Altec 436C Build Project (PCBs, schemes)

[ding]

So, what are your voltages on V1 and V2 anodes?

 

[iprovlek]

Ok I measured V1 and V2 anodes!Without Tubes!

On first V1:

a1 is 285VDC
a2 is 285VDC

On secound V2:

a1 is 292VDC
a2 is 292VDC


And in place 6bc8 I use 6bs8!

 

[ding]

Your voltages are definitely off. V1 plate should be around 65. Your distorting issue is V2. It needs to be around 150. Are you sure you have the correct resistors on your PS?

Edit: You need to have the tubes in and warmed up to get the right voltages. I just noticed you did not. Please be careful.

 

[iprovlek]

I saw that in orginal schematics ,V2 anodes should be 150V!

Talian recomended 200VAC/6.3VAC power transformer!

He said that this cap in the middle 0.1uF is for cleaning power supply!


I try tomorrow measure voltage with tubes in!

 

[iprovlek]

And what real bothering me is output V2 tube, there is four 2K resistors on output after V2 ,on orginal there is no 2K resistors only output trannie and 600ohms attenuator!

 

[ding]

That's because there is no output transformer. If you where to put an output transformer there you would omit those resistors and caps. If I'm correct those 1uf caps prevent dc from going out of your xlr and killing someone and the resistors are there to make it look like an output transformer to the circuit.

 

[iprovlek]

Yes that is true!

I think that this PCB is based on RS124 compressor and this schematics without output transformer!

And PSU is like in Altec436c!

Release is set on potentiometer and attack is add!

 

[ding]

That is not the rs124 schematic. It looks like it's inspired by. The original rs124 scheming is here somewhere in this forum. I see absolutely no feedback resistor on this pcb design. This is a modified 436c. Also the RS124 used the same in/out transformer and the power supply was the same except for the full wave rectifier.

 

[iprovlek]

Ok I measured the voltages with tubes!

V1(6bc8)

a1=41 VDC
a2=41 VDC

V2(6CG7)

a1=112 VDC
a2= 112 VDC

Yes you right this Altec is inspired with RS124!

 

[DaveP]

The anodes/plates of V2 should be  140~150V, which is a good operating point for this tube.  Reduce the B+ dropping resistor until you get that figure.

The anode of V1 varies with the amount of compression.  It is set at low voltage/high current with no compression, but rises almost to the HT/B+ voltage as the CV (control voltage) kicks in.

Best
DaveP

 

[ding]

Ok I measured the voltages with tubes!

V1(6bc8)

a1=41 VDC
a2=41 VDC

V2(6CG7)

a1=112 VDC
a2= 112 VDC

Yes you right this Altec is inspired with RS124!

I agree with DaveP, that V2 voltage seems low. That schematic you posted a few posts ago is way closer to an RS124 than the pcb you built. You can always mod it once it's working and add the feedback resistors and the recovery switch to get it close to the RS124 if you want.

 

[iprovlek]

I agree with you Ding and Dave!

Ill try rise the B+ voltage dropping resitors to get there where should be!


But if you look to this schematics of RS124  and this Aresaudio Altec 436c you will see that this Aresaudio use almost the same value components!
39K on anodes of the V1 and V2 tubes!

 

[iprovlek]

So I need to to drop value of those 39K resistors!?

Am I right?

 

[DaveP]

The 39k feedback resistors are wrong, they both should be 100k.

If these are put right then the voltage on V2 may come back up to 145V from 112V, other wise gradually reduce the 6.8k dropping resistor until you get 145V.

Best
DaveP

 

[ding]

Also if you look at the Aresaudio altec 436c schemo  it has no feedback resistors.

 

[iprovlek]

Thanks a lot guys!

Ill try this!


And HAPPY NEW YEAR!!!

 

[iprovlek]

I pulloff out feedback resistors with 47K in series on anodes of V1 and voltages is:

V1
a1=29V
a2=29V

V2
a1=130V
a2=130V

With 33K in series on anodes of V1 voltages is:

V1
a1=32V
a2=32V

V2
a1=129V
a2=129V

 

[DaveP]

iprovlek,

I can't reply to your PM because your inbox is full!

DaveP

 

[ding]

Any updates????

 

[ForthMonkey]

I have two questions.

What are two 470nf cap's voltage?

And what 100nf cap's voltage on 6,3V?

I guess 63V is ok for them?