Single ended monoblock amp; Is there any practicality or gains to be had by building a separate power supply chassis? There's theoretical advantages in separating power/audio components but in application, is it worth the time & expense?
For a newbie is there any material that works well for prototyping component placement? Masonite, etc? Is it practical to sort components out, build, test then transfer everything to a metal (final) chassis without extensive disassembly and reassembly?
Tube rolling: is it possible to use one transformer with a specific voltage (B+?) for multiple tube types? (6L6, KT-66, 77, 88, 120, etc.)?
Are the advantages of "larger" tubes lost if voltage is not increased?
Thank you!
For a newbie is there any material that works well for prototyping component placement? Masonite, etc? Is it practical to sort components out, build, test then transfer everything to a metal (final) chassis without extensive disassembly and reassembly?
Tube rolling: is it possible to use one transformer with a specific voltage (B+?) for multiple tube types? (6L6, KT-66, 77, 88, 120, etc.)?
Are the advantages of "larger" tubes lost if voltage is not increased?
Thank you!
If you have to ask, it is not worth the expense and time to have separated power supply at this point. I would build an integrated amplifier first. Afterward, find out its limitation, then decide if separated things will solve the problems.
On the voltage and power section, unless your project is a regulated adjustable power supply, it is not a good idea to have more power than you need, Getting rid of excess voltage generate a lot of heat. Lets say you want to reduce 100V at 150mA. That is 15W. In a enclosed chassis, that generate a lot of heat.
Power is voltage square / Rload. KT66 typical use 5K load. KT88 uses 3.5K. If B+ is the same, your power gain is 5/3.5 = 1.4X.
For a single ended Mono-Block, with Indirect Heated tubes, if you do this:
Proper layout;
Proper use of Local ground loops versus long ground loops;
Proper spacing and orientation of the output transformer versus both the power transformer and B+ choke;
A non-magnetic chassis (single ended transformers are more likely to pick up magnetic hum fields than a push pull transformer);
Enough B+ filtering;
AC filaments;
Good wiring dress . . .
It is possible to get less than 100uV of hum at the 4 or 8 Ohm output.
So, given a large enough chassis, using a separate power supply chassis is not necessary.
The filament current for a single 6L6GC is 0.9 Amps.
The filament current for a single KT120 is 1.70 to 1.95 Amps.
The other tubes mentioned in Post # 1 are from 1.3, 1.5, to 1.6 Amps.
If the filament secondary is rated to use KT120 tubes, it will be overkill for a 6L6GC.
That is OK, but may seem like a waste of transformer.
Likewise, depending on the output tube current and voltage, the B+ secondary that will run a KT120 at the current and voltage you may want to run it at, may be somewhat of a waste for some of the other tubes.
Just plugging in anything from a 6L6GC to a KT120 with a fixed B+, and a fixed amount of bias current, and with a fixed single ended output transformer, is not going to be optimum for some, or all of the tubes, because the combination of primary impedance and quiescent current is different.
For tube types that are very similar, enough to be near optimum for tube rolling, without any changes of B+ voltage, tube current, output transformer primary impedance, and the other circuitry, is the EL34 Pentode, versus the KT77 Beam Power tube.
Just remember to connect pin 1 to pin 8 (the EL34 Suppressor grid is on pin 1, and should be connected to the cathode pin 8). The KT77 has no connection to pin 1, so that is OK.
The KT77 Beam Formers are already connected to the cathode, both are pin 8.
Another pair of tube types that are reasonably interchangeable for tube rolling are the 6L6GC, and the KT66.
But there are some differences, for those 2 types respectively:
0.9A versus 1.3A filaments (not a problem, if the 6.3V is rated at say 1.5A or more).
30Watt plate dissipation versus 25 Watt plate dissipation.
Just pay attention to those 2 differences, when designing the amp, and tube rolling will be OK, without changing the circuit.
In a lower power class, and are smaller, and use a 9 pin socket, these 2 types have very similar specifications, and same pin connections, No need to wire the socket differently, and so are good for tube rolling:
EL84 Pentode, and 6BQ5 Beam Power tubes.
But, to really tell the difference, be sure to look carefully at the tube construction, otherwise you will be comparing apples to apples, or oranges to oranges, and you probably should compare apples to oranges in this case:
Some are marked with both numbers on the same tube (and can only be a Pentode, or can only be a Beam Power tube; they can Not be Both).
And some with 6BQ5 marks only, may actually constructed as a Pentode.
And some with EL84 marks only, may actually constructed as a Beam Power tube.
Pentodes have a 3rd grid, the suppressor.
Beam Power tubes do not have a 3rd grid, but they do have Beam Formers.
Happy building, happy tube rolling, happy listening.
Proper layout;
Proper use of Local ground loops versus long ground loops;
Proper spacing and orientation of the output transformer versus both the power transformer and B+ choke;
A non-magnetic chassis (single ended transformers are more likely to pick up magnetic hum fields than a push pull transformer);
Enough B+ filtering;
AC filaments;
Good wiring dress . . .
It is possible to get less than 100uV of hum at the 4 or 8 Ohm output.
So, given a large enough chassis, using a separate power supply chassis is not necessary.
The filament current for a single 6L6GC is 0.9 Amps.
The filament current for a single KT120 is 1.70 to 1.95 Amps.
The other tubes mentioned in Post # 1 are from 1.3, 1.5, to 1.6 Amps.
If the filament secondary is rated to use KT120 tubes, it will be overkill for a 6L6GC.
That is OK, but may seem like a waste of transformer.
Likewise, depending on the output tube current and voltage, the B+ secondary that will run a KT120 at the current and voltage you may want to run it at, may be somewhat of a waste for some of the other tubes.
Just plugging in anything from a 6L6GC to a KT120 with a fixed B+, and a fixed amount of bias current, and with a fixed single ended output transformer, is not going to be optimum for some, or all of the tubes, because the combination of primary impedance and quiescent current is different.
For tube types that are very similar, enough to be near optimum for tube rolling, without any changes of B+ voltage, tube current, output transformer primary impedance, and the other circuitry, is the EL34 Pentode, versus the KT77 Beam Power tube.
Just remember to connect pin 1 to pin 8 (the EL34 Suppressor grid is on pin 1, and should be connected to the cathode pin 8). The KT77 has no connection to pin 1, so that is OK.
The KT77 Beam Formers are already connected to the cathode, both are pin 8.
Another pair of tube types that are reasonably interchangeable for tube rolling are the 6L6GC, and the KT66.
But there are some differences, for those 2 types respectively:
0.9A versus 1.3A filaments (not a problem, if the 6.3V is rated at say 1.5A or more).
30Watt plate dissipation versus 25 Watt plate dissipation.
Just pay attention to those 2 differences, when designing the amp, and tube rolling will be OK, without changing the circuit.
In a lower power class, and are smaller, and use a 9 pin socket, these 2 types have very similar specifications, and same pin connections, No need to wire the socket differently, and so are good for tube rolling:
EL84 Pentode, and 6BQ5 Beam Power tubes.
But, to really tell the difference, be sure to look carefully at the tube construction, otherwise you will be comparing apples to apples, or oranges to oranges, and you probably should compare apples to oranges in this case:
Some are marked with both numbers on the same tube (and can only be a Pentode, or can only be a Beam Power tube; they can Not be Both).
And some with 6BQ5 marks only, may actually constructed as a Pentode.
And some with EL84 marks only, may actually constructed as a Beam Power tube.
Pentodes have a 3rd grid, the suppressor.
Beam Power tubes do not have a 3rd grid, but they do have Beam Formers.
Happy building, happy tube rolling, happy listening.
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Of course, you can also tube roll with tubes of the same type.
Just use different manufacturers of that tube type.
There is No adjustment necessary if you use Self Bias (a parallel RC network that is connected, from the Cathode to ground).
Different manufacturers of one type of the following:
KT66
KT77
KT88
EL34
KT120
But be careful with tube rolling the whole 6L6 Family.
6L6, 6L6-G, 6l6-GA, and 6L6-GB, they have plate dissipation ratings of 19 Watts, and screen maximum voltage of 270V.
But the 6L6GC has plate dissipation rating of 30 Watts, and screen maximum voltage of
450V.
You can design the amp to use the lower ratings, and then use all the 6L6 Family, including the 6L6-GC.
And then you can also use the 5881, with 23W plate, and 270V screen ratings.
Lots of tube rolling possibilities with this large family, including the 5881.
If you use self bias, no more than 19 watts in the plate, and 270V screen, it is plug and play (plug and listen).
Some manufacturers along the way, increased the ratings of the family of the 6L6, and 5881.
They increased the plate dissipation, and the max screen voltage.
But then how do you know if the tube you get in your hands was made to the old specs, or the new and improved specs?
You do not know for sure . . .
So just use different manufacturers of the 6L6-GC if you want to use more than 19W on the plate, and more than 270V on the screen.
Just use different manufacturers of that tube type.
There is No adjustment necessary if you use Self Bias (a parallel RC network that is connected, from the Cathode to ground).
Different manufacturers of one type of the following:
KT66
KT77
KT88
EL34
KT120
But be careful with tube rolling the whole 6L6 Family.
6L6, 6L6-G, 6l6-GA, and 6L6-GB, they have plate dissipation ratings of 19 Watts, and screen maximum voltage of 270V.
But the 6L6GC has plate dissipation rating of 30 Watts, and screen maximum voltage of
450V.
You can design the amp to use the lower ratings, and then use all the 6L6 Family, including the 6L6-GC.
And then you can also use the 5881, with 23W plate, and 270V screen ratings.
Lots of tube rolling possibilities with this large family, including the 5881.
If you use self bias, no more than 19 watts in the plate, and 270V screen, it is plug and play (plug and listen).
Some manufacturers along the way, increased the ratings of the family of the 6L6, and 5881.
They increased the plate dissipation, and the max screen voltage.
But then how do you know if the tube you get in your hands was made to the old specs, or the new and improved specs?
You do not know for sure . . .
So just use different manufacturers of the 6L6-GC if you want to use more than 19W on the plate, and more than 270V on the screen.
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