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 Post subject: Silvertone 69A Console Watts
PostPosted: Aug Thu 06, 2020 2:57 pm 
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Joined: Apr Wed 13, 2016 1:58 pm
Posts: 347
Location: Bartlett, TN
First off, does anyone have the SAMS that they are willing to share for this? All I can find is the power amp.

Second, the output sounds weak to me but everything checks out circuit-wise. I have a home made watt meter that is showing only 5w prior to clipping but now I think that may be in error. See if I am doing this math correct.

I have 315VAC RMS on the 6V6 plates just prior to breakup and about 9v on the output transformer secondary with 8 ohm speaker.
315/9= 35/1 output transformer with 9800 load resistance.
9v*9v/8 ohms = 10w RMS. All readings taken with a Fluke 87V True RMS meter.

Is my watt meter wrong? Seems like it..and also likely nothing wrong with the pre and power amp.

Regardless, the output on the phonograph is way too low to be usable but that may be a cartridge issue.


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 Post subject: Re: Silvertone 69A Console Watts
PostPosted: Aug Thu 06, 2020 3:55 pm 
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Joined: Apr Wed 13, 2016 1:58 pm
Posts: 347
Location: Bartlett, TN
Nevermind on the SAMS. I found what I needed there.


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 Post subject: Re: Silvertone 69A Console Watts
PostPosted: Aug Thu 06, 2020 6:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4471
Location: Boston, MA USA
What is the frequency response of the Fluke meter and your home-made power meter? Many are limited to 60 Hz whereas you are most likely using 1 kHz for your measurements. To be sure use a VTVM, most or all of which are good for several MHz. Even better is an oscilloscope because you can then have a clearer view of when distortion sets in. Vacuum tube amplifiers don't go into hard clipping but rather smoothly compress the waveform one they get out of the linear region.

-David


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 Post subject: Re: Silvertone 69A Console Watts
PostPosted: Aug Thu 06, 2020 7:08 pm 
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Joined: Apr Wed 13, 2016 1:58 pm
Posts: 347
Location: Bartlett, TN
Good question and I am not sure. I'd imagine the fluke is pretty good but will check. I was using a scope to determine the onset of clipping and it was showing about a 13v ptp signal. My watt meter is an old RF Motorola 50uA 0-120 watts movement calibrated down to read speaker wattage. It likely isn't real accurate but I would think it could get within a few watts of actual.
Update: The fluke 87V goes up to 20KHz with varying degrees of accuracy as it climbs not exceeding 2%


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 Post subject: Re: Silvertone 69A Console Watts
PostPosted: Aug Fri 07, 2020 1:23 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4471
Location: Boston, MA USA
It makes no sense that the Fluke was reading 9 VRMS while the oscilloscope was reading 13 VPP. Is your signal a sine wave or are you trying to play music? It must be a sine wave to make power measurements.

-David


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 Post subject: Re: Silvertone 69A Console Watts
PostPosted: Aug Fri 07, 2020 3:07 am 
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Joined: Apr Wed 13, 2016 1:58 pm
Posts: 347
Location: Bartlett, TN
Its a sine wave. My scope needs calibrating so I am not inclined to trust it for voltage measurements. I see now that 9 VRMS should convert to around 25 VPP. That is a bit closer to what my second scope channel reads but I don't trust either and just use my Fluke.


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 Post subject: Re: Silvertone 69A Console Watts
PostPosted: Aug Fri 07, 2020 5:43 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4471
Location: Boston, MA USA
What kind of amplifier are we talking about? Push-pull 6V6s or single-ended? What is the B+ voltage at the output transformer?

-David


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 Post subject: Re: Silvertone 69A Console Watts
PostPosted: Aug Fri 07, 2020 12:58 pm 
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Joined: Apr Wed 13, 2016 1:58 pm
Posts: 347
Location: Bartlett, TN
PP 6V6GT, 290V


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