Two different preamps (one octal and one regular) in a Tweed Delux "clone"

NTC

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I will start with this: the valve pin numbering is reversed. The numbers start the key/gap and increase going clockwise.

This is true if you are looking at the bottom of the tube - which it appears you are in the layout diagram.
 

Jerry garrcia

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Here’s an idea for the power supply without changing the location of anything.

View attachment 930092

If I were designing this, I would probably add another supply capacitor and dropping resistor (or two). Not sure it would be required in your case, but I always play it safe and decouple pairs of valves. Looks like you have 6 valves running off of C11, which seems like a lot and might lead to some interesting low frequency oscillations.
 

ruger9

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Just subscribing to this thread, because this would be one very cool amp. I've been watching that video in the OP for months now, lol
 

Jerry garrcia

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Hi and thank you for inputs. To bad I haven’t checked this forum for a while. To much Covid work…
The layout I presented was a bit wrong regarding the connections to S2 and valves. This one is the updated one that I have used for chassi layout. All connections to S2 is with shielded signal wire and they grounds to a single point on the chassi. All is unfortunate already soldered and mounted 😬. Haven’t tried it yet since I just got the 6SJ7 for V2 (on the layout it says 6SC7 but wrong).
So what should I do? I’m a bit retarded when it comes to constructing a layout.
-Add another capacitor? Where?
- should I remove on pair of diodes? If so, why?
- should I remove the couplings according to your inputs on the layout? Could you please explain why? I’m trying to learn and are reading a lot of books regarding the subject.

One other concern that I have is regarding the preamp. Is one 12ay7 or one 6SJ7 enough for the preamp stage?
Think of me as an infant trying to gain experience and knowledge. I’d really would like this amp to work.
Once again tnx.
9FB6EC3F-60DC-42F1-ACCC-FBB1CD6DF6A4.jpeg
 
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Jerry garrcia

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Here’s an idea for the power supply without changing the location of anything.

View attachment 930092

If I were designing this, I would probably add another supply capacitor and dropping resistor (or two). Not sure it would be required in your case, but I always play it safe and decouple pairs of valves. Looks like you have 6 valves running off of C11, which seems like a lot and might lead to some interesting low frequency oscillations.
Hi. I just posted a reply to your inputs.
 

Jerry garrcia

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Here’s an idea for the power supply without changing the location of anything.

View attachment 930092

If I were designing this, I would probably add another supply capacitor and dropping resistor (or two). Not sure it would be required in your case, but I always play it safe and decouple pairs of valves. Looks like you have 6 valves running off of C11, which seems like a lot and might lead to some interesting low frequency oscillations.
The connections on the back will be tough to remove since it is mounted in the chassi. I’ll have to try though if necessary. I do have some capacitators at home. Do any of them work? Also have a lot of resistors.
 

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andrewRneumann

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Ok I would advise you stop work right now and DO NOT turn it on.

Here are my problems:
1.You have a full-wave bridge rectifier wired to a 660VCT power transformer. That will get you twice the voltage you need.
2. If you turn this on, the power transformer will immediately short and your project will be dead in the water.

Let the smart people here help you. We will, but please DO NOT turn this on.
 

Jerry garrcia

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Ok I would advise you stop work right now and DO NOT turn it on.

Here are my problems:
1.You have a full-wave bridge rectifier wired to a 660VCT power transformer. That will get you twice the voltage you need.
2. If you turn this on, the power transformer will immediately short and your project will be dead in the water.

Let the smart people here help you. We will, but please DO NOT turn this on.
Hi and thank you. I don’t understand why the professional amp builder who designed this layout (got money for it) after my idea that “Printer2” from this forum executed, didn’t see this? I’m really not in the mood to redo it all. Or my wife do want my attention during the evenings😉.
Well, what can you do? There are two pairs of diodes and D2 and D4 are connected to the wire drawn on the back and connected to T1 0 VAC and C13-. D1 and D3 are connected to R13 and C13+.

Is it fixable?
 

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andrewRneumann

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Hi and thank you. I don’t understand why the professional amp builder who designed this layout (got money for it) after my idea that “Printer2” from this forum executed, didn’t see this? I’m really not in the mood to redo it all. Or my wife do want my attention during the evenings😉.
Well, what can you do? There are two pairs of diodes and D2 and D4 are connected to the wire drawn on the back and connected to T1 0 VAC and C13-. D1 and D3 are connected to R13 and C13+.

Is it fixable?
Sorry to hear about your experience with this “professional”, and yes—attend to your wife before amp building. Before I throw a stranger under the bus and pretend I’m infallible, I would suggest courteously taking my concerns to them and see what they say.

The problem with the diodes is easily fixed. Just remove D2 and D4. The wire on the back can stay there, it’s not hurting anything once D2 and D4 are gone.

Next issue with the power supply: power on voltage. When the amp is turned on the tubes are cold and do not conduct electricity. That means the capacitors will top up to the peak voltage being supplied by the power transformer. In your case, you have 330vac. The peaks are 330 x 1.414 = 467VDC once rectified. This is assuming your wall voltage is exactly 240vac. If it goes above 240vac, the turn-on voltage will be even higher. I’ve never cut it so close with capacitor voltage ratings, but I can tell you I would be using 500V capacitors in that power supply if I had a choice. EDIT: I now see the mains voltage is 230vac, so that helps. Peak VDC is then 448VDC…still cutting it close.

Next issue with the power supply: ground side (0VCT) is not referenced to the 0VDC (chassis) at any point. It is floating and will assume a random and varying voltage. You will have issues until you get that circuit a ground reference. Refer to my previous post with diagram showing how this circuit can easily be referenced to ground.

More to come… I’ve got my own family to attend to. 😎
 
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andrewRneumann

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You’ve got to take care of this too.

1641671967730.jpeg


Have you built a light bulb limiter? If not, do a search on TDPRI. It really is a smart investment. We have seen too many transformers go up in smoke because the builder didn’t have a light bulb limiter.
 
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Jerry garrcia

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You’ve got to take care of this too.

View attachment 938070

Have you built a light bulb limiter? If not, do a search on TDPRI. It really is a smart investment. We have seen too many transformers go up in smoke because the builder didn’t have a light bulb limiter.
This one is not soldered yet due to that I was worried that it was a diode problem. I had the same concerns that it might be a shortage risk when I looked at the layout. Because I’m not a professional at this I was doubting myself. But since it is in tough spot to soldier I was waiting with that one.

If it is so easy to solve the main problem by removing the two diodes, why did he put them there in the first place? Is it due to “Printer2’s” post that I’ll attach to this one? Tnx for your explanation in the previous post.
Is it possible to rescue the build?
Will it be enough with just one preamp tube?
 

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andrewRneumann

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This one is not soldered yet due to that I was worried that it was a diode problem. I had the same concerns that it might be a shortage risk when I looked at the layout. Because I’m not a professional at this I was doubting myself. But since it is in tough spot to soldier I was waiting with that one.

If it is so easy to solve the main problem by removing the two diodes, why did he put them there in the first place? Is it due to “Printer2’s” post that I’ll attach to this one? Tnx for your explanation in the previous post.
Is it possible to rescue the build?
Will it be enough with just one preamp tube?

I don’t see @printer2 addressing anything related to power supply except add in a resistor to create some “sag”. It is a common misunderstanding about when a bridge rectifier is required and when not.

@printer2 did you build this or was this a sketch of an idea? I’ve got concerns about the PI. Sometimes these sketch schematics get generated quickly and there are typos.

@Jerry garrcia it seems to me you are kind of in experimental territory. It can be made to “work” with one preamp tube before the PI, but I can’t say whether you will like it or not. I have not done what you are attempting to do.
 

printer2

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I don’t see @printer2 addressing anything related to power supply except add in a resistor to create some “sag”. It is a common misunderstanding about when a bridge rectifier is required and when not.

@printer2 did you build this or was this a sketch of an idea? I’ve got concerns about the PI. Sometimes these sketch schematics get generated quickly and there are typos.

@Jerry garrcia it seems to me you are kind of in experimental territory. It can be made to “work” with one preamp tube before the PI, but I can’t say whether you will like it or not. I have not done what you are attempting to do.
Just a sketch, tweak to taste. I only took a quick look through the thread, it has been a while. No a bridge rectifier is not the right one for the transformer. I usually leave the power supply details up in the air depending on what is being used. A center tapped transfornmer is usually used with a pair of diodes, or if the voltage is getting up there compared to the rating on the diodes, two in series for each leg.

On the PI, you can dial in the value of the resistor to supply the signal to the second triode. Early Fender schematics or Gibsons can be used as a guide. 5B3 as an example. I need to repair a snowblower at the moment otherwise the car is not getting out of the driveway, well, without a lot of shoveling.

 

andrewRneumann

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Here’s a possible solution to wire up the PI given the constraints of what you’ve already done.

1641680626544.jpeg


Please confirm that you didn’t wire all the valve sockets backwards. The socket pin numbering on the layout is reversed from what is standard. I can’t tell from your photos.

EDIT: After looking at the 5B3 schematic @printer2 posted, I would reduce R18 to 6.2K. 47K is way too much.
 
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printer2

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Had to water my plants before I ventured out into the cold. I noticed that the signal going to the top 6V6 is on the wrong side of the 220k resistor. The grid stopper of the 6V6 is suppose to be connected to the coupling capacitor. I thought that error was changed. The layout is a little small for these old eyes, I will look at it later when I get in. I had to look. The schematic with the switched preamps was right, mis-connected it when I simplified the circuit. I will get rid of it to avoid any confusion. I also miss entered the 4.7k value in the PI as 47k. I have been meaning to replace this keyboard, it has been causing me grief, it is worn out. Please accept my apologies.

kUbmJFn.png
 
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Jerry garrcia

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Here’s a possible solution to wire up the PI given the constraints of what you’ve already done.

View attachment 938107

Please confirm that you didn’t wire all the valve sockets backwards. The socket pin numbering on the layout is reversed from what is standard. I can’t tell from your photos.

EDIT: After looking at the 5B3 schematic @printer2 posted, I would reduce R18 to 6.2K. 47K is way too much.
Here’s a possible solution to wire up the PI given the constraints of what you’ve already done.

View attachment 938107

Please confirm that you didn’t wire all the valve sockets backwards. The socket pin numbering on the layout is reversed from what is standard. I can’t tell from your photos.

EDIT: After looking at the 5B3 schematic @printer2 posted, I would reduce R18 to 6.2K. 47K is way too much.
Here’s a possible solution to wire up the PI given the constraints of what you’ve already done.

View attachment 938107

Please confirm that you didn’t wire all the valve sockets backwards. The socket pin numbering on the layout is reversed from what is standard. I can’t tell from your photos.

EDIT: After looking at the 5B3 schematic @printer2 posted, I would reduce R18 to 6.2K. 47K is way too much.
What a mess and this might be the first and last time I’ll consult an expert for drawing up a build schematic… before he started I asked him if it was a possible build that was going to work in theory. After a positive reply I said go on that.

Your solution seems like a manageable re-wiering without resoldering everything.
I have soldered all tube sockets according to pin numbers, not their location in the layout. Unfortunately I don’t have the build in front of me since me and my wife was kicked out of the apartment because dou
Here’s a possible solution to wire up the PI given the constraints of what you’ve already done.

View attachment 938107

Please confirm that you didn’t wire all the valve sockets backwards. The socket pin numbering on the layout is reversed from what is standard. I can’t tell from your photos.

EDIT: After looking at the 5B3 schematic @printer2 posted, I would reduce R18 to 6.2K. 47K is way too much.
What a mess and this might be the first and last time I’ll consult an expert for drawing up a build schematic… before he started I asked him if it was a possible build that was going to work in theory. After a positive reply I said go on that.

Your solution seems like a manageable re-wiering without resoldering everything.
I have soldered all tube sockets according to pin numbers, not their location in the layout. Unfortunately I don’t have the build in front of me since me and my wife was kicked out of the apartment because daughter’s having friends over and do not want to be embarrassed by her parents.
@andrewRneumann: In layman’s words, what does your corrections generate? Regarding the single preamp tube before the PI I know it is experimental but I’ll have to try. It is just time and money spent. If it sounds terrible I’ll just have to resolder everything and make a regular 5E3. Not as fun but since I already have a chassi, speaker and a homemade cab something needs to be created of that. If you have a better idea of a working construction with the same function I’ll try that. The layout constructor had problems with the power supply from the start and the told me he solved it…
 

Jerry garrcia

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Had to water my plants before I ventured out into the cold. I noticed that the signal going to the top 6V6 is on the wrong side of the 220k resistor. The grid stopper of the 6V6 is suppose to be connected to the coupling capacitor. I thought that error was changed. The layout is a little small for these old eyes, I will look at it later when I get in. I had to look. The schematic with the switched preamps was right, mis-connected it when I simplified the circuit.

d3RyY1T.png


Please accept my apologies.

JQeeykk.png
Hi and thank you. With this lack of knowledge from my side, which of the two schematics is the correct one? Computer is home and I just have my phone and a bad pair of glasses.

Does anybody here have the knowledge to convert this layout to a build schematic? Does it differ a lot from the one I have? I have eons of time and a hot soldering iron at home. Since I just have one eyelet board and a limited number of capacitators it would be amazing if it is possible to make with what I have.
 

Jerry garrcia

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I hate to harsh your mellow.

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The 6SC7 socket wiring is incorrect. Pins 7,8 are the heater pins. I have not looked over the layout to find more problems. You have got work to do.🚧
Tnx. Why can’t it just be correct from the first time? Good that I bought more soldering led yesterday. V2 is supposed to be the 6SJ7. It’s named wrong in the schematic.
 




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