R*E*D Forty Seven

[bradb]

What you see on the original REDD47 schematic is a cap and a resistor (100pF and 100K damping network) soldered to an un-used pin on the top of the can.  The pin that is used as this tie point is pin number 6 and it does not go to the winding.  Of course, if you use the CMMI-7C, which I did myself, then you would use a different and appropriate damping network as the resonance is higher on the CMMI-7C. 

Wow, cool info, I've been wondering about that.  Now I feel confident enough to place my CMMI-7C order.... Winston, Can you share the new damping values appropriate for the CMMI-7C?

 

[bradb]

ah, maybe these are correct:

32k and 20 pf

just looked at the turret layout in this thread.

 

[Winston OBoogie]

Was just about to reply to your first post and then saw that you'd found them 
Those will work yes. 

Good luck with the build btw,

W

Edit: just remembered that I think Cinemag specify a 30.1K and a 20pF on the spec sheet but I don't know that it matters too much.  I sometimes used no network, depended on the pre...

 

[bradb]

thanks!

 

[bradb]

Can anyone push me in a direction on these REDD output transformers?

I'm deadlocked....

CM-9661A-H (high-nickel core):    $135.03
CM-9661A-L (50% high-nickel + 50% steel):  $100.41
Sowter's 9980 Output transformer:  $108 + shipping


I KNOW i'm going with the cinemag input.  The sowter output is easier to mount to the PCB... but ordering everything from Cinemag is easier.  The Sowter seems to have the same 50/50 build as the CM-9661A-L.

Also, is the CM-9661A-H worth it?  I'm looking for a high quality pre but with some good character too... so maybe I'll stay away from that one.


Any direction anyone can push me in would help!

 

[seavote]

Winston Oboogie wrote:

How about a pcb with a solid state regulated H.T. supply with L.T. supply and phantom supply + a suitable power transformer to go with it?  It'd be a supply that's useful for various tube projects, not just a REDD47.  It won't be my latest and greatest but it'll be a good supply that has been used in LOTS of units.
If so, as it happens, I was recently speaking on the phone with a regular long time forum member here about putting something together and handing it over to him to make it available.

will this plan be going foward. i'll be building a redd from your  schematic and would like to use your PSU. i imagine they would "play nice" together.

 

[Winston OBoogie]

will this plan be going foward. i'll be building a redd from your  schematic and would like to use your PSU. i imagine they would "play nice" together.

It could yes, as could anything else there might be a need for.  I guess the thing to do would be to see how many peeps might want something like this (or something else, whatever that is) and then see what cost would be for the pcb + power transformer + anything else that might be hard to source parts wise.

John

 

[abby normal]

The output iron is a different story... If i could avoid Sowter (and the INSANE shipping cost) I'd prefer that, but again, the Cinemag doesn't have the threaded bushing mount.  I mean, we are at line level so maybe its not a big deal, but its also easier.

For output
Cinemag's selections are:
CM-9661A-H (high-nickel core):    $135.03
CM-9661A-L (50% high-nickel + 50% steel):   $100.41

Sowter's is:  9980 Output transformer

The 50/50 core is supposed to be more vintagey, and the high nickel core is supposed to be more hi-fi.  I'd prefer something with some character.... Cinemag recommended the high-nickel core version and according to Cinemag, many people like that better



So, all in all, whats the best output transformer for the REDD47??

I was looking into this as a project a while back, I forget the model but there's an Edcor that was a good candidate for OT that you could put on that list.

 

[guavatone]

I was looking into this as a project a while back, I forget the model but there's an Edcor that was a good candidate for OT that you could put on that list.

Edcor doesn't make a 7:1 for OP.

 

[Winston OBoogie]

CM-9661A-H (high-nickel core):    $135.03
CM-9661A-L (50% high-nickel + 50% steel):   $100.41

I've used both of these.  Only the 9661A-L was available at first until I asked them to do it in Hi Nickel about 4 years ago.  I liked it for some units and used it for a while.  Of course, Y.M.M.V.

I don't use any of them now as I have a newer one that I prefer.

No experience with the Sowter so can't comment on that.

 

[bradb]

Winston,
Thanks for the input!

Can you characterize the two... the 50/50 vs the hi-Ni?  I imagine the Hi-Ni is smoother, cleaner, clinical (?).  and the 50 / 50 is grittier?  I'm curious if there is some other quality outside of the characteristics that we'd all assume these transformers having based on their composition....

can you share what the newer one is you prefer?  is it available to the public?  You're killing me here!!       haha!

 

[abby normal]

I was looking into this as a project a while back, I forget the model but there's an Edcor that was a good candidate for OT that you could put on that list.

Edcor doesn't make a 7:1 for OP.

You're right, good catch. But if I remember correctly 7:1 is not the ratio you seek for modern compatibility.

The original notes have its output into a 200 ohm line load. If you do the math and find what the reflected primary impedance is @ 7:1 with a 200 ohm load you'll find that you need a different ratio to achieve the same with a 600 ohm load. I forget what I came up with but that ratio is a common off the shelf transformer type and Edcor does stock them. I forget the turns ratio and I'm too lazy to do the math.   

 

[guavatone]

From my calcs I get
600:30K or a 1:7

200:9000 is 1:7
600:9000 is 1:4

But from my Z calculations for the output of this paralleled E88cc is about 29K since a single e88cc in this stage is 14,426 Ohms.  I could be wrong and maybe it is actually halved.

 

[rotation]

Winston,
Thanks for the input!

Can you characterize the two... the 50/50 vs the hi-Ni?  I imagine the Hi-Ni is smoother, cleaner, clinical (?).  and the 50 / 50 is grittier?  I'm curious if there is some other quality outside of the characteristics that we'd all assume these transformers having based on their composition....

can you share what the newer one is you prefer?  is it available to the public?  You're killing me here!!      haha!

I'm not Winston but i tried different transformers at the output of this preamp. One was Cinemag 50:50 version, the other was standard Edcor 5:1 ratio. I didn't like Edcor here, Cinemag is much better.
I must say this preamp sounds a little bit agressive with transformers i tried. Maybe high nickel output would change this, i don't know. But don't get me wrong, i don't think it sounds bad, cleaner is just my preference..
I think Guitarmaker tried Sowter and Cinemag and said Cinemag was much better.


Miha

p.s.:
here is another thread with some good reading about OT options:
http://www.groupdiy.com/index.php?topic=33228.0

 

[abby normal]

600:9000 is 1:4

That 4:1 looks right. I just looked at Edcor's site and remembering others on the forum success with I think I came up with the XSM10k/600 for the output transformer.

 

[Winston OBoogie]

You're right, good catch. But if I remember correctly 7:1 is not the ratio you seek for modern compatibility.

The original notes have its output into a 200 ohm line load. If you do the math and find what the reflected primary impedance is @ 7:1 with a 200 ohm load you'll find that you need a different ratio to achieve the same with a 600 ohm load.

These amps were NEVER loaded by 200 ohms.  They were built out to 200 ohms which is a big difference.

Mostly, the load on them was bridging.  Worst case would be if a fader was off, then they'd see the build out resistor and the 200 ohm of the fader.  So, a lowish load in that case but they're OFF...so who cares 

The whole idea was that the valve saw as little a load as practical.

 

[Winston OBoogie]

But from my Z calculations for the output of this paralleled E88cc is about 29K

Much lower than that, especially with 18.5mA through the pair.

Again, the idea was to have as little (light) a load as practical on the triode's.

 

[abby normal]

The whole idea was that the valve saw as little a load as practical.

If that is the case wouldn't you want a lower turns ratio like a 4:1 over a 7:1?

 

[Winston OBoogie]

I'm not Winston...

Thank God there's only one of us    Discounting the other Winston's in my head of course...?...

I must say this preamp sounds a little bit agressive with transformers i tried.

Some of that "aggressiveness" is the E88CC.  It can have a most un-triode-like harmonic spread - more 3rd than 2nd.  Some E88CC's are better than others.  And some E88CC's aren't E88CC's either.

 

[Winston OBoogie]

The whole idea was that the valve saw as little a load as practical.

If that is the case wouldn't you want a lower turns ratio like a 4:1 over a 7:1?

When I say "little a load", I mean it loads it as little as practical/possible.  A light load, as opposed to a heavy load.  Not a 'little load' as in 'little impedance'