diytube.com

Hi,

This question is a followup on the "Integrated Mark III" 4-page thread that we talked about before.

I'm starting to wire up the power supplies (one per channel, common chassis), and I'd like to progressively test the voltages as I make connections. Would it be OK to do this without a dummy load? Granted, the readings will not be meaningful until the circuit is loaded, but I'd at least like to test for flash, smoke and volts before I get into the driver boards and power stage. I like to test module by module to make troubleshooting easier if needed later.

Here's what I'm doing. Ed helped me with the integrated 5AR4 recitifier (my toroid has no CT). The second schematic is one I drew of Sheldon Stokes' SDS cap board, all stock except the second stage has 235uF instead of 50.

http://lagunatechnics.com/images/tubeaudio/ewbrown_hybrid_rectifier.gif

http://lagunatechnics.com/images/tubeaudio/filters.jpg

As always, any help and/or comments would be appreciated.

Thanks,

Chris

You could test the power supplies, the balancing resistors across
the high voltage capacitors will act as slow bleeders, just be careful
around the high voltage, let it bleed off for about 5 minutes
and be sure to short the high voltage to ground carefully
before you touch anything. The voltage normally could be
way over the capacitors ratings, but since you are using
series caps it's probably OK. Don't leave it on too long in
any case. If you measure the filament voltages, keep in
mind that they will be quite a bit higher than expected when
they are unloaded, maybe 7 volts ... it will pull down when you
plug the tubes in.

TomMcNally wrote:You could test the power supplies, the balancing resistors across
the high voltage capacitors will act as slow bleeders, just be careful
around the high voltage

Thanks, Tom, for confirming my step by step approach.

The HV warning is always good. In fact, when I work around high voltage I turn of the TV, music, whatever, and just concentrate on where my hands are and whether my brain is engaged.

Regards,

Chris

In one of the upper schematics, the High DC Voltage wire comes out of the pin 8, and in the other- it comes oout of the pin 2.

Is it correct? Shouldn't they both come out of the pin 8? Or it doesn't matter at all?

Greetings

Wiesiek Lipowski wrote:In one of the upper schematics, the High DC Voltage wire comes out of the pin 8, and in the other- it comes out of the pin 2.

Is it correct? Shouldn't they both come out of the pin 8? Or it doesn't matter at all?

Thanks very much for giving that a critical eye. Yes. I think it matters and I have posted a corrected drawing.

Sometimes "copy and paste" makes things a little too easy 8-)

Chris

With directly heated cathode rectifiers such as the 5U4 and 5Y3, the convention is to use pin 8 as the cathode, although pin 2 could be used equally well. With indirectly heated cathodes, such as those in 5AR4s and 5V4s, the cathode connection must be made to pin 8, or you'll get all sorts of weird voltage drop and lack of regulation.

Keep this in mind if you ever decide to run a 5AR4 in an older circuit (pre-convention) that uses a 5U4.

erichayes wrote:With directly heated cathode rectifiers such as the 5U4 and 5Y3, the convention is to use pin 8 as the cathode, although pin 2 could be used equally well. With indirectly heated cathodes, such as those in 5AR4s and 5V4s, the cathode connection must be made to pin 8, or you'll get all sorts of weird voltage drop and lack of regulation.

Keep this in mind if you ever decide to run a 5AR4 in an older circuit (pre-convention) that uses a 5U4.

Thank you, Eric, for clueing us in on that. Absolutely right, I took a look at the data sheets for the 5AR4/GZ34 and instability would surely result with a B+ connection to pin 2 as opposed to the earlier pin arrangement.

Regards and thanks for the help,

Chris

Pin 8 is the correct one, a connection to pin 2 will inject an extra 5VAC 60 Hz onto the B+, which is definitely not a good thing.

/ed B

EWBrown wrote:Pin 8 is the correct one, a connection to pin 2 will inject an extra 5VAC 60 Hz onto the B+, which is definitely not a good thing.

/ed B

Thanks. I started wiring the PS yesterday and got it right. But as I'm working on this, I have a new question.

There's lots of information out there about how "noisy" diodes are and how snubbers should be used to quiet the rectifier circuit down (See: http://www.siteswithstyle.com/VoltSecond/K-12M_AMP/K-12M_Push_Pull.html).

Is this something that might be worth pursuing? I reviewed a lot of schematics of the high-end amps of the 60's, and the designers didn't seem concerned about this. I wonder if there's any perceptible benefit to placing caps across diodes (I'm using 1N5408's) or even across the filament connections as described in the reference. I've also seen designs that place a ceramic cap across the HV trans output.

Any thoughts? I don't like to spend time chasing theoretical gremlins, nor would I know how to calculate component values. On the other hand, if it's worthwhile I don't mind adding a few components.

To recap, this is what I'm doing for a modified Mark III build: http://lagunatechnics.com/images/tubeaudio/ewbrown_hybrid_rectifier.gif

As always, responses are appreciated.

Chris