I got Jolida JD302B recently. The amplifier is EL34 PP with ultra linear. I would like to modify it as triode connection.
I got this schematic and
I was told to cut the connection to the pin #4 and put 100 ohm resistor between pin #3 and pin #4.
Then, I found another schematic about triode mod.
This one tells that I need to cut the connection to pin #3 which is connected to the plate of a tube. And it also shows the disconnection from the output transformer to C2.
I am confused now. Which one is right?
1) cut the connection to pin 3 and put 100 ohm resistor between 3 and 4.
2) cut the connection to pin 4 and put 100 ohm resistor between 3 and 4. additionally, cut the connection between the output transformer and C2.
I don't have much knowledge in circuit theory.
I got this schematic and
I was told to cut the connection to the pin #4 and put 100 ohm resistor between pin #3 and pin #4.
Then, I found another schematic about triode mod.
This one tells that I need to cut the connection to pin #3 which is connected to the plate of a tube. And it also shows the disconnection from the output transformer to C2.
I am confused now. Which one is right?
1) cut the connection to pin 3 and put 100 ohm resistor between 3 and 4.
2) cut the connection to pin 4 and put 100 ohm resistor between 3 and 4. additionally, cut the connection between the output transformer and C2.
I don't have much knowledge in circuit theory.
Good question. I respectfully suggest that before you cut anything you should study more and learn what it means to convert UL to triode mode regarding the connections of elements.
That said, your #2 option is correct, although I can’t comment on the removal of the global negative feedback (GNF)(i.e. disconnecting C2 from output transformer). I would leave the GNF intact at first and listen, only if you don’t like the sound you could read up on GNF and recommendations specific to the modification of your Jolida JD302B.
I don’t see how you got option #1 from the last schematic you posted.
That said, your #2 option is correct, although I can’t comment on the removal of the global negative feedback (GNF)(i.e. disconnecting C2 from output transformer). I would leave the GNF intact at first and listen, only if you don’t like the sound you could read up on GNF and recommendations specific to the modification of your Jolida JD302B.
I don’t see how you got option #1 from the last schematic you posted.
Thanks. I will do it as you suggested.
I think I made the typo. C2 should be C8 in the option 2.
2) cut the connection to pin 4 and put 100 ohm resistor between 3 and 4. additionally, cut the connection from C8 to the transformer.
What does disconnecting the line from the transformer to C8 achieve?
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mongting,
1. The schematic showing the EL34 changes: cutting the UL connection to the screen, and connecting the screen to the plate through a 100 Ohm resistor, is correct. That circuit is Triode Wired Mode.
Because the gain in Triode wired mode is lower than in Ultra Linear mode, the amplifier should be stable with the same circled negative feedback resistor and capacitor.
Perhaps there are slightly more optimum values for that R and C. But if you do not have the proper equipment to measure, and know how to adjust those values, you are still good to go with the old values (assuming that those old values were optimum and stable for Ultra Linear, and the exact models of the output transformers of the production run for your amplifier. Over time, some manufacturers of amplifiers use slightly different output transformers, and re-adjust the negative feedback R and C accordingly.
Be sure to put shrink tubing over the UL wires of the output transformer (insulate them so they do not short to anything).
You will get less power with Triode Wired Mode . . .
But why not try that easy modification?
(you can always easily go back if you want to).
2. As drawn, the second full schematic is still Ultra Linear, but it is Not Triode Mode.
Yes, the text comment tells you to disconnect the UL wires (if indeed the wire colors are correct, but the UL wires of the original amplifier
are connected to the screens, no mater what color)
Instead, as drawn, the 100 Ohm resistors are loads from the 40% to 100% windings of the primary halves (the cuts are not on the schematic).
As drawn, that makes a very heavy load on the primary, and is a very heavy load on the EL34 tubes too.
It would rob power from the EL34 tubes and primary windings.
Do not use this circuit as drawn.
Anybody that copies that schematic, without reading the comment to cut the UL wires will make the amplifier perform very poorly.
Do not cut the output transformer center tap from C8.
1. The schematic showing the EL34 changes: cutting the UL connection to the screen, and connecting the screen to the plate through a 100 Ohm resistor, is correct. That circuit is Triode Wired Mode.
Because the gain in Triode wired mode is lower than in Ultra Linear mode, the amplifier should be stable with the same circled negative feedback resistor and capacitor.
Perhaps there are slightly more optimum values for that R and C. But if you do not have the proper equipment to measure, and know how to adjust those values, you are still good to go with the old values (assuming that those old values were optimum and stable for Ultra Linear, and the exact models of the output transformers of the production run for your amplifier. Over time, some manufacturers of amplifiers use slightly different output transformers, and re-adjust the negative feedback R and C accordingly.
Be sure to put shrink tubing over the UL wires of the output transformer (insulate them so they do not short to anything).
You will get less power with Triode Wired Mode . . .
But why not try that easy modification?
(you can always easily go back if you want to).
2. As drawn, the second full schematic is still Ultra Linear, but it is Not Triode Mode.
Yes, the text comment tells you to disconnect the UL wires (if indeed the wire colors are correct, but the UL wires of the original amplifier
are connected to the screens, no mater what color)
Instead, as drawn, the 100 Ohm resistors are loads from the 40% to 100% windings of the primary halves (the cuts are not on the schematic).
As drawn, that makes a very heavy load on the primary, and is a very heavy load on the EL34 tubes too.
It would rob power from the EL34 tubes and primary windings.
Do not use this circuit as drawn.
Anybody that copies that schematic, without reading the comment to cut the UL wires will make the amplifier perform very poorly.
Do not cut the output transformer center tap from C8.
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A non-functioning amplifier! You must leave the connection from C8 to the transformer, it's the main B+ supply.
I have the same amp, and did the triode mod many years ago. All you have to do is cut and shrink the UL wires, and solder in the 100R resistors between pins 3 & 4. That's it, don't do anything else! Have a look at the pic and you can see the green 2W Kiwami resistors.
jeff
jeff
vinylkid58,
Please report your impressions of the Triode wired amplifier, versus the UL wired amplifier.
mongting,
If you do the Triode wired modification . . .
Please report your impressions of the Triode wired amplifier, versus the UL wired amplifier.
Thanks!
Happy Listening!
Please report your impressions of the Triode wired amplifier, versus the UL wired amplifier.
mongting,
If you do the Triode wired modification . . .
Please report your impressions of the Triode wired amplifier, versus the UL wired amplifier.
Thanks!
Happy Listening!
There have been several reports in the last two decades after the Jolida amps modifications, but before @monting do anything, have to decide that his loudspeaker suitable working with modified amplifier.
Using these PP amp power tubes in triode mode the output power decreasing significantly (rule of the thumb is 50%), and disconnecting NFB increasing output impedance.
If the loudspeaker not enough "tube friendly", these modifications may results insufficient transmissions.
BTW I also modding my Jolida amp -about 15 years ago- and never come back to UL and NFB mode (at the time I have Acoustic Energy Aelite 3 -89dB- speakers, these working well later with my 10W 300B SE amp).
Like this:
https://www.audioasylum.com/cgi/t.mpl?f=tweaks&m=9532
p.s.
IMHO the triode and NFB modification worth it, but I also modded rectifier diodes, capacitors and resistors.
Using these PP amp power tubes in triode mode the output power decreasing significantly (rule of the thumb is 50%), and disconnecting NFB increasing output impedance.
If the loudspeaker not enough "tube friendly", these modifications may results insufficient transmissions.
BTW I also modding my Jolida amp -about 15 years ago- and never come back to UL and NFB mode (at the time I have Acoustic Energy Aelite 3 -89dB- speakers, these working well later with my 10W 300B SE amp).
Like this:
https://www.audioasylum.com/cgi/t.mpl?f=tweaks&m=9532
p.s.
IMHO the triode and NFB modification worth it, but I also modded rectifier diodes, capacitors and resistors.
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It's been so long now I couldn't tell you the difference, but the amp does sound good triode strapped. It's been collecting dust for a few years now, sadly.
I tried removing the GNF, but the amp was just too noisy without it. Adding bypass caps (film) to the missing positions on the PS board really made quite a noticeable improvement.
jeff
I tried removing the GNF, but the amp was just too noisy without it. Adding bypass caps (film) to the missing positions on the PS board really made quite a noticeable improvement.
jeff
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