I'm building another SSE, and of course that means I have LOTS of questions! This time it's about TUBES. On my last SSE, which I used for a short time before selling it, I had EL34 tubes in there. Never swapped out with anything.
For this build, it might be fun to experiment with different tubes. I understand the 6L6 tubes can be used, maybe KT88, maybe others...
Is trying different tubes as easy as switching them out? Or do other modifications need to be made in order to switch from type to type?
For this build, it might be fun to experiment with different tubes. I understand the 6L6 tubes can be used, maybe KT88, maybe others...
Is trying different tubes as easy as switching them out? Or do other modifications need to be made in order to switch from type to type?
I switch between EL34, 6L6GC, and Russian 6P3S-E freely and never had an issue (over many years). They all sound great to me, but if pressed I would say my least favourite are EL34 (perhaps a bit "mid-rangey"). The 6L6GC and 6P3S-E are very close sound-wise, but the Ruskies are FAR better value for money.
The usual suspects like the 6L6GC, EL34, KT88 and 6550 can usually be swapped in with no changes. It would be wise to measure the cathode voltage to make sure that your tubes are not being run too hard. At least look at the internals of the output tubes in a dark room to make sure that the only thing glowing inside the tube is the cathode rod in the center of the tube. The outer metal plate and the thin wound grid wires should not be red hot. My experience with the tubes I had 10 to 15 years ago was that the EL34 was always the most likely to get too hot.
I preferred the EL34 in triode mode for simple music, chick singer and an acoustic guitar kind of stuff. Want to crank some Pink Floyd loud enough to shake the neighbors' walls, KT88 or 6550 in UL! I had 15 inch speakers with 97 db sensitivity.
Smaller tubes like the US 6F6, 6V6GT and 6K6 will work but they need a smaller power transformer that makes about 300 volts of B+ or less. 450 volts will make those tubes very unhappy. There are only two US made sweep tubes that have the same pinout as the typical audio tubes, the 6BQ6 / 6CU6 and the 6DQ6. Neither will work without some parts value changes and a plate cap wired to pin 3 of the socket. Plugging them into an unmodified amp may produce sound for a few minutes until the cathode bypass cap explodes! Yes, I learned this the hard way. Some other sweep tubes can be made to work, but they require PCB modification. Most Sweep tubes don't fare well in SE especially at 400+ volts.
I preferred the EL34 in triode mode for simple music, chick singer and an acoustic guitar kind of stuff. Want to crank some Pink Floyd loud enough to shake the neighbors' walls, KT88 or 6550 in UL! I had 15 inch speakers with 97 db sensitivity.
Smaller tubes like the US 6F6, 6V6GT and 6K6 will work but they need a smaller power transformer that makes about 300 volts of B+ or less. 450 volts will make those tubes very unhappy. There are only two US made sweep tubes that have the same pinout as the typical audio tubes, the 6BQ6 / 6CU6 and the 6DQ6. Neither will work without some parts value changes and a plate cap wired to pin 3 of the socket. Plugging them into an unmodified amp may produce sound for a few minutes until the cathode bypass cap explodes! Yes, I learned this the hard way. Some other sweep tubes can be made to work, but they require PCB modification. Most Sweep tubes don't fare well in SE especially at 400+ volts.
Thanks for the reply, George! I've got the Hammond 274BX power transformer for this build.
For starters, I have a pair of EL34 tubes. I was thinking of starting with EL34 tubes in a basic triode mode at first, since it appears to be the easiest to build.
Can EL34 tubes be run in Ultralinear mode? I'm still not clear on the difference between triode and UL... Or even if I would need UL? This amp will be used to power either my Bozak speakers, which are very sensitive, or my Monitor Audio Bronze 50s, which are... not so sensitive but fairly small and only used for nearfield listening.
Can you help me understand the difference between triode and UL?
For starters, I have a pair of EL34 tubes. I was thinking of starting with EL34 tubes in a basic triode mode at first, since it appears to be the easiest to build.
Can EL34 tubes be run in Ultralinear mode? I'm still not clear on the difference between triode and UL... Or even if I would need UL? This amp will be used to power either my Bozak speakers, which are very sensitive, or my Monitor Audio Bronze 50s, which are... not so sensitive but fairly small and only used for nearfield listening.
Can you help me understand the difference between triode and UL?
In a tube amp equipped with pentode tubes there are three ways to wire the tubes. This is determined by how the connector to the OPT primary in the SSE is wired.
In pure pentode connection the screen grid is connected to B+ through a stopper resistor. This offers the highest gain and power output, but the lowest damping factor and usually higher distortion than the other possibilities. The tube must be rated for full B+ on the screen grid, so this leaves out most TV sweep tubes. pentode mode is common in guitar amps, often seen in push pull HiFi amps that employ suitable feedback to reduce distortion and improve the damping factor. It is not common in SE amps like the SSE.
In triode mode the screen grid is connected directly to the plate of the tube through a stopper resistor. This offers the best damping factor and distortion at the expense of gain and power output. Power output is often 1/3 to 1/2 of thar obtainable in pentode mode. Again, the screen grid needs to be rated for the B+ voltage UNLESS triode wired specs in the data sheet state otherwise.
UL, or UltraLinear mode is a compromise between these two extremes. In this case the screen grid is connected to a tap on the output transformer, so it gets something in between B+ voltage and Plate voltage. Thie requires output transformers with a UL tap which is not always the case. As surmised performance is in between the triode and pentode extremes, and affected by where the tap is placed inside the transformer. Some tubes like the 6550 and KT88 do well in UL, and some do OK. Some tubes have UL specs in their data sheets too.
In pure pentode connection the screen grid is connected to B+ through a stopper resistor. This offers the highest gain and power output, but the lowest damping factor and usually higher distortion than the other possibilities. The tube must be rated for full B+ on the screen grid, so this leaves out most TV sweep tubes. pentode mode is common in guitar amps, often seen in push pull HiFi amps that employ suitable feedback to reduce distortion and improve the damping factor. It is not common in SE amps like the SSE.
In triode mode the screen grid is connected directly to the plate of the tube through a stopper resistor. This offers the best damping factor and distortion at the expense of gain and power output. Power output is often 1/3 to 1/2 of thar obtainable in pentode mode. Again, the screen grid needs to be rated for the B+ voltage UNLESS triode wired specs in the data sheet state otherwise.
UL, or UltraLinear mode is a compromise between these two extremes. In this case the screen grid is connected to a tap on the output transformer, so it gets something in between B+ voltage and Plate voltage. Thie requires output transformers with a UL tap which is not always the case. As surmised performance is in between the triode and pentode extremes, and affected by where the tap is placed inside the transformer. Some tubes like the 6550 and KT88 do well in UL, and some do OK. Some tubes have UL specs in their data sheets too.