M49 Oliver Archut alt version

[Spencerleehorton]

Hi all,

Had a few bits lying around so thought I'd make the Oliver archut alt version with the 5840w tube.
Haven't made the psu yet but wondered if there was a simpler schematic or version of the psu to consider with this?
Will use the 100k lin pot for pattern selection.

 

[Khron]

Transformer (or two), bridge rectifier, some RC filtering... Does one really need a schematic for that? Maybe look up the G7 (or even G9) schematic, if truly necessary?

https://www.gyraf.dk/gy_pd/g7/gic_s.gif

 

[Spencerleehorton]

Dany bouchards version which I've been using is pretty specific due to some noise interference, just wanted to check I there was something easier

 

[Khron]

Specific, in what way?

 

[doqmemory]

Dany bouchards version which I've been using is pretty specific due to some noise interference, just wanted to check I there was something easier

The M49b version uses filament bias on the cathode, and so needs very clean heater voltage. The Oliver Archut M49 Alternate Tube Schematic uses self bias for the cathode (including a cathode bypass capacitor), so can use a simpler heater supply. I have one of each (D-49b and Oliver Alt M49c) and both sound smooth.

 

[Khron]

So an LM317-regulated heater supply (or a capacitance-multiplier one, if you wanna go cheap & low-tech) isn't clean enough, either way?

 

[RuudNL]

Never had a problem with the good old 7806!
(If you need a bit 'extra', lift the ground leg with a Si diode.)
Eventually you can use an extra R-C filter for the bias voltage.

 

[doqmemory]

So an LM317-regulated heater supply (or a capacitance-multiplier one, if you wanna go cheap & low-tech) isn't clean enough, either way?

It works fine for the M49c Oliver Archut Alternate design -- I use the Matador Universal Passive Tube PSU, which uses an LM317 for the heater supply. I have not tried to run the "b" version with that PSU, though, since mine uses a different cable.

 

[Spencerleehorton]

great stuff guys, exactly what i needed thank you.

 

[Spencerleehorton]

what value did you use for the cathode bypass? 10uf or 20uf?

 

[Spencerleehorton]

so by the sounds of it the gyraf G7 psu should be fine?

 

[Spencerleehorton]

i bought a pretty small psu box, didnt measure from ebay thought it was the big brother but im so tempted to try and fit everything in if i can!!

https://www.ebay.co.uk/itm/124973325739

 

[Spencerleehorton]

should have got this one!!

https://www.ebay.co.uk/itm/124948985900?epid=1239462048&hash=item1d178a382c:g:BYMAAOSwUGZhZVxx

 

[doqmemory]

what value did you use for the cathode bypass? 10uf or 20uf?

I used a 22mF Elna Silmic II for the cathode bypass capacitor. BTW, my little avatar picture is of this Oliver M49c squeezed into an MXL 770 donor body.

 

[Spencerleehorton]

Ah nice!! Great stuff.

 

[Spencerleehorton]

seem to be getting good voltages now from m49 psu but again my polar pattern adjust pin 6 doesnt seem to be working?
seems i have had this problem on several mics when testing recently!!

I did have the 3PST lorlin in there but have now changed to 100k pot, one outside leg to 0M and other outside leg to F8, middle leg to COM. I don’t seem to get any change when adjusting the 100k pot?
Any ideas?
cold solder joint, fixed!!

 

[Spencerleehorton]

Just wanted to clarify a few things, as i havent used specificly the right parts but pretty close.
seem to be getting a stray voltage from R2 to R8 when 0v from polar pattern?
R1, 2, R5 and R8 ive used 200meg? these should be ok right?
R3 is 2.2k, R4 is 100k and R6 and R7 are 1M
C1 is 1000pf,, C2 and C4 are 10nf/630v, C3 is 1uf/630v and C5 is 22uf/63v.
B+ = 116v
H+ = 4.7v
polar goes between 0 - 116v
kathode im getting 1.9v
plate is 32.7v
backplate im getting 5.6v and R5/R6/R7 junction im getting 55v

between R2 and R8 im getting 1.6v - 6.98v depending on where polar patten is?
R1 voltage is = 1v

any ideas?

 

[RuudNL]

H+ = 4.7V seems very low to me.
You can't measure the voltage after the 200 M.ohm resistors, because your meter is loading this point in such a way that you won't get a reliable reading. (Like 5.6V on the backplate, while the 'real' voltage is 55V.)

 

[Spencerleehorton]

Is it OK that I've used 200megs rather than the 100megs?

 

[Spencerleehorton]

I'll up the H+ voltage and see what I get