WntrMute, I had the impression that this amp functioned for two years to your satisfaction and, after changing the transformer you have buzz and B+ is too low.
Your circuit, if it really would draw 106mA at 405V, it would cook the 3C24 (unless this is for 2 channels) please answer, is the PS for 1 or 2 channels ???
Worse than that, from your diagram, B+ 450V and 395V at the 3C24 anode drops 55V over the OPT. With the 338ohm from the datasheet this would mean 162ma !!! anodecurrent, more than double plate dissipation !!! (non of this is possible without heavy gridcurrent. And gridcurrent does not go well together with constant cathode current source)
Where did this 450 and 395 volts come from ???
Did the 3C24 redploate in the dark ???
Did this amp otherwise work (soundwise) to your satifaction ???
If it did, does not redplate and function good enough to take measurements, shortcut the input, connect speaker or dummyload and measure the following DC voltages:
ground to B+ ???
ground to cathode of the EF86 ??? (same as voltage over the 2.21k cathode resistor. Cathode current of the EF86=Ik = URk/Rk)
ground to anode of the EF86 ??? ( Ua = ground to anode, where the 390k anode resistor and 470k feedback resistor connect together)
ground to cathode of the 6S4A ??? (same as voltage over the 150H choke dc-resistance, cathode current of the 6S4A=Ik=
ground to cathode of the 3C24 ??? (the voltage across the constant current load)
ground to anode of the 3C24 ???
Would also be helpful to confirm the datasheet resistance values of the choke (3700ohm) and the OPT primary resistance (338ohm)
Any info about that 3C24 constant cathode current source ??? adjustable??? adjusted too .....mA ??? what shunt capacitance ???
Your circuit, if it really would draw 106mA at 405V, it would cook the 3C24 (unless this is for 2 channels) please answer, is the PS for 1 or 2 channels ???
Worse than that, from your diagram, B+ 450V and 395V at the 3C24 anode drops 55V over the OPT. With the 338ohm from the datasheet this would mean 162ma !!! anodecurrent, more than double plate dissipation !!! (non of this is possible without heavy gridcurrent. And gridcurrent does not go well together with constant cathode current source)
Where did this 450 and 395 volts come from ???
Did the 3C24 redploate in the dark ???
Did this amp otherwise work (soundwise) to your satifaction ???
If it did, does not redplate and function good enough to take measurements, shortcut the input, connect speaker or dummyload and measure the following DC voltages:
ground to B+ ???
ground to cathode of the EF86 ??? (same as voltage over the 2.21k cathode resistor. Cathode current of the EF86=Ik = URk/Rk)
ground to anode of the EF86 ??? ( Ua = ground to anode, where the 390k anode resistor and 470k feedback resistor connect together)
ground to cathode of the 6S4A ??? (same as voltage over the 150H choke dc-resistance, cathode current of the 6S4A=Ik=
ground to cathode of the 3C24 ??? (the voltage across the constant current load)
ground to anode of the 3C24 ???
Would also be helpful to confirm the datasheet resistance values of the choke (3700ohm) and the OPT primary resistance (338ohm)
Any info about that 3C24 constant cathode current source ??? adjustable??? adjusted too .....mA ??? what shunt capacitance ???
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I'll give you as many answers as I can:
Not quite. Had B+ of 405 but had significant mechanical hum (Edocor transformers, both were noisy.)
One shorted half of the HV winding after about 2 years.
These are monoblocks. PS if for ONE monoblock.
Voltages came from the designer.
The 3C24 glows red/orange by design.
Sounded nice then as now. No mechanical hum with the new lower B+ transformers.
Sounds great currently. I will have to defer some of the measurements but these are from my measurements when originally built:
B+ 406V
Plate 3C24 392V
Grid 3C24 15.6V
Plate EF86 112V
Cathode 3.33V
Grid 2 167V
First pic below is off the internet second, third and fourth are my amps.
Not quite. Had B+ of 405 but had significant mechanical hum (Edocor transformers, both were noisy.)
One shorted half of the HV winding after about 2 years.
These are monoblocks. PS if for ONE monoblock.
Voltages came from the designer.
The 3C24 glows red/orange by design.
Sounded nice then as now. No mechanical hum with the new lower B+ transformers.
Sounds great currently. I will have to defer some of the measurements but these are from my measurements when originally built:
B+ 406V
Plate 3C24 392V
Grid 3C24 15.6V
Plate EF86 112V
Cathode 3.33V
Grid 2 167V
First pic below is off the internet second, third and fourth are my amps.
I thinck what went down here, is, the designer took a circuit diagram from the internet, thougth it would be cool to exchange a 300B into a cool looking tube like the 3C24 and that would be all there is to it, but unfortunally, the 3C24 is not anything near to a 300B, sorry
The datasheet says nothing about redplatin, says Pa 25W max, but can propably take more.
Anyway, according to the datasheet, this tube has a amplification factor of 24, and a very high plateresistance. It needs substantial gridcurrent to work with such a low plate voltage.
And when the cathode is constant current fed, gridcurrent deducts from anodecurrent.
I am really supriced that it works as good as you say
The datasheet says nothing about redplatin, says Pa 25W max, but can propably take more.
Anyway, according to the datasheet, this tube has a amplification factor of 24, and a very high plateresistance. It needs substantial gridcurrent to work with such a low plate voltage.
And when the cathode is constant current fed, gridcurrent deducts from anodecurrent.
I am really supriced that it works as good as you say
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I wholeheartedly disagree -fully his own design as I know him. The issue really is my B+ is not where it was. The amps sound and seem to be working fine. I just wanted to get back to the B+ specified without dropping another $400 dollars and wasting the Heyboer transformers. But that may not be possible it seems.
A few inconsistencies I can see.
The original amp had 406V supply and 392V on 3C24 anode, but your latest schem says there is a 55V drop not 14V - did you change the output transformer, or the idle current in the 3C24, or ... ?
I can't align the highlighted 3C24 class AB2 values with your latest schem operation. For starters, your amp is class A, and the datasheet operating anode voltages are way more. You also seem to indicate the 'design' is by someone else, and your operating voltages come from them - are you cloning an actual circuit and operating levels and parts, or deviating in some way?
It seems there is a disconnect between wanting to align with specific operating levels, and even contemplating changing transformers to achieve those levels, when there seems no validity or detail to what you are aiming for.
If you had been using ss or normal valve diodes then a 'simple' way to adjust B+ to a higher level would be to add a 'tuned' amount of initial C after the rectifier to operating in the grey zone between normal choke-input and capacitor input. That can work for class A, as the load current is effectively constant. But you want to use 866's, which won't like rectifier current waveforms that are anything but pure choke input.
The original amp had 406V supply and 392V on 3C24 anode, but your latest schem says there is a 55V drop not 14V - did you change the output transformer, or the idle current in the 3C24, or ... ?
I can't align the highlighted 3C24 class AB2 values with your latest schem operation. For starters, your amp is class A, and the datasheet operating anode voltages are way more. You also seem to indicate the 'design' is by someone else, and your operating voltages come from them - are you cloning an actual circuit and operating levels and parts, or deviating in some way?
It seems there is a disconnect between wanting to align with specific operating levels, and even contemplating changing transformers to achieve those levels, when there seems no validity or detail to what you are aiming for.
If you had been using ss or normal valve diodes then a 'simple' way to adjust B+ to a higher level would be to add a 'tuned' amount of initial C after the rectifier to operating in the grey zone between normal choke-input and capacitor input. That can work for class A, as the load current is effectively constant. But you want to use 866's, which won't like rectifier current waveforms that are anything but pure choke input.
If the measurements you made are corrects, the voltagedrop over the OPT where only 14V, that is a good thing, because then if the OPT datasheet of 338ohm is also correct (please measure to conform) the anode current is only a quarter of what it was with the 55V drop. Now, anodepower is only 16W or so, much much better.
6S4A Ik works out as 4.22mA, ok
EF86 Ik works out as 1.51mA, ok
330k+47k resistors take 1.08mA, ok
total current 41.4+4.22+1.51+1.08 = 48.21mA
total voltage needed = 406+7.3 = 413.3 V (the 7.3V are for voltage losses in the smoothing choke)
minimun transformer voltage needed (loaded) 460V + 16V (voltage loss rectifier) + 8V (voltage loss choke) = 484V
equivalent full load resistance = 8.57k
You can now play with PSDU2, use a resistor load of 8.42k and/or constant current of 48.21mA
If you insert a cap at the input the voltage will rise, do the 866A get angry or not, is a different story.
But i hope you know about the DANGER involved with using mercury rectifier tubes.
1 broken 866A is equivalent to 100 of old design, and 500 new design CFL.
If this is NEWS to you, please educate yourself, you NEED to know about this stuff, for the good of yourself and everybody else it migth affect should things go wrong. Safety first!
6S4A Ik works out as 4.22mA, ok
EF86 Ik works out as 1.51mA, ok
330k+47k resistors take 1.08mA, ok
total current 41.4+4.22+1.51+1.08 = 48.21mA
total voltage needed = 406+7.3 = 413.3 V (the 7.3V are for voltage losses in the smoothing choke)
minimun transformer voltage needed (loaded) 460V + 16V (voltage loss rectifier) + 8V (voltage loss choke) = 484V
equivalent full load resistance = 8.57k
You can now play with PSDU2, use a resistor load of 8.42k and/or constant current of 48.21mA
If you insert a cap at the input the voltage will rise, do the 866A get angry or not, is a different story.
But i hope you know about the DANGER involved with using mercury rectifier tubes.
1 broken 866A is equivalent to 100 of old design, and 500 new design CFL.
If this is NEWS to you, please educate yourself, you NEED to know about this stuff, for the good of yourself and everybody else it migth affect should things go wrong. Safety first!
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Dropping load from 100mA to 50mA will give you circa 40V more B+, which is sort of where you want to be.
The current load from the amp is so low one could use diodes and a cap to rise the voltage for the amp to what ever is wanted. And for the "glow" just disconnect them 866A rectifiere entirely from the amp and load them resistively. The maintransformer can easely deal with that.
All thats needed would be 2-4diodes, 1 cap and one wirewound resistor (plus, may be a wirewound pot for glow adjustment)
All thats needed would be 2-4diodes, 1 cap and one wirewound resistor (plus, may be a wirewound pot for glow adjustment)
Right, but the proof is in the pudding so to speak. The working amp with all the parts in place gives me a B+ that is below the desired. I might TRY a very small cap and see what happens. Otherwise, I either live with it or buy a pair of new PTs.
But I don't think you have measured the idle current in the output stage yet, or confirmed that stage is biased ok, or not.
I have set the at 55mA. It is adjustable from the outside of the amp.
I don't really know how to determine idle current.
I don't really know how to determine idle current.
What and how do you set for 55mA ? I see Rod Coleman regulator and mA meter on the schematic - does that refer to something like this link: https://www.lyrima.co.uk/dhtreg/dhtRegIntro.html ? I quickly looked at that link and it doesn't set cathode current. Do you know the circuit of the mA meter? Can you measure the 3C24 cathode voltage, as it isn't part of post #43.
Sorry - you've lost me - which circuit in the middle of that attachment, and are you saying that is the mA meter ?
Correction to my calculation of the total current draw 48.21mA.
The 3C24 operates, even when idle, with gridcurrent. This grid current must be added to the cathode current of the 6S4A ( i would guess it is only a few mA, but that is only an assumption). So this has to be measured !!!
Anyway, this constant cathode current thingy still bothers me, if the 3C4A cathode is really constant current fed as you said, grid current is not allowed to flow at all, so i am quite sure that THERE IS NO constant current source between cathode and ground, WntrMute, is there a constant current source ??? and if there is, what cathode current ???
The 3C24 operates, even when idle, with gridcurrent. This grid current must be added to the cathode current of the 6S4A ( i would guess it is only a few mA, but that is only an assumption). So this has to be measured !!!
Anyway, this constant cathode current thingy still bothers me, if the 3C4A cathode is really constant current fed as you said, grid current is not allowed to flow at all, so i am quite sure that THERE IS NO constant current source between cathode and ground, WntrMute, is there a constant current source ??? and if there is, what cathode current ???
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Geez....so much confusion...my mistake too...
In the diagram the tubes cathode and heater are not connected anywhere, showing only the text: Rod Coleman regulatorS, and I assumed (propably falsly) that there are 2 regulators, one constant current source for the cathode where you can dial in the wanted current, and a second regulator to feed the heater (At the time I did not know that your amp operates in heavy A2 only, I only knew that the grid has positiv voltage and that usually calles for either a bypassed cathode resistor, or CCS).
So, where is that floating cathode connected too? The amp meter only, or is there something else?
In the diagram the tubes cathode and heater are not connected anywhere, showing only the text: Rod Coleman regulatorS, and I assumed (propably falsly) that there are 2 regulators, one constant current source for the cathode where you can dial in the wanted current, and a second regulator to feed the heater (At the time I did not know that your amp operates in heavy A2 only, I only knew that the grid has positiv voltage and that usually calles for either a bypassed cathode resistor, or CCS).
So, where is that floating cathode connected too? The amp meter only, or is there something else?
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