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 Post subject: Re: A new 300B amp project
PostPosted: Dec Mon 25, 2017 5:46 am 
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Pbpix wrote:
john8750 wrote:
The 300b will sit on a display case, custom made, in the den. Above it will sit the turntable and preamp. Imagonna build a new set of speakers just for that amp. Need to be more sensitive. But that's a different topic.
I finished tuning the Little Prince. Now am working on finding a very slight hum in the right channel in the Prince John.
I can see a little wave at the power tubes, maybe from the FB circuit, only in the right channel. Don't know much about the scope, but can get a comparison between channels. This hum is so slight, only heard with headphones.

FB? FaceBook? :?:



I disconnected both facebook circuits. Got the same scope reading on both channels. Reconnected them, now both channels are the same, no hum. I figure it was an inner oscillation in the right channel. But why did it stop. Probably my uncertified
sloppy soldering. :roll: I will reheat all solder joints.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Mon 25, 2017 6:02 am 
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john8750 wrote:
Pbpix wrote:
john8750 wrote:
The 300b will sit on a display case, custom made, in the den. Above it will sit the turntable and preamp. Imagonna build a new set of speakers just for that amp. Need to be more sensitive. But that's a different topic.
I finished tuning the Little Prince. Now am working on finding a very slight hum in the right channel in the Prince John.
I can see a little wave at the power tubes, maybe from the FB circuit, only in the right channel. Don't know much about the scope, but can get a comparison between channels. This hum is so slight, only heard with headphones.

FB? FaceBook? :?:
I disconnected both facebook circuits. Got the same scope reading on both channels. Reconnected them, now both channels are the same, no hum. I figure it was an inner oscillation in the right channel. But why did it stop. Probably my uncertified
sloppy soldering. :roll: I will reheat all solder joints.
The symptoms are all wrong for it to be an 'oscillation' of the circuit. Odds are you were simply seeing the hum waveform, where ever it comes from, but I can't tell because you didn't provide any clues are to where you were looking "at the power tubes."

Disconnecting the FB (FEEDBACK, Pbpix) circuit might have been the loose connection or a coincidence that doing so 'disturbed' the loose connection, where ever it was. Wise idea to recheck all solder joints.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Mon 25, 2017 7:46 am 
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Understand Flip. The scope trace showed a sine wave. Very uneven and pulsating, not hash. The left channel was a flat line. I checked the grid of both power tubes for the right channel, both showed the interference. Pin1 on the inverter tube had the interference, but not pin9. Pin8 had it also. My VOM would not show any difference. But, I don't much about using the scope yet. And the noise is gone now. I will make a final check of the solder joints, then move both units back inside the house for testing.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Mon 25, 2017 8:00 am 
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I charted the problem areas. Just trying to figure where the problem was.
Attachment:
interf.jpg
interf.jpg [ 150.24 KiB | Viewed 453 times ]

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Mon 25, 2017 10:22 pm 
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Flipperhome wrote:

Disconnecting the FB (FEEDBACK, Pbpix)

Thnks ... lol .... I didn't have a clue and w/o the schematic in front of me ... I was lost...
Guess I'm getting C.A. = "circuit-Alzheimers"

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 26, 2017 1:26 am 
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Pbpix wrote:
Flipperhome wrote:

Disconnecting the FB (FEEDBACK, Pbpix)

Thnks ... lol .... I didn't have a clue and w/o the schematic in front of me ... I was lost...
Guess I'm getting C.A. = "circuit-Alzheimers"



No way Peter.
Both amps are good ta go now. Flip, you are right, absolutely quiet, no hum.
Thanks guys. Without the scope, I couldn't find the noise.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 26, 2017 2:50 am 
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john8750 wrote:
...Both amps are good ta go now. Flip, you are right, absolutely quiet, no hum.
Thanks guys. Without the scope, I couldn't find the noise.
Super. Glad to hear it, or not hear it, as the case may be :wink:


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 26, 2017 6:35 am 
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Flipperhome wrote:
john8750 wrote:
...Both amps are good ta go now. Flip, you are right, absolutely quiet, no hum.
Thanks guys. Without the scope, I couldn't find the noise.
Super. Glad to hear it, or not hear it, as the case may be :wink:



Super quiet and sounds great. I'm impressed. Thanks Flip. I connected the Little Prince to The 300b tonight. It would not push the bass, but it was there. The mids and highs seemed very sharp. A pleasant difference of a sound. Which do I like better? Guess that depends on the mood and type music. Classic will sound best on this amp. I am gonna place it in my den-listening room with some better speakers. Then I will report how I like it.
Can you suggest a good 10-12" full range speaker, sensitivity in the 90's-? Could have two 6"-4ohm.
Its almost time to start the new 6V6 thread. I have all the parts.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 26, 2017 6:48 am 
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When you do, plse post a link to t hat new 6v6 thread

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 26, 2017 7:39 am 
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john8750 wrote:
Flipperhome wrote:
john8750 wrote:
...Both amps are good ta go now. Flip, you are right, absolutely quiet, no hum.
Thanks guys. Without the scope, I couldn't find the noise.
Super. Glad to hear it, or not hear it, as the case may be :wink:

Super quiet and sounds great. I'm impressed. Thanks Flip. I connected the Little Prince to The 300b tonight. It would not push the bass, but it was there. The mids and highs seemed very sharp. A pleasant difference of a sound. Which do I like better? Guess that depends on the mood and type music. Classic will sound best on this amp. I am gonna place it in my den-listening room with some better speakers. Then I will report how I like it.
Can you suggest a good 10-12" full range speaker, sensitivity in the 90's-? Could have two 6"-4ohm.
Its almost time to start the new 6V6 thread. I have all the parts.
I don't know of any speakers like that but I'll keep an eye out.

I don't understand why it would not "push the bass" unless it has to do with speaker characteristics. You need to do a frequency sweep to find out what the frequency response really is.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 26, 2017 7:49 am 
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Pbpix wrote:
When you do, plse post a link to t hat new 6v6 thread



I sure will Peter. Its coming right up.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 26, 2017 7:59 am 
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I will do that Flip. My speakers have great bass response, advertised down to 19hz. Prince John, plenty of bass, floor pounding if I want to. Blumoon, the bass is there but just hanging around. It must not be capable of amplifying the bass like the Prince John. Or should it? I will test a few low frequencies.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 26, 2017 8:24 pm 
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john8750 wrote:
I will do that Flip. My speakers have great bass response, advertised down to 19hz. Prince John, plenty of bass, floor pounding if I want to. Blumoon, the bass is there but just hanging around. It must not be capable of amplifying the bass like the Prince John. Or should it? I will test a few low frequencies.
Yes, I know they're 'advertised' down to 19 Hz but +- how many dBs? But, assuming you tried the same speaker on both, that doesn't explain the difference in response between the two amps.

The 300B should 'amplify' the bass too but it has a rather poor damping factor with no feedback to compensate for varying speaker impedance and I suspect that's what the difference is.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Wed 27, 2017 3:31 am 
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Flipperhome wrote:
john8750 wrote:
I will do that Flip. My speakers have great bass response, advertised down to 19hz. Prince John, plenty of bass, floor pounding if I want to. Blumoon, the bass is there but just hanging around. It must not be capable of amplifying the bass like the Prince John. Or should it? I will test a few low frequencies.
Yes, I know they're 'advertised' down to 19 Hz but +- how many dBs? But, assuming you tried the same speaker on both, that doesn't explain the difference in response between the two amps.

The 300B should 'amplify' the bass too but it has a rather poor damping factor with no feedback to compensate for varying speaker impedance and I suspect that's what the difference is.



Agree. The only comparison I can make is with the same music and source, same preamp, and same speakers.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Thu 28, 2017 11:03 pm 
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All I got for Christmas was a case of the flu. :( Just feeling better today. But my little muscles are week.
since I have the scope set up, thought I would do some frequency and power tests on the amps.
Then I will start the new 6V6. Will come back for updates on the Blumoon.
Stay tuned.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 29, 2017 2:08 am 
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I hooked up the Prince John to the scope. Input 1 to input, and speaker output to input 2.
Connected sig gen at 70hz. Brought trace 1&2 together. Went down to 20hz, was digital. Went up
about 50hz at a time to 11khz. Above my hearing, but both traces stayed together.
How did they stay matched? I thought the amplitude would be amplified in trace 2. is there a trigger
selection for that. I have much to learn about that.
The speakers were connected.
Then I disconnected one speaker, installed an 8ohm 5watt resistor on the speaker terms.
Fed in a 170hz signal, full volume, connected voltmeter and read 11.0vac.
That figured to 1.375amps X 11volts = 15.125watt. Is that correct?

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 29, 2017 2:14 am 
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When you measure 11v on the 8 ohm dummy load, you should also have your scope probe looking at that 11vAC signal to be sure there is no flat-topping or other distortion.
You can increase the input signal until just before the output starts to distort.
Then measure that AC rms.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 29, 2017 3:23 am 
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Pbpix wrote:
When you measure 11v on the 8 ohm dummy load, you should also have your scope probe looking at that 11vAC signal to be sure there is no flat-topping or other distortion.
You can increase the input signal until just before the output starts to distort.
Then measure that AC rms.



Thanks peter
I thought I was forgetting something, and remember you saying that. I will do it tomorrow. I need to be quick because the resistor get hot real fast.
Peter, why did the two traces stay together? Was it in the trigger?
Is 170hz good for the test, or what would be better?

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 29, 2017 5:27 am 
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john8750 wrote:
Pbpix wrote:
When you measure 11v on the 8 ohm dummy load, you should also have your scope probe looking at that 11vAC signal to be sure there is no flat-topping or other distortion.
You can increase the input signal until just before the output starts to distort.
Then measure that AC rms.



Thanks peter
I thought I was forgetting something, and remember you saying that. I will do it tomorrow. I need to be quick because the resistor get hot real fast.
Peter, why did the two traces stay together? Was it in the trigger?
Is 170hz good for the test, or what would be better?

400hz is a typical freq used to measure output transformers.

"Together" meaning shape?
or voltage?
... the same value or what?
You'll need to be very specific or it's hard to understand what you are referring to exactly.

I don't know exactly what your two traces were really looking at .
... cause there should be a difference in signal level from input to output... so not sure what you were really looking at.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 29, 2017 7:42 am 
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Pbpix wrote:
john8750 wrote:
Pbpix wrote:
When you measure 11v on the 8 ohm dummy load, you should also have your scope probe looking at that 11vAC signal to be sure there is no flat-topping or other distortion.
You can increase the input signal until just before the output starts to distort.
Then measure that AC rms.



Thanks peter
I thought I was forgetting something, and remember you saying that. I will do it tomorrow. I need to be quick because the resistor get hot real fast.
Peter, why did the two traces stay together? Was it in the trigger?
Is 170hz good for the test, or what would be better?

400hz is a typical freq used to measure output transformers.

"Together" meaning shape?
or voltage?
... the same value or what?
You'll need to be very specific or it's hard to understand what you are referring to exactly.

I don't know exactly what your two traces were really looking at .
... cause there should be a difference in signal level from input to output... so not sure what you were really looking at.



I think I understand now.
The shape of the waveform from the input through the amp should match the output. I adjusted the output trace amplitude and overlaid the input trace. Increasing frequency does not increase volume.
If that is true, then the prince John is flat up to at least 11khz. Above my hearing.
Thanks Peter. I want to be accurate.

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