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 Post subject: Voltage issues
PostPosted: Sun Mar 22, 2015 10:44 pm 
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Just finished assembling a Tweed Deluxe amp kit. Turned it it on, no fire or smoke. I proceeded to do the initial voltage check. they don't seem right.

V5 pins 4 & 6, 362vac
pin 2, 5.65 vac
pin 8, 0 vac
V4 pin 2 & 7, 3.21vac
V3 pin 2 & 7, 3.21vac

V2 pin 4-5 & 9 3.21vac
V1 pin 4-5 & 9 3.21vac

Any suggestions?

Thanks,
Eric


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 Post subject: Re: Voltage issues
PostPosted: Mon Mar 23, 2015 2:54 am 
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Those voltages look OK if you are measuring from the pin to ground. The power transformer's 6.3 volt heater supply center tap is connected to ground so that's why you only see 3.2 VAC between each leg of the heater supply and ground.

You should see about 5 volts AC between pins 2 and 8 of V5. You should also see about 6.3 VAC between pins 2 and 7 on V3 and V4. And you should also see about 6.3 VAC between pins 4/5 and 9 on V1 and V2.

It's a good sign that you aren't getting any smoke! Does the amp work? How do the high DC voltages read?


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 Post subject: Re: Voltage issues
PostPosted: Mon Mar 23, 2015 8:19 am 
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Yes, I was measuring from pin to chassis ground. I will move on to the next test points and see how it goes.

Thanks!


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 Post subject: Re: Voltage issues
PostPosted: Mon Mar 23, 2015 6:55 pm 
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Remember you wont get the same DC readings one the layout until the tubes are installed.

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 Post subject: Re: Voltage issues
PostPosted: Tue Mar 24, 2015 11:00 am 
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I tested voltages with all of the tubes in place and a speaker load, of course. No sound from the speaker. Definitely have problems. Suggestions on where to go from here?

V1, 12AY7
Pin 1, 162V
Pin 3, 8.5V
Pin, 4-5-9, 6.1V
Pin 6, 162V
Pin 7, 0
Pin 8, 8.6V

V2, 12AX7
Pin 1, 100V
Pin 3, 1.0V
Pin, 4-5-9, 6.1V
Pin 6, 130V
Pin 7, 12.3V
Pin 8, 32V

V3, 6V6
Pin 2-7, 6.1V
Pin 3, 412V
Pin 4, 183V
Pin 8, 10V

V4, 6V6
Pin 2-7, 6.1V
Pin 3, 413V
Pin 4, 183V
Pin 8, 10V

The rectifier voltages are
Pin 2-8, 416V
Pin 4, 358V
Pin 6, 358V

On the board from left to right the voltages are, layout voltages listed parenthetically.

11.8V (22V)
190V (348V)
150V (255V)
41V (50V)
18V (18V)
109V (204V)
72V (158V)
1.12V (1.4V)
-149V (130V)
-149V (130V)
0V (2.0V)


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 Post subject: Re: Voltage issues
PostPosted: Tue Mar 24, 2015 3:04 pm 
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Your voltages start going funny in the B+ chain after R22 (the 4.7k 2 watt resistor). None of the preamp tubes are getting the proper voltages at their anodes as the result. Check the voltage on both sides of R22. It should be full B+ (around 400 VDC) on one side and about 350 VDC on the other side. Make sure it's soldered in properly. Check for shorts and bad connections in that area and all over the whole amp. Also check that R22 is the proper value.

The voltage to the anodes of V3 and V4 looks OK, but their screen voltage is way too low for them to work properly. Again that's related to the problem around R22 so if you fix that everything should be fine.

Good luck!


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 Post subject: Re: Voltage issues
PostPosted: Tue Mar 24, 2015 3:41 pm 
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Mitch, yep. There is a 47k resistor in that spot, yellow, purple, orange. I was too much of a rookie to catch that when I measured all of the resistors. Not even supposed to be a 47k with the tweed kit. I'll have to see if can get a 4.7k somehow.


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 Post subject: Re: Voltage issues
PostPosted: Tue Mar 24, 2015 5:22 pm 
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Glad I could help. The voltage measurements you provided made finding the problem easy.

Yes, there isn't supposed to be a 47k resistor anywhere in the amp. Sometimes it's not easy telling red from orange on a color band, though. Stephen will send you the proper resistor but it might be faster to get one locally if you have a good electronics supplier in your area. They don't cost much.


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 Post subject: Re: Voltage issues
PostPosted: Tue Mar 24, 2015 5:43 pm 
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I forgot to say, thanks, in my previous post.

Thank you, Mitch!


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 Post subject: Re: Voltage issues
PostPosted: Tue Mar 24, 2015 8:22 pm 
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You can get away with a 1/2W 4K7 resistor if you can't find a 1W or 2W version. 1/2W will be easier to find (if you have a local source) though you do want a resistor with a higher power handling rating in that spot.

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 Post subject: Re: Voltage issues
PostPosted: Fri Mar 27, 2015 8:09 pm 
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I picked up a resistor of the correct value. I get sound now! Pretty decent guitar tone. But, boy does it make noise. When I poke around with a chopstick, the noise seems to mostly come from the instrument input section.

I should add that when I touch the outside of the chassis, I get a slight reduction in hum. But as I stated before, the input section seems to be where it's coming from. The side without an instrument cable plugged in has the most noise. When I switch the cable, the noise comes from the other side of the inputs.

I will check voltages and post later this weekend. And see if I can figure out the grounding issues.


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 Post subject: Re: Voltage issues
PostPosted: Sat Mar 28, 2015 11:07 pm 
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Check your grounding at the input end. Did you install the insulating washers on the input jacks??

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 Post subject: Re: Voltage issues
PostPosted: Sun Mar 29, 2015 8:35 am 
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Stephen, yes the fiber washers are in place. I will be double checking everything in that area today.


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 Post subject: Re: Voltage issues
PostPosted: Wed May 27, 2015 11:02 pm 
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Finally back at it with this amp build.

I checked values and touched up solder joints. It seems that most of the hum this amp has is associated with the bright volume. When I turn the bright volume to 1, and only use the normal volume, 90% of the hum goes away. Sounds good even.

Any more ideas?


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 Post subject: Re: Voltage issues
PostPosted: Thu May 28, 2015 4:22 pm 
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lesgoldy wrote:
Finally back at it with this amp build.

I checked values and touched up solder joints. It seems that most of the hum this amp has is associated with the bright volume. When I turn the bright volume to 1, and only use the normal volume, 90% of the hum goes away. Sounds good even.

Any more ideas?


Can you try a different tube in V1. It could be a bit noisy. Or just swap the two pre amp tubes to see if the noise reduces?

Check soldering on bright channel inputs and connections.

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 Post subject: Re: Voltage issues
PostPosted: Fri Jul 10, 2015 10:38 am 
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I finally got this all sorted out a couple of weeks ago.

I had a bad solder connection on one of the pins on V1. And I had missed the grounding straps on the input jacks. All sorted out now.

Sounds great, but breaks up too much, way too soon. So, I will definitely be trying the volume mod detailed in another thread here.


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 Post subject: Re: Voltage issues
PostPosted: Sat Jul 11, 2015 3:08 pm 
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Suggest you clip the 25uf on the gain stage on V2 or at least make it 2uf

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