Hi,
I am looking at building my first tube amp based on the ECL82. Just selecting the various transformers. For PT I selected the Hammond 270FX 138VA (same price as 270EX 118VA, I understand the 270DX 83VA is marginal for this application). For a choke I am looking at 156M (3H, 100ma, 86 ohms) or 158Q (5H, 150ma, 105 ohms, 400VDC). OTs are 125CSE just because they're less expensive then 125ASE or 125BSE.
I realize that a SS rectifier will perform just fine. However, I like the glow and I am willing to spend a few extra $$$ just to have a rectifier tube on the chassis. The Hammond transforemers have two secondary filament windings, on at 5V and one at 6.3V. Will the EZ80 or EZ81 function with its heater conencted to the 5V secondary?
As far as transformer choice, should I look at compensating for the additional loss of the rectifier tube via a 300-0-300 sec PT, like the 272BX (300-0-300 @ 100mA) or 272DX (300-0-300 @ 125mA)?
Thanks,
Adi
I am looking at building my first tube amp based on the ECL82. Just selecting the various transformers. For PT I selected the Hammond 270FX 138VA (same price as 270EX 118VA, I understand the 270DX 83VA is marginal for this application). For a choke I am looking at 156M (3H, 100ma, 86 ohms) or 158Q (5H, 150ma, 105 ohms, 400VDC). OTs are 125CSE just because they're less expensive then 125ASE or 125BSE.
I realize that a SS rectifier will perform just fine. However, I like the glow and I am willing to spend a few extra $$$ just to have a rectifier tube on the chassis. The Hammond transforemers have two secondary filament windings, on at 5V and one at 6.3V. Will the EZ80 or EZ81 function with its heater conencted to the 5V secondary?
As far as transformer choice, should I look at compensating for the additional loss of the rectifier tube via a 300-0-300 sec PT, like the 272BX (300-0-300 @ 100mA) or 272DX (300-0-300 @ 125mA)?
Thanks,
Adi
EZ80 & 81 require 6.3 Volts... not good at 5 volts. Barring the temp coefficient of the heater you're looking at a ~40% reduction in heater power... not good.
😉
😉
EZ80/81 need 6.3v on their filament to function correctly. Note that the cathode insulation is sufficient on both types for operation on a grounded 6.3V winding at these voltages provided that the overall current rating of the winding is sufficient for the filaments connected to it.
5AR4/GZ34 are cheaply and readily attained, clearly more than needed here - still a good choice and will run fine off of the 5v winding.
Kevin
edit: fix minor typo
5AR4/GZ34 are cheaply and readily attained, clearly more than needed here - still a good choice and will run fine off of the 5v winding.
Kevin
edit: fix minor typo
I thought about the GZ34 but doesn't it use an octal socket? It therefore wouldn't match the ECL82s from a visual perspective.
Are there any disadvantages to running the EZ80/EZ81 on a grounded 6.3V winding? All the transformers I am considering have ample filament current to support the two ECL82s and a EZ80/81.
One other thought, if I were to run the ECL82 filaments on DC power the 5V secondary should give me more then 6.3V DC if I use a shottky bridge. Not sure if that makes all that much sense, though.
Adi
Are there any disadvantages to running the EZ80/EZ81 on a grounded 6.3V winding? All the transformers I am considering have ample filament current to support the two ECL82s and a EZ80/81.
One other thought, if I were to run the ECL82 filaments on DC power the 5V secondary should give me more then 6.3V DC if I use a shottky bridge. Not sure if that makes all that much sense, though.
Adi
Oodi,
Actually if you "run the numbers" you will find it very difficult To derive 6.3 DC from 5 VAC...even with Schottky... you will need huge capacitance. The same for a 6.3 from 6.3.
As kevinkr pointed out you have very good rating to run a grounded 6.3 V winding.
🙂
Actually if you "run the numbers" you will find it very difficult To derive 6.3 DC from 5 VAC...even with Schottky... you will need huge capacitance. The same for a 6.3 from 6.3.
As kevinkr pointed out you have very good rating to run a grounded 6.3 V winding.
🙂
Great! A single 6.3V heater winding for all tubes is fine with me.
Just need to think about transformer data now. The EZ80/81 require a certain resistance from the transformer. I have not been able to find this information anywhere regarding Hammond transformers. Short of buying the transformer first, where can I find that information? Perhaps the numbers are high enough in practise that there's no need to worry about it?
Just need to decide on the transformer now, which secondary voltage. With a SS rectifier 275V should be ample, but with the EZ80/81 perhaps I should pick a 300V secondary.
Thanks,
Adi
Just need to think about transformer data now. The EZ80/81 require a certain resistance from the transformer. I have not been able to find this information anywhere regarding Hammond transformers. Short of buying the transformer first, where can I find that information? Perhaps the numbers are high enough in practise that there's no need to worry about it?
Just need to decide on the transformer now, which secondary voltage. With a SS rectifier 275V should be ample, but with the EZ80/81 perhaps I should pick a 300V secondary.
Thanks,
Adi
The numbers from a Hammond trans will be very "normal". I would not "worry" about it. Hammond makes "good" transformers; not "great" transformers. You could surely email Hammond and wait for one day.
Do you have the the power supply design software, FREE, from Duncan's Amp Pages?
😉
Do you have the the power supply design software, FREE, from Duncan's Amp Pages?
😉
I've been playing with PSUDII. I have no high voltage transformer so I have no clue as to what resistances to expect. I plugged 350 Ohm source resistance into it since this is minimum requirement for EZ80. I have the circuit configured per datasheet with 50uF cap (followed by 3H/86Ohm and 47uF) and 80mA. PSUDII complains about rectifier IRFM exceeded. I cannot get rid of that message even if I reduce C1 to 2uF...
Adi
Adi
Attachments
Try the EZ81 (6CA4) instead, it is rated for higher currents and voltages than the EZ80 (6V4) - it should also provide a somewhat stiffer supply due to lower internal impedances.
It is acceptable practice to add series resistance between the plates and the transformer winding or if you prefer (and I do) in series with the grounded center tap.
It is acceptable practice to add series resistance between the plates and the transformer winding or if you prefer (and I do) in series with the grounded center tap.
What are the experiences with Hammond power transformers? Are they conservatively rated, i.e. is it acceptable to to run the transformer very close or at the rated loads?
I expect my ciruit to be drawing about 80mA from the tranformer high voltage secondary. Current draw from the 6.3V filament will be <2.2A. If there's a second filament it won't be used. Since I don't have a transformer yet I am looking at this short list:
Then there are these additional choices:
My question, are the 270DX or 270DAX acceptable or should I look at the next higher rated transfomers? The 370DAX is much more expensive then all the other choices, is it worth the difference?
Thanks,
Adi
I expect my ciruit to be drawing about 80mA from the tranformer high voltage secondary. Current draw from the 6.3V filament will be <2.2A. If there's a second filament it won't be used. Since I don't have a transformer yet I am looking at this short list:
- 270DAX 75VA, sec. 260-0-260 @ DC ma 90, 6.3V @ 3.5A
- 270DX 83VA, sec. 275-0-275, DC ma 90, Fil.#1(rct) 5.0v @ 2a, Fil.#2(htr) 6.3v @ 3.0a
Then there are these additional choices:
- 370DAX 76VA, 260-0-260 @ DC ma 90, 6.3VCT @3.5A
- 270EX 118VA, sec. 275-0-275, DC ma 125, Fil.#1(rct) 5.0v @ 3a, Fil.#2(htr) 6.3v @ 4.0a
- 270FX 138VA, sec. 275-0-275, DC ma 150, Fil.#1(rct) 5.0v @ 3a, Fil.#2(htr) 6.3v @ 5.0a
My question, are the 270DX or 270DAX acceptable or should I look at the next higher rated transfomers? The 370DAX is much more expensive then all the other choices, is it worth the difference?
Thanks,
Adi
kevinkr said:
The EZ81 seems to be much harder to come by then the EZ80. It looks like they are interchangeable. So I should be able to switch between them to observer the differences.
Adi
Adi,
Yes you can run the Hammonds at their full ratings. What voltage do you wish for your final B+?
Yes you can run the Hammonds at their full ratings. What voltage do you wish for your final B+?
poobah said:
The ECL82 datasheet has configurations for 200V, 230V and 275V. The variable is the desired transformer impedance. Since the Hammond OT are flexible, I can build any of the three. With the 275V secondary I can comfortable achieve 230V using PSUDII.
Building with tubes is certainly very different then solid state. I've got quite a bit of experience building a wide variety of audio and logic circuits. Grew up repairing televisions and even made a career out of it for over 10 years. My tube experiences are very slim, though. Repairing a few dozen tube apparatuses doesn't help much with designing them.... Thank you for all the help and putting up with my questions!
Adi
I'm talking final B+ here... what voltage do you want???
Your final B+ voltage may actually be higher than the RMS voltage used to rate the secondary of the tranny...
For example, a "300-0-300" transformer could give you 325 Volts DC.
😉
Your final B+ voltage may actually be higher than the RMS voltage used to rate the secondary of the tranny...
For example, a "300-0-300" transformer could give you 325 Volts DC.
😉
Final B+, as in the B+ powering the amplifier Pentode after all filtering has taken place...? I am looking at 230V (I don't think I can get 275V unless I use SS rectifier or 300-0-300 secondary).
The schematic I posted (also below) gives me the following voltages. BTW, if I increase R1 to 470 I get a V(C3) of 230V.
V(C1): 273V
V(C2): 266V
V(C3): 258V
Adi
The schematic I posted (also below) gives me the following voltages. BTW, if I increase R1 to 470 I get a V(C3) of 230V.
V(C1): 273V
V(C2): 266V
V(C3): 258V
Adi
Yes... what is the voltage you want to feed to your amp?
I looked at the 272BX and you could get 290 Volts. Also, change your resistance inthe transformer to a more reasonable value... 150 Ohms. Use the EZ81. Then insert an "RC" in place of C1... use the same C and an R of 200 Ohms and all should work out for you... with no errors messages.
🙂
I looked at the 272BX and you could get 290 Volts. Also, change your resistance inthe transformer to a more reasonable value... 150 Ohms. Use the EZ81. Then insert an "RC" in place of C1... use the same C and an R of 200 Ohms and all should work out for you... with no errors messages.
🙂
I have two designs that I am interested in for the ECL82 output stage, one operating with a B+ of 230V and the other with a B+ of 275V. I am not quite sure which one I should strive for.
Adi
Adi
schema for ecl82
Hi Adi,
I'm not sure if you're intrested, but here's one option for you:
http://www.audiokit.it/ITAENG/KitElettr/KIOM/scherzo/Scherzo.htm
I've built this amp with EZ81 rect tube.
Best regards,
Pete
Hi Adi,
I'm not sure if you're intrested, but here's one option for you:
http://www.audiokit.it/ITAENG/KitElettr/KIOM/scherzo/Scherzo.htm
I've built this amp with EZ81 rect tube.
Best regards,
Pete
This has been a tremendous help. If I place the EZ81 in my power supply the simulation works flawless. It even gets me a B+ of 270V from a 275-0-275 transformer. So that'll be the way I go.
One minor choice left. Run a common B+ for both channels or have common LC filter followed by RC filters for each channel. Is there any reason not to have individual RC filters for each channel?
Adi
One minor choice left. Run a common B+ for both channels or have common LC filter followed by RC filters for each channel. Is there any reason not to have individual RC filters for each channel?
Adi
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