Hi All.
I have a question about using EL84 tubes with an adapter in a 45 amp I have in the works. I am going to build two mono blocks that will employ over specified power transformers and 5K to 8 Ohm Electraprint OPTs. I will be using typical operating points for the 45 tubes at around 260-270 across the plates and around 32-34mA. I have built several EL84 amps over the last few years, including a couple of Decware SE84CS clones, and really like their sound, even with the less than high quality OPTs that I have used in these builds. Although I have a nice selection of 45 tubes at hand, I would like to be able to use EL84/6N14P-EV tubes as well in this amp in order to take advantage of the excellent Electraprint OPTs while using my many vintage EL84 and 6N14P-EV tubes. I bought a pair of noval to octal adapters, and have used them in some of my EL84 amps to run 6P3S tubes with good results. I have, however, been unable to find a commercially available adapter for four pin to noval that doesn't have open wiring. I should be able to put a pair together using socket parts I have available. Is this a crazy idea? Any comments, suggestions or advice would be much appreciated.
I have a question about using EL84 tubes with an adapter in a 45 amp I have in the works. I am going to build two mono blocks that will employ over specified power transformers and 5K to 8 Ohm Electraprint OPTs. I will be using typical operating points for the 45 tubes at around 260-270 across the plates and around 32-34mA. I have built several EL84 amps over the last few years, including a couple of Decware SE84CS clones, and really like their sound, even with the less than high quality OPTs that I have used in these builds. Although I have a nice selection of 45 tubes at hand, I would like to be able to use EL84/6N14P-EV tubes as well in this amp in order to take advantage of the excellent Electraprint OPTs while using my many vintage EL84 and 6N14P-EV tubes. I bought a pair of noval to octal adapters, and have used them in some of my EL84 amps to run 6P3S tubes with good results. I have, however, been unable to find a commercially available adapter for four pin to noval that doesn't have open wiring. I should be able to put a pair together using socket parts I have available. Is this a crazy idea? Any comments, suggestions or advice would be much appreciated.
You could mount both types of sockets on the chassis and wire them in parallel
(except for the cathodes), using only one tube type at a time.
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famousmockingbird:
Thanks. I can’t believe I forgot about the heaters. The transformer I am using has a 6.3 volt winding that will work for the EL84s, and the filaments for the 45s will be run off two separate filament transformers, one per side. Probably adding a separate socket for the EL84s, as Rayma suggested, is the simplest way to do it, but it’s not going to look that great. Assuming I can sort out the heaters with a switch, is an adapter a viable option?
Thanks. I can’t believe I forgot about the heaters. The transformer I am using has a 6.3 volt winding that will work for the EL84s, and the filaments for the 45s will be run off two separate filament transformers, one per side. Probably adding a separate socket for the EL84s, as Rayma suggested, is the simplest way to do it, but it’s not going to look that great. Assuming I can sort out the heaters with a switch, is an adapter a viable option?
The 45 tubes with 260 to 270V Plate to Filament, and 32 to 34 mA are going to have about -50V of grid bias.
You will have to have much much less than -50V grid bias to get an EL84 to work at all; it will be cut off with such a high negative bias.
You will have to have much much less than -50V grid bias to get an EL84 to work at all; it will be cut off with such a high negative bias.
Can you post both of the amplifier circuits that you plan to use?
You probably will have to rebias when changing tube types, but
a variable bias supply with that much range isn't difficult.
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One word.......DON"T
I have an amplifier that can be switched from 300B to 45. I also have a pair of 45's with blown filaments because I forgot to change the switch.
I’m not going to bother with this idea. The thought of accidentally killing a 45 tube because I forgot to throw one of the switches (and I will forget), really frightens me. Thanks for the advice.
This has got me thinking.
I have built many tube amps in the last few years. It's like my hobby. Every time a build a free standing tube amp, I have to build a new power supply and a new circuit that includes expensive (or not) output transformers. I have around 15 single ended tube amps at this point, which is pretty crazy if you consider how many transformers, capacitors, etc. that entails.
If, instead, I had built a chassis with two different power transformers where I could switch between using either of these transformers feeding either a choke input or capacitor input on a switch, that would have given me four different voltages to use. I could get more if I varied the input capacitor size with another switch, as many different voltages as I could fit capacitors on a given switch. Lets say that I ended up with six voltages by using two power transformers, that I could switch between, going to one really nice choke at the input that could have 2 different values of capacitance put in front of it to vary the voltage. Since I would be buying 2 transformers instead of 15, I could buy really nice supersize ones. Same goes for the choke and the capacitors in the supply.
On the other end of the circuit, I could build a chassis with two pairs of really nice output transformers that have multiple output taps. This would provide me a range of input/output impedance ratios that should suit multiple tube circuits and speaker loads.
So now I have two chassis that take care of power supply and output (I suppose they could be combined into one large chassis though). Now all I have to do is build a small chassis for the tube circuit every time I want to build an amp, and I never have to build (and more importantly pay for) another power supply or output transformer again. I could use a different connector type for each circuit that would provide the appropriate connections for each separate tube circuit chassis. This is in order to avoid accidental connections to inappropriate voltages as there would be either the correct voltages once connected or none at all, based upon the correct switches being thrown.
It might make more sense to put the filament supplies in each tube circuit chassis, but maybe 6.3 volts could be supplied with the main connection as many tubes use this voltage, and all other filament supply voltages could be built into the circuit chassis.
So, for example, I build a 45 amp circuit in its own cute little tube circuit chassis. I select power transformer 1 for choke input and 325 volts B+, and output transformer 2 for 5K to 8 Ohms. I then attach the connector (or connectors) that makes all the necessary connections happen between the chassis. In this case, the 45 circuit chassis needs a separate power plug to provide for the 2.5 volt heaters contained in it. I turn on the 45 circuit chassis first, and then turn on the power supply chassis.
I love building amps and listening to them, but it would be nice to just build a small circuit each time instead of an entire amp every single time.
I have built many tube amps in the last few years. It's like my hobby. Every time a build a free standing tube amp, I have to build a new power supply and a new circuit that includes expensive (or not) output transformers. I have around 15 single ended tube amps at this point, which is pretty crazy if you consider how many transformers, capacitors, etc. that entails.
If, instead, I had built a chassis with two different power transformers where I could switch between using either of these transformers feeding either a choke input or capacitor input on a switch, that would have given me four different voltages to use. I could get more if I varied the input capacitor size with another switch, as many different voltages as I could fit capacitors on a given switch. Lets say that I ended up with six voltages by using two power transformers, that I could switch between, going to one really nice choke at the input that could have 2 different values of capacitance put in front of it to vary the voltage. Since I would be buying 2 transformers instead of 15, I could buy really nice supersize ones. Same goes for the choke and the capacitors in the supply.
On the other end of the circuit, I could build a chassis with two pairs of really nice output transformers that have multiple output taps. This would provide me a range of input/output impedance ratios that should suit multiple tube circuits and speaker loads.
So now I have two chassis that take care of power supply and output (I suppose they could be combined into one large chassis though). Now all I have to do is build a small chassis for the tube circuit every time I want to build an amp, and I never have to build (and more importantly pay for) another power supply or output transformer again. I could use a different connector type for each circuit that would provide the appropriate connections for each separate tube circuit chassis. This is in order to avoid accidental connections to inappropriate voltages as there would be either the correct voltages once connected or none at all, based upon the correct switches being thrown.
It might make more sense to put the filament supplies in each tube circuit chassis, but maybe 6.3 volts could be supplied with the main connection as many tubes use this voltage, and all other filament supply voltages could be built into the circuit chassis.
So, for example, I build a 45 amp circuit in its own cute little tube circuit chassis. I select power transformer 1 for choke input and 325 volts B+, and output transformer 2 for 5K to 8 Ohms. I then attach the connector (or connectors) that makes all the necessary connections happen between the chassis. In this case, the 45 circuit chassis needs a separate power plug to provide for the 2.5 volt heaters contained in it. I turn on the 45 circuit chassis first, and then turn on the power supply chassis.
I love building amps and listening to them, but it would be nice to just build a small circuit each time instead of an entire amp every single time.
I have something similar for designing amplifiers, except there is no chassis. I can swap "modules" with a screwdriver and the emphasis is on accessibility so that I can get to everything, hence an open exposed layout. I use lab bench power supplies that are adjustable for all voltages, but your needs are a bit different.
You want a power supply capable of different output voltages.......
There is an easier way. Get an Edcor "Tinker Box" transformer....or two. The TBPWR-HV1 has a single 400 mA secondary with taps every 25 volts from 200-0-200 VAC up to 300-0-300 VAC. With a hand full of diodes and caps you can make a power supply with 5 or more different B+ voltages available all at the same time.
There is a bigger brother, the HV2, that has taps from 350 to 450 VAC in 25 volt steps, but it's rated for 300 mA.
If you connect all the supply voltages to a suitable socket, say an octal tube socket, then the amp "module" could have a suitable plug that's only wired for the correct B+ voltages.
There is a matching heater transformer, the TBPWR-LV1 with taps for the usual common heater voltages, but I would use separate transformers, one 6.3V and two 2.5V. Again use the plug and socket methogd to avoid mistakes.
Connecting the wrong OPT impedance is not fatal to the tubes and often some tube - speaker - music combinations benefit from a mismatch.
You want a power supply capable of different output voltages.......
There is an easier way. Get an Edcor "Tinker Box" transformer....or two. The TBPWR-HV1 has a single 400 mA secondary with taps every 25 volts from 200-0-200 VAC up to 300-0-300 VAC. With a hand full of diodes and caps you can make a power supply with 5 or more different B+ voltages available all at the same time.
There is a bigger brother, the HV2, that has taps from 350 to 450 VAC in 25 volt steps, but it's rated for 300 mA.
If you connect all the supply voltages to a suitable socket, say an octal tube socket, then the amp "module" could have a suitable plug that's only wired for the correct B+ voltages.
There is a matching heater transformer, the TBPWR-LV1 with taps for the usual common heater voltages, but I would use separate transformers, one 6.3V and two 2.5V. Again use the plug and socket methogd to avoid mistakes.
Connecting the wrong OPT impedance is not fatal to the tubes and often some tube - speaker - music combinations benefit from a mismatch.
I think the question you should be asking yourself is if you had an amp that would use 45s or EL84s, would you ever listen to the EL84s?
Maybe.....45's are great for a lot of music, but if you really wanted to crank something with a lot of dynamics through that amp, maybe a different tube would sound better. The EL84 wouldn't be my first choice though.
When I designed the Tubelab SE amp (originally developed for 45's) I tried a bunch of different tubes through the same amp using clip leads to connect up various tube sockets, and a bench power supply for filament / heater voltage. I tested most tubes with the power supply in the TSE which made 325 volts with 45's at 30 mA and a little less with tubes that drew more current. For some of the bigger tubes I connected up a bench power supply for up to 400 volts. In all cased the stock TSE driver and Electra Print 5K OPT's were used.
The surprises, a triode wired 6V6GT sounded remarkably close to a 45. The old grey glass RCA's were best, and modern Sovtek's were the furthest from the 45 sound, but more dynamic. EL84's seemed louder, and more "in your face." The most punchy dynamic sound (think snare drums) cams from a triode wired 6AV5 TV sweep tube. The best low buck (at the time) tube were some military surplus 307A pentodes wired as triodes. They sounded as good as the Russian and Chinese 300B's for about $15 each. The 300B and 307A's each made about 5 watts in the same amp that makes 2 watts with a 45.
This is what led to the jumper selectable 2.5 volt or 5 volt filament option on the TSE, and a switch in one of my amps. I ran the 5.5 volt 307A's on 5 volts, and forgot to flip the switch when I put the 45's back in. I now have two separate amps, the original TSE with 45's Electra Print OPTs and 325 volts of B+. There is a bigger TSE with 307A's Edcor OPT's and a bit over 400 volts of B+.
When I designed the Tubelab SE amp (originally developed for 45's) I tried a bunch of different tubes through the same amp using clip leads to connect up various tube sockets, and a bench power supply for filament / heater voltage. I tested most tubes with the power supply in the TSE which made 325 volts with 45's at 30 mA and a little less with tubes that drew more current. For some of the bigger tubes I connected up a bench power supply for up to 400 volts. In all cased the stock TSE driver and Electra Print 5K OPT's were used.
The surprises, a triode wired 6V6GT sounded remarkably close to a 45. The old grey glass RCA's were best, and modern Sovtek's were the furthest from the 45 sound, but more dynamic. EL84's seemed louder, and more "in your face." The most punchy dynamic sound (think snare drums) cams from a triode wired 6AV5 TV sweep tube. The best low buck (at the time) tube were some military surplus 307A pentodes wired as triodes. They sounded as good as the Russian and Chinese 300B's for about $15 each. The 300B and 307A's each made about 5 watts in the same amp that makes 2 watts with a 45.
This is what led to the jumper selectable 2.5 volt or 5 volt filament option on the TSE, and a switch in one of my amps. I ran the 5.5 volt 307A's on 5 volts, and forgot to flip the switch when I put the 45's back in. I now have two separate amps, the original TSE with 45's Electra Print OPTs and 325 volts of B+. There is a bigger TSE with 307A's Edcor OPT's and a bit over 400 volts of B+.
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