This famous winding was connected a sealed and potted circuit with input from 2 EF86's and output to 2 ECC82's.
Nothing connected and only "F" , Rdc=15.9 ohm , L=811mH , Capacitance=33nF , Z=1k6 ohm . Same wire as primaries.
With 1kHz sine 1.9V to E (or D), I have 1.2V @ F , 57mV @ A , 68mV @ B and 94mV @ C
Nothing connected and only "F" , Rdc=15.9 ohm , L=811mH , Capacitance=33nF , Z=1k6 ohm . Same wire as primaries.
With 1kHz sine 1.9V to E (or D), I have 1.2V @ F , 57mV @ A , 68mV @ B and 94mV @ C
Back to my post #13 for any definitive understanding. I'm sorry.
"sealed and potted" so maybe not just a transformer inside there.
"sealed and potted" so maybe not just a transformer inside there.
For 4 Ohm speaker connect A in parallel with B for 8 Ohm speaker connect A in series with B for 16 Ohm speaker connect A B and C all in series.
Connect the high voltage DC HT+ (or B+) to CT connect one output valve Anode to D connect the other Anode to E.
What to do with F? maybe connect one side of F to a grid of output valve and other end of F to a grid of the other output valve. Or somehow connect F as a feedback to the input valves.
Or forget F and take feedback somehow from the speaker windings A B C
Rdc=15.9 ohm which winding ??
L=811mH which winding ??
Capacitance=33nF which winding ?? Implies that there is a capacitor inside the potting ??
Z=1k6 ohm what's this which winding ??
I don't have a good feeling about having understood this transformer and wouldn't put my name to any of the above.
Connect the high voltage DC HT+ (or B+) to CT connect one output valve Anode to D connect the other Anode to E.
What to do with F? maybe connect one side of F to a grid of output valve and other end of F to a grid of the other output valve. Or somehow connect F as a feedback to the input valves.
Or forget F and take feedback somehow from the speaker windings A B C
Rdc=15.9 ohm which winding ??
L=811mH which winding ??
Capacitance=33nF which winding ?? Implies that there is a capacitor inside the potting ??
Z=1k6 ohm what's this which winding ??
I don't have a good feeling about having understood this transformer and wouldn't put my name to any of the above.
The 4 transformers (2 out & 2 power) come out of a prof constructed stereo (double mono) amp with tubes as mentioned in #1. This amp was already mentioned by a member Zatizati in 2020-02-29 (Artec 225D, mine is 225A).
No problem I 'll make the amp Steve Morley showed as mono blocks with tube rectification as was, and the ECF80 instead of 2 EF86's and 1 ECC82 per channel . My problem was and is: what to do with this "F" winding? Or leave it open or put a resistor (value ?) on it or can I use it as FB.
No problem I 'll make the amp Steve Morley showed as mono blocks with tube rectification as was, and the ECF80 instead of 2 EF86's and 1 ECC82 per channel . My problem was and is: what to do with this "F" winding? Or leave it open or put a resistor (value ?) on it or can I use it as FB.
The F winding leave it open, no connections to it, putting a resistor across it will not achieve any purpose.
Yes alternatively you could use the F winding to give negative feedback at the input valve but remember that the F winding voltage will be high, too high as it is to use as feedback.
But the Steve Morley circuit has R16 and R6 to reduce feedback voltage, If you decide to try winding F for feedback instead of the speaker winding do the following:
Take C7 out (or replace it with a lower value say 33p) remove the connection from the speaker winding to R16 C7 replace it with a wire from winding F, connect the other end of winding F to Ground. Very important is to increase the value of R16 to 10K or more (I can't say exactly what value) - the best value for R16 to give enough feedback to reduce distortion.
If the amp howls winding F is giving positive feedback so swap over the connections to winding F then it should be negative feedback.
You might find the amp sounds better using winding F for feedback - you might find that using the speaker winding for feedback works better.
Hope that helps and you have good luck with it, be careful with the high voltages work safely.
Yes alternatively you could use the F winding to give negative feedback at the input valve but remember that the F winding voltage will be high, too high as it is to use as feedback.
But the Steve Morley circuit has R16 and R6 to reduce feedback voltage, If you decide to try winding F for feedback instead of the speaker winding do the following:
Take C7 out (or replace it with a lower value say 33p) remove the connection from the speaker winding to R16 C7 replace it with a wire from winding F, connect the other end of winding F to Ground. Very important is to increase the value of R16 to 10K or more (I can't say exactly what value) - the best value for R16 to give enough feedback to reduce distortion.
If the amp howls winding F is giving positive feedback so swap over the connections to winding F then it should be negative feedback.
You might find the amp sounds better using winding F for feedback - you might find that using the speaker winding for feedback works better.
Hope that helps and you have good luck with it, be careful with the high voltages work safely.
Have a look at these links:
225 D 1
225 D 2
225 D 3
225 D 4
Artec 1
Artec 2
Aetec 3
Artec 4
Looking at the back speakers are 3, 8, or 15 Ohm:
You can work out a lot of the circuit diagram and how the output transformer was connected to the four EL34 and to the speaker tag strips on the back from this photo.
And you can probably work out what winding F is connected to !! It looks like it is connected by light (grey colour) coax cable to a square box that looks like a radio transformer then coax goes to switches on the front panel, and two wires go to a valve, must be feedback surely but I don't know, but you may be able to work it out more to certainty.
A different Amp
225 D 1
225 D 2
225 D 3
225 D 4
Artec 1
Artec 2
Aetec 3
Artec 4
Looking at the back speakers are 3, 8, or 15 Ohm:
You can work out a lot of the circuit diagram and how the output transformer was connected to the four EL34 and to the speaker tag strips on the back from this photo.
And you can probably work out what winding F is connected to !! It looks like it is connected by light (grey colour) coax cable to a square box that looks like a radio transformer then coax goes to switches on the front panel, and two wires go to a valve, must be feedback surely but I don't know, but you may be able to work it out more to certainty.
A different Amp
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The F winding - the black coax goes to switches marked Filter Rumble and Scratch so Low frequency noise and high frequency noise filters there and yes they could be in the feedback loop. Ask other people on the forum for more info they already know about. I don't see any feedback wiring from the speaker windings.
I see now your drawing in post #23 is the actual top of the transformer where the tags are yes CT is B+ and D and E go to the EL34 valves. The small tagstrip on the transformer is a safety spark gap between D and E.
The speaker windings on the 225 D are only two windings, your transformers have three speaker windings so 225 A and 225 D are different but probably many things the same ???????
I see now your drawing in post #23 is the actual top of the transformer where the tags are yes CT is B+ and D and E go to the EL34 valves. The small tagstrip on the transformer is a safety spark gap between D and E.
The speaker windings on the 225 D are only two windings, your transformers have three speaker windings so 225 A and 225 D are different but probably many things the same ???????
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The transformers look different: only 2 bolds instead of 4 holding the metal together. Indeed there was a coax from "F" to a square potted integrated circuit. 1st picture are the outputs, the 2nd are the power
Yes.
And by the way on the 225D the speaker windings you call ABC are one winding only with 4 pins/tags, so on the photo the left transformer:
Brown is 0 (common)
Red is 3 Ohm
Orange is 8 Ohm
Yellow is 15 Ohm
Good luck !
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Those transformers look damaged and not safe.
I cannot help you anymore with that.
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As the amp was in a terrible state I decided to use the transformers and the EL34 PP config and also the GZ34 setup. With every thing we know now, let's design a good sounding amp.
The output transformers look damaged in the photo, even the laminated cores are separated, I don't think you can use these output transformers.
The power transformers look better now but I'm still worried about the laminates looking like they are separated with a gap (that looks like 1 or 2 mm).
Maybe its just the transformer photo's? What happened to them were they burned or flooded in water or something like that?
I cannot find anything on the internet about 255A but quite a lot about 255D my guess is that the 255A was a lower power version and that's why the output transformers in your photo are different.
I may be wrong but the output transformers in the 255D photos I posted look bigger and better and they look easy to wire up. The 255A output transformers the solder tags look all close to each other and harder to understand.
Its not an easy thing to design a new amp using power valves like the EL34. If you have better output transformers I would be thinking about building a 255D (not 255A) but I would just build what was essential and:
- not build the filtering
- not build the tone controls Bass Treble
- not build the many switches and Jack sockets
- Input preamp
- Volume
- the EL34 type output
- study more circuits
- design a standard circuit using output valves like EL34
- also working out the 255D important stuff by studying the photos of the 255D
- study more about the 255D information that is on the internet.
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Notes about the schematic of Post # 2:
I expected that R9 and C6 would be the dominant pole for the amplifier, until I calculated it to be too high, at 72 kHz.
Perhaps it is just a phase corrector, but not a roll off pole.
Caution: The schematic shows the EL34 with an Internal connection from the cathode to the Suppressor Grid . . .
No EL34 has that Internal connection.
You have to connect Pin 1, Suppressor to Pin 8 Cathode, At the Tube Socket.
I expected that R9 and C6 would be the dominant pole for the amplifier, until I calculated it to be too high, at 72 kHz.
Perhaps it is just a phase corrector, but not a roll off pole.
Caution: The schematic shows the EL34 with an Internal connection from the cathode to the Suppressor Grid . . .
No EL34 has that Internal connection.
You have to connect Pin 1, Suppressor to Pin 8 Cathode, At the Tube Socket.
richgwilliams,
I really like that single ended, ultra linear, parallel EL34 amplifier that you posted in Post # 27.
I notice the EL34 plate to screen network of R16 & C7, 100 Ohm & 3.9 nf, is a pole at 408kHz.
I hope that the 3 major low frequency poles, C2, C4, and the Lundahl primary inductance frequencies do not line up at the same frequency . . . that would equal an oscillator.
The 68pf cap, C8, in parallel with the negative feedback resistor, R19, will be partially negated if the shield over the feedback wire is too much capacitance.
A typical shield to center conductor might be 20pf or 30pf per foot, compare that to the 68pf, C8.
I would like a report of how this amplifier works if anybody builds one.
Just for fun . . . do a Plug-and-Play Tube Roll, from EL34 Pentodes to KT77 Beam Power tubes.
I really like that single ended, ultra linear, parallel EL34 amplifier that you posted in Post # 27.
I notice the EL34 plate to screen network of R16 & C7, 100 Ohm & 3.9 nf, is a pole at 408kHz.
I hope that the 3 major low frequency poles, C2, C4, and the Lundahl primary inductance frequencies do not line up at the same frequency . . . that would equal an oscillator.
The 68pf cap, C8, in parallel with the negative feedback resistor, R19, will be partially negated if the shield over the feedback wire is too much capacitance.
A typical shield to center conductor might be 20pf or 30pf per foot, compare that to the 68pf, C8.
I would like a report of how this amplifier works if anybody builds one.
Just for fun . . . do a Plug-and-Play Tube Roll, from EL34 Pentodes to KT77 Beam Power tubes.
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I'm guessing that @decramer is new to tube amps but they want to build one (assuming transformer problems sorted out). So I'm trying to help with information as regards the Belgian Artec 255 D amp and other circuits.
Also attaching a pdf datasheet of the Lundahl LL1 623 Output Transformer used in LE-EL34 AMP 1 circuit.
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