Hello,
I have been using a professional EL84 line preamp with an output transformer as a tiny power amp on my VOT system.
I agree it is a nice tube and i stocked up on them when they were cheap.
It appears that hum still pops up in several builds. Even if you dont hear hum the iron can still interact in a negative way. Maybe modern transformers are made in a cheaper way to be more competitive.
A bit a sideline question. A choke input in general will give your power supply an easier life. The power transformer will have a much easier task and probably disturb nearby parts in a lesser degree but will the choke input now turn into the part that needs more attention during layout?
Greetings Eduard
I have been using a professional EL84 line preamp with an output transformer as a tiny power amp on my VOT system.
I agree it is a nice tube and i stocked up on them when they were cheap.
It appears that hum still pops up in several builds. Even if you dont hear hum the iron can still interact in a negative way. Maybe modern transformers are made in a cheaper way to be more competitive.
A bit a sideline question. A choke input in general will give your power supply an easier life. The power transformer will have a much easier task and probably disturb nearby parts in a lesser degree but will the choke input now turn into the part that needs more attention during layout?
Greetings Eduard
A choke input filter, LCRC, will have much more magnetic field coming from the choke, but at least it is smooth current with few upper harmonics,
versus . . . the cap input filter, CLC, with the magnetic field being less than with a choke input filter.
But the First Filter Capacitor of a CLC filter will have the following:
Much larger peak current, and very transient in nature.
The fast rise time current (causing lots of upper harmonics), will make any B+ caused ground loop sound worse, if it interferes and gets into the rest of the amplifier circuits.
No one way is best, but each requires attention to the details to make it work best.
A circuit that is already working well, probably does not need modification.
Single ended air gapped transformers tend to pick up hum more easily, versus push pull transformers.
versus . . . the cap input filter, CLC, with the magnetic field being less than with a choke input filter.
But the First Filter Capacitor of a CLC filter will have the following:
Much larger peak current, and very transient in nature.
The fast rise time current (causing lots of upper harmonics), will make any B+ caused ground loop sound worse, if it interferes and gets into the rest of the amplifier circuits.
No one way is best, but each requires attention to the details to make it work best.
A circuit that is already working well, probably does not need modification.
Single ended air gapped transformers tend to pick up hum more easily, versus push pull transformers.
Whether a choke is being used for LC or CLC filtering, it may be worthwhile identifying the choke lead that goes to the innermost layer of the winding, and connecting that to the rectifier 'end'. That may alleviate some of the parasitic coupling from the voltage waveform across the choke.
Hello,
Thank you. I have some encapsuled chokes where the terminals are marked with S and F or 1 and 2 .I thought this was just done in case you need to put two chokes in series / parallel to get optimum results.
Greetings, Eduard
Thank you. I have some encapsuled chokes where the terminals are marked with S and F or 1 and 2 .I thought this was just done in case you need to put two chokes in series / parallel to get optimum results.
Greetings, Eduard
Safety First!
Ground all Magnetics laminations and frames . . . power transformers, chokes, interstage and output transformers.
I have experienced transformers whose coils are shorted to their laminations. Ouch!
Prevent the "Surviving Spouse Syndrome".
Ground all Magnetics laminations and frames . . . power transformers, chokes, interstage and output transformers.
I have experienced transformers whose coils are shorted to their laminations. Ouch!
Prevent the "Surviving Spouse Syndrome".
No choke in my build - HV AC from the transformer (which of course is earthed to the chassis) goes directly to the Maida reg board. But it was a good exercise to (temporarily) hold the PT while still connected and re-orientate it and hear the hum drop to inaudible levels.
Thanks to @v4lve lover for these Maida gerbers - I've used them several times and they are really handy to have.
https://www.diyaudio.com/community/...ree-gerbers-thread.359636/page-6#post-7116136
Thanks to @v4lve lover for these Maida gerbers - I've used them several times and they are really handy to have.
https://www.diyaudio.com/community/...ree-gerbers-thread.359636/page-6#post-7116136
Hello,
Like 6A3sUMMER wrote it is important how things are wired/ executed. Things could look identical and still turn out different.
Twist ac wires from secondary high voltage terminals to the rectifier. What if terminals are like a few inches apart? Try to locate tube socket in between the terminals?
Where would the benefits of limiting wire length the biggest, before or after the rectifier?
There are no endless possibilities but still
Greetings Eduard
Like 6A3sUMMER wrote it is important how things are wired/ executed. Things could look identical and still turn out different.
Twist ac wires from secondary high voltage terminals to the rectifier. What if terminals are like a few inches apart? Try to locate tube socket in between the terminals?
Where would the benefits of limiting wire length the biggest, before or after the rectifier?
There are no endless possibilities but still
Greetings Eduard
Would a CLC section with a low value 1st cap reduce the high frequency hash?
P.S. I have a filter choke from a Hammond L100 that was used in the return (grounded) leg of the supply. Is there any way to tell if it is safe to use on the + side?
P.S. I have a filter choke from a Hammond L100 that was used in the return (grounded) leg of the supply. Is there any way to tell if it is safe to use on the + side?
Hello,
Like 6A3sUMMER wrote it is important how things are wired/ executed. Things could look identical and still turn out different.
Twist ac wires from secondary high voltage terminals to the rectifier. What if terminals are like a few inches apart? Try to locate tube socket in between the terminals?
Where would the benefits of limiting wire length the biggest, before or after the rectifier?
There are no endless possibilities but still
Greetings Eduard
Like 6A3sUMMER wrote it is important how things are wired/ executed. Things could look identical and still turn out different.
Twist ac wires from secondary high voltage terminals to the rectifier. What if terminals are like a few inches apart? Try to locate tube socket in between the terminals?
Where would the benefits of limiting wire length the biggest, before or after the rectifier?
There are no endless possibilities but still
Greetings Eduard
I don't think a lower value 1st cap would achieve what you think it might. There are many ways for 'high frequency hash' to get in to your audio signal. Is that a problem you have?
What choke do you have from the L100 ? I can see controlled/ganged chokes in the vibrato, and a 14H choke in the reverb driver output stage, and a pedal click filter inductor
@woodturner-fran, Hi Fran, can you please add the schematic as an image to the first post. Really hard to follow the discussion without that image. And it looks like it is not hosted anymore. Would like to learn about it some more.
I can't edit the first post, but the link is still live (scroll down a bit):
https://tubecad.com/2010/03/blog0183.htm
My build varies just a bit: I have a red LED for the cathode resistor of the input valve, and a LM317 CCS (15r/80mA) instead of the 400R/1000uF cap in the EL84 cathodes. For what its worth, several people have mentioned that 400R is the wrong value, it should be 200R. Outside of that, my HV supply is from a Maida reg and I'm using DC heaters.
https://tubecad.com/2010/03/blog0183.htm
My build varies just a bit: I have a red LED for the cathode resistor of the input valve, and a LM317 CCS (15r/80mA) instead of the 400R/1000uF cap in the EL84 cathodes. For what its worth, several people have mentioned that 400R is the wrong value, it should be 200R. Outside of that, my HV supply is from a Maida reg and I'm using DC heaters.
Attachments
Just curious about the small cap. I know that it has been used to reduce voltage when using a too high value transformer and PSU Designer II indicated some reduction in peak current values and I wondered if that would affect the hash.I don't think a lower value 1st cap would achieve what you think it might. There are many ways for 'high frequency hash' to get in to your audio signal. Is that a problem you have?
What choke do you have from the L100 ? I can see controlled/ganged chokes in the vibrato, and a 14H choke in the reverb driver output stage, and a pedal click filter inductor
As to the choke I think I was remembering wrong. I think it is the 14H choke. Perhaps it is because I was considering using it in a B+ return not knowing the max voltage.
Thank You very much.
I have bought by mistake Ixys IXTP08N100-P ehancment mode mosfet instead of IXTP08N100-D2 which is depletion mosfet.
On further inspection of the datasheet it looked like an excellent mosfet for Maida regulators and for driving 2A3 / 300B output stages ( low Ciss / Crss comparing to old 2SK1460 which was used as driver for 2A3 PP in one project ).
Of Course it is easier for me to use Your choice first and see if i can use Ixys part without any radical changes later - i'm not really into ss stuff, just understand how tubes work ( it's ongoing process ). HV regulators are currently my weak point.