I built a clone fi SET amp last summer and I am primarily using 2A3 tubes. With Don’s original design one could use 2A3’s or 45’s but when using the 45’s you have to use a 5Y3 to lower the voltages. I’m using a 5U4GB with my 2A3’s safety within spec but when using the 45/5Y3 I’m at the hairy edge with the following numbers: plate voltage 237VDC, 47mA, plate disposition 11.3W. Is there an easy why to lower my B+ as to get in line with the 45 specs?
If you have primary voltage tappings, eg; 220v, 240v use the 240v tap to reduce the produced voltage.
A 5R4GY will drop a few more volts than the 5U4. Maybe enough to help you out but never forget, a valve has a very wide tollerance and will complain, in no uncertain terms, when over driven.
A 5R4GY will drop a few more volts than the 5U4. Maybe enough to help you out but never forget, a valve has a very wide tollerance and will complain, in no uncertain terms, when over driven.
What does the power supply schematic look like? Cap input? Lower the value of the 1st cap after the rectifier...
Then use a bigger input choke, or swap them around, etc. Posting the schematic would make things easier.
There is also an option to use a MOSFET to drop some B+. You need to use one with a big enough power rating and a heat sink. But I would first try the old-school approaches.
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I'm not a fan of 5R4G and prefer 5U4 types or 5V4 where possible.
Easiest way I know is to use a smaller first capacitor. The sensitive range is between 0.47uF and 3uF. I like to size my power supplies to allow this useful variation, because it allows me to use nice PIO first caps like Russian KBG-MN ones. 1uF at 600V isn't too big. and you can parallel a couple for more B+.
Easiest way I know is to use a smaller first capacitor. The sensitive range is between 0.47uF and 3uF. I like to size my power supplies to allow this useful variation, because it allows me to use nice PIO first caps like Russian KBG-MN ones. 1uF at 600V isn't too big. and you can parallel a couple for more B+.
When you say that that you you want to lower the HT to reduce the stress on the 45, does that mean it is cathode biased? The 237V is anode to cathode/filament? Or to ground?
Simply increase the cathode resistor to bring down the current to about 35mA. The HT is fine.
If is fixed biased, just dial in more negative.
Simply increase the cathode resistor to bring down the current to about 35mA. The HT is fine.
If is fixed biased, just dial in more negative.
Another option: use a low voltage transformer wired to "buck" the secondary.
If you need better help, you need to provide more details such as target voltage, current, schematic, etc...
If you need better help, you need to provide more details such as target voltage, current, schematic, etc...
This is a choke input supply, but the inductance of the first choke is too small. Calculate the critical inductance versus the total load current. Then use a small capacitor in front of the new choke, and adjust the amount of capacitance to get the B+ voltage you want.