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 Post subject: UTC W-10 amplifier help.
PostPosted: Apr Sun 01, 2018 3:28 am 
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Joined: Apr Sat 18, 2015 3:01 am
Posts: 119
Location: Lexington KY
Been trying to get a UTC W-10 up and going.
Replaced the caps and have been checking the usual suspects.
It has two test points to check the cathode currents. 55ma each.
What happens is this when it first powers up it looks pretty good.
After about 5 minuets the currents creep up to say 70 ma.
This is due to power supply B+ voltage creeping up.
Here's the circuit http://bit.ly/2H1UjwG
Tubes test OK.
Anyone know what B1 and B2 voltages should be?
Perhaps loading resistor????

Suggestions...........


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 Post subject: Re: UTC W-10 amplifier help.
PostPosted: Apr Sun 01, 2018 4:20 am 
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Joined: Feb Sat 12, 2011 2:29 pm
Posts: 538
Location: Fayette County, Pa
Have you replaced C9-C10-C11? If this is an older amplifier, pre 1970s, that would be a start. Next consider the coupling caps, C5 - C6 as possibly leaky, although the additional plate current that scenario would set up would likely pull the B+ down, not up. Same with a gassy output tube. start with filters the go from there.

Also consider a weak rectifier tube. Low B+ when you start out might drift up to normal as the tube heats. This would cause the output tube current to increase above normal. Can you adjust it back to normal after it drifts high? If so consider the rectifier.


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 Post subject: Re: UTC W-10 amplifier help.
PostPosted: Apr Tue 03, 2018 2:26 am 
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I hate it that you have to sign in to see things on that site. :evil:

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I like things that light up, tubes, bulbs, LEDs, whatever, and things that make noise.


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 Post subject: Re: UTC W-10 amplifier help.
PostPosted: Apr Tue 03, 2018 2:09 pm 
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Joined: Jul Fri 18, 2008 10:02 am
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Location: near ST Louis Mo 62002
The B+ should be about 425 volts .

Are the cathode resistors wire wound or carbon , if they are carbon they may be changing ohmage as they warm up , clean the balance pot . If the amp is homemade make sure the balance and cathode resistors are high enough wattage .


http://www.bunkerofdoom.com/xfm/UTC_1960_WEB/021.jpg

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Last edited by battradio@ on Apr Sun 08, 2018 2:44 am, edited 1 time in total.

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 Post subject: Re: UTC W-10 amplifier help.
PostPosted: Apr Thu 05, 2018 5:11 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1474
Location: Cambridge MN USA
Does the power transformer have the voltages listed on it? Your B+ at the first filter cap should be half the HV winding x 1.414 (sq rt 2) minus the rectifier drop, or about 35-40v for a 5U4. If the voltages aren’t listed, I may have a brochure that has it.

Scott Todd


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 Post subject: Re: UTC W-10 amplifier help.
PostPosted: Apr Sun 08, 2018 2:36 am 
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Joined: Jul Fri 18, 2008 10:02 am
Posts: 2104
Location: near ST Louis Mo 62002
These should be better

Image
Image


R113 power transformer . 400-0-400 volts , 200 ma B+ ,

B1 should be about 360 volts and B2 about 318 volts

http://www.bunkerofdoom.com/xfm/UTC_1955_WEB/030.jpg

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