Altec 436 / RS124-ish Clone

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Falk

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Jun 30, 2013
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98
Good Morning,

I am planing a Vari Mu build which is as close as possible to the named compressors and currently I am designing a front panel.
What would you guys go for? Any feedback is highly appreciated.

Link to three designs:
https://www.dropbox.com/s/dfyqlgxxuoudykc/Design_3colours_Zeichenfl%C3%A4che%201.jpg?dl=0

Thank you!
Falk
 

weiss

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Jun 16, 2014
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Location
Germany
Like the design. I'm also building two clones at the moment.
I would go for the black one. Will you use brushed metal? or powdercoating?
 

Falk

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98
This is how it got in the end.
 

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Falk

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I used the one attached but would recommend to read the threads about the altec 436 and emi rs 124 in the forum. There are a couple of them providing all the information needed.

Best regards,
Falk

 

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giohopper

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Falk said:
I used the one attached but would recommend to read the threads about the altec 436 and emi rs 124 in the forum. There are a couple of them providing all the information needed.

Best regards,
Falk

Thank you very much!

Giovanni
 

Juanaca

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Dec 8, 2019
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Hello good afternoon, I have a power problem in the section of the tube heaters.
my toroidal teansformer on the 6.3v winding has 1.8A to feed the 3 tubes on the 6AL5 pins 3 and 4 on the 6cg7 pins 4.5 and on the 68c8 4 and 5 as well.
My problem is that the filaments do not turn on, I do not get any sound.
With the 3 tubes I measure the alternating voltage and it does not decay, it stabilizes at 6.5v.
I did not tap on the toroidal winding.
I need help because I don't know what happens.
Thanks a lot
 

Falk

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Jun 30, 2013
Messages
98
Have you wired the filaments in parallel?

Heater current:
6AL5  0.3A
6cg7 0.6A
6bc8 0.4A

Thats a total of 1.3A which equals 72% of the current your toroidal can deliver. When the filaments are cold, they act almost as a short circuit so the current is much higher. I would at least use a power tx that can deliver double the current needed.

Other than that: Disconnect the compressor from the power socket. Disconnect the heater wiring from the toroidal. Take out the tubes, connect a multimeter to the heater wiring and check for continuity of the wiring. When no tube is installed there should be no continuity. Install only one tube and you should read continuity. Check this for every tube solely. Check if the heater secondary of the toroidal is okay.

Double check if you counted the pins right. The pins are counted from the side of the pins and not from above.

Good luck!
 

Juanaca

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Falk thank you very much, my lack of experience made me wire the socket of the tube looking at it from above, so as you said I did it the other way around.
now I have another problem, it only sounds a loud hum, I have followed the simple scheme of altec 436 as it is with input transformer escor 10k 10k and output transformer xpp1 600-15,
When I remove the 6bc8 tube the thunderous hum disappears, when I touch the pins of this valve it sounds the touch that I am but no sound when I put music through the input jack.
Thank you very much and greetings.
 

Falk

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Jun 30, 2013
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Do you have an xlr connected to the input? The hot and cold pins must be connected. The input is very sensitive and the hum might come from an open input. What kind of power supply do you use? What kind of hum is it? 50Hz/60Hz or 100Hz/120Hz?
 

Juanaca

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thanks again for answering, I finally undid the project because I was not able to make it sound or remove the buzz.
so I have followed this scheme that I took from another tutrial and now it sounds and the buzzing has gone, but it sounds very low level and distorted,
I have bypassed the transformer input potentiometer by connecting the two tube inputs directly to the jack plug and the same audio is experienced.
Now I don't know where to walk.
 

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Rob Flinn

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Juanaca said:
thanks again for answering, I finally undid the project because I was not able to make it sound or remove the buzz.
so I have followed this scheme that I took from another tutrial and now it sounds and the buzzing has gone, but it sounds very low level and distorted,
I have bypassed the transformer input potentiometer by connecting the two tube inputs directly to the jack plug and the same audio is experienced.
Now I don't know where to walk.

Make sure you have your i/o connections properly made.  Are you connecting to it with a balanced or unbalanced  interface/desk  ?    If you are unbalanced you need a connection bewteen cold & ground
 

Juanaca

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hi Rob how are you?
Well, I have passed sound in both ways and I get the same result, in unbalanced mode connecting pin 1 and 3 of the xlr in point and balanced I get the same result, I have also connected the xlr directly to the first tube, I have to say that I use a 6ES8 instead of 6BC8 (I read somewhere that it gave less problems).
I have connected only the volume potentiometer and the tube balance potentiometer as in the diagram.
Any support would be of great help to me since I don't know where to start.
thank you
 

Rob Flinn

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Juanaca said:
hi Rob how are you?
Well, I have passed sound in both ways and I get the same result, in unbalanced mode connecting pin 1 and 3 of the xlr in point and balanced I get the same result,

If doing this you need in trs terms to connect tip to tip & then sleeve to sleeve & ring.          The point is that since the input & output of the rs124 are transformer balanced you must have connections to both sides of these transformers.  Make sure this is the case or you will have a low level signal that distorts.
 

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