• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

My brew of the "Darling"

Status
Not open for further replies.
Jump to Latest
#21
arnoldc said:
Thanks for the encourgment, Alex 😀 😀

I'd like to do a Parafeed without the plate choke to keep things small. Again, I'd like to use the diyAudio CCS for ths duty. I hope it works 😀

If this works, then I can parafeed my 417A headphone amp also 😎
Click to expand...

Ah ok, so I can get rid of the plate choke use plate resistor, and still have parafeed? Thanks for this info, my understanding was I need both the plate choke and the OPT. :xeye:

Thanks, I have been learning a lot!
 
#23
arnoldc said:
Yes, you can. See this for explanation - http://members.aol.com/sbench/outstru.html

One member did a 2A3 amp with resistor on the plae but you'll need large B+
Click to expand...

Thanks for the link.

I have been reading parafeed output topology and most of the materials I read states that I can "use smaller OPT since there will be no DC on it."

How smaller can it be? Let us say that the 12b4 has 35ma on the plate, what will be the specs of the SE opt?

Thanks.
 
#25
arnoldc said:
I'm not in a position to answer that. You should ask your transformer winder. As an example, look at EXO-35 from MagneQuest.
Click to expand...

Thanks. My winder have never wound a parafeed OPT.

Thanks again, I will just try to compute/research the voltage and current after the capacitor on a parafeed circuit.
 
#26
mach1 said:
The 12B4 sounds really excellent in parafeed mode using cheap line output transformers (10W or 15W) and a decent choke (handmade H3007 or Magnequest BCP-15 - the hammond 157G will also work). With 7-8k line transformers run it around 225 - 240B+ with a 1.2k cathode resistor - the 6au6 version operating point is a bit too low.

As previously mentioned, it has an entirely different sound to the darling. Very clear and punchy with a surprisingly potent bottom end.
Click to expand...

Thanks for this info, I really want to try the parafeed 12b4, can you please share the schema?

Thanks.
 
#27
I have built a few of these with different drivers. You can use virtually any triode with a mu > 35 to drive the 12B4. The 6EJ7 is available, cheap and sounds excellent triode strapped.
The circuit sounds good with non-boutique parts.

Start with a cheap 10 or 15W line transformer as output. I guarantee you will be surprised. They should cost you between $10 and $15 each.

I credit Tom Stoppleworth with the 12B4 parafeed idea.
 

Attachments

  • 12b4 para.jpg
    12b4 para.jpg
    23.2 KB · Views: 749
#28
mach1 said:
I have built a few of these with different drivers. You can use virtually any triode with a mu > 35 to drive the 12B4. The 6EJ7 is available, cheap and sounds excellent triode strapped.
The circuit sounds good with non-boutique parts.

Start with a cheap 10 or 15W line transformer as output. I guarantee you will be surprised. They should cost you between $10 and $15 each.

I credit Tom Stoppleworth with the 12B4 parafeed idea.
Click to expand...

How much current do I need for the 12B4 on your schematic?

Thanks.
 
#31
My winder have never wound a parafeed OPT.
Click to expand...

Don'nt need to, you can use the 110/220 volt primary, 12volt multi-tap secondary 500mA traffo which can be bought for around 100 pesos and you are in business...

😀

using the 6volt tap will reflect around 10k at primary with an 8 ohm speaker load, wheras, using the 6volt tap will reflect around 2.7k primary...

you can even try the 10DE7 from Gerry, makes a 2 tube SET amp.😀
 
#33
mach1 said:
I have built a few of these with different drivers.
Click to expand...

You should connect the parafeed cap from the plate to the transformer primary, and the other side of the primary to ground (or the cathode for a WE connection) -- the way you have it, with the transformer connected to the plate and the cap to ground, charges the parafeed transformer like a cap, which is bad.

If you are looking for very good, very cheap parafeed transformers, check out the Hammond 119DA's. The downside is they are 600:8, the upside is that they work very well 2.5K:32, so are great for headphones.
 
#34
dsavitsk said:
connect the parafeed cap from the plate to the transformer primary, and the other side of the primary to ground (or the cathode for a WE connection) -- the way you have it, with the transformer connected to the plate and the cap to ground, charges the parafeed transformer like a cap, which is bad.
Click to expand...

I've seen that discussion before... as i understand it, it makes no difference which end of the trafo you put the cap, it still performs the same way.

dave
 
#36
dsavitsk said:
You should connect the parafeed cap from the plate to the transformer primary, and the other side of the primary to ground (or the cathode for a WE connection) -- the way you have it, with the transformer connected to the plate and the cap to ground, charges the parafeed transformer like a cap, which is bad.
Click to expand...

With the parafeed cap in the ground leg, the transformer capacitance is biased up with some DC on it, but the AC should be the same either way. Some people feel that caps sound better with a significant DC voltage bias, which seems plausible to me.

In any case, it's easy enough to try it both ways and listen.

-- Dave
 
#37
Tony said:


Don'nt need to, you can use the 110/220 volt primary, 12volt multi-tap secondary 500mA traffo which can be bought for around 100 pesos and you are in business...

😀

using the 6volt tap will reflect around 10k at primary with an 8 ohm speaker load, wheras, using the 6volt tap will reflect around 2.7k primary...

you can even try the 10DE7 from Gerry, makes a 2 tube SET amp.😀
Click to expand...

Tony,

I have seen some schematic using PP OPT (like the Hammond 125E on the End of Zen design), would this work better? I am planning to try the 12b4 circuit using my 832 PP OPT, it is around 8K primary.

My winder is willing to wind me a non-gapped OPT and am planning to use the plate chokes I used on my 7193 preamp on this 12b4 parafeed. Or I can use a CCS for plate load. 🙂

Ultimately, if this will turn out ok, I want to do a 12sl7 into a 6080 parafeed. 😀

What do you think?

Thanks,

Alex
 
#38
planet10 said:
I've seen that discussion before... as i understand it, it makes no difference which end of the trafo you put the cap, it still performs the same way.
Click to expand...


This is what I was told by Jack Elliano which is good enough for me -- as I understood it, connecting the transformer to the plate allows a huge DC across the windings, charging the transformer like a capacitor, which degrades its ability to act as a transformer. You'll have to call him for a better technical explanation than that.
 
#39
arnoldc said:


Say that again? :xeye:
Click to expand...

ah, my mistake, so using the multitap traffos that are abundant and cheap in Manila, you can tap the 6volt winding and get around 10k primary impedance, whereas tapping at 12v you will get about 2.7k...


😀

@alexg,

6sl7 has too much gain imho, you will want something like 20ish mu.
 
#40
connecting the transformer to the plate allows a huge DC across the windings, charging the transformer like a capacitor,
Click to expand...

Since the cap blocks DC I find that statement rather suspect. I don't understand where the 'huge DC' potential comes from. I have built quite a few parafeed amps and have mild preference for placing the cap in the lower leg. There are subtle differences, but nothing that could be attributed to the generation of 'a huge DC across the windings'. If this happened the core would saturate and the bass would suffer. This just doesn't happen.

Build both ways and see which you prefer.

This is a great budget transformer for parafeed use. It is roughly the same size as the ten watt unit but with a thicker stack. It only has one (8 ohm) secondary, which helps maintain sound quality.

http://www.altronics.com.au/index.asp?area=item&id=M1115

Impedance over the whole primary measures 7.2 - 7.5k
 
Status
Not open for further replies.
Top Bottom