How to get a quote for a custom designed mains transformer

This is a custom service for replacement or upgrade of mains transformers in existing equipment and for new builds. We are not able to do rewinds. The price depends on the size which is governed by the total power (VA) rating. To obtain the total power in Watts (VA) simply multiply the voltage and current rating of each secondary winding and add them together. All power transformers are built to order in about 5 weeks and we do not make any charge for design. We need a precise specification to work from and we guarantee to performance to this specification. Below is a form which you can submit to us with your requirement. Once we have accepted the specification we will email you a Design Reference which you can use to order on this site or by telephone to Sales.

If you would like us to quote for a new transformer for a specific piece of equipment we first need to make sure it will fit into the space available. It is usually best to use a larger transformer to improve the performance and ensure it is properly rated for the job. Please choose the size and package style you need form our Dimensions and Styles page. You may find that your original transformer uses Metric dimensions in which case choose a size which is about the same volume or weight and then go to at least the next size up. If the original transformer was designed for 50Hz (US market) you will need to add an extra size up also.
Next we need to know the voltages and currents for each winding. Usually is is possible to get a schematic from the internet. In the case of a valve amplifier you can determine the voltages and currents for the heater windings from the schematic with the aid of the valve specifications which can be found at Franks Electron Tube website. The HT voltage is more of a problem. In reality, unless this can be found by measuring a good unit, from the schematic or you are prepared to make an educated guess, we will not be able to help. Don't forget we need the AC transformer winding voltage. You can calculate this from the dc voltage if you know the rectification method using the formula on our site. if you do not know the HT current we can obtain this when we design the transformer. We simply use the thickest wire for the HT winding that will go in the space available on the bobbin. So long as the transformer is larger than than the original the wire will be large enough for the required current with a margin for error. Obviously we can make the transformer for a different input voltage. We can also offer a World Wide primary.
Once you have determined size, package style and the specification please complete and submit the form below. We will analyze the specification and if we can make it we will send you a formal quotation. There is no obligation to order.

Our standard offering includes up to 5 separate windings which may be any voltage up to 1000V rms and 600 Watts (VA). We can offer more than 5 windings at 5:30 UK Pounds per additional winding. In this case you must specify open frame or drop through type.
Please indicate the voltage and current required for each winding. We design so that the secondary voltages are correct when all secondary windings are on full load. If you measure a winding with no or reduced current load the voltage will rise because each winding has a finite dc resistance. Regulation is typically 5% but may be more or less depending on the wire thickness we use. If space on the bobbin permits we increase the wire size(s) to get the best possible regulation.

Electrostatic shields between the primary and secondary windings for mains noise isolation or between secondary windings are available at a small extra charge per shield.
We can incorporate an external hum band for a small extra charge. This is a copper foil shorted turn round the outside of the transformer which will reduce the stray flux radiating from the transformer. This is useful if the transformer has to be sited near tape heads or microphone transformers which can pick up hum.
Please check your specification values carefully as changes can lead to errors and delays. If you find you need to make a change please email support quoting your design reference to cancel your specification and and resubmit a new one.

The power rating in the table above is a guide. In general the rating may be increased perhaps by 10% if the secondary configuration is very simple. Complex winding arrangements will usually reduce the rating by at least 10%. An electrostatic screen reduces the rating by aout 5%.

Please indicate: HV Insul if low voltage windings are to be connected to high voltage supplies e.g. rectifier heaters. In this case we will fit high voltage lead-out wires.
We are happy to provide center taps or other taps but please minimize the total number of connections as this causes assembly problems with style "S"; particularly with multiple heater windings. Style S, (Shrouded) is possible on the smaller sizes B,D,F and Honly when a maximum of two secondary windings are used. More complex windings may be possible at additional charge.


Click for: PRICES

Approx. power (Watts)
Varies with number of windigs and screens
B 10
D 15
F 25
H 35
I 40
J 50
L 100
K 125
M 150
N 200
P 300
P+ Encapsulated 200
Q 450
T 550
R 600


Please use this form to send us your specification. We will E-Mail you with confirmation that we can make to your specification and the size code. If we cannot make to your spec we will suggest modifications.  With your spec reference and size code you will be able to order or quote at our online shop including shipping cost etc. You can order or quote multiple items to benefit from the lowest possible shipping cost. Please include your own reference such as "T1" etc. so that you can refer to it when you order or if there are any questions.

Your Name:
Your Email Address:
Delivery Address:
Local telephone (for possible shipping company use):


Your reference (e.g. "T1"):
Electrostatic screen (extra charge):
Hum band (extra charge):
Package style:
Secondary windings (Use format e.g. 350-0-350 V @ 3.5 A. see General Information above):
Secondary 1:
Secondary 2:
Secondary 3:
Secondary 4:
Secondary 5:
Secondary 6 (Extra charge. Style "O" only):
Secondary 7 (Extra charge. Style "O" only):
If dimensions are critical state Size and Style CLICK HERE FOR DIMENSIONS
Total V x A (i.e. V x A for eah winding added together. Should not exceed 600 Watts)*: 
Comments or special requirements:

* Please multiply the V x A for each secondary winding and add to get the total for all windings.  (You need to take the full voltage of a center tapped winding.  250-0-250 at 100 mA is 50 VA). This will enable you to obtain a guide price from the table above. We use this number as a check when we do the quotation and the final design if you order.

To confirm you are not a robot PLEASE TYPE THE ABOVE 5 DIGIT NUMBER:

EA Sowter Ltd
The Boatyard Cullingham Road
United Kingdom
Tel: +44 (0) 1473 252794
Fax: +44 (0) 1473 236188