Tube amp experts check for flaws and problems in design.

[ceeya68]

I am trying to design an amplifier that will be a fun project. I made a design and I'm hoping experts could look it over and see if I have missed something or have made a terrible mistake? If the circuit will even work? Will it make noise like terrible? I've been building amps for a while now. But just copies basically. A few Marshall designs and one Soldano 50slo. A couple Fender B.F. Ab763 amps. This is my first attempt at something more grand. Basically just copying things I think I might Like and putting them together.. Kinda wondering how bad I messed up. Please have a look and see what you can see. Thanx!!

[sluckey]

Where's the schematic? Very hard to comment on an amp design by looking at a layout.

[92Volts]

It looks like the neutral/common tap of the OPT secondary goes to the + of one speaker, and the 4/8/16 ohm taps go to the + of the other speaker. This will only work when running 2 speakers in series, which is unusual and likely not what you intended.

It's typical to ground the neutral/common and send 4/8/16 to both speakers, for use in parallel.

You're also pulling negative feedback off the neutral tap, which wouldn't work if you ended up grounding it. You'd normally take negative feedback from one of the 4/8/16 ohm taps, before the selector switch, so you get the same level of NFB regardless of which speaker setting is used.

[PRR]

Bridge rectifier has 4 legs but you only using 3?

[tubenit]

Where's the schematic? Very hard to comment on an amp design by looking at a layout.

+1

[ceeya68]

Where's the schematic? Very hard to comment on an amp design by looking at a layout.

I'm not smart enough for schematics yet. My brain does better with pictures and following wires.. Any help you can give would be appreciated.  Thanx !!

[ceeya68]

It looks like the neutral/common tap of the OPT secondary goes to the + of one speaker, and the 4/8/16 ohm taps go to the + of the other speaker. This will only work when running 2 speakers in series, which is unusual and likely not what you intended.

It's typical to ground the neutral/common and send 4/8/16 to both speakers, for use in parallel.

You're also pulling negative feedback off the neutral tap, which wouldn't work if you ended up grounding it. You'd normally take negative feedback from one of the 4/8/16 ohm taps, before the selector switch, so you get the same level of NFB regardless of which speaker setting is used.

Thank You! 92 volts. Very observant. I think I have addressed the flaws you found. Take another look at this revised picture and see what you think. Please let me know if you see anymore concerns in the amp drawing? Thanx again!

[ceeya68]

Bridge rectifier has 4 legs but you only using 3?

Yes. in the 2204 build that I originally followed by G. Metropoulos only three legs of the rectifier were used. If you noticed anything else in my drawing please let me know. Thanx Much!

[sluckey]

Bridge rectifier has 4 legs but you only using 3?

Only the positive half of the bridge is being used. His PT has a center tap. 312.5-0-312.5vac

[ceeya68]

Bridge rectifier has 4 legs but you only using 3?

Only the positive half of the bridge is being used. His PT has a center tap. 312.5-0-312.5vac

Sluckey, I guess this is a bit over my head. (the terms you have used). I apologize! This is a pic of the transformer I will be using and that I have used in the past with 2204 type builds I have done. I haven't had a problem with the way it's hooked up so far. If you have a better way please explain in layman's terms. I'm still kinda dumb. Sorry! But still I'm trying and learning as I go. (school me). Thanx Much!!

[sluckey]

Nothing wrong with how you have that hooked up. I was looking at that PT pdf when I replied. I was just pointing out why only three legs of the bridge were being used.

[ceeya68]

Nothing wrong with how you have that hooked up. I was looking at that PT pdf when I replied. I was just pointing out why only three legs of the bridge were being used.

Ah! Thanx Much! I could not tell you why it's hooked up the way it is. Or why the PT is hooked up the way it is. I follow directions. Check out the extra gain stage on my drawing. Any trouble there?

[sluckey]

Lot's of trouble. The coupling cap for V1 pin 6 is connected to ground. You have V1 pin 6 connected to V3 pin 6. I'm not gonna look any deeper without seeing a schematic. I don't see how you can possibly design a successful amp by stitching together bits and pieces of various layouts you have seen, especially since you don't seem to understand what those bits and pieces do. You really need to start with a schematic and learn what's going on. When you have a working schematic then you can design a working layout from that schematic.

I don't mean this in a mean spirited way. I'm just telling you how it is, at least IMO.
 

[ceeya68]

Lot's of trouble. The coupling cap for V1 pin 6 is connected to ground. You have V1 pin 6 connected to V3 pin 6. I'm not gonna look any deeper without seeing a schematic. I don't see how you can possibly design a successful amp by stitching together bits and pieces of various layouts you have seen, especially since you don't seem to understand what those bits and pieces do. You really need to start with a schematic and learn what's going on. When you have a working schematic then you can design a working layout from that schematic.

I don't mean this in a mean spirited way. I'm just telling you how it is, at least IMO.

Thanx! Sluckey! I Appreciate the help! I did fix the flaws you advised me on. I understand the how it is bit and I apologize! I'm usually pretty good at figuring things out most the time. But I am glad I posted this. People already have helped me and I appreciate it. I will try and learn how schematic reading works. I'm sure there's stuff on the the net about it. And also I do own an Ugly's book. I did revise the drawing from your corrections. Thanx Again!

[sluckey]

Coupling cap and input jack still aren't right. Also, take a look at pin 5 of the EL34s.

[shooter]

I'm bored so I'm slowly tinkering.

your mains fuse seems wrong , I drew the schematic like I think you want.
I stopped here;

take a look at pin 5 of the EL34s.

the right side of the choke probably shouldn't power G1
you have 3 colors for the choke, red, gray, black, can you post a diagram of the choke?

EDIT:  guessing this is ?close? to how you want your PS?

[ceeya68]

Coupling cap and input jack still aren't right. Also, take a look at pin 5 of the EL34s.

Pin 5 of the power tubes run to the PPIMV. Not sure what to do on the input and coupling cap. Thanx Though!

[ceeya68]

I'm bored so I'm slowly tinkering.

your mains fuse seems wrong , I drew the schematic like I think you want.
I stopped here;

take a look at pin 5 of the EL34s.

the right side of the choke probably shouldn't power G1
you have 3 colors for the choke, red, gray, black, can you post a diagram of the choke?

EDIT:  guessing this is ?close? to how you want your PS?

There are three wires going to the lug on the board, grey from the choke - blk. from the OT-CT and red from the HT fuse. Thanx for schem. Though! I will look it over carefully. Only two wires come from out of the choke blk and grey. There both going to seperate lugs on the board..

[sluckey]

Coupling cap and input jack still aren't right. Also, take a look at pin 5 of the EL34s.

Pin 5 of the power tubes run to the PPIMV. Not sure what to do on the input and coupling cap. Thanx Though!

Look at those yellow wires on pin 5! I don't know about the input and coupling cap either. I have no idea what you are trying to do, but I know that what you show is not right.

The other end of that black wire connected to the 8.2k next to the bias pot is connect to the wrong terminal.

[shooter]

I don't know about the input and coupling cap either

that's where I stopped

EDIT: went to V1B and came up with this.  I think i'll stop til we're all on the same picture

[sluckey]

went to V1B and came up with this.  I think i'll stop til we're all on the same picture

The coupling cap on pin 6 no longer goes to ground. It just goes to the input jack tip switch. The shield for that cable also connects to the switch lug but so what? The shield is not connected at the other end. So, when nothing is inserted into the input jack the switch lug connects to the tip. Therefore, the coupling cap simply connects back to the grid of V1b.   

There is a red/yellow centertap shown on the layout. So the power supply does work.

I finally finished the schematic. I'm done!   

[ceeya68]

Coupling cap and input jack still aren't right. Also, take a look at pin 5 of the EL34s.

Pin 5 of the power tubes run to the PPIMV. Not sure what to do on the input and coupling cap. Thanx Though!

Look at those yellow wires on pin 5! I don't know about the input and coupling cap either. I have no idea what you are trying to do, but I know that what you show is not right.

The other end of that black wire connected to the 8.2k next to the bias pot is connect to the wrong terminal.

Sluckey you are exactly right. I had those yellow wires on the wrong pin. My bad. They should be corrected now. You were right on the blk. wire also. I am getting exactly what I asked for. (my Mistakes have been unveiled). I think I may have the input a bit better also now.  Sluckey Thanx for your help. I appreciate it.

[ceeya68]

I don't know about the input and coupling cap either

that's where I stopped

EDIT: went to V1B and came up with this.  I think i'll stop til we're all on the same picture

Shooter, I know your trying to help and I very much appreciate you for that. I am looking at the pictures you have posted and all I can say is I am trying to understand. I do recognize some things and others I do not. It looks like a loop to me right now. I know I am unfamiliar with schematic drawings it is definetly a weak point in me. But I want to say thank you! To you.

[ceeya68]

went to V1B and came up with this.  I think i'll stop til we're all on the same picture

The coupling cap on pin 6 no longer goes to ground. It just goes to the input jack tip switch. The shield for that cable also connects to the switch lug but so what? The shield is not connected at the other end. So, when nothing is inserted into the input jack the switch lug connects to the tip. Therefore, the coupling cap simply connects back to the grid of V1b.   

There is a red/yellow centertap shown on the layout. So the power supply does work.

I finally finished the schematic. I'm done!   

I got it. :)

[sluckey]

I think I may have the input a bit better also now.

It still does nothing. What is it that you are trying to do?

[ceeya68]

I think I may have the input a bit better also now.

It still does nothing. What is it that you are trying to do?

this is what I am trying to do with a single input and an added gain stage with a switch to turn on and off the added gain stage. I've buillt this amp as it is two times now with no troubles. Thanx for your efforts!!

[sluckey]

I thought that was probably what you were after. But your layout is so FUBAR in that area that I fear you will never get there. Fortunately, Hoffman has already done it. Just copy his Plexi 50 with hotswitch layout.
 

[shooter]

I'm a "picture" guy myself, I would much rather do physics without math
I can "visualize" vectors in my head, I can "intuit" the force of a 300Kg human and a 1meter diving board.  At the end of the day though, the physic teacher wants to see Algebra! 

In electronics repair, we already have the layout, but without a schematic, the time it would take to reverse engineer, (flawlessly), the layout, (circuit board), to a schematic is cost prohibitive.
here's a quick-search start to understanding schematics, happy reading

https://learn.sparkfun.com/tutorials/how-to-read-a-schematic

[ceeya68]

I'm a "picture" guy myself, I would much rather do physics without math
I can "visualize" vectors in my head, I can "intuit" the force of a 300Kg human and a 1meter diving board.  At the end of the day though, the physic teacher wants to see Algebra! 

In electronics repair, we already have the layout, but without a schematic, the time it would take to reverse engineer, (flawlessly), the layout, (circuit board), to a schematic is cost prohibitive.
here's a quick-search start to understanding schematics, happy reading

https://learn.sparkfun.com/tutorials/how-to-read-a-schematic

Thanx! shooter I will do some studying when I can. It does spark my interest. So that's usually the first step.

[ceeya68]

I thought that was probably what you were after. But your layout is so FUBAR in that area that I fear you will never get there. Fortunately, Hoffman has already done it. Just copy his Plexi 50 with hotswitch layout.

Thanx! Sluckey I will check it out.

[pompeiisneaks]

I just want to mirror what I've read here.  I first want to encourage your interest in amp building, it's a TON of fun, and in no way is anyone here trying to say you shouldn't proceed with your aspirations.  But first things first. 

If you don't understand schematics, you can't understand how to find flaws in your layout.
If you don't understand how tubes work, in general, you can't find flaws in your layout.
You can't just grab ideas from one amp and staple them into another (without some tweaks at any rate).

I highly recommend not only learning how to understand schematics, but also read up and watch video's about tube amps and how they work.  For books, I'd recommend Merlin Blencowe's book on tube guitar preamps.  http://www.valvewizard.co.uk/

I highly recommend watching any Youtube videos you can about tubes and tube amps.  Some great content is Uncle Doug's videos.  He has great videos on how resistors and capacitors are used in tube amps, on how tubes work, and on how to build tube amps. 

I highly recommend those.

I've got a ton of video's showing building of amps now, (80 some odd) but they're more middle level showing someone how to build from known schematics and layouts.  (It's somewhat my learning process in real time :D)  www.youtube.com/frenchiefilms

As has been noted, it may be best to just try and build Doug's 50 watt plexi with the gain switch mod.  Found here: http://el34world.com/Hoffman/files/Hoffman_Plexi50.pdf

~Phil

[ceeya68]

I just want to mirror what I've read here.  I first want to encourage your interest in amp building, it's a TON of fun, and in no way is anyone here trying to say you shouldn't proceed with your aspirations.  But first things first. 

If you don't understand schematics, you can't understand how to find flaws in your layout.
If you don't understand how tubes work, in general, you can't find flaws in your layout.
You can't just grab ideas from one amp and staple them into another (without some tweaks at any rate).

I highly recommend not only learning how to understand schematics, but also read up and watch video's about tube amps and how they work.  For books, I'd recommend Merlin Blencowe's book on tube guitar preamps.  http://www.valvewizard.co.uk/

I highly recommend watching any Youtube videos you can about tubes and tube amps.  Some great content is Uncle Doug's videos.  He has great videos on how resistors and capacitors are used in tube amps, on how tubes work, and on how to build tube amps. 

I highly recommend those.

I've got a ton of video's showing building of amps now, (80 some odd) but they're more middle level showing someone how to build from known schematics and layouts.  (It's somewhat my learning process in real time :D)  www.youtube.com/frenchiefilms

As has been noted, it may be best to just try and build Doug's 50 watt plexi with the gain switch mod.  Found here: http://el34world.com/Hoffman/files/Hoffman_Plexi50.pdf

~Phil

Thanx!!!