isolation transformers

[RitzRed]

I have an old 3 tube Kent amp I have been told it is a widow maker and have heard a little about isolation transformers but would like to know more and where to get one

[sgelectric]

A quick search of the archives will generate several threads that deal with this topic.
Try searching "widow maker" or "isolation transformer".

Here's one: http://music-electronics-forum.com/t26220/

SG

[RitzRed]

I found a isolation transformer that seems to be a good price it is listed like this Triad isolation transformer N-68X, Primary 115 or 230 V 50/60 CPS sec 115V, 50VA electrostatic shield will this transformer work with my little Kent amp

[Jazz P Bass]

The key word here is 'VA'.
That is the volts x amps that the transformer can supply. (power)
As we do not know what the Kent is pulling from the mains, it is a guess.
Can you measure it (the mains current that the amp is consuming?)
Going out on a limb, I would 'guess' that the Kent is not pulling 2 amps.
So it should be o/k.

[RitzRed]

yes I am guessing it will work as well I am going to buy it and try it for $27.00 for a new old stock I don,t think I will go wrong

[52 Bill]

yes I am guessing it will work as well I am going to buy it and try it for $27.00 for a new old stock I don,t think I will go wrong

I think that these are available new at Mouser for $12 bucks.

[JHow]

I think that these are available new at Mouser for $12 bucks.

They are. I even provided a link in the other thread. There is a saying about horses and water....

[Tom Phillips]

The key word here is 'VA'.
That is the volts x amps that the transformer can supply. (power)
As we do not know what the Kent is pulling from the mains, it is a guess.
Can you measure it (the mains current that the amp is consuming?)
Going out on a limb, I would 'guess' that the Kent is not pulling 2 amps.
So it should be o/k.

Jazz,
Your math was dyslectic. A 50VA 115V spec isolation transformer is rated to supply 0.44 Amps not 2 amps. It would probably work with the little amp but would probably run hot.
Tom

[loudthud]

Stay away from torroid transformers. These type amps are half wave rectified and don't draw a balanced current from the AC supply. Stick with and E-I type and you must derate by prehaps 50% due to the imbalanced current.

[Enzo]

There is a saying about horses and water....

You can lead a horse to drink, but you can't make him water.


That one?

[RitzRed]

I went to that link and the only ISO Trannys they had for sale were 50 bucks or maybe I did something wrong when I looked there

[g1]

These type amps are half wave rectified and don't draw a balanced current from the AC supply. Stick with and E-I type and you must derate by prehaps 50% due to the imbalanced current.

Great point. The half-wave rectifier will put DC on the secondary of the ISO tranny, saturation and overheating will result with such a small ISO tranny. A lot of people recommend the N-68X (50VA) for isolating small "widow-maker" amps, I don't know if any of those people have tried them .
One guy who did try the N-68 (with a 30W draw amp) found they do overheat , and wrote about it here: Fixing the half-wave rectifier problem
He ended up having to install a bridge rectifier before the half wave rectifier to balance the current through the ISO tranny secondary. Would have been much simpler to just use a bigger ISO tranny, like loudthud suggested. Maybe more like one of these: N-77U Triad Magnetics | Mouser

[RitzRed]

Well the info in this subject is all over the place but I don,t think most of these are cost effective I am going with the 50VA and try it out on one of the little record player amps I bought to see if it works the Kent is not working yet I did get the cap the one with the 4 wires (big paper) this is allot more complicated than I first thought it would be I think I need a class at the CC to get up to speed thanks for all the advice and info

[JHow]

If the heater circuit wants .150A how much more would the plate circuits draw? Another 100mA? How much would the 35w4 plate circuit put out? I think you would be in the range of .250A or less for this amp. What am I missing? The tube data sheets give consumption at typical voltages.

[RitzRed]

I don,t get what you are saying that is why I am going to go get some classes so I can understand all this. I think I will save allot of money on parts alone. I got a picture of the amp from the seller and the tube placement is different than what everyone here on the forum suggested when I put the tubes in that way the buzz is gone But it still does not work the way the tubes are placed are as you look at the amp from the back. from left to right. 12AV6,35W4,50C5 as it turns out I just don,t know enough to do this myself untill I get a better understanding of electronics. I used to think this is just pieces and parts soldered together I can figure it out .Well it is a little more complicated than that.