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If you look at the schematic,the primary settings are 110v,117,and 125v for the US version. My unit is 105v,110v,and 117v. When I use a GZ34 even at 117v,my B+ is too high.At 117v,using a 5V3,the fil voltage is at 5.04 but the B+ is stll a bit high. Other than run a tapped isolation transformer,is there anything I can do outside of changing the 100ohm input resistor to a higher value and recalculating the cathode resistors in the output cathodes?
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Follow Ups:
"When I use a GZ34 even at 117v,my B+ is too high.At 117v,using a 5V3,the fil voltage is at 5.04 but the B+ is stll a bit high."
How high is it? More important, how close is it to the ratings of the filter caps? If it's not too close, and all the filament voltages are as good as that, I'd stay with the 5V3.
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Buy Chinese. Bury freedom.
You could perhaps install a choke between the 5AR4 and the existing first rectifier cap. That would lower the voltages and provide better regulation as well. You're pretty handy with a soldering iron and you'd likely have no problem pulling off the install duties. Just a thought.
roN
GZ34 Anode resistors? I adjust anode resistors on my 300b to dial in the B+. FWIW.
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Have Fun and Enjoy the Music
"Still Working the Problem"
The 5R4 ("potato masher" variety, for toughness) is a very reasonable suggestion. The forward drop difference between a 5AR4 and a 5R4 is large. At the rated 250 mA. max., the forward drop in a 5R4 is a whopping 67 V.
The PSU filter cap. values in the schematic are small. That's good for a 5R4, which can't take the amount of capacitance a 5AR4 can.
Eli D.
Add a small , low-value input choke perhaps ?
Al
mt
While not as good as a bucking transformer, I've had decent luck using a CL-90 to drop the primary voltage a couple of volts on a few of my Dynaco amps.
I'd be using a good 'Mullard' 5AR4 or ditching the VR.
When you can the use the 2-3 amps from the 5V winding to fudge up some 6.3 volt heater current, giving you more options on small-signal valves.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Small bucking transformer? JH
Yes,that's what I was thinking.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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