Hi all I could use some expert advice,
Does anyone have some advice on the following? I am making a tube preamp on basis of a CAT SL-1 PCB I got somewhere (I am a noob who is still learning so I use other peoples pcb's for my builds atm), according to text on the pcb it requires two secondaries:
- 250VAC 80mA
- 6.3VAC 3A
These are the tubes this preamp uses:
1x ECC82
2x ECC83
1x ECC88
Can I use the following toroid?
- 250v 500mA
- 0 - 6,3V - 9V / 8A
Is the amperage not too high for what I need? will that lead to problems?
What best to do with the 9v lead to prevent interference? just snip it off or wind it around the 6,3v lead?
And if instead I use a toroid with a 3,15 - 0 - 3,15V secondary, what to do with the center tap so it doesnt interfere with anything? Just snip it off? braid it with the other leads and leaving it unconnected? or connect to ground via a ground lift circuit maybe?
The groud lift circuit I plan to implement consists of 35A rectifier bridge, 10ohm 5watt resistor, 100nf filmcap that sits between star ground and chassis ground/mains ground, I want to include that for safety regardless of the above, is that a good decision?
Thanks,
Rorenheizer
Does anyone have some advice on the following? I am making a tube preamp on basis of a CAT SL-1 PCB I got somewhere (I am a noob who is still learning so I use other peoples pcb's for my builds atm), according to text on the pcb it requires two secondaries:
- 250VAC 80mA
- 6.3VAC 3A
These are the tubes this preamp uses:
1x ECC82
2x ECC83
1x ECC88
Can I use the following toroid?
- 250v 500mA
- 0 - 6,3V - 9V / 8A
Is the amperage not too high for what I need? will that lead to problems?
What best to do with the 9v lead to prevent interference? just snip it off or wind it around the 6,3v lead?
And if instead I use a toroid with a 3,15 - 0 - 3,15V secondary, what to do with the center tap so it doesnt interfere with anything? Just snip it off? braid it with the other leads and leaving it unconnected? or connect to ground via a ground lift circuit maybe?
The groud lift circuit I plan to implement consists of 35A rectifier bridge, 10ohm 5watt resistor, 100nf filmcap that sits between star ground and chassis ground/mains ground, I want to include that for safety regardless of the above, is that a good decision?
Thanks,
Rorenheizer
First transformer will work fine. The toroid will only supply the board with the current needed, excess will not matter. Current is just there if needed for a more demanding board. I do not see what the current rating is on that toroid for the 6.3V's. As long as it can supple 3amps it will work for the heaters as well.
Tbe toroid will result in higer HV and filament voltage. It is designed to supply 6.3V at 9A, it will probably supply 7+ VAC in your setup. If you got that transformer, better sell, buy one closer to the specs and keep tne change.
Thank you wdecho and jcalvarez for your answers.
The option I can find that is closest in spec has these secundaries:
250V / 300mA
3,15 - 0 - 3,15V / 4,5A
That seems like a better option right?
And what should I do with this center tap lead?
The option I can find that is closest in spec has these secundaries:
250V / 300mA
3,15 - 0 - 3,15V / 4,5A
That seems like a better option right?
And what should I do with this center tap lead?
That is definitely a better option, but still an overkill. Where are you based? I could suggest where to look depending on your location.
The 3.15-0-3.15 centre tap should be grounded, unless you are using heater elevation, in this case the elevation voltage goes into the centre tap.
Am based in The Netherlands. For other builds I use a bunch of Amplimo toroids, and have had one made to order in China. And these are good transformers, but for this build want to try out a "supreme" toroid from Toroidy in Poland. They are potted, have good reviews and look good which in this build is a big plus cos am thinking of putting this preamp in a chassis with glas lid.
The transformer I think is closest in specs is this one: https://sklep.toroidy.pl/en_US/p/TSTA-0100002-Mains-transformer-for-tubes/643
And thank you for your answer about the center tap. Was just now reading this article about PSU grounding and they said the same thing: https://sound-au.com/earthing.htm
The transformer I think is closest in specs is this one: https://sklep.toroidy.pl/en_US/p/TSTA-0100002-Mains-transformer-for-tubes/643
And thank you for your answer about the center tap. Was just now reading this article about PSU grounding and they said the same thing: https://sound-au.com/earthing.htm
Toroidy makes good transformers, no questions. Maybe they can tell you the unloaded output voltages for that transformer, it will give an indication of the output voltages at your specific loads.
I am using a 1.7va tranny for the b+ of a 12ax7 preamp. The secondaries connect to the 6.3v 1A filament transformer. My 6922 preamp I lifted the heaters to 24v via a 1/8 w 47k resistor and 220/35 capacitor.
The remarks of you guys about heater elevation and the effects of higher voltages led me to read up for a few hours. And I decided to order a custom made toroid that is of the right specs instead of having to hack this pcb with other components trying to fix stuff that I dont really grasp yet. My previous project culminated in many hours fixing a mysterious humm. I learned a lot and it was glorious to finally fix that but now its time again for a more straight forward build (hopefully)
Thank you all for your help, you all saved me a lot of time!
Thank you all for your help, you all saved me a lot of time!
You need about 1,5-2 Ampere for the heaters, probably 60-70 mA for the B+. I maybe missed som information but why don`t you find an old radio with tubes. slaughter it and take the transformer?
To answer your original question, 35A bridge is overkill use UF4007 or UF5408 diodes. A 35A diode bridge is likely very slow.
You can always PM if you need boards for the PSU.
You can always PM if you need boards for the PSU.