Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Toxophilite on January 16, 2014, 02:14:42 am
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On my 5F11 Vibrolux build, (the messy point to point one in the small chassis)
I get some high B+ voltages
It's built to the schematic and it has the proper tube compliment for the build all plugged in
THe only changes are a baxandall tone stack and a classic fender 2 input rather than the 3 on the original
At pin 8 of the rectifier I have about 382
at the next cap(after the 470 ohm resistor) I have 380
and on the screens and the plates of the 6V6s 380
the next little node after the 220k resistor and cap I have 299
On my phase inverter I have 247 and 208
and on my preamp 1/2 12AX7 I have - 195
and the tremelo half has - a vacillating voltage around 170 to 235
THese are all around 30-50 over what they should be for the schematic
The amp works well, really quite loud
The tremelo dworks well too
I'm just curious if it could be a problem and what should I do to rectify it?
Just for fun I tried my SS rectifier in there and the B+ at the plates jumped to around 405-407..just like my AB763lite build
This unit has a Hammond transformer that I have the specs for
It's supposed to have 310 on the secondaries but actually reads about 335
This is because of the change in wall current right?
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It might be the "wrong" Hammond transformer for this amp .
Or bias is too cold .
Wall outlet ? Just read it . you'll know.
Did you know , If, for same amp you buy 2 differents transformers . One with 310 volts at 70 ma and the other one 310 volts at 120 ma .
You'll have more B+ voltage with the last one.
Secondary voltage is accurate if you use the proper load ( ma )
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the next little node after the 220k resistor
You really mean 22K, right?
I'm just curious if it could be a problem and what should I do to rectify it?
Those voltages look fine. Using a NOS 5Y3 will drop the B+ some, unless you are already using a NOS 5Y3.
This is because of the change in wall current right?
Yes. Today's line voltage is about 10 to 12% higher than back in the 1950s. Your B+ is about 12% higher than the old schematic shows.
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the next little node after the 220k resistor
You really mean 22K, right?
I'm just curious if it could be a problem and what should I do to rectify it?
Those voltages look fine. Using a NOS 5Y3 will drop the B+ some, unless you are already using a NOS 5Y3.
This is because of the change in wall current right?
Yes. Today's line voltage is about 10 to 12% higher than back in the 1950s. Your B+ is about 12% higher than the old schematic shows.
I understand a new built use a new Hammond PT , Today Hammond PT use today's line voltage . No need to ad 10-15%
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Ooops
Yes , you're right
I mean 22K resistor and the Hammond transformers are probably about 60 years old
The PT is a Hammond 272Z60 rated 310-310 secondary volts 70ma
I'm using an old RCA 5Y3
Thanks! I won't worry about it then
All is well
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Ooops
Yes , you're right
I mean 22K resistor and the Hammond transformers are probably about 60 years old
The PT is a Hammond 272Z60 rated 310-310 secondary volts 70ma
I'm using an old RCA 5Y3
Thanks! I won't worry about it then
All is well
Old hammond are made for 110 Vac primary , today with 120 and sometimes more secondary are higher.
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The PT is a Hammond 272Z60 rated 310-310 secondary volts 70ma
I'm using an old RCA 5Y3
If you look again at that catalog download, you'll see the chart with the 272Z60 has a heading that says the primary is 115v.
It's supposed to have 310 on the secondaries but actually reads about 335
335v-310v = 25v -> 25v/310v = ~8%
124v-115v = 9v -> 9v / 115v = ~7.8%
I'm guessing your wall voltage is between 124-125vac.
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Bonus!
Too bad I don't pay for it here or I'd think I was getting a deal!