Turn down B+ and un-short input.

12) Make sure that R4 is the same as R6

13) Set with VR1 null volts at input and to confirm that the negative voltage at grid is the same as it was when the input was shorted.

14) You are all done now. Still, I would like you to understand the basic operation that you will be able to find out what is wrong:

Higher bias voltage = Less plate voltages
Lovers R6 values = Higher bias voltage
Lovers R5 values = Lower bias voltage

15) So, if you wish to go for 10K in R5 and 500K in R4 and R6 then it is perfectly fine, in fact I had one amp running this way and the first revision of Milq had R5 as 10K and  R4/R6 as 499K. I made many experiments trying to determine what would be better: to keep R5 lover or not. I run the R5 from 5K to 14K. Theoretically it is a large resistor right in grid and to have it too high value should kill some HF (low path filter with tube capacitance).  In practice the filter kicks in above 100KHz and I recognized that there was no effect. The last revision I changed 10K to 12.1K but it is absolutely irrelevant. Use R5 as any best quality resistor you have and juts just R6 to maintain 200V on the plate. In here is not the value are important but the concept the you block DC not with capacitor but with an “active” resistor that backed up with positive voltage. BTW, eventually if you wish to go “kinky Milq” and have a very low impedance front end then you might do not use positive bias at all letting the excessive DC voltage on your Milq input to bias your cables (it might be a different subject and it has own “danger”)

cb wrote:

On the melquiades circuit revision 3.6 the C5 (10uF 250v) is wired up +ve to ground and in revision 4.0 C5 is wired –ve to ground. Revision 3.6 works for me, with revision 4.0, I get around -130v on OA2 and -0.75v on the 6e5p bias. Which is the right way?

Charles, the last revision (Ver4) while I was pained the circuit in colors and made it easier to understand/talk about it, I made a mistake when I moved the C5 cap around making it sexier and forgot to move the polarity identifier. Surely, it is the cap in the negative supply and it should have it negation lead on the negative line and the positive lead on ground. My apologues, though It might be self-explanatory how to hook up the cap in a negative supply. I will make the correction tonight. If you did try this cap in a wrong way then you might partials re-polarized it and if I were you I would get another cap. Thanks God it was a very small caps and it did not blow up…

Yes, it is imposable to have + 0.4V on the grid, 0.0V at input, with R5 resistor in place and the gas tubes outputting +150V and -150V.
My apologies, I meant to say I have  minus 4.4v on the grid with the inputs shorted.
Then I unshort the input to measure the dc voltage at the input and to set it to zero volts via VR1. Here is where I get +0.4v, this is with VR1 at max resistance (20kohm). If I lower the resistance of VR1 the voltage goes up. But if I increase R9 from 5k to 10k, I manage to set the input voltage to zero volts. But R9 should be a little smaller as the R9 + VR1 in the middle of its range should be approximately equal to R10.

And here my mistake, R9 was supposed to be R5.
To get around minus 3.4v on the 6e5p grid and to set 0.0mVdc on the input, I tried 510kohm resistors in R4 and R6 and increased R9 from 5k to 10kohm. Increasing R9 to 10k allows the input to be adjusted to zero volts. The plate on the 6e5p now drops from around 195v to 185volts.

Here going through the list;

1) ok

2) Gas tubes are about 149 and 151 volts. bias lines at 192v, 194v

3) current flow to the gas tubes was at 9mA. Changed R11 and R12 to 3.3k to get 12mA.

4) R9 is 5k,  R10 is 10k, VR1 is 20k

5) R4 and R6 is 390k

6) R5 is 12.1k caddock mk132

7) Shorted the inputs, I get minus 4.4v on grid.

8) ok

9) around 195v on plate

10) This is later on: to get around minus 3.4v on the 6e5p bias I tried 510kohm resistors in R4 and R6, and plate voltage reduces to 186volts.

11) ok

12) ok

13) can't get zero volts. 0.4v is the min i can get, VR1 set at 20k. Why I cant zero it, I dont know...

15) To get around minus 3.4v on the 6e5p bias and 0.0mVdc on the input, I tried 510kohm resistors in R4 and R6 and increased R9 to 10kohm. This seems to work, plate is 186v.

Thanks

Rgs
Charles

cb wrote:

Yes, it is imposable to have + 0.4V on the grid, 0.0V at input, with R5 resistor in place and the gas tubes outputting +150V and -150V. My apologies, I meant to say I have  minus 4.4v on the grid with the inputs shorted. Then I unshort the input to measure the dc voltage at the input and to set it to zero volts via VR1. Here is where I get +0.4v, this is with VR1 at max resistance (20kohm). If I lower the resistance of VR1 the voltage goes up. But if I increase R9 from 5k to 10k, I manage to set the input voltage to zero volts. But R9 should be a little smaller as the R9 + VR1 in the middle of its range should be approximately equal to R10.

If you are around minus 4.4v on grid then you about to be right on money. Your positive bias has too much voltage and it pushes the positive potential over the R5 resistor. To increase R9, or to increase R4 or to flip the gas tubes with a positive tube having less voltage is an easy solution.

cb wrote:

And here my mistake, R9 was supposed to be R5. To get around minus 3.4v on the 6e5p grid and to set 0.0mVdc on the input, I tried 510kohm resistors in R4 and R6 and increased R9 from 5k to 10kohm. Increasing R9 to 10k allows the input to be adjusted to zero volts. The plate on the 6e5p now drops from around 195v to 185volts.

Sorry, I am little confused. Let keep the R5 as is and adjust the positive bias with the resistor of positive chain. If you have 0.000V at input and sub 200V on plate then do not even measure anything else – you are fine.

cb wrote:

15) To get around minus 3.4v on the 6e5p bias and 0.0mVdc on the input, I tried 510kohm resistors in R4 and R6 and increased R9 to 10kohm. This seems to work, plate is 186v.

Which is perfectly fine. Do not worry to get minus 3.4v on the 6e5p grid, worry to get 180-200V on 6e5p’s anode and to get tune to have ~32-35 times of gain. I do not know exactly why you need to drop more voltage on both R4 and R6 but most likely it is because you have too high voltage on the gas tubes. My gas tubes regulate at 145V-146V yours at 149 and 151.  That is approximately 4-5V difference that is approximately the difference between your minus 4.4v and +0.4v. In this case to change R4 and R6 is a perfect solution. I say “perfect” because the higher R4 and R6 is better as higher impedance of those resistors will better separate grid form the noises of gas tube.

What OPT you use? Care to post some pictures? What acoustic system you will be using? When you finish the project and if you feel to do so then post in an appropriately thread your feeling how do you feel the amplifier Sounds.

Hi Romy

I have one gas tube which regulates at 136v and i put it in both sockets to see the effect. Looks like my tubes running at higher voltages gives me the readings I got. Anyway I bought a bunch of gas tubes and will play with them when I get them and am not too concerned and am quite happy with with the voltages I get..

Also i stick a 30k resistor in R3 and the results are very good. The voltage measured at the speaker terminals are 0.3mV AC with the iput unshorted. Also this stabilises some voltage dc drift in the input. The amp is very quiet. Now I will finish off the other onoblok and see how they sound.

i use the lundahl LL1627 amorphous core opt 200mA. maybe later on if I decide to go for a bass amp I will try one from a local  winder with high inductance. i use some home built horns front loaded round tractrix, 3 way. 1/4WL 120hz full size mouth midbass horn, 400hz tractrix and sealed woofers.

i will post some pics soon.

Rgs
Charles

cb wrote:

Also i stick a 30k resistor in R3 and the results are very good.

from email wrote:

…. I have the valves etc. for the Melquiades but have not built it yet. I have begun thinking about the preamplification stage. Right now it is just purely passive. Is this not the optimal input for the Melquiades?

Yes, the last cap of power supply much be on the side of load as it shell have a short path to ground. Without it you will have “less bass”, more crosstalk in case it is a stereo amp with single PS and a few other negative things.

With cables is more complicated and you need to do some thinking: what you need and how you need it and what you might need in future if you are planning this amp to grow. I think if you are planning to add one or more channels then you might allow in the cable to have a couple more wires, who know, you might need other voltage in there. I do not know what would be the best practice all together I might just say what I have done.

I decided to separate filament and none-filament cable between PS and the Amp because the filaments are AC and other voltages are DC and I did not want the AC and DC run in a same cables, even to separate them by shilding. So, I have filament cables made that had 6 wires: two parallel runs for 6.3V, two parallel runs for 12.6V and two parallel runs for ground. Each wire is 15A – as you see it is a huge overbuild, you will understand why in a minute. For high voltage cable I have made a 22 wires cable. It sounds too many but do not forget that my cable care 6 wires for indication what each time delay relay goes off and the service voltages. All auxiliary voltages are not referenced to ground of the amp. Milq is single-ended with signal flows through ground and I did not what to contaminate the ground with return path from fans or LEDs. You also need to consider the fact that your PS and Amp might be disconnected while the caps care the charge so, you do not want any males cable sticking out of chassis. You might use mild bleeders to discharge the PS caps or to active the bleeders what the main relay turn the amp off.

I do not know how about you but for me to fight with those connectors was a pain in ass. So, I outsourced everything. I found a local company, similar to what you found. In my case it was Positronic Industries and they had Front Runner Series Circular Connectors, I am sure you will find somebody local. So, I got their catalog, met this rep and wrote a specification for the cables I need. Since I completely outsourced the cables and the connectors making I wrote a truly over then necessary offensive specification. It was expense (around $800 for everything) but they built all males, females and cables that I needed for the projects and I did not burn my fingers…

Here is another Milq amp looks like was built and it appears to be in Thailand. I do not read Tai and do not know anybody who doe but I am interesting what they discover while they build and after they did.

http://www.kaponk.com/node/648

Romy the Cat wrote:

Here is another Milq amp looks like was built and it appears to be in Thailand. I do not read Tai and do not know anybody who doe but I am interesting what they discover while they build and after they did.

Dominik,

It hard to say what would “work” for you. I usually do not advised what to do in term of the “obtaining efforts” I am not in business to sell the Melquiades idea. Let your friend who can build amplifiers examine Milq or perhaps to bald a prototype and to give you an advise, since he is your friend and he knows your objectives.