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Making component choices (6V6/EL84 PP)

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rockgardenlove

Member
Joined 2008
Hi,
I'm trying to design and build a push pull amp using either 6L6s or EL84s. I'm trying to narrow down parts to buy so that I can do some prototyping and testing.

Power transformer:
Will 275-0-275 get me a rectified B+ of 300 volts?
What current rating should I aim for? If I knew exactly what I wanted to build I could calculate it, but as I'm kind of going to be designing as I go I can't do that. What current rating do I need?

Output transformers:
6V6/EL84s have an 8k or so output impedance, eh?
Are the Edcor transformers a good deal?
http://edcorusa.com/products/transformers/cxpp/cxpp25-ms-8k.html
Yay?
Are those honestly worth the price increase from these?
http://edcorusa.com/products/transformers/xpp/xpp15-8-8k.html

It seems the former can go 50 Hz lower and has multiple impedance taps. I don't think I really need multiple impedances though anyway.

Thanks!
 
E

Eli Duttman

Member
Joined 2004
Buy Edcor's model CXPP25-8-7.6K or its 4 Ohm equivalent, depending on the speakers you use.

The cores of the little $20 trafos will saturate from the NFB induced LF error correction signal. :(

Allow for at least 150 mA. of B+ current. The "El Cheapo" voltage doubler PSU very comfortably supplies 200 mA., while holding costs down. :D
 
HollowState

HollowState

Member
Joined 2006
rockgardenlove said:
If I knew exactly what I wanted to build I could calculate it, but as I'm kind of going to be designing as I go I can't do that.
Click to expand...

In my opinion "designing it as I go" is not the proper way to build an amplifier unless you are very experienced and have a lot of parts at your disposal. All amplifiers are a carefully chosen set of compromises. You would be much better served to decide on that power level (tubes) you want and next choose a circuit that you like. Then proceed to acquire the parts needed. It's easier and better that way.

Are the Edcor transformers a good deal?
Are those honestly worth the price increase from these?
Click to expand...

Yes, they are a good deal. And yes, the price difference is not unfair since it's a bigger unit with more iron, copper and labor in it's makeup.

Victor
 
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rockgardenlove

Member
Joined 2008
Re: Re: Making component choices (6V6/EL84 PP)

HollowState said:


In my opinion "designing it as I go" is not the proper way to build an amplifier unless you are very experienced and have a lot of parts at your disposal. All amplifiers are a carefully chosen set of compromises. You would be much better served to decide on that power level (tubes) you want and next choose a circuit that you like. Then proceed to acquire the parts needed. It's easier and better that way.



Yes, they are a good deal. And yes, the price difference is not unfair since it's a bigger unit with more iron, copper and labor in it's makeup.

Victor
Click to expand...

Thanks for the reply. I actually am going to design the amp first really, it's just that I want to have the power supply so I can build the preamp stages or whatnot first and test them with my scope.
Cheers
 
Ty_Bower

Ty_Bower

Member
Joined 2007
Re: Re: Re: Making component choices (6V6/EL84 PP)

rockgardenlove said:
...it's just that I want to have the power supply so I can build the preamp stages or whatnot first and test them with my scope.
Click to expand...


If you build the AF amp and phase inverter before the finals are constructed, the supply voltages will be higher than in the finished product. That might interfere with whatever testing you were planning to do.
 
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rockgardenlove

Member
Joined 2008
So, how does the Hammond 370 HX sound?
275-0-275
200 mA
6.3 v, 5v filament taps

That looks right to me. The price is 110 though.

The 370 FX is the same except for a 150 mA current and a 90 dollar price tag. But yeah. Maybe I should design the circuit first so I can figure out the current draw...

Cheers!
 
boywonder

boywonder

Member
Joined 2008
rockgardenlove said:
So, how does the Hammond 370 HX sound?
275-0-275
200 mA
6.3 v, 5v filament taps


Cheers!
Click to expand...


The 370HX should work fine for a stereo EL84 amp (shared power supply)

I used the 270EX for monoblock baby hueys. I think they are 100ma each.

If you don't need universal input (115-240v) or the bias tap, you can look at the 270 series, they are equivalent without the above features, and are less cash.

Plan on your recified DC voltage to be 1.41 times your AC voltage depending on your PS design. Can be less depending on if you are using SS or tube rectification. If you do a choke input, you can adjust the first cap value to tune the B+ voltage.

Are you familiar with PSUDII?
 
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rockgardenlove

Member
Joined 2008
Yeah, it's gonna be a stereo amp. :)

I'm looking for a B+ of at 300 V or so. Does this sound right for PP EL84?

Boywonder...I was thinking 275-0-275 would work out to be around 300. According to you 1.41 rule though it works out to be 387.5. I'm planning to use a tube rectifier, so that'll bring it down a bit though, eh? But yeah, do I not need 275-0-275?

And what is PSUDII? :)

Thanks!
 
boywonder

boywonder

Member
Joined 2008
rockgardenlove said:
Yeah, it's gonna be a stereo amp. :)

I'm looking for a B+ of at 300 V or so. Does this sound right for PP EL84?

Boywonder...I was thinking 275-0-275 would work out to be around 300. According to you 1.41 rule though it works out to be 387.5. I'm planning to use a tube rectifier, so that'll bring it down a bit though, eh? But yeah, do I not need 275-0-275?

And what is PSUDII? :)

Thanks!
Click to expand...


PSUDII is Duncan amps Free Power supply design software, super easy to use, and will give you a good feel for how your PS will work. The folks here can help you model the power supply with PSUD, but it is fairly straightforward to figure out. Highly recommended.

Download it here: http://www.duncanamps.com/psud2/index.html

300V B+ for PP84 is fine. My baby hueys are at 320V B+ with a 275-0-275 V 100 ma (each mono). They were originally running a B+ of 380V (and sounded rather good) but I re-did the PS as a CLC (per Gingertube's recommendation on the BH thread) so that I could tweak the 1st cap to get the voltage down. I think many production/classic EL84 designs run B+'s up to around 380V, so the tubes can take it, but it will reduce their life (but it also increases power output)

IIRC, Sy's Red Light District runs at around 380V B+.

Download PSUDII and play with it; to start, model a 275-0-275 xfrmr, Center tapped, the rectifier tube of your choice, then CRC or CLC (try both) with a 200ma constant current load. Once the model is set up look at the voltage at the constant current load. If you email me, I will send you a model of what a tube rectified CLC PS looks like (since I cannot figure out how to paste a pic in my posts) :confused:

PSUDII will let you know if your cap values exceed the current of your rectifier, and will also show AC ripple on your DC, and if your supply is underdamped (you'll see overshoot/ringing)
 
kmtang

kmtang

Member
Joined 2004
Lundahl C-core OPT

I have really good experience with Lundahl's OPT. I built two 45 SE and one pair of 2A3 with them and they all sounds so good to me and my HiFi buddies.

I would like to build a PP amp with Lundahl's OPT as well. Even though I don't know how that sounds but I have confidence with Lundahl.

Johnny
 
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