What amp to build? need direction about transformers

[orangehead72]

I have transformers from a donor amp. I’ve always struggled to understand the values of the transformers. ie: are they big enough or too big for a build. I’d like to build a 50 watt plexi clone or a 50 watt Hiwatt clone. I have successfully built a few amps, including a Hiwatt 10 years ago, but had good direction on the transformers. Any and all help will be useful and appreciated.

[shooter]

always struggled to understand the values of the transformers

the MOST important for a builder (not engineer:) is;
what did they power before they became donors
6V6's? 6L6s?........ how many?
once that question is answered, it's just a matter of finding other PROVEN amps, with those power tubes that float your boat.

we can wiggle a bunch on pre-amp stuff 

[orangehead72]

Thank you shooter. These came out of a 50 watt amp  I’ve seen some transformers labeled 340 and 340 or whatever value. This PT is labeled 340 / 0. So I get in doubt. This particular amp had 2 EL34’s   

[Colas LeGrippa]

May I suggest you build a Marshall JCM800 MODEL 2204. You won t be disappointed.

[orangehead72]

That amp was in my thinking as well. Is there a layout for this here or anywhere. Is there a choke involved with this particular build.

[orangehead72]

Found the layout and info here. Thank you.

[shooter]

These came out of a 50 watt amp

find that schematic, figure out how the power was wired and use it as a "guide" for you new build

[orangehead72]

I did shooter and I’m trying to figure it out. Thank you.

[orangehead72]

Shooter....I actually found a post of the exact transformers on here from 2019 from a reply by dummyload. This was helpful. I’m just fuzzy. It’s been 10 years or so. Near fatal heart attack, stroke and a couple of mild heart attacks since. So I’m retired, have lots of time on my hands and have a lot of parts and I love to learn. It’s like my memory is there but faint at times. Thank you.

[orangehead72]

May I suggest you build a Marshall JCM800 MODEL 2204. You won t be disappointed.

In regards to this 2204. Do you or any of you have a preference to a particular layout. I don’t mean in terms of preamp and stages, but the overall layout.

[shooter]

this is what I do;
I get a layout that is "close"
https://el34world.com/schematics.htm#Hoffman_Plexi_50

I get the exact schematic I want
I use pencils and X out out, draw in new
pretty soon you have your layout.
read my build thread on the 1482esq.  I came up with "my version", took Sluckeys actual layout, tweaked and built my board

[orangehead72]

I have been reading your thread. I like this layout and will build this and buy what I can here. I’m just always in doubt of the right transformers. I’ll get past it soon. More experience will help my confidence. Thank you shooter.

[shooter]

power transformers - PT
reading, with some understanding is the beginning, sounds like you're there n wanting more 

http://www.valvewizard.co.uk/psu.html
once you look at the cool pic's, do a read through n go play guitar 
repeat til it makes sense 70%.
He has 3(?) more sections on PS, rectifiers, filtering......
when you get through all that you'll want to go on tour or hide!

Output transformers - OT
they are way easier, but somehow seem complex, do 'em one at a time otherwise...

[orangehead72]

Well shooter I’m going to start. I’ve been told to stay home because of the virus and my heart issues. So now is a good time to start reading. I will read it until I understand and continue to read. Thank you once again.

[orangehead72]

Ok shooter....so from my reading I’m thinking I can use the 6.1/0 and make CT with resistor for heaters to get 6.1/6.1. The 340/0 will be good for the tube circuit. Having stated that, when I create the CT, will the other voltages balance for each leg of the PT.  340/0 now and with CT 340/340 ??  If I understood the article correctly.

[shooter]

you can get away with the resistors forming an artificial CT for filaments.

the 340 - 0 has no CT, so look at the schematic the PT came from, what type rectifier did it use?

[66Strat]

A full wave bridge rectifier would be the best way to implement the power transformer that you have.

Edited tp correct FWB rectifier. The previous schematic I posted was drawn wrong.

[orangehead72]

Thank you 66strat. I’m still reading shooter. It’s been awhile and I’m a little confused because I see a full  wave bridge (bridge) utilizing the 13 0 13 voltage, but this donor was part tube part solid state. I need to look at this more and follow the schematic through. I’ll get it. I don’t give up easy. If I have to read for the next few weeks I will. It never hurt anyone to read.

[orangehead72]

Ok now I understand. I had it all backwards earlier. Full wave bridge rectifier for no CT and a two phase if CT is available.

[orangehead72]

I believe it’s a full wave rectifier. Looking at the plexi, that’s a full wave to.

[sluckey]

That schematic shows a full wave bridge (FWB) rectifier.

[pdf64]

Just to be clear, the two phase rectifier arrangement is also a full wave type.

[shooter]

I don’t give up easy

just like Easter egg hunting 
panin is like that, a pan full of muddy, unclear cold unknowns, the longer you "wash n rinse", the clearer things become 

Note what was said about full wave, and full wave bridge.

[orangehead72]

Just to be clear, the two phase rectifier arrangement is also a full wave type.

The article I read said the 2 rectifiers are different.

[orangehead72]

Note what was said about full wave, and full wave bridge.

A bridge rectifier is used for a single wire from the transformer.

[pdf64]

Just to be clear, the two phase rectifier arrangement is also a full wave type.

The article I read said the 2 rectifiers are different.

Indeed their differences are significant and self evident; however, both are full wave.
There's an interesting and enlightening thread that's diverted on to the topic of rectifiers over on MEF currently https://music-electronics-forum.com/showthread.php?t=50722

[sluckey]

A bridge rectifier is used for a single wire from the transformer.

Not true. You must have two wires from the transformer for a bridge rectifier to work.

[shooter]

+1

the take away is in the CT / ground

a 2 wire secondary feeds the rectifier, the rectifier provides "circuit ground"
a 3 wire secondary has more options, one being it, the PT provides ground NOT the rectifier.  IF they both provide ground, you produce smoke 

[orangehead72]

A bridge rectifier is used for a single wire from the transformer.

Not true. You must have two wires from the transformer for a bridge rectifier to work.

From the article:
Bridge Rectifier
A bridge rectifier is used to rectify AC from a transformer with a single winding (i.e. no centre tap) or whenever you need to direct AC current into a single direction. At any one time, two diodes conduct while the other two are switched off. Notice that all the diodes 'point' towards the positive output.

So this just pertains to NO CT.
I am really trying to understand this. “Single winding” is where I believe I misunderstood. 

[orangehead72]

+1

the take away is in the CT / ground

a 2 wire secondary feeds the rectifier, the rectifier provides "circuit ground"
a 3 wire secondary has more options, one being it, the PT provides ground NOT the rectifier.  IF they both provide ground, you produce smoke 

Thank you shooter. I was hung up on “single wire” I am re-reading the article. I have a few old small transformers I look at while reading.

[orangehead72]

Just to be clear, the two phase rectifier arrangement is also a full wave type.

The article I read said the 2 rectifiers are different.

Indeed their differences are significant and self evident; however, both are full wave.
There's an interesting and enlightening thread that's diverted on to the topic of rectifiers over on MEF currently https://music-electronics-forum.com/showthread.php?t=50722

Thank you.....I will read all I can.

[orangehead72]

Shooter......so when I look at the label on the HT, it stats blue/blue 340/0 I need to understand it is without CT, one leg delivers voltage the other not and the rectifier will provide the the voltage to the other leg by its direction.
Am I understanding it correctly ?

[sluckey]

I was hung up on “single wire” I am re-reading the article.

Yes, I think that's the case. But, the article said...

A bridge rectifier is used to rectify AC from a transformer with a single winding

The key is "single winding". Yes, it's a single winding, but any winding has two ends (wires).

Look at the simple FWB drawing above. Do you see two wires from the transformer connecting to the bridge?

so when I look at the label on the HT, it stats blue/blue 340/0

Don't get hung up on 340/0. What that really means is there is 340V ***BETWEEN*** the two blue wires. Makes no difference which you call 340 or 0.

[orangehead72]

so when I look at the label on the HT, it stats blue/blue 340/0

Don't get hung up on 340/0. What that really means is there is 340V ***BETWEEN*** the two blue wires. Makes no difference which you call 340 or 0.
[/quote]

Thank you Sluckey.
The other Amps I built years ago were laid out, almost in kit form. There was really no figuring, as it was laid out in front of you. Use this HT, use these values and etc. I’ll still build that way for the moment, but having the HT, I thought if I could understand that part and create the right voltages for a particular amp build, I’d be further ahead in my knowledge. I appreciate all the direction I get from all of you.

[sluckey]

It's a learning process. When you start using junkbox parts, you're in the deep end of the pool. Better learn to swim!   

Asking questions and reading will get you far. 

[orangehead72]

I don’t mind being in the deep end. Sometimes it can be better. I like to learn in any direction.

[orangehead72]

Shooter/Sluckey

So the center tap provides the path for returning current. If you use a transformer without a center tap then a 4 diode bridge rectifier is needed to provide a current return path from the amp circuit back to the transformer.
And if the Tx I have had a CT, I could use the 2 diode method

[orangehead72]

Anyone....please suggest a good meter for these projects. I have a couple. One greenlee and some other junk. I want a good one that can handle the voltages. A good all around meter. Cost doesn’t matter

[shooter]

Cost doesn’t matter

then go for the '59 Caddy 

I did this for a living so Fluke has been with me since '76
the 87W is now the gold standard, the V was

again, read, find tech forum, surf up "dependable, reliable, industrial standard DVM meters"
good can be had for ~~~~ $50, the fluke will set you back $400

[sluckey]

Well, since cost doesn’t matter, get the industrial standard... Fluke 87V

Shooter, I had to look. Quote from fluke.com search...

0 search results for 87w.

Sorry, we make a lot of great stuff, but '87w' is not one of them.

[orangehead72]

I have a chance to by this as well for $250. Will this be a good investment for future builds ?

[orangehead72]

Well, since cost doesn’t matter, get the industrial standard... Fluke 87V

Shooter, I had to look. Quote from fluke.com search...

0 search results for 87w.

Sorry, we make a lot of great stuff, but '87w' is not one of them.

Thanks Sluckey and shooter ordering after dinner from Fluke-direct.com.
Appreciated

[66Strat]

Is the power transformer residing in an amp now? If so, it would be a good idea to make note of how the primary windings are connected. The transformer can be wired for either 115 or 230 volts AC. For 115 volts, the primary windings would be connected parallel. For 230 volts, the windings would be connected in series.

[orangehead72]

66strat it is still in the amp. The amp works well, except the DSP side and the pots are shot. Scratchy and touchy when adjusting. The amp is loud, very loud. So the tyranny’s seem healthy. Exactly why I want to build a 50 watt Hiwatt or the 2204. I’m not into the effects stuff anyway. Of course this is wired for 110 at the moment. I’ll take the chassis out of the head and trace.
Thank you

[shooter]

Shooter, I had to look

I musta went down a rabbit hole full of crayons 

In Oct (my birthday:) I searched for calibrations 87V
none, linked to fluke, said the new 87W was out replacing the V, find distributor, linked, $389 + shipping. welcome to disappearing data   

ah well, the V really can't be beat, unless Pete has a secret up his sleeve

[sluckey]

Amazon has a better price on the 87V. Post some pics of that amp please.

[orangehead72]

I will Sluckey. Still trying to figure out how to reduce pic size without compromising the the pic itself.
I’ll look on Amazon as well. Did you or shooter see the oscilloscope I can buy for $250. Will that be good to have for the future.

[66Strat]

Microsoft Paint works well at resizing photographs.

[orangehead72]

Test to see if these reduced enough

Ok now that I have figured that out, what pics should I post Sluckey ?

[sluckey]

A fully functional 2246A with a bright, sharp trace is a good deal for $250. That's the going price on eBay. I don't think you are quite ready to learn a scope, especially a sophisticated Tek 2246A. You need to nail down this power transformer/diode thing first. Then probably a lot more stuff. Honestly, I would put this amp project on the shelf and start with a simple Fender champ. Maybe even a kit. Plenty of documentation. A good project to learn some basics and get some hands-on experience with building and using that sophisticated Fluke. A scope is not a necessity for building an amp. I have an old Tek (but I made a living for 40 years looking at a scope) but rarely turn it on for my amp work. Until you can read a schematic and understand what's going on, a scope is just a complicated toy that may just baffle you. But once you understand the circuits a scope can be a real pleasure to work with.

You've shown an interest to learn and a willingness to research, so this is definitely something you can do. But, as the Ventures once expressed, "Walk, Don't Run". 

PS... about the pics... Post some hi-rez pics of the outside and inside (guts) of the chassis. These kind of pics can help zero in on just all this amp can be. We need much bigger pics than that!