Hello everyone !
I found a great Double EL84 Push-Pull amplifier schematic (28 Watts) but my problem is that I can't find adquate power transformer. I need the following :
Primary : 120 Volts / 60Hz (Canada)
Secondaries : 2 X 220 Volts and enough current for 4 EL84 tubes + 12AX7
As for the 6.3V, I can cope with the idea of an extra transformer
Anyone know where I could find this ? Hammond seems to have one with correct voltages but it doesn't provide enough current....
Also, would it be possible to use a switching suppply instead ?
Any information would be greatly appreciated !!!
Thanks !
I found a great Double EL84 Push-Pull amplifier schematic (28 Watts) but my problem is that I can't find adquate power transformer. I need the following :
Primary : 120 Volts / 60Hz (Canada)
Secondaries : 2 X 220 Volts and enough current for 4 EL84 tubes + 12AX7
As for the 6.3V, I can cope with the idea of an extra transformer
Anyone know where I could find this ? Hammond seems to have one with correct voltages but it doesn't provide enough current....
Also, would it be possible to use a switching suppply instead ?
Any information would be greatly appreciated !!!
Thanks !
And there it is !
Hope this helps !
By the way I'm still looking for a Power Transformer for this amp
Primary : 120 Volts / 60Hz (Canada)
Secondaries : 2 X 220 Volts and enough current for 4 EL84 tubes + 12AX7
Oh, by the way, don't forget, the output tranformer has a primary impedance of 4kOhms
Hope this helps !
By the way I'm still looking for a Power Transformer for this amp
Primary : 120 Volts / 60Hz (Canada)
Secondaries : 2 X 220 Volts and enough current for 4 EL84 tubes + 12AX7
Oh, by the way, don't forget, the output tranformer has a primary impedance of 4kOhms
Elkaid,
Why two secondaries? This is more than enough transformer for you for an EL84 amp...
270HX 176VA, sec. 275-0-275, DC ma 200, Fil.#1(rct) 5.0v @ 3a ct, Fil.#2(htr) 6.3v @ 6.0a ct
220V is too low, IMO. I'd run EL84's with at least 250V on the plates. And I'd run them UL too.
Why two secondaries? This is more than enough transformer for you for an EL84 amp...
270HX 176VA, sec. 275-0-275, DC ma 200, Fil.#1(rct) 5.0v @ 3a ct, Fil.#2(htr) 6.3v @ 6.0a ct
220V is too low, IMO. I'd run EL84's with at least 250V on the plates. And I'd run them UL too.
Thanks you very much 🙂
I've attached the reason why I'm looking for a 2 X 220 Volts 🙂 .
Also :
Should I connect the suggested transformer exactly the same way as on the schematic ? Will the voltage be too high once the two secondaries connected to the two diodes ?
Also, correct me if I'm wrong but I thought that EL84 were drawing around 60mA each. So a 200mA transformer is a bit tight right ?
Thank you !!!
I've attached the reason why I'm looking for a 2 X 220 Volts 🙂 .
Also :
Should I connect the suggested transformer exactly the same way as on the schematic ? Will the voltage be too high once the two secondaries connected to the two diodes ?
Also, correct me if I'm wrong but I thought that EL84 were drawing around 60mA each. So a 200mA transformer is a bit tight right ?
Thank you !!!
Attachments
Ok, I see why you are confused. That's not "two secondaries", it's 220V, center-tapped.
You only have one secondary.
And the current draw depends on the op point you chose, but if you like, go for the 250mA model that Hammond makes.
You only have one secondary.
And the current draw depends on the op point you chose, but if you like, go for the 250mA model that Hammond makes.
Heheheh oops
I feel like "stupid" 🙂
Thanks !
Just to be sure, the previously mentionned transformer should do the job right ?
I feel like "stupid" 🙂
Thanks !
Just to be sure, the previously mentionned transformer should do the job right ?
You're not stupid. That's how you learn.
Anyway, I think this amp is biased very far into class A, with 82 ohm cathode resistors? So, I would say definitely use the bigger 250mA model.
Anyway, I think this amp is biased very far into class A, with 82 ohm cathode resistors? So, I would say definitely use the bigger 250mA model.
Well, there's some ways to learn without looking so stupid 🙂
According to the original Power Supply schematic, we're supposed to get around 300Volts DC if I'm correct.
Using a higher voltage transformer implies that I'll get a higher voltage at the output of the power supply. Is there any risk to blow up something ? (my experience taught me that TDA7294 doesn't like little overvoltage).
Also, I guess that I'll need to increase capacitor voltage (previously rated @ 400Volts)
According to the original Power Supply schematic, we're supposed to get around 300Volts DC if I'm correct.
Using a higher voltage transformer implies that I'll get a higher voltage at the output of the power supply. Is there any risk to blow up something ? (my experience taught me that TDA7294 doesn't like little overvoltage).
Also, I guess that I'll need to increase capacitor voltage (previously rated @ 400Volts)
I would...
a) get rid of the diodes.
b) use the 300V-0-300V@250mA hammond transformer.
c) use a 5U4GB rectifier tube, and a 10Hy choke immediately after it.
This will give you around 250V.
a) get rid of the diodes.
b) use the 300V-0-300V@250mA hammond transformer.
c) use a 5U4GB rectifier tube, and a 10Hy choke immediately after it.
This will give you around 250V.
Joel said:
440v CT if you want to get technical.
220v either side of the center tap 🙂
I would drop the SS power supply, and use tubes, but thats personal opinion.
OMG !! 
Is there any way to avoid using that ? 🙂
(ouch....90$can + main power transformer (112$can) + output transformer (115$)).
Is there any way to avoid using that ? 🙂
(ouch....90$can + main power transformer (112$can) + output transformer (115$)).
Elkaid said:
Sure is - go with the original schematic instead.😉
But I don't think $200USD is that bad... how much do you think building a tube amp should cost???😕 😀
You're right ! Thank you very much !
Maybe I could buy a bigger Power transformer and a bigger choke and supply two amplifier from the same power supply.
Thanks again for your help !
Maybe I could buy a bigger Power transformer and a bigger choke and supply two amplifier from the same power supply.
Thanks again for your help !
Elkaid, I would just do this as a monoblock configuration. Otherwise it's just too much stuff on one chassis.
Got another idea.
Why couldn't I use a standard transformer but connected "backward".
By example, this transformer :
Primary : 120V
Secondary : 60V
This transformer has a ration of 2/1
Connected backward (120V connected on the secondaries), we should mesure 240 volts on the primary right ?
Does that make sense ? I saw that once in an hybrid amp. From a low voltage transformer, the guy was able to drive output ICs + high voltage for the preamp tubes.
I'd like to get your impressions. Thanks !
Why couldn't I use a standard transformer but connected "backward".
By example, this transformer :
Primary : 120V
Secondary : 60V
This transformer has a ration of 2/1
Connected backward (120V connected on the secondaries), we should mesure 240 volts on the primary right ?
Does that make sense ? I saw that once in an hybrid amp. From a low voltage transformer, the guy was able to drive output ICs + high voltage for the preamp tubes.
I'd like to get your impressions. Thanks !
Elkaid,
You cannot run any winding at a higher than rated voltage. There are 2 reasons:
1) The core will probably saturate.
2) Even if it doesn't, there are breakdown of insulation issues.
Also, concerning running transformers backwards:
It will work, but there are safety issues to be considered before putting it into service.
Cheers,
You cannot run any winding at a higher than rated voltage. There are 2 reasons:
1) The core will probably saturate.
2) Even if it doesn't, there are breakdown of insulation issues.
Also, concerning running transformers backwards:
It will work, but there are safety issues to be considered before putting it into service.
Cheers,
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