Akg Solid Tube Power Supply SCHEMATIC

[opacheco]

Hi Again!!

Someone knows where I can find the Akg Solid Tube Power Supply Schematic??....I need the Akg Power Supply for this mic only in order to repair the power transformer, because I need to check for the Power Transformer output voltages......my akag solid tube power transformer is literaly burn(the bobbin is burn with the windings too!!) and I can not to unwind in order to get the rigth turns for re-wind process.

Any Idea??....

Thanks a lot anticipated for any comments and help!
Opacheco.

 

[zebra50]

The circuit is over at RadioMuseum.org, but you need to be a member.

But I can see that the power transformer outputs are 270V AC and 27V AC for the heater and high voltage supplies.

Hope that helps a bit!

Stewart

 

[opacheco]

The circuit is over at RadioMuseum.org, but you need to be a member.

But I can see that the power transformer outputs are 270V AC and 27V AC for the heater and high voltage supplies.

Hope that helps a bit!

Stewart

Stewart,

Thanks a lot for you response but I saw 27Vac very rare for the filament of the tube; Could you verify that for second time for  me please??.....

Thanks a lot again
Opacheco.

 

[zebra50]

Actually I think it might be 23V. That is before the rectifier and regulator and so on, so the tube is presumably seeing much less.

The scan is a bit tricky to reads but here is a screenshot of part of the power supply. Radiomuseum doesn't show the full schematic unless you join.

BTW, did you notice that the tube is lit with an LED? Naughty AKG, they should be better than that!

 

[abbey road d enfer]

Actually I think it might be 23V. That is before the rectifier and regulator and so on, so the tube is presumably seeing much less.

This schemo doesn't make much sense. Look at all these caps across the bridge rectifiers, the nasty surge protectors, and 23Vac for powering a 12Vdc filament! There's more energy wasted in the regulator than supplied to the filament.
I would think 15Vac to be largely enough in a sensible design.

 

[opacheco]

Stewart,

Thanks a lot for the schematic!

abbey road d enfer the schematic hold for 23vac and if this the oficial AKG Solid Tube Power Supply Schematic then I think that voltage is correct....You don't??

Thanks
Opacheco.

 

[abbey road d enfer]

abbey road d enfer the schematic hold for 23vac and if this the oficial AKG Solid Tube Power Supply Schematic then I think that voltage is correct....You don't??

I'm not questioning the veracity of the schemo.
Unfortunately the schematic is not complete but I don't think there's anything that justifies the need for more than 12.6Vdc after the regulator (even the ohmic loss in the cable is negligible in respect ot the 150mA current draw. A 23Vac secondary will produce about 30V pre-regulator. that means that 17V are lost in the regulator, or 2.5W dissipated in heat.
When I look at this schemo, it looks to me like the work of an intern trying to amass all the things, right or wrong, he has amassed reading DIY and audiophool magazines and webpages, mixed with some tradition.
It is noticeable that the venerable N12B power supply starts also with a 23Vac secondary, that is regulated down to 5V. That was probably an heritage of the N12K (the companion to the original C12), which had no regulator and used cascaded R-C filters to smooth the voltage, making necessary to start with a rather high rectified value.
This is not worthy of AKG. They could have done much better and I think you have an opportunity to be a little more clever than the "designer" of this pathetic piece.

 

[RuudNL]

Scan of the schematic

 

[abbey road d enfer]

Scan of the schematic

Thanks a lot for this schemo.
It shows that they have kept the heritage of the past with the 10R resistor intended to reduce the current surge at turn-on, so the regulated voltage must be slightly increased in order to compensate for the 1.5V drop across it (10R x 0.15A). I maintain that in order to achieve that, a 16Vac secondary is enough, leaving 6V for the regulator in normal conditions and 4V worst-case at -10% mains voltage.

 

[moamps]

AKG uses traditionally CCS for the tube filament in order to keep the triode current (and power) independent of the cable length and voltage loss. In the C12VR schematic, downloadable from the AKG site, one additional section on the filament secondary is present (20V and 3V) for the total of 23V if the cable between the microphone and power supply is longer than 20 meters. So, I suggest 20-23V for the filament secondary, as stated in the schematic.
BTW, full specs of the LM317 are reached if the Vin-Vout is more than 5V, IMO. 
Regards 

 

[opacheco]

My Transformer is almost not repairable!! and I am searching for one new transformer replacement.
Someone knows where I can buy one power transformer for this Solid Tube Power Supply??

Thanks,
Opacheco.

 

[abbey road d enfer]

AKG uses traditionally CCS for the tube filament in order to keep the triode current (and power) independent of the cable length and voltage loss. In the C12VR schematic, downloadable from the AKG site, one additional section on the filament secondary is present (20V and 3V) for the total of 23V if the cable between the microphone and power supply is longer than 20 meters.

That is true but doesn't make much sense for the SolidTube, as I'm going to demonstrate. The SolidTube is a different animal. The fact that the inter-stage connection travels back and forth the cable between mic and PSU suggests that even the standard 5-meter length challenges the HF response. 20 meter would cut the HF response to about 4kHz.

So, I suggest 20-23V for the filament secondary, as stated in the schematic.

  I suggest that 23Vac is far from being necessary and that a lower voltage would be perfectly adequate.

BTW, full specs of the LM317 are reached if the Vin-Vout is more than 5V, IMO. 

Not a matter of opininons, but specs. They indicate that the relevant parameters (line regulation in particular) are correct for Vin-Vout> or =3.5V.

Why does the 3Vac increase for length >20m make not much sense for the SolidTube?
Demonstration:
Even with the smallest cable gauge (0.08mm²) the two-way resistance per meter is 0.42 ohm (assuming copper), accounting for 63mV drop per meter. 20 meters result in less than 1.3V drop. In real life, the actual wire gauge for heaters is between 0.18 and 0.4 mm².

The supplementary 3Vac tap for the original C12 is to be put in perspective with the maximum recommended cable length of 200ft. The original cable standard length was 65ft. These mics were originally intended for film-stage applications.

I understand why AKG have done it that way, part heritage, part optimization of the use of the available parts bin, part neglect; all theses factors are irrelevant to the OP, who just wants to make his stuff work.

 

[moamps]

My Transformer is almost not repairable!! and I am searching for one new transformer replacement.
Someone knows where I can buy one power transformer for this Solid Tube Power Supply??

Did you ask AKG for replacement transformer?
This one on ebay may fit:
http://www.ebay.com/itm/Toroid-Transformer-T30-55W-for-Tube-Amplifier-Amp-/280416409885?pt=US_Home_Audio_Amplifiers_Preamps&hash=item414a1ed91d

 

[Rob Flinn]

If it's any use I had one of these in for repair a while back.  Allegedly they are known for having flaky mains transformers, & this is in fact what the problem was with the Solidtube I had in.  I kept thinking it was one of the surge protectors, because one was popped when I first opened it, but in the end it was the mains transformer.  You can get a replacement from AKG of that is what the problem is.

 

[mikeyB]

Late bump!
Rob - did you ever buy a replacement transformer from Ashley Styles of Saturn Sound (He's long retired now)? He use to do a replacement for £25 - I'm trying to remember the spec, but from the size I guess it was a 12VA open frame EI. I seem to recall him telling me that the HT was rated 270V @ 25mA. That would be 6.75VA and the remaining 5.25VA would cater for a 18V winding at 300mA-ish.
I've looked at the back to back solution but space is tight for 2 TXs without butchering the pcb. I'm thinking of taking a 12VA 18+18(or even 15+15, removing a 15V winding and replacing with a 270V winding. Watched a few vids on utube and fancy a bit of "rolling my own" just as a learning experience. I have other things to rewind should I be successful.
Any advice from the transformer gurus would be much appreciated.
Thanks in advance.