80hinhiding
Well-known member
- Joined
- Sep 27, 2016
- Messages
- 97
.
Did you put a capacitor? The 1.414 factor works only if the voltage is filtered. In case there's no capacitor, the rectified signal is not DC, the measurement is absolute value, identical to AC.80hinhiding said:I just tried a 6x4 tube rectifier. Put 269VAC on each plate, took a reading from the transformer high voltage center tap and the cathode, and got a reading of 244VDC.
I had been expecting to see around 358VDC, thinking it'd be (VAC * 1.414) -22 on the secondary.
Is something wrong or do tube rectifiers not increase the voltage?
Adam
That's what the OP did in measuring the voltage between cathode and center tap.Gregg Johns said:"I just tried a 6x4 tube rectifier. Put 269VAC on each plate, took a reading from the transformer high voltage center tap and the cathode, and got a reading of 244VDC".
Greetings ,First post.
I thought the 6x4 was a full wave rectifier, I think you need to ground the secondary HV center tap.
Actually, the formula used by the OP is more specific.A solid state bridge would be 1.414 x full winding. no center tap.
220uF with a 6X4? Wow! You're gonna fry this poor valve.80hinhiding said:Okay perfect guys thanks as always. I just added a high voltage 220uF 450V cap and a resistor divider and it now reads 341VDC, and drains pretty quickly after the power is turned off.
Adam
abbey road d enfer said:220uF with a 6X4? Wow! You're gonna fry this poor valve.
I stand corrected sir.abbey road d enfer said:That's what the OP did in measuring the voltage between cathode and center tap.
Actually, the formula used by the OP is more specific.
Those schematics in the old RCA manuals are a wealth of information, with good circuit descriptions. There is much to be learned from good ol' fashioned paper and ink.80hinhiding said:It was cool seeing all the old designs and seeing references to picture tubes, etc.
As far as I can see, this graph ignores the effects of the transformer's inductance, which is generally adequate in the context of vacuum rectification, where the dominant factor is the added resistance of the valve and the DCR of the xfmr.CJ said:so lazy engineers use a graph and then maybe check it in the lab.
I don't really understand this graph, because the rectified voltage is not smoothed; in audio applications, there's always a smoothing cap. It looks to me like the rectification used with high-po DC motors.CJ said:here is a figure showing how a choke, which resists a change in current, can provide a steady current flow to the rectifier tube, I1 and I2 , but resulting in bigger voltage peaks, which means more capacitance or more pi sections needed to flatten that out,
and a cap input pic showing a smother ripple voltage but increased stress on the tube in the form of higher peak current values,
You're inferring too much; constant current would not result in more headroom. Headroom is essentially voltage dependant. Sag is counter-productive for headroom, and although choke input and cap input differ in that respect, there is no practical difference in the context of a preamp. Power amps are another issue.80hinhiding said:So, does this mean using an inductor should yield constant current, more headroom in the dynamics, but cause a shorter life span for the rectifier tube?
Tubetec said:Applying ht before the cathodes of the tubes have had a chance to get up to temp can have a drastic effect on tube life.
Enter your email address to join: