Hello all, I have a few questions if I may. I apologize, I was only able to figure out how to insert a photo of the Boyuu A9's schematic.
(1) Are the 0.22uf "C102" the coupling caps?
(2) I know this may not be an easy question, but is there any info on the web
someone could recommend to convert this particular amp to allow for
6L6's?
(3) Is it safe to assume I can use 6CA7's as is?
I purchased this amp factory build on Amazon. What a nice little amp! It runs
my Klipsch speakers very nicely.
(1) Are the 0.22uf "C102" the coupling caps?
(2) I know this may not be an easy question, but is there any info on the web
someone could recommend to convert this particular amp to allow for
6L6's?
(3) Is it safe to assume I can use 6CA7's as is?
I purchased this amp factory build on Amazon. What a nice little amp! It runs
my Klipsch speakers very nicely.
Attachments
Yes, the 0.22 μF. parts are interstage coupling capacitors.
They might "work", but I would steer clear of 6L6 family tubes in the unit.
6CA7 and KT77 beam power tetrodes are electrically "equivalent" to true 5 grid pentode EL34s. If the amp had adjustable O/P tube bias, "tube rolling" would be just fine. Since the unit employs non-adjustable self bias, contact a reliable vendor for suitable replacement O/P tubes. Even a given group of EL34s could be problematic. A competent tube vendor knows the cathode current of his/her stock.
They might "work", but I would steer clear of 6L6 family tubes in the unit.
6CA7 and KT77 beam power tetrodes are electrically "equivalent" to true 5 grid pentode EL34s. If the amp had adjustable O/P tube bias, "tube rolling" would be just fine. Since the unit employs non-adjustable self bias, contact a reliable vendor for suitable replacement O/P tubes. Even a given group of EL34s could be problematic. A competent tube vendor knows the cathode current of his/her stock.
There's a large thread here that's been active recently. Try posting there for specific questions regarding this amp.
Boyuu EL34 A9 Tube Amp
jeff
6L6GC are almost just plug and play, but you might have to increase R107 and R108 resistance value to make the 6L6GC Quiescent cathode current the same as it was with the EL34.
Be sure to check that the 6L6GC filament voltage is not too high, it is only 0.9 Amps, and the EL34 / 6CA7/ KT77 filaments are 1.5 Amps. The 6L6GC's lighter filament current might cause the power transformer's filament secondary to output more than (6.3V + 10%), more than 6.9V.
The 6L6GC transconductance is about 1/2 of the EL34 transconductance, so you will get a little less output power.
But you may like the sound of the 6L6GC.
Be sure to check that the 6L6GC filament voltage is not too high, it is only 0.9 Amps, and the EL34 / 6CA7/ KT77 filaments are 1.5 Amps. The 6L6GC's lighter filament current might cause the power transformer's filament secondary to output more than (6.3V + 10%), more than 6.9V.
The 6L6GC transconductance is about 1/2 of the EL34 transconductance, so you will get a little less output power.
But you may like the sound of the 6L6GC.
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Thx 6A3aSUMMER,
I do prefer the 6l6 sound. I have a Saga+ tube preamp in order. Do you see any reason why I couldn’t bypass the input selector and the volume control? More or less run the unit like a block amp?
I do prefer the 6l6 sound. I have a Saga+ tube preamp in order. Do you see any reason why I couldn’t bypass the input selector and the volume control? More or less run the unit like a block amp?
Post #1 schematic does not show an input selector.
What input selector?
If you mean input selector and volume controls on the Saga + tube preamp, many preamps have lots of gain, and can not take the full scale output voltage of a CD player. So the preamp may need a volume control.
What is a Saga?
What preamp?
What are your signal sources, and what output voltage do they present to the Saga and preamp?
The schematic in Post # 1 does not show the connection of pin 1 to pin 4 of the input tube.
Be sure to tie those grids together.
There are more than one thread on the Boyuu A9 amplifier.
And if memory serves me correctly, over the years even the factory build may have had different circuit versions.
SRPP, parallel triode input, Ultra Linear, Pentode, Negative Feedback, no Negative Feedback, Triode wired output, etc.
Some of those schematics may just be user modified on the various threads.
Believe no schematic, unless you check that it exactly follows your actual factory build.
EL34 max plate dissipation is 25 Watts, 6L6GC max plate dissipation is 30 Watts.
All other 6L6 tube types max plate dissipation is 19 Watts.
The actual plate dissipation of the amplifier output tube is the Plate to Cathode voltage x the Plate current). For a reasonable estimate of plate current,
It will be the cathode current minus the screen current (minus about 1 to 7mA).
You will almost certainly want more self bias resistance than the two 2k parallel cathode resistors (parallel of 1k), in order to get the same current as the EL34 tubes are getting.
You do not want more current in the 6L6GC, because that would overload and heat the Boyuu B+ power supply.
The 6L6GC filament voltage (@ 0.9 Amp/6L6GC) will be slightly higher than the EL34 filament voltage (@ 1.5 Amp/EL34).
Depending on your power mains voltage, the 6.3V filament secondary may be more than 6.9V. In that case, you need to put series resistors in each leg of the filament secondary to get the voltage to the filaments close to 6.3V.
Let us know the actual schematic of your version of the Boyuu A9.
What input selector?
If you mean input selector and volume controls on the Saga + tube preamp, many preamps have lots of gain, and can not take the full scale output voltage of a CD player. So the preamp may need a volume control.
What is a Saga?
What preamp?
What are your signal sources, and what output voltage do they present to the Saga and preamp?
The schematic in Post # 1 does not show the connection of pin 1 to pin 4 of the input tube.
Be sure to tie those grids together.
There are more than one thread on the Boyuu A9 amplifier.
And if memory serves me correctly, over the years even the factory build may have had different circuit versions.
SRPP, parallel triode input, Ultra Linear, Pentode, Negative Feedback, no Negative Feedback, Triode wired output, etc.
Some of those schematics may just be user modified on the various threads.
Believe no schematic, unless you check that it exactly follows your actual factory build.
EL34 max plate dissipation is 25 Watts, 6L6GC max plate dissipation is 30 Watts.
All other 6L6 tube types max plate dissipation is 19 Watts.
The actual plate dissipation of the amplifier output tube is the Plate to Cathode voltage x the Plate current). For a reasonable estimate of plate current,
It will be the cathode current minus the screen current (minus about 1 to 7mA).
You will almost certainly want more self bias resistance than the two 2k parallel cathode resistors (parallel of 1k), in order to get the same current as the EL34 tubes are getting.
You do not want more current in the 6L6GC, because that would overload and heat the Boyuu B+ power supply.
The 6L6GC filament voltage (@ 0.9 Amp/6L6GC) will be slightly higher than the EL34 filament voltage (@ 1.5 Amp/EL34).
Depending on your power mains voltage, the 6.3V filament secondary may be more than 6.9V. In that case, you need to put series resistors in each leg of the filament secondary to get the voltage to the filaments close to 6.3V.
Let us know the actual schematic of your version of the Boyuu A9.
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There is quite a bit of useful info in the Boyuu thread link. Including using 6L6GCs and other output tubes.
Something to evaluate before you go down the 6L6GC path. The EL34 has half the plate impedance of the 6L6GC. The output transformer in the Boyuu is 3200 ohms impedance. This is very low for a single ended 6L6GC and will result in higher distortion and less power than a more appropriate OT.
The folks that did make the change you are considering used the 4 ohm tap with 8 ohms speakers and the 8 ohm tap with 16 ohms speakers. That produced lower distortion but also at the expense of lower output power because at 6400 ohms the 330 volt HT is low for a 6L6GC.
I have built 6V6, 6L6GC, EL34, KT88, 4D32 and several types of sweep tube SE Pentode amps. The circuit and proper matching of components made more difference in sound quality than the type of tube. My preference after years of experimenting with many tubes is plate to grid feedback with pentode or mosfet drivers. I have several quality OTs that I can configure from 2k - 10k impedance with my speakers. I liked the KT88 and 6L6GC implementations with 500 volt B+ and the 5k ohm output transformer.
Just my opinion but, I would try some of the basic EL34 circuit improvements in the Boyuu thread and evaluate if i liked the sound before going down the path you are considering. I would not expect the 6L6GC to perform better than the EL34 unless you change the output transformer.
Steve
"Oftentimes free advice is worth what you pay for it"
Something to evaluate before you go down the 6L6GC path. The EL34 has half the plate impedance of the 6L6GC. The output transformer in the Boyuu is 3200 ohms impedance. This is very low for a single ended 6L6GC and will result in higher distortion and less power than a more appropriate OT.
The folks that did make the change you are considering used the 4 ohm tap with 8 ohms speakers and the 8 ohm tap with 16 ohms speakers. That produced lower distortion but also at the expense of lower output power because at 6400 ohms the 330 volt HT is low for a 6L6GC.
I have built 6V6, 6L6GC, EL34, KT88, 4D32 and several types of sweep tube SE Pentode amps. The circuit and proper matching of components made more difference in sound quality than the type of tube. My preference after years of experimenting with many tubes is plate to grid feedback with pentode or mosfet drivers. I have several quality OTs that I can configure from 2k - 10k impedance with my speakers. I liked the KT88 and 6L6GC implementations with 500 volt B+ and the 5k ohm output transformer.
Just my opinion but, I would try some of the basic EL34 circuit improvements in the Boyuu thread and evaluate if i liked the sound before going down the path you are considering. I would not expect the 6L6GC to perform better than the EL34 unless you change the output transformer.
Steve
"Oftentimes free advice is worth what you pay for it"
The Boyuu 3.5k output transformer primary is a fixed inductance . . .
So if you put an 8 Ohm speaker on the 4 Ohm tap, the low frequencies will be rolled off earlier.
Try it.
Yes, I have done that with some of my amplifiers.
As a plus, it does increase the damping factor that the 8 Ohm speaker sees.
So if you put an 8 Ohm speaker on the 4 Ohm tap, the low frequencies will be rolled off earlier.
Try it.
Yes, I have done that with some of my amplifiers.
As a plus, it does increase the damping factor that the 8 Ohm speaker sees.