I'm going through a schematic and the cathode is tied to the output transformer primary, the plate and grid 2 are both tied to the same B+ rail for triode.
In this situation, how will an EL84 differ from a 6AQ5? Is the difference in the grid voltage that the tubes can handle?
The cut sheets I have don't say much for the EL84, I'm guessing it's 6.7V compared to the 6AQ5s 12.5V.
Any ideas?
Curtis
In this situation, how will an EL84 differ from a 6AQ5? Is the difference in the grid voltage that the tubes can handle?
The cut sheets I have don't say much for the EL84, I'm guessing it's 6.7V compared to the 6AQ5s 12.5V.
Any ideas?
Curtis
1. Post the schematic. Cathode tied to the output primary - sounds like an unusual design.
2. Are you referring to heater voltage? In that case your guess is wrong.
Thanks for the help, I’ll post the schematic when I get back from the office. The voltage on grid one is 145V, plate is 350V, and the cathode apparently has 160V connected to the output transformer.
From the cut sheets on the 6AQ5 and 6V6 they have a max rating of 250V for grid one, while the EL84 has 100V limit. My hope is that I can knock down the grid voltage from 145V to under 100V and continue on my merry way.
This is going into a MEQ5 clone and I’m aware of the 6P1P, however I want to use tubes I have on hand and are readily available locally as 6AQ5 and 6P1P are online order items.
Thanks,
Curtis
From the cut sheets on the 6AQ5 and 6V6 they have a max rating of 250V for grid one, while the EL84 has 100V limit. My hope is that I can knock down the grid voltage from 145V to under 100V and continue on my merry way.
This is going into a MEQ5 clone and I’m aware of the 6P1P, however I want to use tubes I have on hand and are readily available locally as 6AQ5 and 6P1P are online order items.
Thanks,
Curtis
I should specify a bit more the reason for going to current production tubes, I have a tube tester that does EL84s, so when I get them I can test and grade them, but I can’t do that for 6P1P or 6AQ5s. I do have 6P1P-EV and 6AQ5As, I’m more trying to create something that is easier to maintain and keep stock for.
This is my first MEQ build and I’m leaning about it, it’s the first time I’ve seen the cathode tied to the OT as well.
I really do appreciate any help on this, thanks again!
Curtis
This is my first MEQ build and I’m leaning about it, it’s the first time I’ve seen the cathode tied to the OT as well.
I really do appreciate any help on this, thanks again!
Curtis
I have breadboarded a pair of experiments using 6p1p (USSR) and 6v6 (Western common valve) using 3k SE OPT I can´t remember which sounded better if that will ever mean something.
Those valves can be pretty similar in the same circuit, even in fact have breadboarded more exotic USSR tubes (6P15P, 4P1L, 6P21S, 6C4C) and can´t even recall a sound characteristic from those to be "superior" to a plain triode strapped 6P1P, they are pretty linear and cheap may be because they have been used in lots of chinese amplifiers, and had to chime with that reputation, but who knows I'm still very young to cope with the HIFI industry and its standards.
Those valves can be pretty similar in the same circuit, even in fact have breadboarded more exotic USSR tubes (6P15P, 4P1L, 6P21S, 6C4C) and can´t even recall a sound characteristic from those to be "superior" to a plain triode strapped 6P1P, they are pretty linear and cheap may be because they have been used in lots of chinese amplifiers, and had to chime with that reputation, but who knows I'm still very young to cope with the HIFI industry and its standards.
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Cathodes connected to an output transformer suggest they're wired to another winding for feedback reasons. McIntosh, Webcor, others, have used that idea.
Thanks Leadbelly for looking up the schematic, you didn't have to but I really appreciate the help.
With that said, if the heater is elevated to 115V and the cathode is at 160, I'm within the 100V h-k range, so the EL84 is back in the game. As mentioned previously I need to consider the draw of the different tube, will I be OK with 1.66A off a 2A tap? How close can I go to that limit?
With that said, if the heater is elevated to 115V and the cathode is at 160, I'm within the 100V h-k range, so the EL84 is back in the game. As mentioned previously I need to consider the draw of the different tube, will I be OK with 1.66A off a 2A tap? How close can I go to that limit?
Build a good amplifier design that puts a tube in the middle of a sweet spot operating area. Then carefully inspect all the wiring versus the schematic; and use an Ohmmeter to test the parts and wiring as per the wired schematic.
The amp needs to use Individual self bias for the tubes. Now you have a real good 'tube tester' . . . As long as you are prepared to turn the amp off quickly if the currents are too high (too much larger than the predicted current from the data sheet curves). To test a pair of output tubes, you will need 2 meters to simultaneously monitor the 2 self bias voltages.
This method is neither for the in-experienced nor faint of heart.
The amp needs to use Individual self bias for the tubes. Now you have a real good 'tube tester' . . . As long as you are prepared to turn the amp off quickly if the currents are too high (too much larger than the predicted current from the data sheet curves). To test a pair of output tubes, you will need 2 meters to simultaneously monitor the 2 self bias voltages.
This method is neither for the in-experienced nor faint of heart.
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I went through the design steps and in theory it should work, how it will sound might be another thing, what's left is to build the prototype and see how I go. From the Pulse specs they estimate a really low current draw of 9.01mA compared to the 41mA from the tube data sheets. I'll start out with a solid state rectifier and see what happens.
You need to look at the schematic for your tube tester and change the selector settings to properly select the elements inside the tube. Then you can test the 6P1P.
I did this for my Mercury 1000 and it is very reliable.
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