Bridge rectifier vs. two-diode rectifier?????????

[Enzo]

Well, one detail... You cannot have 350-0-350 without a center tap, 350-0-350 means 350 volts to either side of a center tap. No center tap means you have two wires? SO that means you have a simple voltage, like 350v. 350-0-350 means 700 volts center tapped.

So do you have 600vCT and 350v?

Grounding a center tap doesn't affect anything if the winding ends are not going anywhere. You need to draw up a schematic of just what you plan to show us.

[eschertron]

Ive got a question related to this topic. I have a PT that has 2 HT windings one higher, about 350-0-350 and other 300-0-300

Have you checked continuity between the windings? I've seen PTs advertised as 350-0-350, for example, that may offer taps at the 300v points, sharing the same CT. This makes ONE winding with 5 taps. Could this be similar to the PT you describe?

[vmazz]

Sorry for the confusion. You are right about the 350-0-350. I was guessing as I tested voltages in an existing circuit and dont have the actual specs of the PT. It was from a Conn Organ and ran 2 tube rectifiers, one 5y3 and one 5u4. I got higher B+ from one rectifier and estimated what their specs would look like, and assumed there was a center tap. But when I pulled it and tested continuity I must have mislabeled something. i didnt find continuity between the 2 HT taps? Turns out I had mistakenly labeled a 5v tap. Now I see I have 2 HT windings which share a center tap. One about 300-0-300 other about 350-0-350. Anyone have much experience with a dual voltage setup like the metro amp kits used to have?

[vmazz]

This is a similar PT I believe.
http://www.classictone.net/40-18054.pdf

[vmazz]

But mine does not have a bias tap. Confusing to me is they seem to refer to the bias tap as the CT? IS that right?

[eschertron]

But mine does not have a bias tap. Confusing to me is they seem to refer to the bias tap as the CT? IS that right?

No. The text printed alongside the wiring does not correspond to the physical location. The Red/Blue is the bias. The colors are called out in various tables and text descriptions sprawled along the bottom of the page.

edit: The voltage on the bias tap is of course referenced to the CT.

[vmazz]

Thank you for clarifying eschertron. I wondered if that was not the physical locations. I have 2 5v taps that I will not use unless try to run dc heaters regulated. I wondered if there is any alternatives to getting a bias voltage, other than tapping into the HV. Are there other options for bias when there isnt a dedicated bias tap?

[eschertron]

Thank you for clarifying eschertron. I wondered if that was not the physical locations. I have 2 5v taps that I will not use unless try to run dc heaters regulated. I wondered if there is any alternatives to getting a bias voltage, other than tapping into the HV. Are there other options for bias when there isnt a dedicated bias tap?

There are ways to generate bias voltage without a tap off the HV winding. Hopefully someone will chime in with details, because I've just told you about all I know on the topic.

[g1]

I'm a bit confused as to the wording 'tapping into' and winding tap.
The other methods I'm aware of do not have a dedicated bias tap but do 'tap into' the HV. Like Marshall JTM45 via resistors or like Ampeg V series/Marshall JCM900 via capacitor.

[eschertron]

There are ways to generate bias voltage without a tap off the HV winding. Hopefully someone will chime in with details, because I've just told you about all I know on the topic.

I'm a bit confused as to the wording 'tapping into' and winding tap.
The other methods I'm aware of do not have a dedicated bias tap but do 'tap into' the HV. Like Marshall JTM45 via resistors or like Ampeg V series/Marshall JCM900 via capacitor.

I stand corrected. I did not mean "without a tap" when I said... erm... "without a tap". Without a dedicated bias voltage tap would be more precise. My experience with deriving bias voltage off of the HV taps is limited. Sorry for any confusion I may have caused.

[vmazz]

I understand what your saying. I was wondering if there was a way to utilize the 5v heaters x2 to create some negative bias tap. But likely I will wire as you say like a jtm50/45 and tap of the HV into a bias circuit.

[eschertron]

The 5v heater winding can supply some good current, but with not much voltage to speak of. The bias requires the other combination; a fairly high voltage (50-70vdc or thereabouts) but with almost no current draw. The inconsequential current draw allows the dedicated bias tap to not imbalance the HV windings. It also allows it to be tapped off about anywhere else on the PT without much extra engineering. Taking a gander at the JTM circuit should be a good start towards understanding how to implement it.

[vmazz]

Appreciate your input eschertron.

[Enzo]

Oh you COULD wire two 5v in series for 10vAC, rectify it with a voltage doubler or tripler circuit, but really, I'd try one of the other ways.

[vmazz]

Yep. A lot of work and cost..but not necessary. Thank you Enzo. Straight talk. I will go with a more traditional approach. Tap into the HV pre rectifier diodes.Is there any potential issue with having the bias voltage off when in standby mode? Or do I need to tap in prior to standby switch, and if so how can I go back and forth from high voltage to low voltage ona dual voltage PT? Hmm more questions..