Hello noob question here.
If a schematic for a tube amp calls for a 300-0-300@ 200ma can a 300-0-300@390ma be used or will the extra ma's cause problems?
If a schematic for a tube amp calls for a 300-0-300@ 200ma can a 300-0-300@390ma be used or will the extra ma's cause problems?
Hi!
Difference will only be noticed when loaded. In load condition, the 390mA will provide some more voltage.
These two transformers should provide the same rectified voltage when in open circuit.
300VAC will be 423VDC after rectifier. Is that what you are looking for?
If you circuit handles 423VDC, there is no problem in using the 390mA transformer.
The secondary voltages listed by the mfr are always for FULL RATED LOAD on all secondaries.
So loading with only half of the rated load will cause a significant rise in the secondary voltages,
and even for the other windings, like the filaments. You'd have to measure to find out exactly how much.
So loading with only half of the rated load will cause a significant rise in the secondary voltages,
and even for the other windings, like the filaments. You'd have to measure to find out exactly how much.
Ok! If the voltages are specified for full load, then the transformer rated for higer current might not be suitable.
So first thing is to check how the 300-0-300V are specified for - open circuit or fully loaded.
So first thing is to check how the 300-0-300V are specified for - open circuit or fully loaded.
Thanks for all your replies, i am beginning to grasp the issues. This transformer is not suitable as the amp requires 300v ct and a 6.3v but the transformer i currently have from a yard sale has 300v ct along with 2 6.3v 8.8a and 3a and a 5v secondary. All overpowered for this project.
Transformer secondary voltages are always specified at full loading, of all secondaries simultaneously,
at the specified AC line voltage.
I took a look at some Mouser transformer specs and they do specify secondary voltages at rated current.
But where I live (I know it's not a good reference for electric/electronic components), I use local manufactured transfomers.
For the transformers normally used for power supply in audio, voltages from 6 to 50V and currents from 100mA to 10A, the nominal voltage are in general specified for open circuit. 220V to 110V auto-transformers follow the same - open circuit specs.
I always used the rule of thumb of derating 10 to 15% nominal voltage to find the fully loaded voltage.
Thanks for the info! Always learning and understanding how other countries specify, specially the more advanced ones, such as US.
It makes more sense to specify output voltage at the rated current.
The unloaded secondary voltages can rise more than expected, in a nonlinear fashion from full load.
The VA rating also has a lot of effect on this behavior.
The VA rating also has a lot of effect on this behavior.
There are always creative ways to use an overspec'd transformer. 10-20 V higher B+ is almost never a problem, or, if it is, add resistance to filter. Heater voltage can be trimmed the same way. I like bigger transformers because they heat less and have better regulation.
The trouble with diyAudio is you get so many contradictory answers.
Bigger transformer will give higher voltage or have better regulation?
Help the poor noob build his amp.
Transformers are expensive and he has one already.
Advise him to measure the outputs in a safe manner and to post his circuit so you can then advise the suitability and any mitigating actions.
Nobody has mentioned the oft stated issue of higher mains (110 rising to 120V) in the US.
This is likely to have a bigger effect even on new equipment spec'd for 110V.
A buck transformer would be far cheaper than a new Power transformer but would need to be planned for in the layout of a new build.
Bigger transformer will give higher voltage or have better regulation?
Help the poor noob build his amp.
Transformers are expensive and he has one already.
Advise him to measure the outputs in a safe manner and to post his circuit so you can then advise the suitability and any mitigating actions.
Nobody has mentioned the oft stated issue of higher mains (110 rising to 120V) in the US.
This is likely to have a bigger effect even on new equipment spec'd for 110V.
A buck transformer would be far cheaper than a new Power transformer but would need to be planned for in the layout of a new build.
Is it a branded transformer? Do you have a bit more details, like windings, DC resistance etc?
As above, you are probably going to bve fine, just a bit higher voltages. Nothing that cannot be fixed with a small buck transformer.
Another option is selling your transformer (seems like a big expensive one), getting a smaller one and keeping the change.
As above, you are probably going to bve fine, just a bit higher voltages. Nothing that cannot be fixed with a small buck transformer.
Another option is selling your transformer (seems like a big expensive one), getting a smaller one and keeping the change.
Since nobody else is going to ask the obvious question, I will:
What amplifier circuit is the OP talking about?
What amplifier circuit is the OP talking about?
It it a Stancor transformer , I will post the specs on the box when i get home. I was looking at a number of schematics for darling amps as i have a number of 1626 tubes. As well as possibly building a point to point version of a zenkit 1 as i breadboarded this amp like 2 years ago and have most of the parts for it. I think i used an underpowered 540v ct edcor at the time. Anyway I'll post better info when i get home.
So here are the specs, Stancor P-8335
300-0-300 325ma, 5v 6.0A, 6.3v 8.8A, 6.3v 1.25A.
The amps I was looking at were just for a fun project and to learn. I was looking at 1626 Darling amps because i happen to have nearly a dozen nos tubes. There is a parallel tubed version that uses 300vct 150ma transformer that is why i originally asked. This transformer is more than twice the current.
So what kind of amp would you build with this transformer?
300-0-300 325ma, 5v 6.0A, 6.3v 8.8A, 6.3v 1.25A.
The amps I was looking at were just for a fun project and to learn. I was looking at 1626 Darling amps because i happen to have nearly a dozen nos tubes. There is a parallel tubed version that uses 300vct 150ma transformer that is why i originally asked. This transformer is more than twice the current.
So what kind of amp would you build with this transformer?
Oh and i believe the primary is 117v its not totally Visible on the box but it looks like a 7 on the end.
choke input power supply may give you the necessary voltage. Depending on the choke. your power transformer is huge for a darling amplifier
Yes i think its overkill for a darling so I might just buy an Edcore that is more suitable.
That's why i also asked what others would build with the Stancor. Any idea's?
That's why i also asked what others would build with the Stancor. Any idea's?
No, not at all. The extra current capability will give better B+ (high voltage) regulation, or stability under varying loads depending on the power the amp is asked to deliver. So long as the voltage is what's needed, 300-0-300 in your case, the stiffer (390mA one) transformer will perform better.