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Re: Jesus; Mary and Joseph; will he never go home! [message #54053 is a reply to message #54052]

Mon, 02 August 2004 15:59

Wayne Parham
Messages: 18686
Registered: January 2001

Illuminati (33rd Degree)

I think probably the B+ plate supply is diode rectified and then filtered with a resistor, cap and coil. That's pretty basic stuff. The cathode filaments are probably driven by a separate transformer winding that provides low voltage AC.

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Re: Jesus; Mary and Joseph; will he never go home! [message #54054 is a reply to message #54053]

Mon, 02 August 2004 17:05

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Thats exactly right, except the filament winding of the power tranny provides for a seperate bridge rectified pi filter to the 300b's and a seperate winding to the driver tubes.

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Re: Jesus; Mary and Joseph; will he never go home! [message #54055 is a reply to message #54054]

Mon, 02 August 2004 17:36

Wayne Parham
Messages: 18686
Registered: January 2001

Illuminati (33rd Degree)

Let me see if I understand you about the DRD amp:

1. The filament on the 300B is driven with DC. It comes from a transformer winding that is rectified and filtered.

2. The driver tube heaters are driven with AC that comes from a different transformer winding than the 300B filament supply.

Is that right? Do you happen to know the filament voltages for each tube? Do you know the plate voltages? Is there a single rectifier for B+ for all tubes?

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Re: Jesus; Mary and Joseph; will he never go home! [message #54056 is a reply to message #54055]

Tue, 03 August 2004 07:09

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Yes they have A center tapped secondary that provides 700V for B+;
Then the there is 6.3v 1a AC secondary for the filaments of the driver tubes and then they have 7.2V 2a filament winding that is rectified by a 4a 50 piv bridge into a pi filter for 5vdc for the 300b's. B+ is connected at the primary. The plate voltages would be fairly simple to figure mathemagectly but it takes me some time. There is not much more to the circuit.

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Re: Jesus; Mary and Joseph; will he never go home! [message #54057 is a reply to message #54056]

Tue, 03 August 2004 12:14

Wayne Parham
Messages: 18686
Registered: January 2001

Illuminati (33rd Degree)

Is the 300B filament supply the one that is sometimes too high?

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Re: Jesus; Mary and Joseph; will he never go home! [message #54058 is a reply to message #54057]

Tue, 03 August 2004 12:18

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

You know what; they have provision in the schematic for a trimmer resistor adjustable to 5v for the 300b fil supply. I can't say for sure since the posts were deleted but can you tell if that would account for the issue at hand?

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Re: Jesus; Mary and Joseph; will he never go home! [message #54059 is a reply to message #54058]

Tue, 03 August 2004 12:58

Wayne Parham
Messages: 18686
Registered: January 2001

Illuminati (33rd Degree)

Yeah, I'm thinking that's probably it. If the transformer secondary is supposed to provide 7.2V, then the peak value is about 10V. A lightly loaded supply could rise to almost double the intended 5 volts.

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