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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 11, 2018 8:53 pm 
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Max plate voltage for the 6V6 lists at 315. I would like to make it about 300. Need to measure the voltage at the plate. I only have the B+.
So would it be best to increase resistance on the 220ohm in the power supply, or the 5ohm?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 11, 2018 10:36 pm 
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I fixed the B+. Just changed the 5ohm to a 50ohm. Now the B+ is 300volts. And cleaned up the wiring. And connected the NFB through a switch. It cuts the volume in half.
So whats the advantage of NFB?
Amp sounds nice.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 11, 2018 10:37 pm 
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john8750 wrote:
Max plate voltage for the 6V6 lists at 315. I would like to make it about 300. Need to measure the voltage at the plate. I only have the B+.
So would it be best to increase resistance on the 220ohm in the power supply, or the 5ohm?

You shouldn't need 50 ohms!
Your AC input must be too high. What is the AC feeding the system?

What is the voltage drop across the 220 ohm?
If you are drawing 100ma... then it should be 22v
If you truly have +315 B+ and 22v across the 220 ohm resistor, that means you must have 337v feeding into the 220 ohm.
That seems very high to me.

What is the AC feeding the system?

I have 122vAC on the mains, feeding mine.
That gives me 292v B+ ( with 22v dropped across the 220 ohm resistor) that means I only have 314v feeding the 220 ohm. And that results in 292vB+

So your AC mains must be high. No?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 11, 2018 10:43 pm 
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john8750 wrote:
How is this for the 8uf dropper cap.
https://www.ebay.com/itm/US-CBB61-AC450 ... Sw4A5YpAqW

What 8uf cap are you referring to?

The mains dropper for the filaments is 10uf.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 11, 2018 10:50 pm 
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Pbpix wrote:
john8750 wrote:
Max plate voltage for the 6V6 lists at 315. I would like to make it about 300. Need to measure the voltage at the plate. I only have the B+.
So would it be best to increase resistance on the 220ohm in the power supply, or the 5ohm?

You shouldn't need 50 ohms!
Your AC input must be too high. What is the AC feeding the system?

What is the voltage drop across the 220 ohm?
If you are drawing 100ma... then it should be 22v
If you truly have +315 B+ and 22v across the 220 ohm resistor, that means you must have 337v feeding into the 220 ohm.
That seems very high to me.

What is the AC feeding the system?

I have 122vAC on the mains, feeding mine.
That gives me 292v B+ ( with 22v dropped across the 220 ohm resistor) that means I only have 314v feeding the 220 ohm. And that results in 292vB+

So your AC mains must be high. No?



Peter. I have a strong 145v on the PT secondary. You figured 120v, would work fine.
That makes the filaments over 30volts, B+ over 340volts.
The 50ohm replacing the 5ohm worked out perfect.
And the 8uf should be right for about 26volts.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 11, 2018 10:53 pm 
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Pbpix wrote:
john8750 wrote:
How is this for the 8uf dropper cap.
https://www.ebay.com/itm/US-CBB61-AC450 ... Sw4A5YpAqW

What 8uf cap are you referring to?

The mains dropper for the filaments is 10uf.



10uf for 120volts input. But what for 145volts. I figured 8uf, hillbilly math.



BTW- 20volt supplies are right in there.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 11, 2018 10:58 pm 
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john8750 wrote:

Peter. I have a strong 145v on the PT secondary. You figured 120v, would work fine.
That makes the filaments over 30volts, B+ over 340volts.
The 50ohm replacing the 5ohm worked out perfect.
And the 8uf should be right for about 26volts.

But you shouldn't be having 145vAC on the transformer secondary.
That's the problem.
You AC feeding the transformer must be too hig.

What is the AC on each side?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 11, 2018 11:26 pm 
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Are you using your SolarPower system?
If so didn't you tell us a while back that it was too high?

If so that's t he main problem... and if you try to adjust the amp to compensate... then your cousin will be on a different public AC supply right?

Also... here's another cause:
The FD8-120 transformer was designed for 115v primary/120v secondary.
And so ....it boosts the 115vAC up to 120vAC

So whatever AC volts you are feeding the primary is also getting boosted by a factor of 1.05 and more.
A ratio of at least 1:1.05 at full load ....but much higher under partial load.


Now:
on the other hand the N77U transformer would have been better because it is 115v Primary and 115v secondary.
No voltage boosting.

The N77U will only give a 1:1 ratio

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 11, 2018 11:44 pm 
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I'm trying to call you.
no answer

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 11, 2018 11:50 pm 
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john8750 wrote:
Test results.
No problems, but some situations.
The acv leaving the PT is 145. That makes the B+ 343. And the filaments above 36.
I figured on changing the 10uf dropper in the filament circuit to 8uf. Should give about 26v.
Is the B+ too high?

L1-----25.38v----25ma-----grid .132
L2-----25.83v-----25ma-----grid -.131
R1-----26.21v-----24ma-----grid .158
R2-----24.06v-----24ma-----grid -.158


These will be noted as actuals.
Here she is under test. Now I will tidy up the wiring before proceeding on.
Attachment:
20180211_111201.jpg
The isotransformer you're using must have a higher 'regulation factor' plus you've gone down to low idle current (25mA). Use larger series resistors in the cap filter chain.

Look at your cathode volts. It would take an opamp with over 50 V peak to peak to drive those 6V6's to full output but the OPA275 is only good for less than half that.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 12, 2018 12:00 am 
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Flip:
Let's not jump to quick solutions just yet.
I saw the cathodes way up at 25v ... yes ... but i think this is all due to the same root problem.. TOO much AC input to the PT.
And a boosting PT too.

Also the FD8-120 is a 115 to 120 (full load).... so it's probably boosting a bunch too if he's at less than full load.

The N77U is a better choice 115primary 115v secondary
A ratio of 1:1

And if he's taking AC from his Solar supply .... remember that's too high too.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 12, 2018 12:26 am 
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My ac entering the PT is 125.1 using house current, not from the inverter.
No problem, I have the correct voltages now. I don't know how the higher voltage affects the zener regulators.
Will call you later Peter, phone is on charge in another room of my castle.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 12, 2018 12:32 am 
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ok 125.1 going in... so what is on the secondary? 130v+ ?

Here's what I see:

if you feed the AC input with 125vAC
Then the PT with a (ratio 1:1.04) will boost 125v up to 130vAC on the secondary.
130AC x 1.414 = 184v DC
doubled (voltage doubler) = 368v approx.
368v feeding the 220 ohm resistor (drops 22v @ 100ma) so 368v- 22v drop = 346v B+

So if you have 125v AC feeding that PT it kicks it up to 130vAC

That's too high... for the components shown on the print.

I'd leave the 5 ohm alone and add resistance to the 220ohm instead.

Then recalculate the filament dropper too.
But why are you suggesting 8 uf? What is that based on?

I calculate closer to 9uf
if input to the dropper cap AC is approx 130v, then a 9uf will provide a current of 450ma @25v

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 12, 2018 12:43 am 
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Pbpix wrote:
ok 125.1 going in... so what is on the secondary? 130v+ ?

Here's what I see:

if you feed the AC input with 125vAC
Then the PT with a (ratio 1:1.04) will boost 125v up to 130vAC on the secondary.
130AC x 1.414 = 184v DC
doubled (voltage doubler) = 368v approx.
368v feeding the 220 ohm resistor (drops 22v @ 100ma) so 368v- 22v drop = 346v B+

So if you have 125v AC feeding that PT it kicks it up to 130vAC

That's too high... for the components shown on the print.

I'd leave the 5 ohm alone and add resistance to the 220ohm instead.

Then recalculate the filament dropper too.
But why are you suggesting 8 uf? What is that based on?



I have stated the PT output voltage 145, a few times now. I cant change that.
I did change the voltage for the B+ with the 50ohm resistor replacing the 5 ohm.
And I tack soldered 4 caps together to make 7.9uf to get about 25volts to the filaments. So I just ordered an 8uf.
Its really needs to be no more complicated than that.
https://www.ebay.com/itm/2-x-8uF-8-0uf- ... 1438.l2649

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 12, 2018 12:54 am 
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john8750 wrote:
Pbpix wrote:
ok 125.1 going in... so what is on the secondary? 130v+ ?

Here's what I see:

if you feed the AC input with 125vAC
Then the PT with a (ratio 1:1.04) will boost 125v up to 130vAC on the secondary.
130AC x 1.414 = 184v DC
doubled (voltage doubler) = 368v approx.
368v feeding the 220 ohm resistor (drops 22v @ 100ma) so 368v- 22v drop = 346v B+

So if you have 125v AC feeding that PT it kicks it up to 130vAC

That's too high... for the components shown on the print.

I'd leave the 5 ohm alone and add resistance to the 220ohm instead.

Then recalculate the filament dropper too.
But why are you suggesting 8 uf? What is that based on?



I have stated the PT output voltage 145, a few times now. I cant change that.
I did change the voltage for the B+ with the 50ohm resistor replacing the 5 ohm.
And I tack soldered 4 caps together to make 7.9uf to get about 25volts to the filaments. So I just ordered an 8uf.
Its really needs to be no more complicated than that.
https://www.ebay.com/itm/2-x-8uF-8-0uf- ... 1438.l2649


Well John:
better or correct is not really being "more complicated"

the 50 ohm is not good there. It is much better to add it to the 220ohm resistor because that first resistor takes a hell of a beating in very short but ultra high current bursts.
So the 5 ohm is better off left there where it is now.
.. as it just helps reduce surge... not meant to drop big volts.
The better place for dropping the volts you need to drop is the 220ohm to increase.

measure the DC on the input and calculate the value based on 100ma load.

As far as paralleling 4 other caps together .... did you measure them with your meter to to get 7.9 uf or did you just add up the printed values?

If you measured that exact capacitance with your meter and the drop also came out correctly to 25 or so volts... then ok.

The 8uf you ordered may have a tolerance of 20% too so watch that.

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Last edited by Pbpix on Feb Mon 12, 2018 12:59 am, edited 1 time in total.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 12, 2018 12:59 am 
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john8750 wrote:
Pbpix wrote:
ok 125.1 going in... so what is on the secondary? 130v+ ?

Here's what I see:

if you feed the AC input with 125vAC
Then the PT with a (ratio 1:1.04) will boost 125v up to 130vAC on the secondary.
130AC x 1.414 = 184v DC
doubled (voltage doubler) = 368v approx.
368v feeding the 220 ohm resistor (drops 22v @ 100ma) so 368v- 22v drop = 346v B+

So if you have 125v AC feeding that PT it kicks it up to 130vAC

That's too high... for the components shown on the print.

I'd leave the 5 ohm alone and add resistance to the 220ohm instead.

Then recalculate the filament dropper too.
But why are you suggesting 8 uf? What is that based on?



I have stated the PT output voltage 145, a few times now. I cant change that.
I did change the voltage for the B+ with the 50ohm resistor replacing the 5 ohm.
And I tack soldered 4 caps together to make 7.9uf to get about 25volts to the filaments. So I just ordered an 8uf.
Its really needs to be no more complicated than that.
https://www.ebay.com/itm/2-x-8uF-8-0uf- ... 1438.l2649
The 50 Ohm resistor will certainly drop B+ but that's the hard way to do it. It'll be dissipating something on the order of 24 Watt. Increasing the series filter resistors would add only 3 Watt (30 V drop at 100 mA B+) with the added benefit of increased filtering (lower ripple)


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 12, 2018 1:00 am 
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Flipperhome wrote:
The 50 Ohm resistor will certainly drop B+ but that's the hard way to do it. It'll be dissipating something on the order of 24 Watt. Increasing the series filter resistors would add only 3 Watt (30 V drop at 100 mA B+) with the added benefit of increased filtering (lower ripple)

+1

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 12, 2018 1:10 am 
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OK. I understand guys. Let me see if I can calculate and change R1, 220ohm. I will leave the 5ohm there.
How in the heck do we have 145volts?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 12, 2018 1:39 am 
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john8750 wrote:
OK. I understand guys. Let me see if I can calculate and change R1, 220ohm. I will leave the 5ohm there.
How in the heck do we have 145volts?
I'd split it between the two. Btw, the 5 Ohm isn't needed because of the transformer winding DCR.

The transformer you've got multiplies the voltage up somewhat and you're not fully loading it to boot with only 25 mA per tube.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 12, 2018 1:39 am 
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john8750 wrote:
OK. I understand guys. Let me see if I can calculate and change R1, 220ohm. I will leave the 5ohm there.
How in the heck do we have 145volts?

You have 145 because... as I just explained :

That PT is meant for 115vAC primary... and then it boosts that to 120vAC on the secondary.
That's a boost of 1:1.04

120v/115 = 1.043 factor at full load

At a lower load it's much higher boost. ..

You are getting a 1:1.16 boost

For every 1volt AC volt on the input you are getting 1.16volts out.

so 125vAC x 1.16 = 145VAC

To change the 220 ohm resistor value ... just measure the DC v on the input to that resistor.

So if you measure 350v and you want 300v B+
That means you need to drop 50v @ 100ma right?
50v / .1A = 500 ohms
power = IxE
.1A x 50v = 5 watts ... tripled for safety= 15 or 20 watts

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