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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 11:56 pm 
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john8750 wrote:
OMG- You all will not believe this. I never changed the power transformer. Just using the old one I had there. Don't know the rating of it. But not 100va, might be half that. I was just playing the amp, went to feel the power tranny for heat, about a thousand degrees, very hot. So, let me mount the correct transformer. Could be why your figuring was off, Flip.
I think I will also remodel the amp, power amp only.

That will bring the B+ up nicely.
Please measure it and measure the ripple voltage too
Scope probe x1 ... vert gain=AC mode

I have 20v peak to peak
you should have something maybe like 50v pp and maybe higher since my filter caps are so much larger.
I use 820uf filters

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Last edited by Pbpix on Feb Tue 06, 2018 12:04 am, edited 1 time in total.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 12:02 am 
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john8750 wrote:
OMG- You all will not believe this. I never changed the power transformer. Just using the old one I had there. Don't know the rating of it. But not 100va, might be half that. I was just playing the amp, went to feel the power tranny for heat, about a thousand degrees, very hot. So, let me mount the correct transformer. Could be why your figuring was off, Flip.
I think I will also remodel the amp, power amp only.
As Jamie of Mythbusters says, "well there's your problem." :lol:


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 12:52 am 
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Stripped the thing down. Ready to mount the new PT. Also removed the 12volt filament transformer. Wont need it.
That's so stupid of me. I remember liking that transformer because of how I will mount it. Will need some metal straps to hold it down. I ripped out the whole power supply. But will be simple to rebuild, only the power amp.
Attachment:
20180205_153658.jpg
20180205_153658.jpg [ 147.17 KiB | Viewed 236 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 1:08 am 
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Pbpix wrote:
john8750 wrote:
OMG- You all will not believe this. I never changed the power transformer. Just using the old one I had there. Don't know the rating of it. But not 100va, might be half that. I was just playing the amp, went to feel the power tranny for heat, about a thousand degrees, very hot. So, let me mount the correct transformer. Could be why your figuring was off, Flip.
I think I will also remodel the amp, power amp only.

That will bring the B+ up nicely.
Please measure it and measure the ripple voltage too
Scope probe x1 ... vert gain=AC mode

I have 20v peak to peak
you should have something maybe like 50v pp and maybe higher since my filter caps are so much larger.
I use 820uf filters



I am rebuilding the whole amp Peter. Will build just the power amp. Preamp will be built separately, just like you guys suggested. I like the op275, and 25ma CCS. I have one 820uf, so will use it in the final stage.
What would be the advantage of using the opa604?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 1:10 am 
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Flipperhome wrote:
john8750 wrote:
OMG- You all will not believe this. I never changed the power transformer. Just using the old one I had there. Don't know the rating of it. But not 100va, might be half that. I was just playing the amp, went to feel the power tranny for heat, about a thousand degrees, very hot. So, let me mount the correct transformer. Could be why your figuring was off, Flip.
I think I will also remodel the amp, power amp only.
As Jamie of Mythbusters says, "well there's your problem." :lol:




Yes, I like it.
Cant believe I forgot all about it :oops: :oops:

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 1:14 am 
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Flipperhome wrote:
john8750 wrote:
I hear ya Flip. I have some new ones commin. That's an easy fix.
Do you think I damaged my tubes with the grid-cathode problem? I fixed it, sounds ok.
Could be, being the small wooden chassis, is building up the heat underneath. Maybe a larger metal chassis would be better.
Or, just for a power amp. Build a separate preamp box. I mean, the amp circuit is so simple by itself.
I know what you are saying right now, ' here we go again, every one of John's projects drags us to hell and back '
Sorry about it. I hope you guys have fun helping me. I sure do enjoy it.
I doubt you damaged the tubes. For one, I don't believe those numbers from when you had positive volt on the grid anyway. Don't misunderstand, I believe that's what you THINK they were but something must have been amiss with the measurement or else, as I said, you'd have seen a rash of other, rather spectacular, problems real quick.

I've been meaning to suggest that your 'heat' problem is likely due to the case and confining 'hot' components in a small area so they mutually warm each other by radiation. "Free air" dissipation depends on spacing and, well, FREE air circulation. Without it they will heat the air, it 'stays' there, and everything (in the area) gets hotter than if it were allowed to circulate. It doesn't seem like much but you'd be surprised how fast it mounts up. I ran into that with my first amp, also in a wooden chassis, and before I vented it I was seriously cooking the insides.



No problem there Flip.
Like I told ya, if I did something right, I made a mistake.
Thank you for your kindness.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 1:19 am 
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john8750 wrote:
I am rebuilding the whole amp Peter. Will build just the power amp. Preamp will be built separately, just like you guys suggested. I like the op275, and 25ma CCS. I have one 820uf, so will use it in the final stage.
What would be the advantage of using the opa604?
Oh, hope soon we forget. The OP275 doesn't have enough voltage swing to fully drive the output tubes. The OP604 uses 24 V (instead of 20 V) rails so it can swing more voltage. The idea is to be able to drive the 6V6.

Why lower the CCS below spec?

The larger cap will, of course, work but why?


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 2:26 am 
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Flipperhome wrote:
john8750 wrote:
I am rebuilding the whole amp Peter. Will build just the power amp. Preamp will be built separately, just like you guys suggested. I like the op275, and 25ma CCS. I have one 820uf, so will use it in the final stage.
What would be the advantage of using the opa604?
Oh, hope soon we forget. The OP275 doesn't have enough voltage swing to fully drive the output tubes. The OP604 uses 24 V (instead of 20 V) rails so it can swing more voltage. The idea is to be able to drive the 6V6.

Why lower the CCS below spec?

The larger cap will, of course, work but why?



I can stay with the opa604, not a problem, as long as I have enough power for everything including the filament circuit. And it will be better.
I have a big cap, might as well use it. Should be plenty of room now.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 3:05 am 
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I can still get a 310v B+ with that cap, right?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 3:19 am 
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Back to basics boys. All the 1ohm carbon resistors read 1.1ohm.
Attachment:
20180205_153734.jpg
20180205_153734.jpg [ 157.69 KiB | Viewed 231 times ]


The front plate will be blanked. The rear input plate will be redone with a single input, and gain pot.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 3:29 am 
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john8750 wrote:
I can stay with the opa604, not a problem, as long as I have enough power for everything including the filament circuit. And it will be better.
I have a big cap, might as well use it. Should be plenty of room now.
I see, you're going back to the original PS with +-24V and heaters included. Seems a shame when you were so close to having the other working. Anyway, this is the PS schematic, if I understood right.

Attachment:
Doubler - heaters - opamp N-77U.jpg
Doubler - heaters - opamp N-77U.jpg [ 132.88 KiB | Viewed 231 times ]


Note, there's not enough current for the full 38 mA idle but we could get closer than 25 mA, say 30 mA.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 3:31 am 
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john8750 wrote:
I can still get a 310v B+ with that cap, right?
Yes. It doesn't affect the B+ voltage.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 3:44 am 
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Flipperhome wrote:
john8750 wrote:
I can stay with the opa604, not a problem, as long as I have enough power for everything including the filament circuit. And it will be better.
I have a big cap, might as well use it. Should be plenty of room now.
I see, you're going back to the original PS with +-24V and heaters included. Seems a shame when you were so close to having the other working. Anyway, this is the PS schematic, if I understood right.

Attachment:
Doubler - heaters - opamp N-77U.jpg


Note, there's not enough current for the full 38 mA idle but we could get closer than 25 mA, say 30 mA.



But we were supplying 38ma. Is that because of the separate filament transformer? I could leave it in if we need it.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 3:47 am 
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Here is the new PT.
Are these taps correct?
No info on transformer.
Attachment:
20180205_153307.jpg
20180205_153307.jpg [ 126.38 KiB | Viewed 230 times ]

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 3:58 am 
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4 tubes at idle of 30ma is 120ma B+.
The HV print is showing only 100ma on B+.


Btw
As per my bench measurements the opa604 @24v Vcc produces a max output of 35v peak to peak

The op275 @ 20v Vcc produces 30v peak to peak drive signal
and at 21v Vcc produces 32v peak to peak drive signal.

How much pp drive volts does it require to drive the 6V6 fully?

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Last edited by Pbpix on Feb Tue 06, 2018 4:07 am, edited 1 time in total.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 3:59 am 
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john8750 wrote:
Here is the new PT.
Are these taps correct?
No info on transformer.
Attachment:
20180205_153307.jpg

Here:
https://www.alliedelec.com/m/d/007d06f2 ... bce35b.pdf

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To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 4:05 am 
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Yes, I had the amp kinda working. Didn't feel the satisfaction though. And it was a real mess after troubleshooting all the problems. And I have time to do it again if it will be better. So, why not.
If I go with the opa604, 38ma CCS, and 310v 150ma for the B+, will the amp perform better?
My old 6V6 rocks out very nicely the way it is with op275, 25ma CCS, 290v 100ma B+.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 4:08 am 
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Pbpix wrote:
john8750 wrote:
Here is the new PT.
Are these taps correct?
No info on transformer.
Attachment:
20180205_153307.jpg

Here:
https://www.alliedelec.com/m/d/007d06f2 ... bce35b.pdf



Thanks Peter. I figured it correctly. I hope that removing the outer case wont hurt it.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 4:17 am 
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john8750 wrote:
Pbpix wrote:
john8750 wrote:
Here is the new PT.
Are these taps correct?
No info on transformer.
Attachment:
20180205_153307.jpg

Here:
https://www.alliedelec.com/m/d/007d06f2 ... bce35b.pdf



Thanks Peter. I figured it correctly. I hope that removing the outer case wont hurt it.


I don't know if the outer frame was helping to clamp the laminations together tightly, or just creating a mount.

Are you tying the two 120v input windings in parallel as shown in the spec.
1 to 4 and 2 to 5

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Tue 06, 2018 4:36 am 
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Yes, I thought that's how it works. Looks like the transformer plates are stuck together pretty good. If it rattles, I will know what went wrong.
I will ask My Cousin what he wants. If he wants the best in power, I will build the Opa604 version. If he don't care, I will build the one we already have. It don't really matter to me. He and I listen to my 6V6 when he is here on some weekends. That's why he finally wanted a tube amp, the great sounding amp I have. It blows his modern amp away, in sound.

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