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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 05, 2017 9:57 pm 
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john8750 wrote:
Thank you Men. I am getting the picture here.
I noticed that some guys test this amp firstly with a lower AC supply, say 24volts.
Then measure for voltages of 20%. Is this a good thing to do?

or 1.2vAC and test for 1% :mrgreen:

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Wed 06, 2017 1:16 am 
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Pbpix wrote:
john8750 wrote:
Thank you Men. I am getting the picture here.
I noticed that some guys test this amp firstly with a lower AC supply, say 24volts.
Then measure for voltages of 20%. Is this a good thing to do?

or 1.2vAC and test for 1% :mrgreen:



Safer Yet....

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Wed 06, 2017 3:46 am 
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john8750 wrote:
Thank you Men. I am getting the picture here.
I noticed that some guys test this amp firstly with a lower AC supply, say 24volts.
Then measure for voltages of 20%. Is this a good thing to do?
You can certainly do that to see if things are astronomically off but voltages won't be "20%" because nothing is pulling the same current as when fully powered.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Wed 06, 2017 6:25 am 
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Flipperhome wrote:
john8750 wrote:
Thank you Men. I am getting the picture here.
I noticed that some guys test this amp firstly with a lower AC supply, say 24volts.
Then measure for voltages of 20%. Is this a good thing to do?
You can certainly do that to see if things are astronomically off but voltages won't be "20%" because nothing is pulling the same current as when fully powered.




Great. I understand, but will be better to check at a lower voltage. I have a 24volt 5amp transformer.
I just need to get the input wired. Or I could at least connect speakers and go for the test. It is getting near.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Wed 06, 2017 6:54 am 
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Go for it!
Easy trouble shooting and testing:
Tune for maximum smoke.
Whatever starts smoking most will be the likely culprit.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Wed 06, 2017 7:50 am 
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john8750 wrote:
Flipperhome wrote:
You can certainly do that to see if things are astronomically off but voltages won't be "20%" because nothing is pulling the same current as when fully powered.

Great. I understand, but will be better to check at a lower voltage. I have a 24volt 5amp transformer.
I just need to get the input wired. Or I could at least connect speakers and go for the test. It is getting near.
You don't need an input to see if everything at least settles to the right voltages.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Wed 06, 2017 7:51 pm 
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Here we go guys.
Inputs not connected-
Install all tubes, man those 300b's are purty.
Turn on ac.
Warm up, B+ settles at 432volts. 300b filaments- 5.4v.
12sl7 comes up slow, stops at 14v.
Then, a massive roar from the speakers.
Powered off and wondered, what the heck.
Wait a minute, I have heard that roar before.

Short out open inputs.
Retest, no roar. Nothing.

Will now finish input wiring.
Connect MP3 and retest.
I like it so far.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Wed 06, 2017 10:23 pm 
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SFSG

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Thu 07, 2017 4:33 am 
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john8750 wrote:
Here we go guys.
Inputs not connected-
Install all tubes, man those 300b's are purty.
Turn on ac.
Warm up, B+ settles at 432volts. 300b filaments- 5.4v.
12sl7 comes up slow, stops at 14v.
Then, a massive roar from the speakers.
Powered off and wondered, what the heck.
Wait a minute, I have heard that roar before.

Short out open inputs.
Retest, no roar. Nothing.

Will now finish input wiring.
Connect MP3 and retest.
I like it so far.
For all the worrying, 432 V came out darn close to 435 V, didn't it? :mrgreen: What was the max surge you saw?

We probably need to do something about the 5.4 V on the filaments but that too was expected since the filaments don't present a full load to the transformers. It's still within 10%, so not a problem for now, but since you're concerned with 'life' it'd be best to nudge it down to 5V.

The 12SL7 at 14V suggests we have bias running a teensy bit high. Again, not enough to be a problem for now but, sooner or later, we should probably lower it down to spec.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Thu 07, 2017 4:58 am 
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Flipperhome wrote:
john8750 wrote:
Here we go guys.
Inputs not connected-
Install all tubes, man those 300b's are purty.
Turn on ac.
Warm up, B+ settles at 432volts. 300b filaments- 5.4v.
12sl7 comes up slow, stops at 14v.
Then, a massive roar from the speakers.
Powered off and wondered, what the heck.
Wait a minute, I have heard that roar before.

Short out open inputs.
Retest, no roar. Nothing.

Will now finish input wiring.
Connect MP3 and retest.
I like it so far.
For all the worrying, 432 V came out darn close to 435 V, didn't it? :mrgreen: What was the max surge you saw?

We probably need to do something about the 5.4 V on the filaments but that too was expected since the filaments don't present a full load to the transformers. It's still within 10%, so not a problem for now, but since you're concerned with 'life' it'd be best to nudge it down to 5V.

The 12SL7 at 14V suggests we have bias running a teensy bit high. Again, not enough to be a problem for now but, sooner or later, we should probably lower it down to spec.



I saw a surge of about 5volts, but will check it again. I was still checking at 1/4 volts.
Yes, we can make adjustments.
I am happy about the 60hz hum, there wasn't any. But will tell better with an input connected. Gotta be a little.
I like the slow startup on the 12sl7. How would we lower that to 12v? Same with the 5v transformers.
Should I check the other heater volts?

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Thu 07, 2017 5:30 am 
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john8750 wrote:
Flipperhome wrote:
For all the worrying, 432 V came out darn close to 435 V, didn't it? :mrgreen: What was the max surge you saw?

We probably need to do something about the 5.4 V on the filaments but that too was expected since the filaments don't present a full load to the transformers. It's still within 10%, so not a problem for now, but since you're concerned with 'life' it'd be best to nudge it down to 5V.

The 12SL7 at 14V suggests we have bias running a teensy bit high. Again, not enough to be a problem for now but, sooner or later, we should probably lower it down to spec.
I saw a surge of about 5volts, but will check it again. I was still checking at 1/4 volts.
Yes, we can make adjustments.
I am happy about the 60hz hum, there wasn't any. But will tell better with an input connected. Gotta be a little.
I like the slow startup on the 12sl7. How would we lower that to 12v? Same with the 5v transformers.
Should I check the other heater volts?
Well, a surge of 20 V is certainly no problem. As a side note, with your idea for 'delayed B+' you'd have to contend with the full 565 V.

Sure, check all the heaters. The 6SN7s will probably be running high too because, if I remember correctly, we're not fully loading the 6.3 V winding either.

Heaters can be reduced with a series R in the winding. The 300B filaments take two, say .18 Ohm each, because 'hum' reduction depends on winding balance. Idle current, and the current through the 12SL7, can be reduced by increasing the cathode resistor. Crude calculation indicates it should be 980 Ohm instead of 820 Ohm.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Thu 07, 2017 7:07 pm 
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Flipperhome wrote:
john8750 wrote:
Flipperhome wrote:
For all the worrying, 432 V came out darn close to 435 V, didn't it? :mrgreen: What was the max surge you saw?

We probably need to do something about the 5.4 V on the filaments but that too was expected since the filaments don't present a full load to the transformers. It's still within 10%, so not a problem for now, but since you're concerned with 'life' it'd be best to nudge it down to 5V.

The 12SL7 at 14V suggests we have bias running a teensy bit high. Again, not enough to be a problem for now but, sooner or later, we should probably lower it down to spec.
I saw a surge of about 5volts, but will check it again. I was still checking at 1/4 volts.
Yes, we can make adjustments.
I am happy about the 60hz hum, there wasn't any. But will tell better with an input connected. Gotta be a little.
I like the slow startup on the 12sl7. How would we lower that to 12v? Same with the 5v transformers.
Should I check the other heater volts?
Well, a surge of 20 V is certainly no problem. As a side note, with your idea for 'delayed B+' you'd have to contend with the full 565 V.

Sure, check all the heaters. The 6SN7s will probably be running high too because, if I remember correctly, we're not fully loading the 6.3 V winding either.

Heaters can be reduced with a series R in the winding. The 300B filaments take two, say .18 Ohm each, because 'hum' reduction depends on winding balance. Idle current, and the current through the 12SL7, can be reduced by increasing the cathode resistor. Crude calculation indicates it should be 980 Ohm instead of 820 Ohm.



Roger that. Will first check with the inputs. Then correct the heater voltage. Heck no for the delayed B+ then :wink:

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 08, 2017 2:28 am 
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I don't see a need to have any delays connected. I wont have the inputs defeated either.
What will I do with the indicator lights :?:
I started connecting the input circuits today. I need to redo it because I'm not happy about
the solder joints. Its a hard to reach area so the connections were hard to solder. They stuck,
but look like crap. Will fix it tomorrow, and should move on to the test.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 08, 2017 2:37 am 
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Now here is an amp for me :lol:

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 08, 2017 3:20 am 
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Flip- will add the resistance for the amp changes. I am ready to order. Is the 120ohm added to each Cathode resistance correct? And .18ohm for each 300b heater lead also correct?
And, I guess I can run amp as is just for testing.
Thanks Flip.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 08, 2017 4:14 am 
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john8750 wrote:
Flip- will add the resistance for the amp changes. I am ready to order. Is the 120ohm added to each Cathode resistance correct? And .18ohm for each 300b heater lead also correct?
And, I guess I can run amp as is just for testing.
Thanks Flip.
If your current cathode resistor is 820 Ohm then it's adding 160 Ohm to get 980 Ohm. Should be a 2 Watt or more. Yes, .18 Ohm each leg. 1/2 Watt or more.

Note, those values are an approximation but should get you close enough to the target voltage/current.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 08, 2017 6:00 pm 
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Flipperhome wrote:
john8750 wrote:
Flip- will add the resistance for the amp changes. I am ready to order. Is the 120ohm added to each Cathode resistance correct? And .18ohm for each 300b heater lead also correct?
And, I guess I can run amp as is just for testing.
Thanks Flip.
If your current cathode resistor is 820 Ohm then it's adding 160 Ohm to get 980 Ohm. Should be a 2 Watt or more. Yes, .18 Ohm each leg. 1/2 Watt or more.

Note, those values are an approximation but should get you close enough to the target voltage/current.




I will make the change Flip. Sure is good to have the help from you guys.
I already mounted the added cathode resistors, but not in the circuit yet.
I need to rework two areas where I just cant stand the sloppy soldering I did.
Still considering removing the component mounting board also.
I want my work to look respectable, not usually the case though.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 08, 2017 6:16 pm 
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I ordered this converter to power the cooling fan and indicator lights. It will be powered from a rectified and filtered 6.3vac filament supply. I need 12vdc for the fan.
https://www.ebay.com/itm/2-PCS-MT3608-D ... SwXY5ZQfsY

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 08, 2017 6:42 pm 
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Been listening to the amp for about an hour. No hum, or any type static audible. Connected to the Zenith Console. The speakers have been replaced with a medium quality car 3 way type.
B+ settled at 437. 5volt filaments are at 5.43 and 6.3volt filaments are at 7.16.
The sound, plenty. Very good highs, bass is there and lives in the back. Gain from the MP3
needs some boost. Flip has that considered in the preamp, coming later.
While I can feel the real opera house filling sound, it does not have a place for rock and roll.
Peter, your cocktail music, which I also like, needs this amp. It makes a real nice difference,
I guess it is the SE type that is different.
I feel, so far, It is not better than the other amps I have. And I need to complete the amp,
and connect better speakers for a better comparison. Sitting out in the shop is quite different
than relaxing in the listening room. I will describe it better as we go.
Thanks for the good job on this one Flip.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 08, 2017 10:10 pm 
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john8750 wrote:
I ordered this converter to power the cooling fan and indicator lights. It will be powered from a rectified and filtered 6.3vac filament supply. I need 12vdc for the fan.
https://www.ebay.com/itm/2-PCS-MT3608-D ... SwXY5ZQfsY

Cool John...lol

It puts out four hundred thousand volts? That's great hillbilly gain outta 2-24v volts in !!

Application
- Connect 2~24V to IN + and IN -
- Adjust the pontentiometer to putput your desired voltage
- Output voltage is always higher than the input voltage
- Output voltage: 400000 v

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