Just about done with a new amp using MM iron in a Dumble clone. When I fired it up everything seemed fine until I removed the lightbulb limiter and measured the supply voltage.
The PT measures 340-0-340 but the output after the diodes measures 301VDC.
I disconnected everything except the PT and 2 diodes. Each diode measures 151VDC even with the supply measuring 340VAC. Somehow it's dropping 181V across a single diode
Are you measuring the DC voltage with the standby switch open and no caps connected to the diodes? If this is the case then you will see low readings like youre seeing. Take out all of the tubes. Turn the standby on and see if your voltages are more normal.
UR12 wrote:Are you measuring the DC voltage with the standby switch open and no caps connected to the diodes? If this is the case then you will see low readings like youre seeing. Take out all of the tubes. Turn the standby on and see if your voltages are more normal.
Everything is disconnected except the PT and 2 diodes hanging from the PT secondaries.
I think you need the first filter caps attached to get a good measurement there. (with a ground reference also - if you're doing the "Precision Power" totem poles you'll have your ground ref in the "balancing resistors.")
Wife: How many amps do you need?
Me: Just one more...
mlp-mx6 wrote:I think you need the first filter caps attached to get a good measurement there. (with a ground reference also - if you're doing the "Precision Power" totem poles you'll have your ground ref in the "balancing resistors.")
mlp-mx6 wrote:I think you need the first filter caps attached to get a good measurement there. (with a ground reference also - if you're doing the "Precision Power" totem poles you'll have your ground ref in the "balancing resistors.")
I tried that too. Still the same measurement.
Strike that..... the dummy assembling this amp forgot to ground the filters. I'm now getting 440V, thx mlp-mx6, you got me to look in the right place.
UR12 wrote:Why do you think we knew the answer. Not sure about mx6 but I have been the dummy at least once on that one too.
Notice my Avatar? I flipped my layout drawing (to obtain tubes up orientation) for a Hybrid A without accounting for what that does to the tube pin view. That's been half a year ago and I'm in the middle of making amps for others now. Haven't gotten to fixing my own! I'll wear the Avatar until I get it right!
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Seek immediate medical attention if you suddenly go either deaf or blind.
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UR12 wrote:Why do you think we knew the answer. Not sure about mx6 but I have been the dummy at least once on that one too.
Ohhh, yeah. I ABSOLUTELY earned knowing that answer!
That's one of the things about me that I may never get over - I can figure out (and usually get right) the really complicated things - but the basics, like grounding, ugh.
FYI - you need to ground the bias supply also! Just in case... (grin )
Wife: How many amps do you need?
Me: Just one more...
Heh... I just finished up a D'Lite yesterday and when I fired it up for the first time I wansn't getting any sound and a loud hum... turns out that I forgot to wire the input jack to v1A's grid... that was a dunce moment...
Since I'm over 50 I can call it a senior moment. I'm having them frequently these days. Friday at a gig I forgot one of the changes in a I-IV-V progression
