M49 Oliver Archut alt version

[RuudNL]

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

I don't suppose this will cause a problem, although extreme high values (1 G.ohm) can become problematic.

 

[Spencerleehorton]

ah ok, so it should at least work, which it isnt at the moment!! Im getting intermittent signal so somethings up, will clean it all up a bit and try another capsule as im pretty sure all i have left are the capsules that are completely shot!!
Also pretty sure i need 10:1 transformer and im only using a 5:1 i think!!
winding time!!

 

[Spencerleehorton]

Also probably best to get a 70pf cap out in place of the capsule and put a sinewave through it, at least I can see it working then.

 

[Drosselmeier]

ah ok, so it should at least work, which it isnt at the moment!! Im getting intermittent signal so somethings up, will clean it all up a bit and try another capsule as im pretty sure all i have left are the capsules that are completely shot!!
Also pretty sure i need 10:1 transformer and im only using a 5:1 i think!!
winding time!!

the sound should be even if you use a 1:1 ratio transformer, ratio of the transformer has nothing to do with the lack of sound

 

[Spencerleehorton]

sucess is all about taking your time, rather than use the vox style pcb, ive got a bit of turret board and drilled some holes and put in some turrets (nickel posts i had lying around), 13 pairs, remounded the components and used the dodgy capsule to test!!!.
put inside a mock up body and hey presto, m49 goodness, sounds great, will finish off and record some doodles!!

 

[Spencerleehorton]

Started to make the psu now, will test with the variac just incase there isn't any problems!!
Then I just need to fit it all in this small enclosure!!

 

[Spencerleehorton]

The new mic pcb wrapped up in loads of tape!! Will try and make it pretty if I get time!!

 

[Spencerleehorton]

Psu wise I just wanted to check, I've made the gyraf g7 psu.
Two diode bridges but the 0v are not connected?
On the mic socket pin 1 and 2 are from txf, pin 3 is H- (0V) , pin 4 is H+,(6V) pin 5 is B+(120v), pin 6 is polar patterns (0-120v) and pin 7 is gnd from B+.

 

[Ivan K.]

Started to make the psu now, will test with the variac just incase there isn't any problems!!
Then I just need to fit it all in this small enclosure!!

Hi, I'm going through about 6, original M-49, U-47, U-67 Telefunken CM 51 & 61 PSUs, replacing capacitors, selenium rectifiers and the odd resistor. BUT, given the +/- 10% spec on most mains supplies (132Vmax in NA & 264V in the EU /UK), plus surges to much higher voltages, I worry about the tubes, especially filaments.

I have found quite nice HV & LV regulator modules on eBay. The LV IC is rated for 0.8uV noise (LT3045) and generally good specs. The HV IC is rated to 125VDC and is also low noise, ripple and good CMRR (TL783). The TI datasheet even shows an up to 200V Darlington pre-reg. Before I commit to using regulators, I'm curious why folks still use unregulated supplies?

Regards,
Ivan

 

[Khron]

Hi, I'm going through about 6, original M-49, U-47, U-67 Telefunken CM 51 & 61 PSUs, replacing capacitors, selenium rectifiers and the odd resistor. BUT, given the +/- 10% spec on most mains supplies (132Vmax in NA & 264V in the EU /UK), plus surges to much higher voltages, I worry about the tubes, especially filaments.

Well, with such heavy RC filtering (read: LOOOONG time constants) such "surges" better last a good long time, if one might expect them to have any (significant) effect by the time they reach the load (in this case, a tube's filament or plate supply).

But i guess that's another (good?) reason to perhaps underrun the heaters a slight bit (say, down to 6.2 or 6.1v, down from the "standard" 6.3v).

 

[Tubetec]

The amount of HT current is very small ,often less than 1ma , this makes it easy to get a quiet supply with RC smoothing . The circuits in tube microphones are almost always class A ,therefore the variation in current from zero to full signal is also miniscule . Some mics do use stabiliser tubes or zeners in the PSU and typically dump several times the current the mic itself uses , then the variation due to signal current becomes an even smaller fraction of the total current flowing . A simple bleeder resistor is used in the NU67 PSU , see discussion on WA47 .

 

[Spencerleehorton]

New psu built and powered up and getting good B+ 120v and good H+ 6v, no smoke or bangs yet!!
Will put in case and fingers crossed!!
Then finish making the mic body and job done!!!

 

[mrgrooves666]

Sorry to ask, but what kind of light bulb are you using?

 

[Spencerleehorton]

Light bulb? You mean pilot light on the psu?

 

[Spencerleehorton]

https://www.ebay.co.uk/itm/5Pcs-AC-...2349624.m46890.l49286&mkrid=710-127635-2958-0

 

[Spencerleehorton]

Not exactly what I've got but probably what I'd order now

 

[Spencerleehorton]

Quite surprised I got everything in this little tiddler of a psu but works well.
Now onto finishing the mic insides!!!

 

[Spencerleehorton]

 

[Spencerleehorton]

Sorted the mic now, few little bits to tidy up but all is looking good.
Will do some internal pictures and finish up and then test

 

[Spencerleehorton]

doing a version 2 now and just made the turret board, rather than 200Meg resistors ive used 100Meg on this version and will be edge terminated capsule rather than centre terminated.
Will also wind a 9.5 or 10:1 ratio transformer.