Looking for a Redd .47 Schematic

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There used to be a schem at Sowter:
http://www.sowter.co.uk/cgi-bin/sh000001.pl?REFPAGE=http%3a%2f%2fwww%2esowter%2eco%2euk%2fcgi%2dbin%2fss000001%2epl%3fRANDOM%3dNETQUOTEVAR%253ARANDOM%26PAGE%3dSEARCH%26SS%3dredd%2047%26TB%3dA%26PR%3d%2d1%26GB%3dA%26ACTION%3dSearch&WD=redd47&PN=SOWTER_TRANSFORMERS_PRO_VINTAGE_TRANSFORMERS_5%2ehtml%23a148#a148

but the link is broken...
Redd schemos are well known to have a tendency to disappear!

Axel
 
The schematic is still there, they just messed up the link:

http://www.sowter.co.uk/schematics/redd47.gif
 
Hmmmm, yes I've just found people discussing that on the recording.org forum.  Also, apparently David Hinson, who made the Revolution versions of the 47, had a schematic that had the EC88's cathode tied to ground, which isn't the case on the above version.

The schematic looks fairly straight forward (it'll be my first P2P build) so I thought this might be a good beginner's P2P project.  Is there a reason why it's not built by more people?
 
letterbeacon said:
Is there a reason why it's not built by more people?

The thought of doing metal work on an all steel chassis is the main thing holding me back.


 
Ha!  I'm going to try and build it in a standard rack mount case.

Just found the original schematic over on the Sowter website: http://www.sowter.co.uk/schematics/EMI-REDD47.pdf

Looks like it is 8.2K on the output tube anode.  Think I'm gonna give this a go... gulp!
 
I thought it said 82K on V2's anode, but the specs say 30mA max.  82K would put the amp in the  3mA range though.  Mine are sounding great at 8K2.  The schematic says V2 is at 18mA which seems in line with 8K2.  82K would be like having a 160K Resistor.  16k4 makes more sense.
 
just tweak it to sound good.

the trick in these amps is spending big bucks for the NOS  bugle boy ef86, ot the other number, which i forget.

6387 or something,

if the writing on the tube is in a small orange font, you will be in heaven.

just drop the screen volts, as hinson did with his 375 k resistor.

less noise, longer life.

best amp i ever played was ef86 vox circuit with 6bq5 bugle boy output tubes thru a fischer output transformer.

telefunken v72  v76 tubes are the same as ef86, as well as 6sj7.

ef804= ef 86 = 6sj7

 
CJ said:
just tweak it to sound good.

the trick in these amps is spending big bucks for the NOS  bugle boy ef86, ot the other number, which i forget.

6387 or something,

if the writing on the tube is in a small orange font, you will be in heaven.

just drop the screen volts, as hinson did with his 375 k resistor.

less noise, longer life.

best amp i ever played was ef86 vox circuit with 6bq5 bugle boy output tubes thru a fischer output transformer.

telefunken v72  v76 tubes are the same as ef86, as well as 6sj7.

ef804= ef 86 = 6sj7

Noted. Thanks CJ.
 
I was more interested in the info about the bugle boy tube for my orange 86 project but thanks

Now im curious about how my RCA BA-2A is using 2x 1612 tubes (the ones with the grid caps) which I was told is half of a 6sj7 by PRR (I think)

Sooooo half of an EF86 is also similar to the single triode 1612?  :)
 
Nope, 1612 is an industrial grade 6L7 - "pentagrid amplifier".  6SJ7 is a sharp cutoff pentode, not related.
EF86 = 6267 = [EF804(s) with diff pinout] is also a pentode.  Haven't compared them to 6SJ7, but 6SJ7 is octal so not so easy to retrofit.

No triodes to be seen!
 
I have made this point to point and it works fine, of course the Plate resistor of the E88CC is 8.2K not 82k, I used an Al clad wire wound type.

For best results use the best DC supply you can make for the heaters.  3.15V 0V 3.15V would be ideal

The components across the input TX are critical and will vary depending on the TX.  You need a scope to set up the square wave response correctly, too rounded off and you lose the top end, too pointed and it will ring.  This has been covered elswhere.  The output wires should be twisted and kept as short as possible, input wires from XLR should be shielded in best quality cable.

Use good quality ceramic holders for the tubes gold pins are a good idea.

CJ is probably right about the Bugle Boys but I expect they used stock Mullard tubes at Abbey Road back in the day.

Last tip; use toroidal mains TX or a remote box for the power supply like the original.

best
DaveP
 
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