HF-86 clone update.

Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

Still haven't gotten rid of that very pesky hum. I have to say this amp is doing some strange things. They all seem to be stemming from the power supply. Now I'm talking hum big time I did try grounding th e input just to test, the hum was still there.
Measuring all the voltages at the power supply output caps (all oil cans), the voltages are about 100 volts down from spec. Voltage from the power tranny is is about 10-15 volts below spec. But I dont know how that coud bring everything else down by 100v. That is really mystifying me. The caps and resistors are all the correct values, the power readings just way off. What the...?
So back to the hum. I thought that since I've tried just about everything else by now, that I would add more capacitance. Viola, I had extra oil caps laying around and doubled each stage on the dc output.
Adding a cap at each stage reduced the hum little by little, but still not gone. ...seemed too extreme and still didn't eradicate the noise.
I've seen builders put together some rather extreme power supplies with tons of caps. I like the oils in the power supply, but are such extremes necessary to get things listenably quiet?
Maybe the umbilicals are the problem? To long (they are a couple of feet)? Not properly shielded?
It's an interesting experiment, but doesn't solve the problem. With the voltage anomolies and having to go to such extremes to get the hum down, something is wrong. But maybe these observations will help get at the problem.
Could it be that the oil caps, making the amp sound as good as they do, just don't filter out the noise as effectively as electrolytics? I thought the oil caps were going to be a big upgrade, and they did necesitate an outboard power supply, but is there a tradeoff? Sounds better, but now I have more problems with noise.
Something I read about chokes being better than caps for this.
I also tried refining the grounding in the power supply. Since it has a wood chassis, I ran a strip of copper starting on one end with the earth ground, the star grounding the rest further upstream. It didn't help.
Anyway that's were I am. Anyone got any ideas. I'm thinking about trying the stock electrolytics called for in the original plans.
I've never heard a stock HF-86, but the stock configuration couldn't have all these issues.
Seems to me that -noise- is the biggest challenge in building an amp.
I always seem to get myself into trouble trying to do something "different." :)
Time to hit the sack.
-Charles

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Topic - HF-86 clone update. - wolfy 00:02:45 08/20/06 (9)

PING WOLFY - MIchael Samra 22:23:25 08/20/06 (0)

Re: HF-86 clone update. - Jimmy 17:39:54 08/20/06 (0)

Sounds like those oil caps are bad - Russ57 12:02:47 08/20/06 (1)

Re: Sounds like those oil caps are bad - wolfy 19:26:45 08/20/06 (0)

Re: HF-86 clone update. - elflow 07:10:14 08/20/06 (0)

Need more Info......... - Jimmy 07:04:31 08/20/06 (3)

Re: Need more Info........./power supply wiring - wolfy 08:36:36 08/20/06 (0)

PS schematic - Jimmy 07:17:34 08/20/06 (1)

HF-86 schematic - wolfy 08:58:38 08/20/06 (0)

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