Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on October 30, 2013, 02:47:14 am
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The question is about the AC voltages of the two secondary windings that cascaded supply the amply with B+
In the web the info about the B+ voltage on the plates of the power tubes is that there are ~640v, unfortunately I've no more info about
Here attached the schematic of the amp
Thanks
K
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The question is about the AC voltages of the two secondary windings that cascaded supply the amply with B+
So, is the question how much AC on each secondary?
Based on the circuitry of the PA I'd assume that each secondary puts out the same voltage. And with ≈640V on the plates I'd guess each bridge puts out ≈320V. You would need to put 226VAC (320\1.414) into the bridge to get 320VDC.
The actual AC into the bridge should be slightly higher (maybe more like 250VAC) to account for loading.
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Many thanks Steve
Looking on the web I've find an unofficial info that says
210v
250v
50v
6.3v
May be the lower voltage is used for grids and preamp tubes
Franco
K
p.s.: Certain that the schematic could also be drawn a little better
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I have a Mig60. The upper section (D1-D4) supplies B+ to the plates. Mine is about 640VDC. The lower section (D5-D8) is the screen supply and the supply for the rest of the the preamp nodes. As I recall my screen supply is about 340-350VDC. I don't know what the raw AC voltages into the bridge rectifiers are. I have never measured those. My amp has had the PT and OT replaced with Mercury iron. The original PT and OT in those amps (and other Sovtek models) was a real weak point in regard to reliability. I recall seeing an interview with Mike Matthews (New Sensor/Sovtek/Electro-Harmonix) where he basically said that too many of the amps were blowing up. That's what caused the demise of the line. Mine has been hot rodded but it is one of the best hard rock amps I have ever played. Maybe the best.