Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: johngovan on January 22, 2020, 08:09:06 am
-
I have a 2 6L6wgb that i will use in push pull power section of a guitar amp. What PT voltage should i use? The datasheet says that 360vdc max for plate voltage. So what ideal PT voltage in ac (unloaded) should i buy?
By the way. I will use solid state rectifier.
-
It's common to see 6L6s using anything between 350 and 500V.
-
Will my current PT work? It has a 340-0-340 @ 280mA, 50v bias tap and 6.3v for filament. Since i will use a ss rectifier, I don't need the 5v tap. Will this work or not?
-
Multiply the AC RMS voltage by 1.414 to find the AC peak voltage which is the maximum unloaded DC voltage.
-
483.588vdc unloaded. I think its too much for a push-pull 6L6wgb. :(
-
Why dumble use 3 series diodes in each HV tap? What's the reason for that kind of rectification?
-
483.588vdc unloaded. I think its too much for a push-pull 6L6wgb. :(
I don't. Look at some Fender blackface schematics. Look at this schematic...
https://el34world.com/charts/Schematics/files/Fender/Fender_twin_reverb_ab763.pdf
Dumble use three diodes to insure the PIV rating is not exceeded.
-
Thank you sluckey. I appreciate your response to my inquiry. I just dont want to fry my tubes that i really want some advice before trying this one out.
I need some knowledgeable people like you to guide me through.
So I'll try to use this PT and see if it will do the job to build a poweramp for my existing guitar preamp.
-
483.588vdc unloaded. I think its too much for a push-pull 6L6wgb. :(
Have you measured this? If not, the calculation seems strangely a little high?
-
Maybe he's using an abacus. :icon_biggrin:
-
I have a 2 6L6wgb that i will use in push pull power section of a guitar amp. What PT voltage should i use? The datasheet says that 360vdc max for plate voltage. So what ideal PT voltage in ac (unloaded) should i buy?
By the way. I will use solid state rectifier.
What kind of 6L6WGB's are these? Real ones are rated for 400V plates, 300V screens and 26W. They were tougher 6L6GB's with an upgraded wattage rating, but the same voltage ratings. Nowadays 6L6WGB will probably handle anything a 6L6GC can.
The 360V plate voltage may have been an example of an application rather than a maximum rating.
I would go ahead and use your 340-0-340 PT and design the amp for 6L6GC's. It will probably wind up in the 450Vdc range once the load is connected, just like a zillion Fenders.
-
No. I don't use abacus. I just use my imagination. 😆
This is new wgb. Thank you for your response. I'll try to read and learn more stuff as i build this project. I hope i will soon succeed. 😁
-
This is the DC unloaded using solid state rectifier.
-
Voltage is fine. But 280mA current capacity really wants a 4x6L6 amp like a Twin Reverb. That PT is gonna just be loafing with a 2x6L6 amp for a load. Don't expect that B+ to drop much.
-
What's the ideal current for 2 6L6's?
-
This is Hammond transformer for bassman 5f6a that uses 2x5881. Having a 230mA. I'm getting a bit confused.
-
That's a good transformer. I would rather have that for a 2x6L6 amp than that 280mA monster.
-
Thank you sir. My friend have 325-0-325v @ 180mA for sale. I think that's more fitting than my 280mA transformer.
-
Thank you sir. My friend have 325-0-325v @ 180mA for sale. I think that's more fitting than my 280mA transformer.
That sounds about perfect. Do you have a particular amp in mind?
-
I would like to build a dumble 50w version sir. The mains voltage in our country is 220v @ 60Hz. Someone suggested to me to use the bandmaster PT and OT specs. But when i check the bandmaster specs in Hammond's site, it has a 330-0-330v @ 275mA. That's what makes me confused.
-
super reverb PT is rated at ~230-250mA - twin reverb PT typically have ~450-500mA rating. those ratings depend on who the winder is.
http://el34world.com/Transformers/files/Mojo763.pdf (http://el34world.com/Transformers/files/Mojo763.pdf) twin PT.
http://el34world.com/Transformers/files/MOJO762.pdf (http://el34world.com/Transformers/files/MOJO762.pdf) super PT.
when loaded you should see about 450V B+ - perfect for 5881/6L6GB cold biased.
--pete
-
Does both 330v capable of delivering 230mA or it was calculated in half? For example the 330v @ 115mA - 0 - 330 @ 115mA?
-
Does both 330v capable of delivering 230mA or it was calculated in half? For example the 330v @ 115mA - 0 - 330 @ 115mA?
usually the current rating when specified with with a CT transformer, is the DC current rating with a Full Wave rectifier.
--pete
-
Thanks pete.
-
Yes, for a 2 phase CT winding, full wave rectified, cap input smoothed arrangement, Iac = Idc.
See http://www.hammondmfg.com/pdf/5c007.pdf
-
> Iac = Idc. See http://www.hammondmfg.com/pdf/5c007.pdf
That table has multiple errors. The plan you reference, how can V(Peak)D.C. and V(Avg)D.C. be two different values? (assuming not-Huge ripple)
-
Yikes you’re right 😬
Not sure what is meant by V(avg) in this context, doesn’t seem relevant?
-
I suggested to Hammond that they should correct or remove that document, but they didn't.
They found it "on the web". YOU should apply all your usual BS-detection. Yes it seems to be (re)posted by a Trusted Source. But it has some nonsense. And Hammond's position seems to be that they just make these things, you should have your own Design Engineer.