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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 04, 2018 10:55 pm 
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I need to re-think this.
I just replaced a bad volume pot. Turned on for a test. Now have a squeaky sound, affected by volume control but not controlled. Balance pot has no control.
I connected straight in to amp, problem has developed at preamp opa604's.
The problem is exactly what you guys said. I cant keep up with the different sections I am trying to make work all at once.
Here comes the Itodaso.
SO, thinking about just getting amp working, alone. Then adding stuff after that.
I don't like the complexity of the opa604, or the 24volts needed. So will use the op275 at 20volts.
Build the tone amp on a separate board, preamp-CCS on a separate board. Skip the MP3 booster for now, and the RIAA.
Let me think about this a little. Suggestions are most needed here.....

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 04, 2018 11:23 pm 
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The output loads are higher typically and certainly higher if you allow for max limits.

A) the 13v supply typically = 35ma but max is 48ma (as per Flip)

B) The opa604s typically draw 22.5 ma per +/- side = 45ma and max is 56ma

C) The other 15v supply I think you changed to 20v? for op275? ... = 10ma per +/- side = 20ma and max = 22ma

So those add up to:
A= 35ma typical max 56ma
B= 45ma typical max 56ma
C= 20ma typical max 22ma

Total typical = 100ma -110ma
Total max = 126ma -135ma


So what are your alternatives.

Remember you and Flip are redesigning this whole supply in reverse.

(Initially MY bench tested design was simple and allowed for the efficient low-cost and convenience of NO transformers, albeit less "safe".)


Here's where everything started to be added as an afterthought
:

So ...then the first (safety) modification adds a 100VA transformer. (cost, space, weight)

Then the next mod uses dual power supplies for the op275

Then the next loads are a RIAA board, and a pre-amp, and opa604 chips (increased load)

This becomes too much load so:
The next mod is to use a separate filament transformer. (cost, space, weight)

Then next mod is to boost the idle current to 37ma x four = 150ma (increased load)

That changes the HV supply components and also attempts to boost HV to +310v or more.

Then add the extra all the pre amps boards and their currents and here we are.

Everything is an after thought.

Your alternative (if you want to keep all the extra loads) is to scrap everything in the supply as it is and re-design a more conventional supply using a HV winding and a few lower voltage winding or separate transformers.
Then design a sub supply using voltage regulators or Zeners for +13v
and then two +/- supplies for the 24v lines and the 15v lines.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 04, 2018 11:53 pm 
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john8750 wrote:
Here is the power supply showing the power needed for the cap dropper IC section. 313ma.
Not very practical. The output load demand is only 65ma. That's for the tone amp, and preamp only.
Attachment:
maa.png
The 313 mA is right spot on, compared to my simulation.

You're not counting the full load, which includes max available (whether you use it or not) and the residual for the zeners to maintain robust regulation, plus the allowance for AC line variation (which increases the current at nominal). Remember, zener regulators (besides being simple and cheap) pull the same current whether you have a load or not. The current simply goes through the zener, or the load, but the overall current demand is constant. That's necessary for the cap dropper to work.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 04, 2018 11:56 pm 
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john8750 wrote:
I need to re-think this.
I just replaced a bad volume pot. Turned on for a test. Now have a squeaky sound, affected by volume control but not controlled. Balance pot has no control.
I connected straight in to amp, problem has developed at preamp opa604's.
The problem is exactly what you guys said. I cant keep up with the different sections I am trying to make work all at once.
Here comes the Itodaso.
SO, thinking about just getting amp working, alone. Then adding stuff after that.
I don't like the complexity of the opa604, or the 24volts needed. So will use the op275 at 20volts.
Build the tone amp on a separate board, preamp-CCS on a separate board. Skip the MP3 booster for now, and the RIAA.
Let me think about this a little. Suggestions are most needed here.....
What 'complexity'? The OP604 circuit is exactly the same as the OP275 circuit, just at a higher voltage.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 04, 2018 11:56 pm 
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I got 164ma feeding the 13volt supply-149ma for the rest. Flip said that the cap dropper is not very efficient.
I can get the power from the tone amp from the filament supply, I think, don't need to be regulated. The 20volts for the opamp will need to come from the 120ac line, through a dropper cap, or a separate transformer.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 04, 2018 11:58 pm 
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Flipperhome wrote:
john8750 wrote:
I need to re-think this.
I just replaced a bad volume pot. Turned on for a test. Now have a squeaky sound, affected by volume control but not controlled. Balance pot has no control.
I connected straight in to amp, problem has developed at preamp opa604's.
The problem is exactly what you guys said. I cant keep up with the different sections I am trying to make work all at once.
Here comes the Itodaso.
SO, thinking about just getting amp working, alone. Then adding stuff after that.
I don't like the complexity of the opa604, or the 24volts needed. So will use the op275 at 20volts.
Build the tone amp on a separate board, preamp-CCS on a separate board. Skip the MP3 booster for now, and the RIAA.
Let me think about this a little. Suggestions are most needed here.....
What 'complexity'? The OP604 circuit is exactly the same as the OP275 circuit, just at a higher voltage.



Only meaning that we need 4 instead of 2 chips, and different power pins.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Sun 04, 2018 11:59 pm 
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Flipperhome wrote:
john8750 wrote:
Here is the power supply showing the power needed for the cap dropper IC section. 313ma.
Not very practical. The output load demand is only 65ma. That's for the tone amp, and preamp only.
Attachment:
maa.png
The 313 mA is right spot on, compared to my simulation.

You're not counting the full load, which includes max available (whether you use it or not) and the residual for the zeners to maintain robust regulation, plus the allowance for AC line variation (which increases the current at nominal). Remember, zener regulators (besides being simple and cheap) pull the same current whether you have a load or not. The current simply goes through the zener, or the load, but the overall current demand is constant. That's necessary for the cap dropper to work.




That's a lot of power. You were right about that.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 12:04 am 
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john8750 wrote:
I got 164ma feeding the 13volt supply-149ma for the rest. Flip said that the cap dropper is not very efficient.
I can get the power from the tone amp from the filament supply, I think, don't need to be regulated. The 20volts for the opamp will need to come from the 120ac line, through a dropper cap, or a separate transformer.
I think you're worrying about the wrong things. The power supply doesn't have anything to do with 'squeals', tone controls not working correctly, or broken volume pots.

You just need to work backwards from the power tubes (disconnect the opamp drivers) and get each section working as you add them in one by one so you know what you're working on and where the problems are.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 12:24 am 
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Flipperhome wrote:
john8750 wrote:
I got 164ma feeding the 13volt supply-149ma for the rest. Flip said that the cap dropper is not very efficient.
I can get the power from the tone amp from the filament supply, I think, don't need to be regulated. The 20volts for the opamp will need to come from the 120ac line, through a dropper cap, or a separate transformer.
I think you're worrying about the wrong things. The power supply doesn't have anything to do with 'squeals', tone controls not working correctly, or broken volume pots.

You just need to work backwards from the power tubes (disconnect the opamp drivers) and get each section working as you add them in one by one so you know what you're working on and where the problems are.




Just what I will do Flip. I will cut out the tone section, connect directly to the opa604 inputs. Get that working first. I will need a temporary gain pot at the input, 100K dual for testing.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 12:32 am 
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john8750 wrote:
Flipperhome wrote:
john8750 wrote:
I got 164ma feeding the 13volt supply-149ma for the rest. Flip said that the cap dropper is not very efficient.
I can get the power from the tone amp from the filament supply, I think, don't need to be regulated. The 20volts for the opamp will need to come from the 120ac line, through a dropper cap, or a separate transformer.
I think you're worrying about the wrong things. The power supply doesn't have anything to do with 'squeals', tone controls not working correctly, or broken volume pots.

You just need to work backwards from the power tubes (disconnect the opamp drivers) and get each section working as you add them in one by one so you know what you're working on and where the problems are.

Just what I will do Flip. I will cut out the tone section, connect directly to the opa604 inputs. Get that working first. I will need a temporary gain pot at the input, 100K dual for testing.
Usually pots are okay but you don't have to have it connected to test. Just lower the volume on whatever you're using to drive the amp, probably an MP3 player.

You can also test the opamp circuitry without connecting them to the output tubes (disconnect from the grids). Just feed a signal to them and see what the output is. The two sides should be equal but 180 degrees out of phase with each other. And it would be a good idea to check their offset with no signal. It should, of course, be 0 (within a few millivolts).


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 12:42 am 
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John:
What is the HV at now?
You said you were unable to get it over 300v I think?
Why is that I wonder?

Whatever B+ voltage you have .. put your scope on it (AC mode) and measure the peak-peak ripple voltage level.
I'm very curious.

As I have mine now I get less than 20mv pp ripple.

But I'm using larger filter caps.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 1:14 am 
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I just checked the MP3 into the opamp, and then to the tubes. Big problem with either the opamp or the tube amp. Scratchy just like with the tone amp. I will check the opamp with a tone input and scope. Can I do the same with the tube amps?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 2:15 am 
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john8750 wrote:
I just checked the MP3 into the opamp, and then to the tubes. Big problem with either the opamp or the tube amp. Scratchy just like with the tone amp. I will check the opamp with a tone input and scope. Can I do the same with the tube amps?
Well, yes and no. You can't drive it 'normally' because, without the opamps, you don't have a phase inverter but you can drive one side, then the other, and see that the plate varies.

If the idle current is, indeed, correct I suspect the output tubes are okay although you could, possibly, have a problem with the CCS, like the bypass caps not wired right (or a bad solder joint). But the most likely thing, I would think, is a problem in the opamp circuit.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 3:18 am 
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Flipperhome wrote:
john8750 wrote:
I just checked the MP3 into the opamp, and then to the tubes. Big problem with either the opamp or the tube amp. Scratchy just like with the tone amp. I will check the opamp with a tone input and scope. Can I do the same with the tube amps?
Well, yes and no. You can't drive it 'normally' because, without the opamps, you don't have a phase inverter but you can drive one side, then the other, and see that the plate varies.

If the idle current is, indeed, correct I suspect the output tubes are okay although you could, possibly, have a problem with the CCS, like the bypass caps not wired right (or a bad solder joint). But the most likely thing, I would think, is a problem in the opamp circuit.



SOLDER JOINT you say. Well, whoever built the preamp circuit had an open solder joint. I checked the grid voltages. One was over 21 volts, no signal. Others were close to 0volts. Checked the cathode voltages. The same tube was, of course, way low, like 2.3volts. Others were around 18volts. So I traced the bad grid wire back to the preamp output, IC2 pin6. In that circuit there is a 4.7K connected to another 4.7K, then to pin6 on IC1. Bad solder joint at that connection. I made the repair.
Connected the MP3 and have some ok music again. It has some weird edges, needs to be worked out. I will hookup the tone amp tomorrow for another test. Thinking about mounting an additional tranny just for the opamp power.


Forgot to say, it was an intermittent problem.
Kind of amazing how you guess it so close Flip. :roll:

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 3:38 am 
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john8750 wrote:
SOLDER JOINT you say. Well, whoever built the preamp circuit had an open solder joint. I checked the grid voltages. One was over 21 volts, no signal. Others were close to 0volts. Checked the cathode voltages. The same tube was, of course, way low, like 2.3volts. Others were around 18volts. So I traced the bad grid wire back to the preamp output, IC2 pin6. In that circuit there is a 4.7K connected to another 4.7K, then to pin6 on IC1. Bad solder joint at that connection. I made the repair.
Connected the MP3 and have some ok music again. It has some weird edges, needs to be worked out. I will hookup the tone amp tomorrow for another test. Thinking about mounting an additional tranny just for the opamp power.


Forgot to say, it was an intermittent problem.
Kind of amazing how you guess it so close Flip. :roll:
Good, you're narrowing it down. But one thing stuck out in the above numbers. With one grid over 21 V the cathode should have been way high, like 40 V or more, attempting to 'counter' the grid being so high but you say it was only 2.3 V. Unless you missed a sign in those numbers that tells me the CCS isn't working. Perhaps it (or a cap) blew when it tried to go to such a high voltage.
At any rate, I'd check all the CCS circuits again and verify proper current on each.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 4:03 am 
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Pbpix wrote:
John:
What is the HV at now?
You said you were unable to get it over 300v I think?
Why is that I wonder?

Whatever B+ voltage you have .. put your scope on it (AC mode) and measure the peak-peak ripple voltage level.
I'm very curious.

As I have mine now I get less than 20mv pp ripple.

But I'm using larger filter caps.



Its right about 295-300 Peter. I need to consider where the rough sounding edges are coming from. Did you say that the opa604 had a harsh sound?

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 4:15 am 
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Flipperhome wrote:
john8750 wrote:
SOLDER JOINT you say. Well, whoever built the preamp circuit had an open solder joint. I checked the grid voltages. One was over 21 volts, no signal. Others were close to 0volts. Checked the cathode voltages. The same tube was, of course, way low, like 2.3volts. Others were around 18volts. So I traced the bad grid wire back to the preamp output, IC2 pin6. In that circuit there is a 4.7K connected to another 4.7K, then to pin6 on IC1. Bad solder joint at that connection. I made the repair.
Connected the MP3 and have some ok music again. It has some weird edges, needs to be worked out. I will hookup the tone amp tomorrow for another test. Thinking about mounting an additional tranny just for the opamp power.


Forgot to say, it was an intermittent problem.
Kind of amazing how you guess it so close Flip. :roll:
Good, you're narrowing it down. But one thing stuck out in the above numbers. With one grid over 21 V the cathode should have been way high, like 40 V or more, attempting to 'counter' the grid being so high but you say it was only 2.3 V. Unless you missed a sign in those numbers that tells me the CCS isn't working. Perhaps it (or a cap) blew when it tried to go to such a high voltage.
At any rate, I'd check all the CCS circuits again and verify proper current on each.



I will rebuild the CCS and preamp board. I want them separate from the tone amp. Should have done that before. But, after repairing the bad solder joint, all voltages are back to normal. But a little weird edge on the music. At least we are back in business. All CCS caps seem ok. I checked them, in the circuit to ground. An open or short would be easy to see.
That cathode was way low, grid high. Go figure that one.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 4:34 am 
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john8750 wrote:
I will rebuild the CCS and preamp board. I want them separate from the tone amp. Should have done that before. But, after repairing the bad solder joint, all voltages are back to normal. But a little weird edge on the music. At least we are back in business. All CCS caps seem ok. I checked them, in the circuit to ground. An open or short would be easy to see.
That cathode was way low, grid high. Go figure that one.
I don't know because those voltages don't make sense. Maybe some 'protection' circuitry (heat?) kicked on in the CCS.

Something else that doesn't make sense, is the tube should have red plated big time with PLUS voltage on the grid.


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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 5:32 am 
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Flipperhome wrote:
john8750 wrote:
I will rebuild the CCS and preamp board. I want them separate from the tone amp. Should have done that before. But, after repairing the bad solder joint, all voltages are back to normal. But a little weird edge on the music. At least we are back in business. All CCS caps seem ok. I checked them, in the circuit to ground. An open or short would be easy to see.
That cathode was way low, grid high. Go figure that one.
I don't know because those voltages don't make sense. Maybe some 'protection' circuitry (heat?) kicked on in the CCS.

Something else that doesn't make sense, is the tube should have red plated big time with PLUS voltage on the grid.



Cant say I understand how it all works. If the cathode voltage was very low, don't that figure the plate current was low? Does the grid need to be lower than the cathode to conduct the tube into operation? This is a great learning experience for me.
All cathode and grid voltages are right in there, now.

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 Post subject: Re: 6V6 amp project- with a twist
PostPosted: Feb Mon 05, 2018 5:55 am 
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I could swap this transformer for the 12volt 1amp I have in there. It could power filaments with 450ma 24volts.
Will I have enough power left, 1.6amp output, for the IC supplies? Could use zeners for +- 20volt and +13volt supplies.
Don't need the 24volts.
https://www.ebay.com/itm/24-VOLT-HVAC-t ... SwmSdadQo9

Could use 78-79 IC regulators.

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