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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 7:48 pm 
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Maybe you hit the wrong switch. 3position switch ... ch1, both, ch2
Center position allows both.

Or trigger
I think you need trigger on chop

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 8:39 pm 
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Pbpix wrote:
Maybe you hit the wrong switch. 3position switch ... ch1, both, ch2
Center position allows both.

Or trigger
I think you need trigger on chop



Will check it out shortly. I did not change the trigger switch, but will check.
I will call tonight, could use some scope instruction.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 9:49 pm 
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john8750 wrote:
Pbpix wrote:
Maybe you hit the wrong switch. 3position switch ... ch1, both, ch2
Center position allows both.

Or trigger
I think you need trigger on chop



Will check it out shortly. I did not change the trigger switch, but will check.
I will call tonight, could use some scope instruction.


Correction:
Vertical Mode switch:
Add, Alt, Chop = Chop

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 04, 2018 11:33 pm 
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Peter- The instruction book says the same thing 'alt-chop' on chop. I don't see those selections though.
Check out the front of my scope. Notice the dual trace is working again.
Attachment:
20180304_125152.jpg
20180304_125152.jpg [ 109.61 KiB | Viewed 529 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 05, 2018 12:19 am 
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john8750 wrote:
Peter- The instruction book says the same thing 'alt-chop' on chop. I don't see those selections though.
Check out the front of my scope. Notice the dual trace is working again.
Attachment:
20180304_125152.jpg

How can I ? ...Your photo does not show the whole front.

But the mode = dual
So maybe that's it .... but still should be a add-alt-chop setting =chop

Anyway... let's see both the input and the output of op275 signals.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 05, 2018 12:49 am 
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Pbpix wrote:
john8750 wrote:
Peter- The instruction book says the same thing 'alt-chop' on chop. I don't see those selections though.
Check out the front of my scope. Notice the dual trace is working again.
Attachment:
The attachment 20180304_125152.jpg is no longer available

How can I ? ...Your photo does not show the whole front.

But the mode = dual
So maybe that's it .... but still should be a add-alt-chop setting =chop

Anyway... let's see both the input and the output of op275 signals.



You can see the mode switch. It has no such selections.
Here is the whole front panel.
Attachment:
20180304_134212.jpg
20180304_134212.jpg [ 121.31 KiB | Viewed 525 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 05, 2018 12:51 am 
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john8750 wrote:
Pbpix wrote:
john8750 wrote:
Peter- The instruction book says the same thing 'alt-chop' on chop. I don't see those selections though.
Check out the front of my scope. Notice the dual trace is working again.
Attachment:
20180304_125152.jpg

How can I ? ...Your photo does not show the whole front.

But the mode = dual
So maybe that's it .... but still should be a add-alt-chop setting =chop

Anyway... let's see both the input and the output of op275 signals.



You can see the mode switch. It has no such selections.
Here is the whole front panel.
Attachment:
20180304_134212.jpg
It probably auto-selects based on the sweep speed.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 05, 2018 12:52 am 
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I would still like to have a switchable scratch/pop filter for LP vinyl. Here is an idea to play with.
http://www.muzines.co.uk/articles/vero- ... ilter/2630

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 05, 2018 12:55 am 
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I think your correct Flip. My instruction book has several different models covered. Although it shows the alt/chop selections, could have been a mix-up with a different model.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 05, 2018 12:59 am 
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Before you move on to other circuits like pop scratch filter ...Will you show the 2 scope traces of op275 input and output?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 05, 2018 1:16 am 
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Pbpix wrote:
Before you move on to other circuits like pop scratch filter ...Will you show the 2 scope traces of op275 input and output?



Of course I will Peter. Will need to set it back up, but need the practice....

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 05, 2018 1:44 am 
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Her it is Peter, at 1khz
Attachment:
20180304_162911.jpg
20180304_162911.jpg [ 121.11 KiB | Viewed 521 times ]

But volume turned high, clipping in the opamp section. At 2khz
Attachment:
20180304_163135.jpg
20180304_163135.jpg [ 101.57 KiB | Viewed 521 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 05, 2018 3:34 am 
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Looking clean now... good.

Yes you should get approx 37v pp just before clipping
Is that what you get?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Mon 05, 2018 4:24 am 
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Pbpix wrote:
Looking clean now... good.

Yes you should get approx 37v pp just before clipping
Is that what you get?



Not sure Peter. I believe it was set for 5v/div. At that volume, with the speakers turned on, the sound would be way to high. The tone amp has a big level boost.
Don't know what I could do to improve it more. Sounds very good now.
The new turn table works ok. Wont pass as hi-fi, but not bad. Good for testing.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 10, 2018 2:36 am 
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Just rapping her up I have two considerations. One problem is I still think a small distortion is there. I'm looking for other possible interfering situations. The speaker output conductors parallel the ac input circuits in the rear. So I will re-route them. I can also re-locate the actual star common point to the second filter capacitor.
The other problem is the 470ohm resistor in the 13volt supply circuit is getting hotter than it should. Would it be better to add some resistance feeding the circuit, or reduce the 2.2uf cap?
Attachment:
13v supply.png
13v supply.png [ 27.41 KiB | Viewed 479 times ]


Ready to install the lettering. I added a simple circuit, switchable, to treat record pop. Of course, it also attenuates the high notes slightly.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 10, 2018 5:28 am 
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john8750 wrote:
Just rapping her up I have two considerations. One problem is I still think a small distortion is there. I'm looking for other possible interfering situations. The speaker output conductors parallel the ac input circuits in the rear. So I will re-route them. I can also re-locate the actual star common point to the second filter capacitor.
The other problem is the 470ohm resistor in the 13volt supply circuit is getting hotter than it should. Would it be better to add some resistance feeding the circuit, or reduce the 2.2uf cap?
Attachment:
13v supply.png


Ready to install the lettering. I added a simple circuit, switchable, to treat record pop. Of course, it also attenuates the high notes slightly.

Go back to the measurements for the 13v sipply... I think you had more than 45ma going through that resistor
If it were me I'd adjustable the cap for about 40ma only. But go back and show the actual curent you measured... I forgot.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 10, 2018 6:32 am 
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john8750 wrote:
Just rapping her up I have two considerations. One problem is I still think a small distortion is there. I'm looking for other possible interfering situations. The speaker output conductors parallel the ac input circuits in the rear. So I will re-route them. I can also re-locate the actual star common point to the second filter capacitor.
The other problem is the 470ohm resistor in the 13volt supply circuit is getting hotter than it should. Would it be better to add some resistance feeding the circuit, or reduce the 2.2uf cap?
Attachment:
13v supply.png


Ready to install the lettering. I added a simple circuit, switchable, to treat record pop. Of course, it also attenuates the high notes slightly.
The changes you mention are all good.

How hot 'should' the 5 Watt 470 ohm resistor get?


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sat 10, 2018 9:23 am 
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Here's the measurements you took that I was asking for:
If you are dropping 25.6v across 470 ohm then you are putting 54ma through that 470 resistor.
25v x 54ma = 1.4 watts dissipated .... so triple that = 4.2 watt resistor ... 5 watts is closest.
A 5 watt resistor should be able to handle 1.4 watts of heat.
If you feel that's too hot for your liking (1st double check your readings) .... and if the numbers are correct; ... then you can choose to reduce the dropper cap until you get only either 45ma or 40ma.
Then you will be generating only either 0.95watts of heat or 0.75 watts of heat.

Image

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 11, 2018 2:35 am 
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Just checked it again. I have a 25.7volt drop through the 470ohm resistor. 54ma X25.7volts=1.38watts X3=4.14watt resistor.
I have a 5watt resistor there. Or, is it a four watt..... I will replace it with a 10watt sand type. Plenty of room. Then can find a way to cut it down to 40ma.
Flip- that resistor is so hot I can feel the heat without touching it, about 1/2 inch away.
Ya know- I could install a cooling tower, plumb in some liquid cooling :lol:

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Mar Sun 11, 2018 3:08 am 
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john8750 wrote:
Just checked it again. I have a 25.7volt drop through the 470ohm resistor. 54ma X25.7volts=1.38watts X3=4.14watt resistor.
I have a 5watt resistor there. Or, is it a four watt..... I will replace it with a 10watt sand type. Plenty of room. Then can find a way to cut it down to 40ma.
Flip- that resistor is so hot I can feel the heat without touching it, about 1/2 inch away.
Ya know- I could install a cooling tower, plumb in some liquid cooling :lol:
I don't know what wattage resistor you have in there but resistors get hot. A 5 Watt resistor will rise about 50 C above ambient at the loading you've got (28%) and at 25 C (which would be low for the insides) that's 75 C or 167 F (significantly over the temp for 'hot water'). If it's a 4 Watt resistor it'll be higher.

I wouldn't be surprised at all if your ambient inside the case was 50 C, which would make the resistor temp 212 F, hot enough to boil water.


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