It's my first amplifier project, but it's not my first project in general. I'm a senior mechanical engineering student, and I also work as a machinist. I know a decent amount about electronics, especially digital stuff, but this would be my first purely analog project.
how about this one ?
KT88 SINGLE ENDED (SE) TUBE AMP | Vintage Stereo Equipment
or EL84 driving EL84
http://home.comcast.net/~jafix/SakumaEL84.html
KT88 SINGLE ENDED (SE) TUBE AMP | Vintage Stereo Equipment
or EL84 driving EL84
http://home.comcast.net/~jafix/SakumaEL84.html
That's true if you use it is in the classical way. However you can still go for a parafeed where you need a choke or a current source to feed the tube anyway.
A good choke can be quite cheaper than a good SE OPT.
For sure it is not as good as a decent OPT in terms of losses and frequency response.
45
When you rectify AC voltage to get DC voltage, you need to multiply the AC voltage by sqrt 2, which is roughly 1.41.
Your transformers are center tapped, so using a full wave center tapped PS (FWCT), will give you no more than 375*1.41=528 for a B+ voltage. You'll need to subtract series resistance losses provided by a resistor or a choke (which you will need for smoothing) to get your final B+ voltage.
Download, install, and play with Duncan Amps Power Supply Designer II (PSUDII). It's easy to use and will quickly help you get a power supply designed.
PSUD2
Something I have often wondered about; if you use a SE OPT in a parafeed configuration would you expect a higher level of performance or is it true what I have heard said about the DC current creating an offset, if one could call it that, with operation then in a more linear part of the BH curve?
OK, I got the software, but I have a question. Are the voltage specifications on the transformer given in RMS voltage or peak to peak voltage. Also, if you hook up to the center tap and outer tap of a center tapped transformer, do you get half the voltage? Also, do I need to calculate the resistance of the entire amplifier circuit and plug it in for the load on the power supply in order to get things right, or is there a ballpark figure that I can use?
Furthering what Tom said above, right click on the load block in PSUD and change it to constant current. Note that in PSUD you can right click on the block/stage or right click on components......in this case you want to right click on the block/stage.
The current load is the sum of each individual tube current in the amp circuit. In the case of your larger transformer, it cannot be much above 100-110ma or so, so this will determine what output tubes and operating conditions are viable. If you exceed the current rating of your transformer, the voltage will sag and the transformer may overheat. Note also that if you draw less than the rated current, the voltage will be a little high. This is easy to see in PSUD by changing the load current.
The nonlinearity of the BH curve by itself does not mean that the transformation ratio will be affected. However, each time the applied MMF crosses zero, it takes a little bit of energy to change the direction of magnetization of the Weiss areas in the core. As this energy can only be delivered through the primary winding, the tube must supply it. Low rp tubes would be better able to deal with this load abberation, and hence would better 'mask' the effect, than high-rp types.
Of course this is all happening on a very low scale (compared to, say, electrical zero-crossing effects in AB stages) and it is very much the question if this can be heard at all. But some claim that it is one of the reasons for the transformer-coupled SE amp 'magic.'
IIRC the whole story is in one of Menno van der Veen's books.
Kenneth
Ok, if it is a moot point whether or not this "magnetic stiction" is audible or not then,with the increase in primary inductance available for the AC signal, would we expect an improvement in LF performance when a SE OPT is used in parafeed? Common sense says yes but have I missed something?
Should I include the filament current in this calculation, or is it just the plate current that I'm concerned with?
This is the schematic that I would like to build. It's for a GEC 912 amplifier. On the schematic, the high voltage supply is 350 volts. From the Duncan amps power supply designer, my expected high voltage output will be about 290 volts. What effect will this have on the amplifier. Also, is there something easy I can do like apply a scale factor to all of the resistor values to adjust for the different input voltage? Thanks for your help.
An externally hosted image should be here but it was not working when we last tested it.
not poking....asking. cause i dont know. but, why?
is there more to using a opt on a se tube than changing high V to higher I. and other than as the names state (air core..or not)....whats the diffrence? is it for sound or it just wont work?
truely asking.
Not for sound. It would just not work.
A transformer which has no air gap in its core can only deal with a very small DC current. Any significant DC current will cause the core to saturate magnetically, rendering the transformer ineffective (the tube will see a short circuit, and no power can be delivered to the speaker).
In a SE amp, the above situation applies because the bias current of the output tube runs through the transformer primary winding. The usual solution is that an air gap is inserted in the core, this allows the core to stay out of saturation. (Why is this?: The energy of the magnetic field is concentrated in the air gap, "offloading" the core, so-to-speak, and air cannot be magnetically saturated.)
Power transformers never have air gapped cores, this is why you cannot use them as OPT in SE amps.
Note1: in a push-pull amp, no air gap is needed: the bias currents of both tubes run in opposite direction inside the transformer windings, and therefore no net magnetization of the core takes place.
Note2: as someone else mentioned, SE parafeed is still possible without an air gap. In parafeed, a capacitor is used to keep the DC current out of the transformer.
Hope this helps,
Kenneth
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