Good evening
My brother gave me the amp or one very similar to this one:
https://www.diyaudio.com/community/threads/chinese-single-ended-class-a-questions.278409/
I would like to use, if possible, 6ar6 or 6v6 tubes as I have lots of them.
I can change the wiring for the 6ar6 but am concerned (from googling) about the screen voltage for the 6ar6 and all voltages for the 6v6.
My tube knowledge is minimal but I can follow instructions and will not electrocute myself.
Thanks for looking, mouse.
My brother gave me the amp or one very similar to this one:
https://www.diyaudio.com/community/threads/chinese-single-ended-class-a-questions.278409/
I would like to use, if possible, 6ar6 or 6v6 tubes as I have lots of them.
I can change the wiring for the 6ar6 but am concerned (from googling) about the screen voltage for the 6ar6 and all voltages for the 6v6.
My tube knowledge is minimal but I can follow instructions and will not electrocute myself.
Thanks for looking, mouse.
1. First problem is to find out how many volts there are in the B+ secondary . . . .
Example, 300-0-300, 350-0-350, etc.
2. Suppose you do have to reduce the B+ voltage
If the amplifier is using a tube rectifier, the way to reduce the B+ is:
Either use a high wattage rating series resistor from the rectifier output to the first filter capacitor. That will create lots of heat.
Or use a choke input filter. A choke connected from the rectifier to the first filer capacitor. But that takes room/real estate.
And, the choke has to have an inductance large enough to meet the critical inductance rule.
Another solution is to add a very low capacitance filter cap, a resistor from there to what was/used to be the first filter cap.
3. But to properly do any of the above, you also have to decide how much current your amplifier circuit will load the B+
(input tube current, output tube current, bleeder resistor current). Call this the total B+ current.
What answers do you have for:
1. Secondary voltage
2. Total B+ current
If you do not have a schematic, you are going to have quite a time trying to make something that works (especially if all you have is a few parts, and perhaps some missing ones.
Does this amplifier use point to point wiring?
Or is it wired on a PCB?
Output transformers that do not have a UL tap, do not plan on doing a ultra linear amp (can be done with a lot of extra circuitry, but this amplifier does not sound like a good candidate.
Either plan on Beam Power Mode, or Triode wired Mode.
And, with no output taps to match the nominal impedance of a speaker, the primary impedance will vary widely versus the speaker's nominal impedance.
Your amplifier that is "very similar" to the one in the other thread, does not tell us much about what it will take, to just get the amplifier working with the prescribed EL34 tubes.
We need more details.
parts
tubes
etc.
Example, 300-0-300, 350-0-350, etc.
2. Suppose you do have to reduce the B+ voltage
If the amplifier is using a tube rectifier, the way to reduce the B+ is:
Either use a high wattage rating series resistor from the rectifier output to the first filter capacitor. That will create lots of heat.
Or use a choke input filter. A choke connected from the rectifier to the first filer capacitor. But that takes room/real estate.
And, the choke has to have an inductance large enough to meet the critical inductance rule.
Another solution is to add a very low capacitance filter cap, a resistor from there to what was/used to be the first filter cap.
3. But to properly do any of the above, you also have to decide how much current your amplifier circuit will load the B+
(input tube current, output tube current, bleeder resistor current). Call this the total B+ current.
What answers do you have for:
1. Secondary voltage
2. Total B+ current
If you do not have a schematic, you are going to have quite a time trying to make something that works (especially if all you have is a few parts, and perhaps some missing ones.
Does this amplifier use point to point wiring?
Or is it wired on a PCB?
Output transformers that do not have a UL tap, do not plan on doing a ultra linear amp (can be done with a lot of extra circuitry, but this amplifier does not sound like a good candidate.
Either plan on Beam Power Mode, or Triode wired Mode.
And, with no output taps to match the nominal impedance of a speaker, the primary impedance will vary widely versus the speaker's nominal impedance.
Your amplifier that is "very similar" to the one in the other thread, does not tell us much about what it will take, to just get the amplifier working with the prescribed EL34 tubes.
We need more details.
parts
tubes
etc.
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The schematic lists 376V B+. I wouldn't worry about the B+ being too high for 6V6. I have a deluxe reverb that runs 478V on 6V6s and I've run NOS American tubes in it with no issues. I have a guitar amp I built with 6K6s that runs about 400V on them, despite the datasheet max of 300V. That's been around since 1993. Smaller tubes do have lower max B+, but I've always thought the 6V6/6K6 and similar octals were deliberately underrated in the manuals to sell the bigger 6L6s/etc...
If the schematic is correct and it is an ultra-linear tap, I wouldn't worry about the screen voltage. You might up the 100 ohm resistor if you are concerned, I probably wouldn't. Most people forget the max screen voltage is for pentode style operation and it NOT changing as plate voltage does. In ultra-linear the screen voltage follows plate voltage and is forgiving (IMO) of exceeding the screen max B+ value as long as the bias and circuit is working correctly.
6V6, you will need to change out the cathode bias resistor to set the plate dissipation in it's proper (and about 1/2 of EL34) range. You will lose some output power as well, but otherwise that's it.
Looks like the 6AR6 would get you a little more output with no worry on B+ voltage at all, but you'll need to re-wire the socket as well as swap the cathode resistor... but again, either should work fine. That said, EL34s are great tubes too... maybe just use them until they wear out before you swap them... but I wouldn't hesitate to do what you're asking. I don't think you'll have any issues at all...
If the schematic is correct and it is an ultra-linear tap, I wouldn't worry about the screen voltage. You might up the 100 ohm resistor if you are concerned, I probably wouldn't. Most people forget the max screen voltage is for pentode style operation and it NOT changing as plate voltage does. In ultra-linear the screen voltage follows plate voltage and is forgiving (IMO) of exceeding the screen max B+ value as long as the bias and circuit is working correctly.
6V6, you will need to change out the cathode bias resistor to set the plate dissipation in it's proper (and about 1/2 of EL34) range. You will lose some output power as well, but otherwise that's it.
Looks like the 6AR6 would get you a little more output with no worry on B+ voltage at all, but you'll need to re-wire the socket as well as swap the cathode resistor... but again, either should work fine. That said, EL34s are great tubes too... maybe just use them until they wear out before you swap them... but I wouldn't hesitate to do what you're asking. I don't think you'll have any issues at all...
In your amplifier the plate current is around 57 mA and the voltage between cathode and plate is 327 V. The plate dissipation is around 18.6 Watt (P = I x V = 0.057 x 327 = 18.6).
For single ended power pentodes and beam tetrodes the optimum primary load is given by the voltage between cathode and anode divided by the plate current. If we asume that the primary impedance of the output transformers in your amplifier matches the optimum load, than the primary impedance of the output transofmrer will be around 327 / 0.057 = 5K7.
Like Cycline3 wrote, the 6V6 has a lower maximum plate dissipation than the EL34 (12 Watt for the 6V6 against 25 Watt for the EL34) so if you would want to run 6V6's in your amplifier, the plate current has to be lower. With a cathode resistor of 600 Ohm the plate current will be about 34 mA (and the screen current will be about 3.5 mA), giving a cathode voltage of about 22 V. The optimum primay load for this situation would than be 327/0.034 = 9K6. which is quit a bit higher than 5K7.
So operating your amplifier with 6V6's is not ideal (both power wise and distortion wise). Also note that the EL34 and 6V6 are not completely pin compatible (compare pins 1 and 8).
The maximum plate dissipation of the 6AR6 is 19 Watt. The datasheets for the 6AR6 only contain curves in pentode mode for Vg2 = 300 V. At that screen grid voltage Vg1 would have to be around -40 V for a plate current of about 57 mA. I estimate the screen current to be 4 mA. So the cathode resistor would have to be: R = V / I = 40 / 0.061 = 656 Ohm.
Because the cathode voltage for a 6AR6 has to be around 40 V instead of 20 V, the voltage between cathode and screengrid will be around 20 V lower, but would still be around 321 V (instead of the 300 V from the datasheet) so the plate current would be higher than 57 mA. But if you choose 720 Ohm for the cathode resistor, I think you will be safe.
I agree with Cycline3 that the somewhat high screengrid voltage is less critical in ultra linear mode than it would be in pentode mode. The datasheets for the 6098 (which is identical to the 6AR6) gives 315 V as the abosolute maximum for the screengrid voltage. This is the voltagte between cathode and screengrid. With a 6AR6 and a cathode resistor of about 720 Ohm I think this voltage will be very close to that 315 V anyway.
Like you already know, the 6AR6 is not pin compatible with the EL34. Perhaps you could make two adapters, which would also take care of the needed higher value of the cathode resistor. This could be done by putting a 330 Ohm resistor, paralleled by an electrolityc capacitor of 220 uF, in the adapter so that when used they are in series with the cathode resistor of 390 Ohm and the capacitor of 220 uF that is already in your amplifier. In that way you don't have to alter anything in the amplifier itself.
For single ended power pentodes and beam tetrodes the optimum primary load is given by the voltage between cathode and anode divided by the plate current. If we asume that the primary impedance of the output transformers in your amplifier matches the optimum load, than the primary impedance of the output transofmrer will be around 327 / 0.057 = 5K7.
Like Cycline3 wrote, the 6V6 has a lower maximum plate dissipation than the EL34 (12 Watt for the 6V6 against 25 Watt for the EL34) so if you would want to run 6V6's in your amplifier, the plate current has to be lower. With a cathode resistor of 600 Ohm the plate current will be about 34 mA (and the screen current will be about 3.5 mA), giving a cathode voltage of about 22 V. The optimum primay load for this situation would than be 327/0.034 = 9K6. which is quit a bit higher than 5K7.
So operating your amplifier with 6V6's is not ideal (both power wise and distortion wise). Also note that the EL34 and 6V6 are not completely pin compatible (compare pins 1 and 8).
The maximum plate dissipation of the 6AR6 is 19 Watt. The datasheets for the 6AR6 only contain curves in pentode mode for Vg2 = 300 V. At that screen grid voltage Vg1 would have to be around -40 V for a plate current of about 57 mA. I estimate the screen current to be 4 mA. So the cathode resistor would have to be: R = V / I = 40 / 0.061 = 656 Ohm.
Because the cathode voltage for a 6AR6 has to be around 40 V instead of 20 V, the voltage between cathode and screengrid will be around 20 V lower, but would still be around 321 V (instead of the 300 V from the datasheet) so the plate current would be higher than 57 mA. But if you choose 720 Ohm for the cathode resistor, I think you will be safe.
I agree with Cycline3 that the somewhat high screengrid voltage is less critical in ultra linear mode than it would be in pentode mode. The datasheets for the 6098 (which is identical to the 6AR6) gives 315 V as the abosolute maximum for the screengrid voltage. This is the voltagte between cathode and screengrid. With a 6AR6 and a cathode resistor of about 720 Ohm I think this voltage will be very close to that 315 V anyway.
Like you already know, the 6AR6 is not pin compatible with the EL34. Perhaps you could make two adapters, which would also take care of the needed higher value of the cathode resistor. This could be done by putting a 330 Ohm resistor, paralleled by an electrolityc capacitor of 220 uF, in the adapter so that when used they are in series with the cathode resistor of 390 Ohm and the capacitor of 220 uF that is already in your amplifier. In that way you don't have to alter anything in the amplifier itself.
Hey thanks for the detailed replies!
I will take some photos and try sketch the power supply and output section and get as much info as I can.
Can I measure voltages with tubes removed or should they be in?
Also any tips on making an adaptor, I have the sockets but what about the male part, do I break open a faulty tube?
Thanks again, mouse
I will take some photos and try sketch the power supply and output section and get as much info as I can.
Can I measure voltages with tubes removed or should they be in?
Also any tips on making an adaptor, I have the sockets but what about the male part, do I break open a faulty tube?
Thanks again, mouse
Measure the voltages with the tubes in, but please be carefull.
I never made an adapter like this so I can't really advise you on that one. I suggest you do a search on this forum because this topic must have been discussed before. I do think that you can buy the male part so breaking a tube for that is not needed.
I never made an adapter like this so I can't really advise you on that one. I suggest you do a search on this forum because this topic must have been discussed before. I do think that you can buy the male part so breaking a tube for that is not needed.
The EL34 and 6CA7 pin # 1 (suppressor grid and beam formers, respectively) must be connected to pin #8 (cathode).
The 6V6 (beam formers are internally connected to the cathode) does not have any connection to pin #1, so the connections are compatible with a socket that is wired for an EL34 / 6CA7. Only the bias voltage, plate voltage, screen voltage, plate current, and screen current are lower for a 6V6, so the circuit parameters around the tube have to be changed.
EL34 / 6CA7 connections do not have be changed to work with a 6V6 (do not forget to change the parameters listed above, or you will cook the 6V6).
There is Plug and Play, and . . .
There is Plug and Pray (when it is not done properly).
Male Octal Plugs are available at such places like this:
https://www.tubesandmore.com/search/node/Octal+Plug/
Have fun building and listening!
The 6V6 (beam formers are internally connected to the cathode) does not have any connection to pin #1, so the connections are compatible with a socket that is wired for an EL34 / 6CA7. Only the bias voltage, plate voltage, screen voltage, plate current, and screen current are lower for a 6V6, so the circuit parameters around the tube have to be changed.
EL34 / 6CA7 connections do not have be changed to work with a 6V6 (do not forget to change the parameters listed above, or you will cook the 6V6).
There is Plug and Play, and . . .
There is Plug and Pray (when it is not done properly).
Male Octal Plugs are available at such places like this:
https://www.tubesandmore.com/search/node/Octal+Plug/
Have fun building and listening!
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Thanks for correcting what I wrote about the pin (un)compatibility of the EL34 and 6V6.
Only the original, all metal 6V6 has pin 1 connected to its metal envelope. The envelope would than sit at the cathode voltage in the working amplifier but as long as the envelope doens't come into contact with the chassis, there's no danger.
Only the original, all metal 6V6 has pin 1 connected to its metal envelope. The envelope would than sit at the cathode voltage in the working amplifier but as long as the envelope doens't come into contact with the chassis, there's no danger.
PFL,
Thanks!
I forgot about the Metal 6V6 (and I think other tubes too, like the metal 6L6).
Some of those old metal tubes have paint coming off of the metal.
I do not want to grab the metal, if pin # 1 is connected to pin # 8, and the self bias of some 6L6 cathode is at +30V
(I am sensitive to lower voltage than many other people's hands/fingers are).
Thanks!
I forgot about the Metal 6V6 (and I think other tubes too, like the metal 6L6).
Some of those old metal tubes have paint coming off of the metal.
I do not want to grab the metal, if pin # 1 is connected to pin # 8, and the self bias of some 6L6 cathode is at +30V
(I am sensitive to lower voltage than many other people's hands/fingers are).
I'm back with news!
My brother told me to stop messing around with this amp and came up with new 5881 and el34. He said use el34 in winter because the transformer will get hotter.
Still want to use the 6ar6 and 6v6 with some se 3.5k transformers he will find and or these amps from an Akai tape player. It uses an el84 which he has but won't give me.
He also gave me some old Hitachi MOSFETs and some rather nice cast heatsinks so I'm not complaining.
Any advice on using these new transformers appreciated.
mouse
My brother told me to stop messing around with this amp and came up with new 5881 and el34. He said use el34 in winter because the transformer will get hotter.
Still want to use the 6ar6 and 6v6 with some se 3.5k transformers he will find and or these amps from an Akai tape player. It uses an el84 which he has but won't give me.
He also gave me some old Hitachi MOSFETs and some rather nice cast heatsinks so I'm not complaining.
Any advice on using these new transformers appreciated.
mouse