Altec 436 / RS124-ish Clone

[syn]

Maybe it's because you're using different valves than specified. The right ones aren't a fortune to buy.

please disregard pinout and octal/noval types
6n5p=6bc8
6cg7=6sn7=6n8s
so I've been told.
I might be wrong but they look alike from the data sheet. Not identical, but close. Please, bear in mind that all voltages are spot on, as on the schematic with no gain reduction applied, apart from 6al5 generated CV.

 

[Rob Flinn]

please disregard pinout and octal/noval types
6n5p=6bc8
6cg7=6sn7=6n8s
so I've been told.
I might be wrong but they look alike from the data sheet. Not identical, but close. Please, bear in mind that all voltages are spot on, as on the schematic with no gain reduction applied, apart from 6al5 generated CV.

Right. You should be able to get around 18dB of GR before the vari mu valve loses the will to go on. I can't remember how low the sidechain voltage goes though. As WInston has said the ECC189 works a bit nicer in this box than the 6bc8.

 

[syn]

I can't get more than -3.5VDC from the side chain. If I get more, I get nasty distortion to go with it. No signal = 0VDC at the sidechain.

 

[Rob Flinn]

I had something like this happening at one point & I think it was an error I had made around the input transformer.

 

[syn]

thnx I'll recheck everything, once more

 

[Bernardo]

hello everyone, i have a vari-mu following the altec/rs scheme with edcor 10k/10k input transformer and 15k/600r output.
I have an input gain problem, directly injecting the signal from my converter that has an output of (600R) to the compressor, I have to put the input to the maximum, is there any way to fix this?
Another question I have is if the output transformer is 600R, is it necessary to put two 300R resistors on pin 2 and 3 of the xlr?
thank you

 

[Rob Flinn]

hello everyone, i have a vari-mu following the altec/rs scheme with edcor 10k/10k input transformer and 15k/600r output.
I have an input gain problem, directly injecting the signal from my converter that has an output of (600R) to the compressor, I have to put the input to the maximum, is there any way to fix this?
Another question I have is if the output transformer is 600R, is it necessary to put two 300R resistors on pin 2 and 3 of the xlr?
thank you

Not sure what your gain issue is, I didn't have this.

If you have the attenuator after your output transformer as in the diagram then you don't need to add a load across the output because the attenuator does this for you.

 

[Bernardo]

Thank you very much for the answer Rob, I have the diagram attenuator, I have removed the two resistors and the output is now more powerful.

 

[Rob Flinn]

Not sure what your gain issue is, I didn't have this.

If you have the attenuator after your output transformer as in the diagram then you don't need to add a load across the output because the attenuator does this for you.

Probably because by adding the 2 resistors you are halving the load on the output because the resistors are in parallel with the attentuator. It may also screw with the attenuation amount.

 

[rankot]

please disregard pinout and octal/noval types
6n5p=6bc8
6cg7=6sn7=6n8s
so I've been told.
I might be wrong but they look alike from the data sheet. Not identical, but close. Please, bear in mind that all voltages are spot on, as on the schematic with no gain reduction applied, apart from 6al5 generated CV.

Have you manage to fix this? 6N5P is similar to 6BC8, but maybe not enough. Amplification factor of the first one is 27, while at 6BC8 it is 35. Also, the curves are different.

 

[Bernardo]

I have an important question, I have mounted an edcor wsm 10/10 as input transformer, edcor pin one goes to xlr pin2, edcor pin 4 to xlr pin 3. When I connect pin 2 (CT) of the edcor to ground, there is a noticeable reduction in sharpness, when I leave it unconnected, the high treble appears again. how should this pin go? thank you very much for your patience.

 

[Bernardo]

This pin.

 

[Script]

CT unconnected ?
XLR pin1 to chassis.

 

[Cranehazard]

This pin.

CT unconnected ?
XLR pin1 to chassis.

Leave that ct unconnected

 

[Script]

 

[Bernardo]

If it seems that it is more reasonable that it is disconnected, but what explanation does connecting pin 2 to ground have to filter treble? Cancellations and phase shifts usually occur in the lower part of frequencies.

 

[Cranehazard]

Maybe the primary of the transformer is creating some kind of lc filter with the stray capacitance? Bleeding treble to ground

 

[EugeneKei]

Has anyone tried this layout? It's from the first page of this thread, but it would be good to have any feedback, so maybe someone tried it? Comparing to scheme it looks like it's 124-ish layout. Maybe someone has more better layout of RS124? or this one is pretty good?
Thank you in advance

 

[Rob Flinn]

Has anyone tried this layout? It's from the first page of this thread, but it would be good to have any feedback, so maybe someone tried it? Comparing to scheme it looks like it's 124-ish layout. Maybe someone has more better layout of RS124? or this one is pretty good?
Thank you in advance

The 124 is a very simple circuit. It is quite easy to design your own layout. However, if this layout follows the diagram there is probably no reason why it wouldn't work ok. Personally I try to avoid hanging resistors off pots, & transformers where possible but that shouldn't prevent it from working.

 

[vitopower]

I used a 2 x 180V and 2 x 6,3V toroidal power tx. Works great. I am not sure if I get the exact 255V from the EMI schematic. It can be that I changed the drop resistor but I cant really remember. I am in contact with a manufacturer for mu-metal cans regarding shielding for the the Edcore WSM series. Lets see what the price tag is going to be. I ll keep you posted. I put a mu-metal shield around my power tx and have a rms noise of -82dB(FS) which equals -63dB(U) in my setup. Professional tube gear I bought for several thousand euro per unit is about 6dB better regarding SNR.

great info, Falk. Prepping a 2x build right now . Where did you find the mumetal toroid shield?