Eros 2 capacitor minimum voltage rating?

[hmbscott]

Can I get away with a 300V rating for the output capacitor on an Eros 2? I"m thinking about V-Cap TFTF 2uF 300V.

 

[Paul Joppa]

It's a near-run thing - the operating voltages are less than 300 volts, but just barely. However, the startup transient voltage spike can be as much as 350v, and the TFTF manufacturer specifically warns against voltage spikes exceeding the rated voltage. For that reason, I can't recommend it. (Film and foil capacitors do not self-repair in the way that metalized-film capacitors do.)

 

[Paul Birkeland]

The soft-start parts could be added to the D socket C4S to keep the voltage seen at that capacitor pretty low.  The problem is that if you run the Eros with no tubes in it, you'll cause big problems. 

While there is a lot of room in the Eros chassis for caps, there might not be that much room for the teflon Vcaps.  The ODAM is certainly viable though.

 

[hmbscott]

The soft-start parts could be added to the D socket C4S to keep the voltage seen at that capacitor pretty low.  The problem is that if you run the Eros with no tubes in it, you'll cause big problems. 

While there is a lot of room in the Eros chassis for caps, there might not be that much room for the teflon Vcaps.  The ODAM is certainly viable though.

Soft start parts? What would that entail? Or, can you point me to a reference? I think I can fit the TFTF 2uF in the space available. I currently have an Audyn Cu 1uF 630V that’s similar size installed.

 

[hmbscott]

Hi Paul, For a soft start, it appears to me that the problem is that the HV voltage regulation doesn't kick in until the 12AU7 cathode has heated up. My solution is to use a time-delay relay powered by the heater secondary of the power transformer that interrupts the 130VAC secondary until the tube cathodes have heated up. I selected a Little Fuse KDRM121 time-delay relay, knob settable delay of 1-100s. The coil is 12V (AC or DC) 170mA coil current draw, the contacts are rated 250VAC. It's 2" X 2" X 1.21" and uses 1/4" spade connections.

Can the heater secondary tolerate an additional 170mA load?

Is this a viable solution?

 

[hmbscott]

Hi Paul, For a soft start, it appears to me that the problem is that the HV voltage regulation doesn't kick in until the 12AU7 cathode has heated up. My solution is to use a time-delay relay powered by the heater secondary of the power transformer that interrupts the 130VAC secondary until the tube cathodes have heated up. I selected a Little Fuse KDRM121 time-delay relay, knob settable delay of 1-100s. The coil is 12V (AC or DC) 170mA coil current draw, the contacts are rated 250VAC. It's 2" X 2" X 1.21" and uses 1/4" spade connections.

Can the heater secondary tolerate an additional 170mA load?

Is this a viable solution?

Oops, just figured out that the heater circuit isn't 12.6VDC but rather is 6.3VDC, so above doesn't work. Rather, I am proposing a Little Fuse KDRM421 that has a 125VAC coil and power it off line voltage after the on/off switch. The NO contact will be interrupt the 135VAC secondary of the transformer to delay HV turn on for 30sec.

 

[Paul Joppa]

That will work.

That's one of the reasons I've been using voltage doublers for a long time now - most power switches are rated for 240vAC or 30vDC, maximum. With a doubler, you can switch the high voltage of a high voltage rectifier-filter up to 500 volts safely.

 

[hmbscott]

Thanks Paul!

I will keep in mind that all tubes must be in place whenever i power the amp.

 

[hmbscott]

I installed the time delay relay and tested it. It works a treat! Heaters start heating on turn-on, and 30 seconds later high voltage turns on. My testing indicates regulated voltage is achieved less than 5 seconds later and never exceed the regulation target. So, perfect! Here'a a couple pics of my installation.

 

[hmbscott]

Installed the V-cap TFTF 2uF 300V yesterday. Sounds great and no magic smoke, Yay!