15-05-2020, 07:49 PM
Amie wrote:
I suppose if you were going to start making a smaller valve with the same spec., then you may consider using the smaller structure for both to save some money.
Seems a good idea, economies of scale - assuming everything equal.
On the other hand, the 6AQ5, with its piddling little anode, is going to run hotter and have a shorter life than the 6V6 electrode structure. Unless... The 6AQ5 anode is made of a purer, more expensive material, that exudes less gas when heated (or it undergoes extra heat treatment to remove absorbed gas) so it can run hotter without problems - either of which would shift the cost balance. I guess we'll never know
Amie wrote:
Circling back to Andy's amplifier ideas, that push pull guitar amp that I had played with recently that had the 6BW6 op valves, had a decent sized output transformer and was an "ultralinear" but had a couple of controls that altered the bias on the output stage that were on the front panel, one allowed the amp to run into starved distortion at low level, the other altered the balance a little. They did alter the character of the sound considerably, so weren't just a sales gimmick for guitar use.
Interesting! Did the amplifier have NFB around it all - which would have reduced the distortion up to a point, but also made the onset of severe distortion more acute? Or was it open-loop? I'd guess the latter.
Increasing bias to increase distortion has the benefit that standing current will be reduced, giving a somewhat easier life for the valves. Win-win!
Michael Watterson wrote:
The heater power is related to the electron emission needed.
True, but it boils down to keeping the cathode at the right emitting temperature. Cathodes emit so many milliamps per square mm of area. You want more current capability? Then you have to increase the area. And more area means more heat loss, so you have to up the heating power.
However, a nice snug anode, shiny on the inside, will reflect radiant heat back to the cathode, meaning less is lost - so the heater does not need so many watts to maintain temperature. Hence my thinkings!
Michael Watterson wrote:
The UL84 is 100mA and 45V (4.5W), the EL86 is 6.3V 0.76 A, surprisingly 4.8W, apparently the same valve with a different heater. I'd have thought the UL84 would need more. Comparison of heater power of a selection of series and parallel power valves with otherwise the same spec would be interesting. You'd imagine the UL84 is the 100mA version of an EL84, but allegedly not.
The different heater power, UL84 and EL86, which have same characteristics, is a surprise!
It's true that UL84 and EL84 are different, quite apart from the heater. It's a mistake to think that if only the 'heater' letter changes, then characteristics are the same apart from heater. This is a good counter-example, others are DF91 and EF91, the first being vari-μ and the second, straight. Or (even more extreme), DM71 and EM71, which aren't even the same base!
I suppose if you were going to start making a smaller valve with the same spec., then you may consider using the smaller structure for both to save some money.
Seems a good idea, economies of scale - assuming everything equal.
On the other hand, the 6AQ5, with its piddling little anode, is going to run hotter and have a shorter life than the 6V6 electrode structure. Unless... The 6AQ5 anode is made of a purer, more expensive material, that exudes less gas when heated (or it undergoes extra heat treatment to remove absorbed gas) so it can run hotter without problems - either of which would shift the cost balance. I guess we'll never know
Amie wrote:
Circling back to Andy's amplifier ideas, that push pull guitar amp that I had played with recently that had the 6BW6 op valves, had a decent sized output transformer and was an "ultralinear" but had a couple of controls that altered the bias on the output stage that were on the front panel, one allowed the amp to run into starved distortion at low level, the other altered the balance a little. They did alter the character of the sound considerably, so weren't just a sales gimmick for guitar use.
Interesting! Did the amplifier have NFB around it all - which would have reduced the distortion up to a point, but also made the onset of severe distortion more acute? Or was it open-loop? I'd guess the latter.
Increasing bias to increase distortion has the benefit that standing current will be reduced, giving a somewhat easier life for the valves. Win-win!
Michael Watterson wrote:
The heater power is related to the electron emission needed.
True, but it boils down to keeping the cathode at the right emitting temperature. Cathodes emit so many milliamps per square mm of area. You want more current capability? Then you have to increase the area. And more area means more heat loss, so you have to up the heating power.
However, a nice snug anode, shiny on the inside, will reflect radiant heat back to the cathode, meaning less is lost - so the heater does not need so many watts to maintain temperature. Hence my thinkings!
Michael Watterson wrote:
The UL84 is 100mA and 45V (4.5W), the EL86 is 6.3V 0.76 A, surprisingly 4.8W, apparently the same valve with a different heater. I'd have thought the UL84 would need more. Comparison of heater power of a selection of series and parallel power valves with otherwise the same spec would be interesting. You'd imagine the UL84 is the 100mA version of an EL84, but allegedly not.
The different heater power, UL84 and EL86, which have same characteristics, is a surprise!
It's true that UL84 and EL84 are different, quite apart from the heater. It's a mistake to think that if only the 'heater' letter changes, then characteristics are the same apart from heater. This is a good counter-example, others are DF91 and EF91, the first being vari-μ and the second, straight. Or (even more extreme), DM71 and EM71, which aren't even the same base!
