Rob Robinette's Micro Champ EF80 Power transformer EU equivalent question.

RicciAntoni_07

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Hello all, this is my first time posting on this site, so forgive me if I don't have this in the right place or if I am asking a dumb question.

Here is the build--https://robrobinette.com/Champ_Micro.htm#Champ_Micro_EF80

I am going to build Rob's EF80 Micro Champ, but I can't figure out which Toroidal power transformer I can use here in Europe.

maybe this one? https://www.tube-town.net/ttstore/toroidal-30va-8808.html

I am new to all this, so I am hoping to find some help here!

*update, I found a thread from 2012 I think where a guy here in Europe used this one, so I just bought it. Can't wait to try to build this!! But I have zero idea of how to wire it, but I have time to learn. I'll for sure have a ton of questions, so if you are wiling I would kill for someone or a bunch of you to chime in on my questions.

Thanks in advance.
 
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tschwarz

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Hi! I've used that PT from Tubetown in several Projects. With a bridge rectifier (no center tap) you can expect 270..280V HT. My amp had an ECC99 P/P power stage. Rob must have made a typo in the schematic, you can't get 370V HT from a 240-0-240 V CT secondary. More like 320..330V. I'd go ahead withbthat PT you got and use a bridge rectifier...
 

RicciAntoni_07

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Thank you! I appreciate the response, I hope I can figure all this out, It’s my first build. I need to learn a lot about the power transformer. Will be a dream come true if I can get this to work. I’m a little worried I will be in over my head once I start to wire the pt but I will comb through all the threads on here and ask questions so hopefully I’ll be able to do it!
 

2L man

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Welcome!

I just bought two of those tt30VA toroids and in two weeks use one will get used on a Champ where I use SS bridge rectifier. When transformer deliver much lower current than its rating the output voltage comes higher. Math when rectifying using high efficiency silicon bridge and filtering with plenty of electrolyts is Sqr2 × 200VAC = 282VDC.

We will quide you thru your first build :)
 

RicciAntoni_07

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Welcome!

I just bought two of those tt30VA toroids and in two weeks use one will get used on a Champ where I use SS bridge rectifier. When transformer deliver much lower current than its rating the output voltage comes higher. Math when rectifying using high efficiency silicon bridge and filtering with plenty of electrolyts is Sqr2 × 200VAC = 282VDC.

We will quide you thru your first build :)
Thank you!!! it's a life dream just to make one. I know the flood gates will open up once I do, but I already wake up and give an hour to studying the pages I've printed, while listening to the "truth about vintage amps" I am in absolute love with this all and have a huge appetite for it, it would really be amazing to be able to learn from the people who know this all. I am very thankful for Rob's page, I'm sure he knows, but it is a total gift he has put out into the world. I couldn't be more thankful. This would have been totally impossible for me with that page. Seems like here is the right place too! Much appreciated!
 

RicciAntoni_07

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Like 2L man said, the micro amps pull so little power the voltage you get is higher than spec.
This is sad, but I don't fully understand this yet. My transformers will arrive end of the week, then I will start the build Sunday or Monday. Also, hello Rob, I apologize in advance for the beginner questions I'm inevitably going to have. I printed out your "how amps work, trouble shooting, and the micro champ" So I am going through all that with a highlighter. My main worry is the power transformer and the wiring. But I have a week to learn it. I'll know more by the time I start.
 

2L man

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Transformer phenomenon is that its output voltage depends of output current. Secondary coil is wound copper wire and when output voltage is high there must be a lot of wounds so wire length is long and there comes resistance which leads to voltage drop. Also transformer iron core efficiency is not 100%. I recall primary coil efficiency also has effect but don't remember is mechanism resistance like on secondary or is it core efficiency only?

Transformer should produce rated output voltage when it outputs rated current (or 80% obviously there is no single standard) and therefore voltage is higher when current is lower.
 

RicciAntoni_07

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Question for @RicciAntoni_07 : Are you already good with a soldering iron? If so it should be simple, just make sure you are careful at first start up. Rob's guide is great.
Question for @RicciAntoni_07 : Are you already good with a soldering iron? If so it should be simple, just make sure you are careful at first start up. Rob's guide is great.
Hello, I’m by no means great, but I’m not terrible I think. I have been preparing for this by building pedals on turret boards. I’ve gotten a lot better and will make one more pedal that way before I start this build. The fact you say it’s easy, gives me hope that I will be able to do this and have this in my life going forward. When I started the pedal journey in August it was like total magic to start with a schematic, solder onto a turret board and have the pedal work, so the amp is like the holy grail for me. I didn’t make the pedal kits, I was mainly focused on what would translate to building and repairing an amp. My solder gun goes up to 750 degrees, and I use 60/40. I actually got eyelets for the amp instead of turrets because I feel I could do a cleaner job with eyelets. I will do my best to make good joints. I read a post yesterday on Reddit of a champ build attempt and the guy got crushed in the comments for the solder job and his leads being too long. I took a screen shot of all the crushing so that I can remind myself what to YouTube before I start, just to makes sure I have a better chance of success.
 

RicciAntoni_07

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Yep, sounds good. Just be patient. The information available is more than enough for anyone to do this. It does get dangerous when power is flowing, but you can stay safe if you pay attention. Good luck
Thanks. Making my discharge tool this week. I have been looking into all the safety stuff possible, even the rubber gloves! haha, but I should be alright, I will take it slow for sure.
 

2L man

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I actually got eyelets for the amp instead of turrets because I feel I could do a cleaner job with eyelets.
After you have made pedals soldering tube amps is easy. More powerful soldering iron, which you already have, and courage to heat target enough make solders good.

If eyelet hole is large and is occupied with only one component leg and a wire the solder might be challenging to fill hole smoothly. Then folding component leg and/or wire 180 decrees give solder more material to attach.

For resistors this already 180 decree bent wire leg, which now comes up, bending again 90 decrees and then cut about 2mm is a neat way to rise resistors stay above the circuit board.
 

King Fan

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You're getting great advice here. Has someone mentioned a lightbulb limiter for startup? You don't need a variac, but a limiter is great for safety, information (amp running without bad shorts) and reassurance. OTOH, finding a true incandescent bulb in the EU is apparently a big challenge. This Google search may contain some threads here that have helpful hints.

https://www.google.com/search?q="incandescent"+bulb+EU+site:TDPRI.com
 
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RicciAntoni_07

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You're getting great advice here. Has someone mentioned a lightbulb limiter for startup? You don't need a variac, but a limiter is great for safety, information (amp running without bad shorts) and reassurance, but finding a true incandescent bulb in the EU is apparently a big challenge. This Google search may contain some threads here that have helpful hints.

https://www.google.com/search?q="incandescent"+bulb+EU+site:TDPRI.com
You're getting great advice here. Has someone mentioned a lightbulb limiter for startup? You don't need a variac, but a limiter is great for safety, information (amp running without bad shorts) and reassurance, but finding a true incandescent bulb in the EU is apparently a big challenge. This Google search may contain some threads here that have helpful hints.

https://www.google.com/search?q="incandescent"+bulb+EU+site:TDPRI.com
yes! I am in the right place! I will make the light bulb limiter for sure. Ah great to know about the bulb, that is a big help, thank you! I am fairly transient so I shouldn't get a variac anyway.
 

RicciAntoni_07

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After you have made pedals soldering tube amps is easy. More powerful soldering iron, which you already have, and courage to heat target enough make solders good.

If eyelet hole is large and is occupied with only one component leg and a wire the solder might be challenging to fill hole smoothly. Then folding component leg and/or wire 180 decrees give solder more material to attach.

For resistors this already 180 decree bent wire leg, which now comes up, bending again 90 decrees and then cut about 2mm is a neat way to rise resistors stay above the circuit board.
Good advice about filing the eyelet hole. I need to look into that resistor way you say to do. Kiitos
 

RicciAntoni_07

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Hi! I've used that PT from Tubetown in several Projects. With a bridge rectifier (no center tap) you can expect 270..280V HT. My amp had an ECC99 P/P power stage. Rob must have made a typo in the schematic, you can't get 370V HT from a 240-0-240 V CT secondary. More like 320..330V. I'd go ahead withbthat PT you got and use a bridge rectifier...
Hello, I wanted to ask you, and anyone else a few questions as I begin to embark on this first amp build odyssey. I got the PT here and I wanted to see if I am correct about these numbers
--All in one heat sync wrap--

BK wire has 0v.
Yellow wire has 120v.
Violet 230v.
Red 240v.

other side of the PT

Secondary 1--RED RED 200V
Secondary 2--GREEN GREEN 6.3v


I am going to try to learn as much about all this as I can before I start, but just wanted to see what feedback I'd get here first! As far as the layout goes, I'm not there quite yet. Because I have a different PT, I am not 100% sure what goes where. I don't have the power chord with the Black, White, and Green wires--not entirely sure what to get for that. They layout for the EF80 version has different wires and wiring. If you could clarify that'd, it would help me a lot!

Appreciate the feedback!
 

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Paul-T

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Red red secondary are just like your white/yellow on the Antek and go to the bridge rectifier . Green/green go to the lamp/heaters. I think your Primaries should be black/violet .

Check with others before wire as above.
 

2L man

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Use black/0V and red/240V now for mains input but do not cut 230V wire because possibly it is correct input, which you find later when amp operates and you can measure true filament voltage!!!

Holding wire end with pliers push insulation back with wire cutters few mm and then cut the wire and insulation slide back hiding the naked wire and the voltage which there will come does not cause danger. There will be mains voltage although mains is feed to other input because it is part of the primary and if you end up using 230V input there might come about 240VAC to 240V input depending which way mains plug get inserted because it does not have polarity so remember to finish it same way if you change inputs.

It is good practice to fold this unused wire end 10mm and put a 20mm piece of heat shring tube over it and when this fold make a "clump" and tube is shrinked both side it won't come away. Do the same for 120V input. Now voltage is "double insulated" when first step you make insulation slide back over conductive wire and second step add heat shring tubing over it :)
 
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RicciAntoni_07

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Use black/0V and red/240V now for mains input but do not cut 230V wire because possibly it is correct input, which you find later when amp operates and you can measure true filament voltage!!!

Holding wire end with pliers push insulation back with wire cutters few mm and then cut the wire and insulation slide back hiding the naked wire and the voltage which there will come does not cause danger. There will be mains voltage although mains is feed to other input because it is part of the primary and if you end up using 230V input there might come about 240VAC to 240V input depending which way mains plug get inserted because it does not have polarity so remember to finish it same way if you change inputs.

It is good practice to fold this unused wire end 10mm and put a 20mm piece of heat shring tube over it and when this fold make a "clump" and tube is shrinked both side it won't come away. Do the same for 120V input. Now voltage is "double insulated" when first step you make insulation slide back over conductive wire and second step add heat shring tubing over it :)
Wow, thanks for all this! Hopefully I’ll figure it all out, but I suspect I’ll be back for more questions.
 




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