Hey Anyone,
Does anyone know of good quality audio tubes that were manufactured to work in car radios? The idea of using battery powered tubes is interesting?
Does anyone know of good quality audio tubes that were manufactured to work in car radios? The idea of using battery powered tubes is interesting?
Blencowe has a good article here:
http://www.valvewizard.co.uk/Triodes_at_low_voltages_Blencowe.pdf
and there is this site with a nice list:
http://www.junkbox.com/electronics/lowvoltagetubes.shtml
I don't see much on European tubes though and I know the EF98 is a low voltage tube so there are probably others as well.
http://www.valvewizard.co.uk/Triodes_at_low_voltages_Blencowe.pdf
and there is this site with a nice list:
http://www.junkbox.com/electronics/lowvoltagetubes.shtml
I don't see much on European tubes though and I know the EF98 is a low voltage tube so there are probably others as well.
Google "space charge tubes" there are hundreds of them out there.
Old car radios used a vibrator power supply to deliver 250 to 300 volts to the tubes. My first car was a 1949 Plymouth with a 6 volt electrical system. The original radio used a pair of 6V6GT's to deliver about 8 watts. I had a pair of these radios in the trunk to run 6 X 9 speakers from a Panasonic portable cassette player.
In the 50's the space charge tube was invented, but a pair of 12K5's in push pull could deliver only 1/2 a watt on a 12 volt supply. Radios from the late 50's used space charge tubes for everything except the audio output stage which was a large germanium transistor. GM used the 2N174, and even made their own. It ran class A SE for about 5 watts using a step up OPT.
By the early 60's all the stages ran germanium transistors and the space charge tubes were gone.
I have seen small guitar amps made with 12U7's and 12K5's that ran on batteries, but the heaters in those tubes sucked a lot of current to get the emission needed for 12 volt plates. It takes about 1.2 Amp from 12 volts for 2 X 12U7 and 2 X 12K5 to make a half watt amp. I made such an amp maybe 20 years ago but it ate batteries quickly. Google "12K5" for examples.
I then found that a much better sounding amp with longer battery life can be made with 12AX7's and 6AK6's and a step up power supply that makes about 250 volts. 2 X 12AX7 and 2 X 6AK6 in series will draw 450 mA from 12 volts and make 5 watts.
Old car radios used a vibrator power supply to deliver 250 to 300 volts to the tubes. My first car was a 1949 Plymouth with a 6 volt electrical system. The original radio used a pair of 6V6GT's to deliver about 8 watts. I had a pair of these radios in the trunk to run 6 X 9 speakers from a Panasonic portable cassette player.
In the 50's the space charge tube was invented, but a pair of 12K5's in push pull could deliver only 1/2 a watt on a 12 volt supply. Radios from the late 50's used space charge tubes for everything except the audio output stage which was a large germanium transistor. GM used the 2N174, and even made their own. It ran class A SE for about 5 watts using a step up OPT.
By the early 60's all the stages ran germanium transistors and the space charge tubes were gone.
I have seen small guitar amps made with 12U7's and 12K5's that ran on batteries, but the heaters in those tubes sucked a lot of current to get the emission needed for 12 volt plates. It takes about 1.2 Amp from 12 volts for 2 X 12U7 and 2 X 12K5 to make a half watt amp. I made such an amp maybe 20 years ago but it ate batteries quickly. Google "12K5" for examples.
I then found that a much better sounding amp with longer battery life can be made with 12AX7's and 6AK6's and a step up power supply that makes about 250 volts. 2 X 12AX7 and 2 X 6AK6 in series will draw 450 mA from 12 volts and make 5 watts.
The lists shows only 12V heater tubes, exept the 6GM8 also called ECC86.
EF97 and EF98 both have 6V3 heaters and have a 7pin miniature socket.
The 97 is not so interesting, has a sliding transconductance for agc in receivers.
The 98 is a penthode with a slope of 2mA/V.
Mona
Thanks guys. I wasn't familiar with the 'vibrator' power supply. I was unaware that there was a way to increase voltage in a DC circuit. I found a few on eBay. They aren't expensive but have been out of production for a long time. I think it would be better to leave them to the old car guys that really need them.
I did find a DC to DC converter at Digikey, (R12-150B Recom Power | 945-2053-5-ND | DigiKey) it uses a 10 to 14 volt input to achieve a variable output voltage between 95 and 210 volts @ 50ma. I could run three of them in parallel for a small SE EL84 or 6V6 amp.
But I think a better application might be a preamp? The blurb says they could be cascaded to produce 420 volts. Building alarms use some fairly large 12 volt batteries that are completely sealed. With the battery in a power supply box along with a trickle charger you could rig it with a two pole switch. One pole would turn the amp on, the other turn the amp off and the trickle charger on. The converter is both a step up and a regulator so I could set the voltage for 300 volts. I was thinking of using 12xxx and LM317 filament regulators that would draw directly from the battery. So DC heaters as well.
The amp would be DC coupled running 5751 front and with 12AU7 second stage. The amp would have no AC in the chassis except the signal.
I did find a DC to DC converter at Digikey, (R12-150B Recom Power | 945-2053-5-ND | DigiKey) it uses a 10 to 14 volt input to achieve a variable output voltage between 95 and 210 volts @ 50ma. I could run three of them in parallel for a small SE EL84 or 6V6 amp.
But I think a better application might be a preamp? The blurb says they could be cascaded to produce 420 volts. Building alarms use some fairly large 12 volt batteries that are completely sealed. With the battery in a power supply box along with a trickle charger you could rig it with a two pole switch. One pole would turn the amp on, the other turn the amp off and the trickle charger on. The converter is both a step up and a regulator so I could set the voltage for 300 volts. I was thinking of using 12xxx and LM317 filament regulators that would draw directly from the battery. So DC heaters as well.
The amp would be DC coupled running 5751 front and with 12AU7 second stage. The amp would have no AC in the chassis except the signal.
The old vibrator power supplies worked, but had plenty of problems. They used a mechanical chopper, the vibrator, to turn 6 or 12 volts DC (cars were 6 volts until the 50's) into two 6 or 12 volt P-P square waves that fed a step up transformer. The system ran in the 20 to 50 Hz range so the transformer was large and the vibrator wore out quickly.
Space charge tubes and transistors made the vibrator system obsolete for receiving duty, but radio transmitters used them well into the 60's.
Big germanium transistors replaced the mechanical contacts and the frequency of operation moved up into the 500 Hz to 2 KHz range.
Mosfets and controller chips have replaced the germanium transistors and moved the frequency up to 200 KHz to 2 MHz. The SG3325 and TL494 controller chips appeared in the 70's and are still made today. This technology is used in most of the big power solid state car audio amps. They step 12 volts up into the 50 to 150 volt range to run a mega mosfet or class D audio amp. It is possible to liberate the parts from a dead amp and modify the secondary side of the power supply for voltage doubler use.
There are zillions of little power invertors made for running small household electronics in the car. They make 120 volts AC from 12 volts DC. You can find these things cheap from places like Amazon or Newegg.
The old ones used a pair of switching mosfets to make two 60 Hz square waves to feed a big iron transformer. These are obsolete.
Anything made in the last 5 years has a step up converter that makes either 160 VDC or 320 VDC. The second stage chops up the DC at a 60 Hz rate to make "AC".
There are two ways to go here, and I have done both.
1) Simply buy a 100 to 200 watt inverter and plug your existing tube amp power supply into it and call it DONE. I took this to the extreme case and plugged my 845 SET amp into a 700 watt inverter and stuffed it all into the trunk of my Mustang about 10 years ago. I found out that DHT's don't like potholes! A 10 watt guitar amp running on batteries works good. You can save some power by wiring the tube heaters directly to the batteries to avoid conversion losses.
2) Open up the inverter and find the DC source, use it directly as the tube amps B+. You will need to add a small choke and polypropylene cap to filter out the inverter noise. This will eliminate two power conversion stages and improve efficiency by as much as 50%. Most of these cheap inverters are isolated, but I have seen some that are not. There should be infinite resistance between the DC source and the 12 volt input. If this is the case, then two or more of these can be wired in series for more voltage.
If you can DIY a power supply, it is possible to make your own 12 volt to HV power supply. I have made small ones for tiny tube guitar amps, including one that will go inside the guitar. See this thread for ideas:
http://www.diyaudio.com/forums/tubes-valves/277263-13-8-volt-smps-kt120-se-amp.html
http://pjlelectronics.com/images/SE_MONO_BLOCK_power_supply.pdf
SLA (sealed lead acid) batteries like those found in alarm systems are cheap and heavy. Being a relative of the car battery, they will have the same issues. They die after 3 to 5 years, and discharge themselves, often permanently, after months of non use. The charging circuits are simple and the batteries are relatively safe. If the weight isn't an issue, they are the likely choice.
LIPO batteries like those used in model aircraft are very light and have extreme power density. As we have seen with some cell phones and laptops, they, unfortunately have a fire problem. The chemistry is inherently unstable and these batteries must not be completely discharged. They also must be charged using a proper balancing charger. I used these in my "inside the guitar" amp.
LiFePo4 batteries are a relatively new technology that is the best of both worlds. You can find a battery that looks like, and is a direct replacement for the SLA battery used in alarms, UPS's and kids battery cars, that is about half the weight. Like all new tech, they are about twice the cost of SLA's but deals can often be found on Ebay.
Space charge tubes and transistors made the vibrator system obsolete for receiving duty, but radio transmitters used them well into the 60's.
Big germanium transistors replaced the mechanical contacts and the frequency of operation moved up into the 500 Hz to 2 KHz range.
Mosfets and controller chips have replaced the germanium transistors and moved the frequency up to 200 KHz to 2 MHz. The SG3325 and TL494 controller chips appeared in the 70's and are still made today. This technology is used in most of the big power solid state car audio amps. They step 12 volts up into the 50 to 150 volt range to run a mega mosfet or class D audio amp. It is possible to liberate the parts from a dead amp and modify the secondary side of the power supply for voltage doubler use.
There are zillions of little power invertors made for running small household electronics in the car. They make 120 volts AC from 12 volts DC. You can find these things cheap from places like Amazon or Newegg.
The old ones used a pair of switching mosfets to make two 60 Hz square waves to feed a big iron transformer. These are obsolete.
Anything made in the last 5 years has a step up converter that makes either 160 VDC or 320 VDC. The second stage chops up the DC at a 60 Hz rate to make "AC".
There are two ways to go here, and I have done both.
1) Simply buy a 100 to 200 watt inverter and plug your existing tube amp power supply into it and call it DONE. I took this to the extreme case and plugged my 845 SET amp into a 700 watt inverter and stuffed it all into the trunk of my Mustang about 10 years ago. I found out that DHT's don't like potholes! A 10 watt guitar amp running on batteries works good. You can save some power by wiring the tube heaters directly to the batteries to avoid conversion losses.
2) Open up the inverter and find the DC source, use it directly as the tube amps B+. You will need to add a small choke and polypropylene cap to filter out the inverter noise. This will eliminate two power conversion stages and improve efficiency by as much as 50%. Most of these cheap inverters are isolated, but I have seen some that are not. There should be infinite resistance between the DC source and the 12 volt input. If this is the case, then two or more of these can be wired in series for more voltage.
If you can DIY a power supply, it is possible to make your own 12 volt to HV power supply. I have made small ones for tiny tube guitar amps, including one that will go inside the guitar. See this thread for ideas:
http://www.diyaudio.com/forums/tubes-valves/277263-13-8-volt-smps-kt120-se-amp.html
http://pjlelectronics.com/images/SE_MONO_BLOCK_power_supply.pdf
SLA (sealed lead acid) batteries like those found in alarm systems are cheap and heavy. Being a relative of the car battery, they will have the same issues. They die after 3 to 5 years, and discharge themselves, often permanently, after months of non use. The charging circuits are simple and the batteries are relatively safe. If the weight isn't an issue, they are the likely choice.
LIPO batteries like those used in model aircraft are very light and have extreme power density. As we have seen with some cell phones and laptops, they, unfortunately have a fire problem. The chemistry is inherently unstable and these batteries must not be completely discharged. They also must be charged using a proper balancing charger. I used these in my "inside the guitar" amp.
LiFePo4 batteries are a relatively new technology that is the best of both worlds. You can find a battery that looks like, and is a direct replacement for the SLA battery used in alarms, UPS's and kids battery cars, that is about half the weight. Like all new tech, they are about twice the cost of SLA's but deals can often be found on Ebay.
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