ST-35 power transformer

[johnf]

Thinking of using a Hammond 260K (325-0-325 @200ma. 5v @3amp. 6.3v @5amp) for a tube rectified version with choke. Does anyone see a problem? The 372HX is no longer listed and I can live with the open frame.
Thanks in advance.

[EWBrown]

AES still has the 272HX listed for $64.00:

TRANSFORMER, POWER, HAMMOND, 300-0-300 V, 200 mA

RoHS Compliant


Primary 115 VAC, 60 Hz.
Secondary DC current measured with cap. input filter, full wave (two diode) C.T., rectifier circuit.
Enclosed, 4 hole chassis mount.
Minimum 6" long leads.
Class A insulation (105 degrees C).
Hi-Pot test of 2,000 V RMS.
Conservative designs - CSA certified (# LR3902).
Secondary: 300-0-300 V, 200 mA
Filament winding 1: 5 V, 3 A
Filament winding 2: 6.3 V, 6 A CT
Mounting centers: 2.5" x 2.69" vertical mount

The do not have the 372HX.

The 260K should work fine, the voltages and currents look to be in the correct range.

HTH

/ed B in NH

[SteveH]

Also,
Not sure if you are going for a tube rectifier or not; but dependent upon which rectifier you want to go with; you can 'dial-in' your voltages, dependent upon what Vdrop the rectifier has.

[johnf]

Thanks, I am in England so need 240V Primary. I wondered whether the unshrouded xformer would pose any noise problems.
I Would like to know more about "dialing in the voltage"? by choice of rectifier.

[SteveH]

John,
Ok - basically you have your choice of 5v Full-wave rectifiers (We won't talk about the mercury vapor ones now; as they require special consideration):

5AR4
5AS4
5R4
5AU4
5Y3

All of these tubes will have a different voltage drop. For example, lets take the 5R4 - and say you are pulling the max specified current from the tube (250mA). The data sheet says that at 250mA; the tube's Voltage Drop is 67v. So, if we imagine a circuit where your end B+ was say 300v with solid state rectifiers - then you can expect your B+ to be about 233v with a 5R4 rectifier in it.
On the flip side; the 5AR4 only has a Vdrop of 17v @ 225mA. So taking the imaginary circuit above, your end B+ would be somewhere around 283v.
Keep in mind that Vdrop is dependent upon current draw. Once you figured out what your draw is; I encourage you to look at the tube data sheets to find a rectifier that will work for you.

Hope that helps,
Steve

[EWBrown]

I did some experiments with an open frame / unshrouded power transformer, check here:

http://diytube.com/phpBB2/viewtopic.php?p=14019#14019

for the results. Bottom linre is that open frame / unshrouded power trannies can cause some persistent and "incurable" ac magnetic field generated hum problems, if certain precautions are not observed.

/ed B in NH