In paragraph 6 of the Theory section for the squirrel monkey amp, he talks about rewiring the dual-primary transformer so that one of the primaries becomes a secondary and he implies that this is found in other amp designs. I haven't been able to find any details of how this is done and I can't find other examples. Can someone explain to me how you'd do this?
Provided the dual primaries are fully isolated from each other then this will work. The secondary primary is just treated as a normal 110 / 120Volt secondary along with the other secondaries.
the transformer needs to be 110 / 230volt device and be running on 110 volt mains.
The only problem with this method is the transformer needs de-rating I believe as the primary circuit has now only half the power capability. so a 100VA transformer would be capable of 50VA only - anyone with more knowledge please correct if this is wrong.
I would go with a correct transformer by preference
the transformer needs to be 110 / 230volt device and be running on 110 volt mains.
The only problem with this method is the transformer needs de-rating I believe as the primary circuit has now only half the power capability. so a 100VA transformer would be capable of 50VA only - anyone with more knowledge please correct if this is wrong.
I would go with a correct transformer by preference
Hi,
I wouldn't say that. Assuming the limit is core saturation,
the single primary can run more current than parallel dual
primary, so IMO your looking just at more resistive loss.
Generally you only derate a transformer by half if you
run a 230 primary at 115, by definition the same max
current can only transfer half the power for the latter.
rgds, sreten.
I wouldn't say that. Assuming the limit is core saturation,
the single primary can run more current than parallel dual
primary, so IMO your looking just at more resistive loss.
Generally you only derate a transformer by half if you
run a 230 primary at 115, by definition the same max
current can only transfer half the power for the latter.
rgds, sreten.
Each one of the primaries in a dual primary is designed and sized to carry 1/2 the rated overall current, my experience also is that running on a single primary and attempting to draw the rated VA will result in overheating. I would not run it much beyond half the nominal rating and I would probably look for a more appropriate transformer.
Depending on the quality of the insulation in the primary there is a low probability safety downside to doing this as well. Magnet wire often has voids in the insulation and should one line up between your primary and your repurposed secondary there could be an unintended leakage path between the two windings. Normally this would just blow the fuse, but in this usage it would result in line voltage on the secondary side of the transformer.
Depending on the quality of the insulation in the primary there is a low probability safety downside to doing this as well. Magnet wire often has voids in the insulation and should one line up between your primary and your repurposed secondary there could be an unintended leakage path between the two windings. Normally this would just blow the fuse, but in this usage it would result in line voltage on the secondary side of the transformer.
Wow, it's a guitar amplifier, the last place I would want to take this sort of short cut.
Find a power transformer with 150V and 6.3V secondaries or get Edcor to make one for you.
Also since this is a guitar amplifier it really ought to be in the Instrument & Amps forum where guitar amp mavens hang out. Moving it.
Find a power transformer with 150V and 6.3V secondaries or get Edcor to make one for you.
Also since this is a guitar amplifier it really ought to be in the Instrument & Amps forum where guitar amp mavens hang out. Moving it.Hi,
Whilst you will get more resistive losses the issues are
nowhere near as dire as some imply, derating it is true,
but it is nothing like down to half power, that's clueless.
rgds, sreten.
Its not a short cut or any compromise in the original design :
The Squirrel Monkey One Tube Guitar Amp
Its just a good way of getting the secondary voltage,
though the secondary tap will have far lower resistance than
is really needed to be put in series with one of the primaries.
Whilst you will get more resistive losses the issues are
nowhere near as dire as some imply, derating it is true,
but it is nothing like down to half power, that's clueless.
rgds, sreten.
Its not a short cut or any compromise in the original design :
The Squirrel Monkey One Tube Guitar Amp
Its just a good way of getting the secondary voltage,
though the secondary tap will have far lower resistance than
is really needed to be put in series with one of the primaries.
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Wanted a small flat transformer for a 6AK6 project running in the 150-180V range. Would not be too crazy about dual HV windings wound on each other but the primaries and both secondaries in this transformer are isolated from each other. Forgot about this project, need to get back to it.
229C12 - HAMMOND - BOBBINS TRANSFORMER | Newark element14 Canada
229C12 - HAMMOND - BOBBINS TRANSFORMER | Newark element14 Canada
Thanks for all the comments. This has been very instructional.
I would generally opt for the right transformer, but when it comes to amp building, I'm on a pretty tight budget and the savings from taking this route can be surprisingly substantial. For example, for $11, I can get this transformer. (~twice the power rating at about 40% the price of the transformer in the above post). I think you'd have a very hard time finding a "proper" equivalent transformer for anywhere close to that price.
I would generally opt for the right transformer, but when it comes to amp building, I'm on a pretty tight budget and the savings from taking this route can be surprisingly substantial. For example, for $11, I can get this transformer. (~twice the power rating at about 40% the price of the transformer in the above post). I think you'd have a very hard time finding a "proper" equivalent transformer for anywhere close to that price.
you get used to the comments of the member from Brighton without any backup. Me, I'd design a transformer with the minimum needed copper to save a few pence and would expect when using one primary for there to be substantial derating required. Like to see the maths from a transformer make though.I think this sums up my real worries about using a primary as a secondary, very nicely explained.
alan
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