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Old 21st August 2008, 03:21 PM   #31
zcables is offline zcables  United States
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Sorry for one last question,
The "270K bleeder resistors on filter caps" in the original post, where are they soldered in? If they are discharging the caps when the amp is off (which is the purpose of a bleeder I believe), I would assume that the resistor would be soldered between one of the lead of the cap and a ground maybe? Thanks for the help again.
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Old 21st August 2008, 05:37 PM   #32
gofar99 is offline gofar99  United States
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Hi, You are correct. It doesn't have to be physically right at the cap, but it is good practice to place it there. It is put there to bleed off the charge on the caps when the power is removed. Without it, large caps (like the ones you are using) will store a potentially deadly charge for quite some time. Depending on where in the circuit you place it, there can still be a delay of several minutes before the charge on all the caps is drained to a safe level. Always assume a cap is charged. If there is any doubt, use a meter on it.

I try to warn everyone not to treat high voltages casually, please ask about any problems, concerns or just for information. Don't assume anything about tube circuits. I don't know of any diyers that would feel offended to answer such questions.
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Old 21st August 2008, 08:20 PM   #33
zcables is offline zcables  United States
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Do the bleeder resistors provide anything to the audio aspect as well, or are they just there to drain the caps when power is removed? I heard that they can provide some regulation to the power moving through the caps, but I might be way off.
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Old 21st August 2008, 08:32 PM   #34
gofar99 is offline gofar99  United States
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Hi, Generally, they will not have such an effect. It is possible that if the circuitry used very little current that the bleeders might act as a partial load. This is rather unlikely in a power amp though. The amp will draw many milliamperes of current and the bleeder only 1 or 2 typically. In a preamplifier circuit with very low drain tubes it would have to be considered in calculating the resistors between the power supply filters as it would have some effect on the voltage drop from section to section. For example, I have one stage in a current project that draws only 1.2ma. Because of the geometry of the stage, if the bleeder were attached at the final filter cap it would drop the voltage available to the tube by a significant amount if not included as a load on that section of the power supply filters.
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Old 21st August 2008, 08:45 PM   #35
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Hi Jake,

in some power supplies with high HT voltages, people use capacitor with lower voltage rating in series, since they are cheaper and easier to source. In that case there are two "bleeder" resistors - one parallel to each cap. The main function of those is to make sure that each cap gets exactly 1/2 HT voltage. This is important because each single cap is not able to handle the full voltage.
They also serve as bleeder resistor when the amp is turned off.
There is no real audio function besides keeping the caps happy and therefore the power supply working and ultimately the amp running.
If you have single caps in the power supply the bleeder resistor is really only for your safety in there - and it should be there. Those caps are just waiting for this one second of sloppiness

I'd connect them parallel to the cap right at the same spot. The resistor lead is also a good spot to attach a probe to measure voltages since the cap leads are often very short.

Martin

edit: I see that gofar99 answered simultaniously
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Old 23rd August 2008, 09:12 PM   #36
zcables is offline zcables  United States
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Are the filaments heated by AC or DC?
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Old 24th August 2008, 03:24 AM   #37
gofar99 is offline gofar99  United States
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Hi, At the present time I'm on a DC heater kick. All the projects for the last year or so have DC. The one exception is the K-12 mods. I stuck with AC there. It could be done rather easily though, I just didn't think it would be worth the effort. The quickest and easiest way would be to use a 12 Volt SMPS. They run about $18 from several sources. I would want to (if possible)scope the output for switching noise. If not possible, a simple pair of RF chokes and a few small caps would be in order to be sure the was no trash getting into the amp. I have used similar supplies and find them trouble free. The biggest problem doing this with a K (other than a K-12) amp is rewiring the heaters for 12 Volts. The reason for 12 and not 6 is that 6 volt SMPS are scarce and more costly.
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Old 24th August 2008, 04:17 PM   #38
zcables is offline zcables  United States
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Here is my K-16LS. The wiring is a little crazy since this was my first amp build, but everything work well and I'll be even better once I get a few of those mods on it.
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Old 24th August 2008, 04:18 PM   #39
zcables is offline zcables  United States
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Here is the front with the cover on.
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Old 24th August 2008, 06:30 PM   #40
gofar99 is offline gofar99  United States
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Hi, It looks pretty good to me. It is rather difficult to get the wires to transformers and jacks to look neat. I sometimes use small nylon wire ties to bundle some together. Don't bundle input and AC wires with anything though. It will cause noise and hum pickup. Nice woodwork, what is the top made of?
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