Transformer Questions
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Transformer Questions
I have here a 2 piece of 6L6WGB that i will use as a push-pull configuration and according to the datasheet, it's limiting value is 360vdc plate voltage. What transformer voltage (in AC without load) should i use given that i will use 1N4007 as rectifiers.
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Stevem
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Re: Transformer Question
360 volts is not the limit in class AB ,be your circuit set for cathode bias or fixed bias.
If you where to run class AB in fixed bias you can go much higher in VDC on the plates, but your current will need to be less.
With SS rectified AC you would want a transformer with a 250 to 255 VAC center to center rating to end up with 360 VDC for the output tubes.
If you wanted to build for class A push pull then 325 is about the limit for VDC.
In class A you will also need a output transformer spec'ed for class A and a power transformer of a good bunch more current output then if your output stage where class AB.
Keep in mind that the wattage a tube can handle is determined by the voltage and current applied to it just like ohms law states.
If you where to run class AB in fixed bias you can go much higher in VDC on the plates, but your current will need to be less.
With SS rectified AC you would want a transformer with a 250 to 255 VAC center to center rating to end up with 360 VDC for the output tubes.
If you wanted to build for class A push pull then 325 is about the limit for VDC.
In class A you will also need a output transformer spec'ed for class A and a power transformer of a good bunch more current output then if your output stage where class AB.
Keep in mind that the wattage a tube can handle is determined by the voltage and current applied to it just like ohms law states.
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wpaulvogel
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Re: Transformer Questions
I’ll add that I’ve never gotten anywhere near 47 watts output power with 400 volts on the plates of a 6l6 type tube. It usually takes about 450 volts. A more reasonable estimate will be 38-40 watts. I don’t know your expectations from the amp but keep this in mind for headroom and power.
Re: Transformer Questions
Thank you for your replies. My current transformer here as of now is a 340-0-340v AC @ 280mA. Will this PT do the job or it is over or under? Thank you.
It will run in fixed bias circuit.
It will run in fixed bias circuit.
Re: Transformer Questions
Multiply the AC RMS voltage by 1.414 to find the AC peak voltage which is the maximum unloaded DC voltage.
Re: Transformer Questions
That 'data sheet' isn't really valid info, it may have come from manufacturer's preliminary info or soon after the tube's release. As time went on they got comfy with revising the ratings, upward usually. Also have to contend with the differing rating systems / changing names for those rating systems, used over time.johngovan wrote: ↑Wed Jan 22, 2020 10:18 am I have here a 2 piece of 6L6WGB that i will use as a push-pull configuration and according to the datasheet, it's limiting value is 360vdc plate voltage. What transformer voltage (in AC without load) should i use given that i will use 1N4007 as rectifiers.
The 6L6WGB is the exact same type type as the 5881, just the latter is the military reference for it.
See the Oct 1 1955 Absolute max ratings https://tubedata.altanatubes.com.br/she ... 5/5881.pdf
Then the Jun 1 1962 Design centre ratings (design centre is about 20% lower below the absolute max) https://tubedata.altanatubes.com.br/she ... 5/5881.pdf
However I suggest caution regarding your plan of designing an amp to suit a particular pair of tubes; how do you know they're any good?
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Stevem
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Re: Transformer Questions
Your 340/ 340 transformer @ 280 ma is too much for those tubes as you will have a unloaded D.c of 480'volts,this would be pushing even 6L6GC tubes close to there limit and you would have a output of over 50 watts RMS if that matters to you so you would need a output transformer that could handle that.
It sounds like your new to building amps so I would suggest you go for a lower first build then cobbling together this.
A kit may be the best thing for you to learn on, or take 2 big steps back and use one tube and build a 8 watt single ended class A amp.
It sounds like your new to building amps so I would suggest you go for a lower first build then cobbling together this.
A kit may be the best thing for you to learn on, or take 2 big steps back and use one tube and build a 8 watt single ended class A amp.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Transformer Questions
This is my dc unloaded voltage using solid state rectifier.
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Stevem
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Re: Transformer Questions
Not really if you do not have filters hooked up, with one filter node it will go up even higher!
You seem fairly hung up on using this power transformer, and if you do not have a output transformer already then I would look into other output tubes to handle that voltage and live more then a few days.
I would look into 7027 outputs or EL77, or the Groovetubes version of the KT66, if you have a OT already , or if not then EL34 / 6CA7 or 6550 tubes.
You seem fairly hung up on using this power transformer, and if you do not have a output transformer already then I would look into other output tubes to handle that voltage and live more then a few days.
I would look into 7027 outputs or EL77, or the Groovetubes version of the KT66, if you have a OT already , or if not then EL34 / 6CA7 or 6550 tubes.
Last edited by Stevem on Fri Jan 24, 2020 11:59 am, edited 1 time in total.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Transformer Questions
It has two 4007 diodes and one 22uf 450v capacitor.
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Stevem
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2 others liked this
Re: Transformer Questions
Ok so that is then the max voltage you will see, but one diode on each leg of the PT is not enough inverse voltage capablity, you need 2.
Your V+ voltage will drop like 1.2 volts on each leg with the needed two diodes.
Your V+ voltage will drop like 1.2 volts on each leg with the needed two diodes.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Transformer Questions
Noted sir Stevem. I appreciate your advices. 
Re: Transformer Questions
340-0-340 @280mA is perfect for a 2x6L6 amp! Take any 4k or 4.2k 50W output transformer and you are set for the transformer. Pair it with a regular 4H choke.
That being said, and I need to be honest here, you need to read more about power supply design. Start by studying the 2nd and 3rd gen Dumble amps. That is, ps-wise, in abstract what you're looking at for a 50W build.
If I were you, I'd save some extra money (again, if you have that opportunity), for a reverb tank, some extra passive parts, two tubes and sockets.
That being said, and I need to be honest here, you need to read more about power supply design. Start by studying the 2nd and 3rd gen Dumble amps. That is, ps-wise, in abstract what you're looking at for a 50W build.
If I were you, I'd save some extra money (again, if you have that opportunity), for a reverb tank, some extra passive parts, two tubes and sockets.
Re: Transformer Questions
Thanks rootz. Appreciate all your help. I'll take all your comments here. I learned so much from you reading your posts here in TAG and even your kindness to help. Yes. I will study more about psu. Until the time i can build my own dumble 50w amp.rootz wrote: ↑Fri Jan 24, 2020 5:16 pm 340-0-340 @280mA is perfect for a 2x6L6 amp! Take any 4k or 4.2k 50W output transformer and you are set for the transformer. Pair it with a regular 4H choke.
That being said, and I need to be honest here, you need to read more about power supply design. Start by studying the 2nd and 3rd gen Dumble amps. That is, ps-wise, in abstract what you're looking at for a 50W build.
If I were you, I'd save some extra money (again, if you have that opportunity), for a reverb tank, some extra passive parts, two tubes and sockets.
Again, Thank you so much.
Re: Transformer Questions
You're welcome John. As I see it there are a couple of standard solutions to guitar amps when it comes down to transformers. 20 Watter: Deluxe (reverb) iron, 50 Watter: Bassman iron; 100 Watter: Twin iron. At least for Fender inspired builds. That includes Dumbles. Marshalls are a different kind here, because of EL34's. Reflected plate loads are a bit lower normally, but EL34's would work with a 4 or 4.2k load for a push/pull pair. Standard Marshall practice is 3.4k though. You can find loads of info from e.g. Blencowe about loadlines and plate loads for output stages.
Anyway, for a standard 50W output stage with 2x6L6 in push/pull a 4.2k secondaries output transformer is a good start. An 8k deluxe transformer will work, just very not optimal. Those transformers are too small to deliver 50 Watts and present an unideal load to the power tubes (which can be corrected by equally mismatching the speaker load). In short: you won't gain much (or anything) from 6L6 tubes with a small output transformer.
As a power transformer 320-0-320V @ 200mA will work. That is what is in e.g. a Bassman. Classictone has got what is needed. Or Hammond. Can't recall what you have got already.
Suggestion: let's get back to what you've already got and make that work. My only point of doubt was your choice of output tubes, the 6L6's with the transformers you have.
Anyway, for a standard 50W output stage with 2x6L6 in push/pull a 4.2k secondaries output transformer is a good start. An 8k deluxe transformer will work, just very not optimal. Those transformers are too small to deliver 50 Watts and present an unideal load to the power tubes (which can be corrected by equally mismatching the speaker load). In short: you won't gain much (or anything) from 6L6 tubes with a small output transformer.
As a power transformer 320-0-320V @ 200mA will work. That is what is in e.g. a Bassman. Classictone has got what is needed. Or Hammond. Can't recall what you have got already.
Suggestion: let's get back to what you've already got and make that work. My only point of doubt was your choice of output tubes, the 6L6's with the transformers you have.