Opinions on Redd47 P2P Layout please

[sonolink]

The input tube's plate resistor (100k) should be connected to B2 (after 51k resistor).

Ok I think I've corrected it. Please check
Thanks again
Sono

 

[moamps]

Sorry I don't understand what you mean with "B2"

.

 

[abbey road d enfer]

Regarding the secondary windings, from the PSU schem it looks like 0v is the same for both phantom and heaters  ???
If that's going to blow any of my transformers I'm a bit puzzled since this is a product sold on a webpage (belonging to a forum member btw) so I assumed it would work ok without harming my components.

You haven't read my answer? This PSU needs two separate 12Vac windings.

I found JP2 strange too but I didn't bother with it much since I would use only 48v. Maybe some test point?

No. It just doesn't make sense. 

On the other hand, Rochey has rised an interesting point regarding using a BC550 for the slow start phantom. Any comments on that?

No; I think BC550 is adequate for handling 48V/10mA.

 

[moamps]

The voltage 12Vac for heater secondary isn't optimal value, IMO.
The heaters of EF86 and ECC88 can't be connected in series and supplied with 12dc without an additional equalized resistor on EF86's heater. If PF86 and PCC88 are used, that's possible.
So, the heaters should be connected in parallel, the heater voltage should be set to 6,3Vdc,  and the power dissipation on regulator will be unnecessarily high if the heater secondary is 12Vac.
There are three possibilities, IMO:
1. Use of AC heater voltage of 6,3V, so the secondary voltage is 6,3Vac,
2. Use of DC unregulated heater voltage of 6,3Vdc (a rectifier with few RC stages), where the optimal secondary voltage is 7-8Vac  and
3. Use of DC regulated heater voltage of 6,3Vdc where the optimal secondary voltage is about 9Vac.

 

[sonolink]

You haven't read my answer? This PSU needs two separate 12Vac windings.

I did and precisely because I did I am surprised that people sell stuff that is dangerous....
I have a toroid that has 3 secondaries: 200+12+12. If I use one 12v secondary for heaters and the other for phantom would that sort out the issue?

The voltage 12Vac for heater secondary isn't optimal value, IMO.[...]So, the heaters should be connected in parallel, the heater voltage should be set to 6,3Vdc,  and the power dissipation on regulator will be unnecessarily high if the heater secondary is 12Vac.
There are three possibilities, IMO:
1. Use of AC heater voltage of 6,3V, so the secondary voltage is 6,3Vac,
2. Use of DC unregulated heater voltage of 6,3Vdc (a rectifier with few RC stages), where the optimal secondary voltage is 7-8Vac  and
3. Use of DC regulated heater voltage of 6,3Vdc where the optimal secondary voltage is about 9Vac.

Isn't there a way to get one of my toroid's 12VAC winding voltage down to 6VAC to directly connect the heaters? Or maybe that's not very elegant designwise?

Cheers
Sono

 

[abbey road d enfer]

I have a toroid that has 3 secondaries: 200+12+12. If I use one 12v secondary for heaters and the other for phantom would that sort out the issue?

Yes.

 

[sonolink]

Yes.

Excellent! What about the heaters? Any suggestions?......please.....

 

[abbey road d enfer]

Yes.

Excellent! What about the heaters? Any suggestions?......please.....

I would think moamps 1st suggestion is the easiest for you. put a 39R 2W+ resistor in parallels with the EF86 heater, then connect in series with the ECC88 heater.

 

[sonolink]

Like this?

 

[abbey road d enfer]

Like this?

No, this is parallels. See attachment.

 

[DaveP]

I would never wire up heaters for a mic pre-amp like that.  You need the best hum rejection you can get, so give it the 6.3V DC it needs.

It's not just the hum in the tubes, its all the feed wires trailing around with AC on.  No-one can predict what gets picked up like that.

Moamps gave you good advice and you should take it IMHO.  If you cut too many corners it will not perform like a REDD47.

I have found an over spec 6V toroid will give you around 8.5V, rectify with two 47,000uF caps with a suitable metal clad resistor clamped to chassis between the two caps, end of problem.  Supply the tube heaters via screened cable if you want to go to town.

DaveP

 

[sonolink]

No, this is parallels. See attachment.

Sorry, you're right. I misunderstood you.
What's the resistor for? If the Voltage source is 12VAC wouldn't placing the heaters in series give 6Vac to each one?

I would never wire up heaters for a mic pre-amp like that.  You need the best hum rejection you can get, so give it the 6.3V DC it needs. It's not just the hum in the tubes, its all the feed wires trailing around with AC on.  No-one can predict what gets picked up like that.

Not to sound arrogant or to neglect your opinion, I know you have built this circuit (and many more) but I've built several tube amps using twisted AC heaters without any hum. BUT you do have a point that for such a project no care is enough and I appreciate your input sincerely

Moamps gave you good advice and you should take it IMHO.  If you cut too many corners it will not perform like a REDD47.

Moamps always gives good advice
I don't want to cut corners especially in loss of quality and performance. The only reason for trying a different PSU is to reduce cost but as I said earlier if it's not clean then I would build the OA2 based.

I have found an over spec 6V toroid will give you around 8.5V, rectify with two 47,000uF caps with a suitable metal clad resistor clamped to chassis between the two caps, end of problem

Is this what you mean (please see attachment)? If not, could you please elaborate a bit more? I have a secondary 12VAC free winding for heaters.

Supply the tube heaters via screened cable if you want to go to town.

You mean with the screen connected to chassis on one end only?

Thanks again to all for all the input, good ideas and advice. I can't wait to start soldering

Cheers
Sono

 

[abbey road d enfer]

I would never wire up heaters for a mic pre-amp like that.  You need the best hum rejection you can get, so give it the 6.3V DC it needs.

It's not just the hum in the tubes, its all the feed wires trailing around with AC on.  No-one can predict what gets picked up like that.

My suggestion was based on using DC voltage, as the OP had posted.
Anyway, I don't think that using 12Vac is unfeasable; it needs to be taken into account, with a specific hum rejection that would "center" the 1st stage heater voltage about 0v. It takes a couple of resistors and a pot to achieve.

 

[abbey road d enfer]

What's the resistor for? If the Voltage source is 12VAC wouldn't placing the heaters in series give 6Vac to each one?

That is true only if each half takes the same current; the EF86 takes 200mA and teh Ecc88 takes 365mA.  The 39R resistor absorbs 165mA.

 

[My3gger]

Solder 1k grid stopper resistors directly to E88CC pins, join their other ends and wire them to 1M/22n point. This is good general practice with tubes like this one.
If you turn tube sockets around, it is easy having power connections on the bottom, away from sensitive parts like grid inputs, which helps get lower noise and smaller current loop. Also, each tube gets its components closer, V72's schematic is drawn pretty much like this:
http://smg.photobucket.com/user/maxwall/media/V72.jpg.html
I think your layout will work good enough, just wanted to give some hints about improving it when you do another one.
Btw, OEP A262A3E isn't output transformer, so use something else there. Edcor or Carnhill have proper and cheap output transformers.

 

[sonolink]

That is true only if each half takes the same current; the EF86 takes 200mA and teh Ecc88 takes 365mA.  The 39R resistor absorbs 165mA.

Of course....I should read the datasheet instead of assuming....
Thanks for the lesson Abbey

 

[sonolink]

Solder 1k grid stopper resistors directly to E88CC pins, join their other ends and wire them to 1M/22n point. This is good general practice with tubes like this one.
If you turn tube sockets around, it is easy having power connections on the bottom, away from sensitive parts like grid inputs, which helps get lower noise and smaller current loop.

Like this? (see attachment)

 

[sonolink]

I think your layout will work good enough, just wanted to give some hints about improving it when you do another one.

That's the way I usually place tube sockets in my guitar amp builds with twisted heaters going right to the chassis edge (see attachment)  8)

I think your layout will work good enough, just wanted to give some hints about improving it when you do another one.

Glad to hear that. I appreciate your hints and hope to get some more soon

Btw, OEP A262A3E isn't output transformer, so use something else there.

I know it's not. Precisely my objective is to experiment with this. The OEP A262A3E is a 1:7 transformer. At the output I've placed it REVERSED since a 7:1 is needed.
I'm sure it'll work fine. I'm curious to see how it sounds....

Thanks for your input!

 

[DaveP]

Is this what you mean (please see attachment)? If not, could you please elaborate a bit more? I have a secondary 12VAC free winding for heaters.

No this is what I mean, it's a very basic CT power supply.  Diode drops have less effect on voltage than a bridge and the diodes are very low drop Schottky type.

Good luck
DaveP

 

[sonolink]

Ok I see what you mean....isn't there a way of doing that starting from 12 vac without a CT? I have a toroid with a free 12 vac winding that would be great to use for heaters

In any case thanks a lot for your input

Cheers
Sono