Just bought a pair of Hammond 125DSE output transformers. I am gonna to use them in an el84 se amp. Just one question..I am a little comfused because of all the wires on the secondary side. Am I right if I use the black wire for ground and the yellow wire for 5k Ohm and 8 Ohms?, and the rest shall not be connected to anything?
That is correct. The more wire you use on the secondary wiring, the better the transformer is likely to work. It starts to look OK as a 2.5K transformer...
Stenak,
How were you going to use the EL84? . . .
Pentode wired with 5k to 8 Ohm ratio, and use some Global negative feedback? (or at least Schade negative feedback?)
Or were you going to use the EL84 in triode wired mode, and drive the 5k to 8 Ohm ratio?
Try both of those and see what you think.
Pentode wired has more power, and is harder to make it work well.
Triode wired has less power, but is easier to make work well.
Or, you could use 2 or three EL84 tubes in parallel triode wired mode, and connect the transformer for a 2.5k to 8 Ohm ratio, and no negative feedback.
But that would require more power supply current.
How were you going to use the EL84? . . .
Pentode wired with 5k to 8 Ohm ratio, and use some Global negative feedback? (or at least Schade negative feedback?)
Or were you going to use the EL84 in triode wired mode, and drive the 5k to 8 Ohm ratio?
Try both of those and see what you think.
Pentode wired has more power, and is harder to make it work well.
Triode wired has less power, but is easier to make work well.
Or, you could use 2 or three EL84 tubes in parallel triode wired mode, and connect the transformer for a 2.5k to 8 Ohm ratio, and no negative feedback.
But that would require more power supply current.
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I think i will use a ecc88 as an input tube and maybe triode wired mode. Maybe 2 watts are not enough to drive my Klipsch RF15, so maybe pentode wired are the best for me? I have been looking at different schematics and noticed that some have "floating minus" on the secondary on the output transformer, no ground connected to the minus of secondary of the output.
A floating transformer secondary is not considered a particularly safe practice unless the amp is parallel feed, thten it's a bit less of an issue.
The RF15 may be OK on the power provided by triode wired EL84s. The suggestion of paralleling two EL84s per channel and running that OT as a 2.5K transformer is exactly what I would do.
The RF15 may be OK on the power provided by triode wired EL84s. The suggestion of paralleling two EL84s per channel and running that OT as a 2.5K transformer is exactly what I would do.
I have already built the enclosure, mountet the choke, and transformers, so there are no space left for more sockets and tubes. I think this build can be an experiment, and I can rebuild and make another enclosure later. Thank to all of you for your help!
Maybe I should build my el84SE as triode wired? Anybody out there who can recommend a nice/good schematic? Have some 6n2p(Russian ecc83), and think I will use them with the el84 tubes. 2 Watts are probably enough for my Klipsch, thanks audiowize...
stenak,
Do you want to quickly know the difference between the sound of a pentode wired versus a triode wired EL84 single ended amplifier?
And be able to easily do that in your home, on your loudspeakers?
Then build your stereo EL84 single ended amplifier. Wire it this way:
Wire the left channel as pentode, connect the screen to the B+ end of your output transformer.
Wire the right channel as triode wired, connect a 100 Ohm resistor from the screen to the plate.
Use the same driver tubes, same driver circuits, and same bias points on the EL84 tubes.
Start with both output transformers wired for 5k operation.
Use individual self bias resistors and individual bypass caps on the EL84s.
Now, purchase a Y RCA phono connector splitter (takes one channel output from the CD player, and puts that signal to both your amplifier’s L and R inputs.
If you have separate L and R volume controls on your stereo EL84 amp, this makes the comparison simple. Otherwise, you need to use a preamplifier with either separate L and R volume controls or a balance control.
Using a favorite music CD, and with your loudspeakers connected to the amplifier:
1. Turn the R channel (triode wired) up until it sounds barely distorted, then turn it down a little bit. Try and remember that sound level.
2. Turn the R channel all the way down.
3. Turn the L channel (pentode wired) up until the sound is at or near the same sound level as it was with the R channel (not louder).
Now, repeat 1, 2, 3, until you have matched the sound levels of the pentode channel to the triode wired channels undistorted output.
Which one do you like better at the maximum undistorted output level of the triode wired channel?
Yes, the pentode wired channel can be turned up more for more undistorted power, but the real comparison needs to be at the triode wired channel’s capability.
If there is not enough power from the triode wired channel, then temporarily disconnect the plate and screen from the L channel (pentode wired), and connect that plate and screen in parallel with the plate and screen of the R channel (parallel triode wired); and re-wire the output transformer to set it to 2.5k.
Now listen again to that one channel, but noe at twice the un-distorted power of the original single triode wired channel.
If you do all this, you will have likely made some very revealing discoveries.
It will help you determine what works best for you, on your system, your room, your music.
Trust your ears, not someone else's preference for different music, different sound character, etc.
Have Fun!
Do you want to quickly know the difference between the sound of a pentode wired versus a triode wired EL84 single ended amplifier?
And be able to easily do that in your home, on your loudspeakers?
Then build your stereo EL84 single ended amplifier. Wire it this way:
Wire the left channel as pentode, connect the screen to the B+ end of your output transformer.
Wire the right channel as triode wired, connect a 100 Ohm resistor from the screen to the plate.
Use the same driver tubes, same driver circuits, and same bias points on the EL84 tubes.
Start with both output transformers wired for 5k operation.
Use individual self bias resistors and individual bypass caps on the EL84s.
Now, purchase a Y RCA phono connector splitter (takes one channel output from the CD player, and puts that signal to both your amplifier’s L and R inputs.
If you have separate L and R volume controls on your stereo EL84 amp, this makes the comparison simple. Otherwise, you need to use a preamplifier with either separate L and R volume controls or a balance control.
Using a favorite music CD, and with your loudspeakers connected to the amplifier:
1. Turn the R channel (triode wired) up until it sounds barely distorted, then turn it down a little bit. Try and remember that sound level.
2. Turn the R channel all the way down.
3. Turn the L channel (pentode wired) up until the sound is at or near the same sound level as it was with the R channel (not louder).
Now, repeat 1, 2, 3, until you have matched the sound levels of the pentode channel to the triode wired channels undistorted output.
Which one do you like better at the maximum undistorted output level of the triode wired channel?
Yes, the pentode wired channel can be turned up more for more undistorted power, but the real comparison needs to be at the triode wired channel’s capability.
If there is not enough power from the triode wired channel, then temporarily disconnect the plate and screen from the L channel (pentode wired), and connect that plate and screen in parallel with the plate and screen of the R channel (parallel triode wired); and re-wire the output transformer to set it to 2.5k.
Now listen again to that one channel, but noe at twice the un-distorted power of the original single triode wired channel.
If you do all this, you will have likely made some very revealing discoveries.
It will help you determine what works best for you, on your system, your room, your music.
Trust your ears, not someone else's preference for different music, different sound character, etc.
Have Fun!
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Something more or less along the lines of the RH84, with its short "plate to plate" NFB loop, seems good for a pentode mode setup. IMO, the 125DSE "iron" lacks the magnetic headroom needed to support a global NFB configuration.
Russian 6Π15Π-EB (6p15p-ev) O/P tubes, whose screen grid B+ is regulated by a 0A2 gas discharge tube, should work out quite nicely. The key difference between the 6Π15Π and the EL84 (6Π14Π) lies in the toughness of the screen grid. The screen grid (g2) in the 6Π15Π is fragile, but regulating the voltage on it disposes of the matter. Open loop linearity of pentode mode is maximized, when g2 B+ is regulated at a fraction of anode B+.
BTW, sockets correctly wired for the 6Π15Π accept EL84s, without incident.
Russian 6Π15Π-EB (6p15p-ev) O/P tubes, whose screen grid B+ is regulated by a 0A2 gas discharge tube, should work out quite nicely. The key difference between the 6Π15Π and the EL84 (6Π14Π) lies in the toughness of the screen grid. The screen grid (g2) in the 6Π15Π is fragile, but regulating the voltage on it disposes of the matter. Open loop linearity of pentode mode is maximized, when g2 B+ is regulated at a fraction of anode B+.
BTW, sockets correctly wired for the 6Π15Π accept EL84s, without incident.
pentodes rocks, i recently did a 12gt5 pentode mode single ended amp driven by 6bn11 dual pentode compactron also in pentode mode using O'schade local feedback, and without global negative feedback sounded superbly on my US Audio 90db floorstander ...
psu is a full wave voltage doubler with the screens fed from the midpoint of the psu, a depletion mosfet CCS set to about 30mA and shunted by 150 volt zeners was used to feed the G2's of the tubes...
btw, the OPT is the same center leg as the hammond 125se although a bit thicker stack, i made these myself...using m6/z11 steel cores..
psu is a full wave voltage doubler with the screens fed from the midpoint of the psu, a depletion mosfet CCS set to about 30mA and shunted by 150 volt zeners was used to feed the G2's of the tubes...
btw, the OPT is the same center leg as the hammond 125se although a bit thicker stack, i made these myself...using m6/z11 steel cores..
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Here's a Hammond 125DSE and EL84 from a Finnish site.
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Putkivahvistinrakennusohje SE/84 Brachyera - Osa 2 - AudioVideo
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Putkivahvistinrakennusohje SE/84 Brachyera - Osa 2 - AudioVideo
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Eli Duttman,
Correct me if I am wrong, but Schade negative feedback also suffers when the output transformer runs out of laminations (saturates).
Negative feedback that comes from either the primary, or from the secondary of the output transformer will try and correct for the saturation.
But that means that in both cases, it will increase the current even more, which will cause it to saturate even more.
Correct me if I am wrong, but Schade negative feedback also suffers when the output transformer runs out of laminations (saturates).
Negative feedback that comes from either the primary, or from the secondary of the output transformer will try and correct for the saturation.
But that means that in both cases, it will increase the current even more, which will cause it to saturate even more.
TonyTecson,
Nice looking amplifier.
I like your organic "chassis"
Is that mahogany, or what?
When I returned from the Philippines they used a mahogany crate to ship my belongings.
Nice looking amplifier.
I like your organic "chassis"
Is that mahogany, or what?
When I returned from the Philippines they used a mahogany crate to ship my belongings.
ChrisABC,
That Finnish amplifier really utilizes the 125xSE series transformers.
Using the full secondary makes the cathode feedback high enough to effectively reduce the pentode's high output impedance.
But the speaker can tap down on the secondary, to get the desired load reflected back to the pentode.
That Finnish amplifier really utilizes the 125xSE series transformers.
Using the full secondary makes the cathode feedback high enough to effectively reduce the pentode's high output impedance.
But the speaker can tap down on the secondary, to get the desired load reflected back to the pentode.
When the short loop is employed, the error correction signals do not pass through the O/P "iron". The net signal, after correction, is what the "iron" "sees". Any linearity aberrations in the trafo are not corrected by short loop NFB.
The advantage of the global configuration is linearization of the O/P "iron", particularly at the frequency extremes. However, the deep bass error correction signal passing through the trafo can cause core saturation. So, extra magnetic headroom is needed, when the global configuration is employed. Even when plenty of magnetic headroom is present, filtering infrasonic noise out, at the amp's I/P, is in order. Trying to get close to DC in a GNFB tube amp is not a good idea.
bamboo simulated wood made from lawanit, sides are bamboo..
i got them from the home improvement section from a big mall...
i missed the US bases, that is where we get high quality equipment and even surplus electronics.....M6 grade steels for making traffos, both EI's and toroids....
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Eli Duttman,
Are you telling me that if an output transformer is in saturation,
The resultant distorted waveform that appears on the secondary can not also be seen on the primary?
If it can be seen in the primary waveform, then the Schade negative feedback sees that as an error term.
And negative feedback will try and reduce that error, therefore will apply more current to the already saturated transformer.
Yes?
No?
I guess I have to go to my test bench (a humble card table), and check it out for myself.
That way I will remember the answer to my own question.
Are you telling me that if an output transformer is in saturation,
The resultant distorted waveform that appears on the secondary can not also be seen on the primary?
If it can be seen in the primary waveform, then the Schade negative feedback sees that as an error term.
And negative feedback will try and reduce that error, therefore will apply more current to the already saturated transformer.
Yes?
No?
I guess I have to go to my test bench (a humble card table), and check it out for myself.
That way I will remember the answer to my own question.
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In the global configuration, an error correction signal attempting to improve frequency response linearity can be the root cause of core saturation. That's not the case in the short loop configuration.
What is the root cause of core saturation in the short loop case? Is it mid-band power in excess of the general capability of the "iron"? IMO, there is no truly good answer to this problem. Is it a deep bass or infrasonic signal of "modest" strength? Bandwidth limiting of the active circuitry to dispose of this problem is easy.
What is the root cause of core saturation in the short loop case? Is it mid-band power in excess of the general capability of the "iron"? IMO, there is no truly good answer to this problem. Is it a deep bass or infrasonic signal of "modest" strength? Bandwidth limiting of the active circuitry to dispose of this problem is easy.