Apex 460 mod with some Telefunken ELA M 251 influences

[saxmonster]

Magneto,
I did start out wanting to build a clone but I can't find a real clean schematic of the 251.  I am learning more and more as I go along here.  I will keep my eyes out for a great schematic and probably build another another one or change this one to an actual clone and see what the differences are. 

Wave,
I will definitely order those styrenes from justradios.

Parsarski,
thanks for the invaluable information.  I will leave it out for now and test later with it in and see if I like the difference.  Its all about what I hear.

Thanks so much guys.  Going to change the title too.

 

[saxmonster]

Which one of these would make a great apex 460 C8 2.2ufd metal film cap

http://www.newark.com/jsp/search/productcompare.jsp?N=422+2203+202089+810059735+810304663+810070744+810064263+810005842+810014721+810020565+810035646+810014719+810051051+810099219+810322820+810094555+810115803+810029809&No=25&Ntk=gensearch&Ntt=2.2mf&Ntx=mode+matchallpartial&locale=en_US&appliedparametrics=true&getResults=true&originalQueryURL=/jsp/search/browse.jsp%3FN%3D422%2B2203%2B202089%26Ntk%3Dgensearch%26Ntt%3D2.2mf%26Ntx%3Dmode%2Bmatchallpartial%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_US%26divisionLocale%3Den_US%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D422%2B2203%2B202089


Or does anyone know where to get a 2.2ufd polystyrene I can't find any.

 

[saxmonster]

What size heat shrink tubing should I get for this type of project. Will use it on a few components like C8 and on the 7 pin connections, transformer etc.

Thanks
Scott

 

[saxmonster]

If I switch both zeners in the PS to 56V I will be in the ballpark of 110-120volts for the polarization of tim's Ct12 Capsule.

I just don't want to damage the capsule by having the wrong voltage.  Dave Thomas said to only switch one.  But I am thinking both need to be changed.

Am I right in thinking this?

Thanks
-Scott

 

[pasarski]

If I switch both zeners in the PS to 56V I will be in the ballpark of 110-120volts for the polarization of tim's Ct12 Capsule.

I just don't want to damage the capsule by having the wrong voltage.  Dave Thomas said to only switch one.  But I am thinking both need to be changed.

Am I right in thinking this?

Thanks
-Scott

Tim said the capsule sounds best with 55-60V and that's the ELA M ballpark so I guess you're on the right track. Or maybe just change the other zener for 38-48V.

 

[saxmonster]

Ok so I did some testing on the apex 460 power supply today after work.

So zener 5 = 69.5vdc
    zener 6 = 71.6vdc

which = 141.1vdc so why is it that when i measure pin 1 i get 142.9 and not 141.1vdc.

For pin 1 its 142.9 VDC so I definetly need to get new zeners as this is 22vdc over what it should be, by why doesn't it equal 141.1vdc with the two zeners added together?

Pin 2 = 6.63 which is great for the heater right?

pin 3 starting from omni to figure 8 goes like this

0.010vdc ---- Keeps dropping for some reason
15.45vdc
30.6vdc
45.6vdc
60.6vdc
75.9vdc
91.2vdc
106.5vdc
123.5vdc  ----- Keeps rising for some reason.


Do theses look good?  Now if I put lower zeners in will they affect the numbers for polarity patterns?

Pin 5 = .053
Pin 6 = .04

I think these pins are for the transformer?

I did all this with just the PS turned on and the cable attached.  No mic attached on it.

Tim's Capsule is on its way so I need to start modding this mic and getting it ready.

Can't wait.

-Scott

 

[saxmonster]

What does B+ 120vdc mean?  I know what 120vdc means but what does B+ does B pertain the right side plate or the left side?  How do i tell what side it what?  I have been going by holding the tube with the pins facing me and the gap /space at the top and the center pin 9 at the bottom?  Does it matter what side of the tube I shut down if i make it a plate follower?

 

[david-p]

I hope I understand your question.

B+ is the high voltage supply, the voltage delivered by the power supply that doesnt power the filament.  (This puzzled me for a while: I call it HT+)

David

 

[dmp]

What does B+ 120vdc mean?

If I recall correctly this terminology comes from battery supplies for tube equipment long ago. There was B+ and B- for the high voltage supply. A+ and A- was for the tube heaters

 

[Matador]

Ok so I did some testing on the apex 460 power supply today after work.

So zener 5 = 69.5vdc
    zener 6 = 71.6vdc

which = 141.1vdc so why is it that when i measure pin 1 i get 142.9 and not 141.1vdc.

If you measured these individually out of circuit, then the discrepancy is likely the difference between the voltage meter vs. actually pulling current through the devices.  Remember the diodes have a non-zero resistance so the voltage drop rises slightly as current is flowing through them.  Your meter probably just barely turns the diode on during measurement so you see less voltage.

 

[gary o]

Im experimenting with Ela & apex circuits....have question about 20uf cathode capacitor, am I right saying it will influence the sound of the mic....thanks

 

[Matador]

Im experimenting with Ela & apex circuits....have question about 20uf cathode capacitor, am I right saying it will influence the sound of the mic....thanks

Gain will be higher...if the cap is big enough, the gain step will be below the audible range.  Without it, gain drops, and the stage also become cleaner (due to local negative feedback).

So in short:  yes, it changes the sound.  Worse...better...up to the ears of the beholder.  Without it, the stage is less 'tubey', if that makes any sense.  It's a bit quieter and a bit cleaner sounding (to my ears).  I actually like the Apex circuit without it.

 

[gary o]

Thanks Matador , I know what you mean tubey......I will experiment now....I read earlier in this thread Dave Thomas words I believe....that the 20uf in a real EL M251 was too small but thats how they wanted the mic for  german radio.....sadly never got my hands on a real Ela M251 but from what I read its one of the finest sounding mics ever , I have original T14/1 original 6072 borrowed from ex BBC AKG C28A... so I copied the Ela M251 circuit tried it with several capsules but DIDNT like the lack of bass , I thought id wired it wrong, I since learnt about the 20uf bypass cap & I read about the low mega ohm grid resistor.......so did the original Ela M251 sound bass light......

I threw together a Ela but with a 5840 tube intead of AC701 & a 1 gig grid resistor, its sounds full and nice to me, I also copied a Studio Projects TB1 which looks bit like Ela circuit I used a 6072 my T14/1 again the TB1 circuit has 3K cathode resistor & 220uf bypass cap & larger than Ela grid resistor, these two mics sound about the same much nicer to my humble ears than my copy of 6072 Ela M251 circuit

I also then re wired the TB1 circuit as cathode follower CCDA circuit BUT used same T14/1 that is NOT 5:1 ratio & it didnt sound bad but nothing special either, dont know if would sound better with 5:1 tranny tho.....

 

[saxmonster]

Gary and others,

When you built you elam 251 circuit did you use the actual apex 460 circuit board or replaced the board with a home made one.  I am waiting for a few parts to arrive still such as some styrene's and c8's caps to try but the main goal was to build a 251 (many of the sax players i listen to use it or a c12) but I think I might have gone in over my head.  I might just do what dave first emailed me about which would be on the safer side for me since everything is written out and documented.  Almost like making a cake.  I can the always change it to a 251 later.  With building a 251 I would have to depend on my schematics readings which I have learned a lot from.  Still a little shaky.  But I have figured out all the cap and resistor values on the original ela schematic, so if I get all those part to swap in the circuit I just need to find out where they would go on the 460 pcb.  Can i use the 460 pcb to make a exact clone of the 251?

What i should do is over lap a drawing of the 251 on top of the 460 and see how they line up. The part that scares me is the ps and the capsule part since that will have to be wired like a c12 with the switchable polar pattern knob.

What does the M wire on the 6 pin wire /cable from the ps of the 251 to the actual mic mean?  Some type of ground?

The ps zeners will be changed to 56volts  for 112vdc.

Anything else need to be changed on the Apex ps to make it a 251 ps?

Capsule will be Tim's which is on its way. I will wire it for a c12 right just like the apex 460 is already wired?

A bv11 is on its way from Dave thomas if I do what dave emailed me.

But if I go for the 251 I will need a t14.


errrr. such decisions 

 

[saxmonster]

Anyone know what this silver cap is?

is this is?

http://www.newark.com/vishay-sprague/te1501/capacitor-alum-elec-2uf-150v-axial/dp/18F877

 

[saxmonster]

What about this yellow one?

Also I only see 3 caps where is the 4th like in the schematic of the body section.

And where is the transformer hiding?  the bottom area doesn't look that big for it.  Oh i see it its behind the red board.  Also what does the two written 50's and the written 200 mean at the bottom of the body where the transformer should be? Is this running at 200vdc and not 110-120vdc?

Thanks

 

[MagnetoSound]

What does the M wire on the 6 pin wire /cable from the ps of the 251 to the actual mic mean?  Some type of ground?

Yes. The M wire connects the mic housing to the cable screen - which is connected to the PSU chassis (via pin 6). The mic housing is also connected to the 0v rail inside the mic which returns to 0v at the PSU via the wire on pin 3.

The idea was to keep the tube currents from returning to 0v via the cable screen.

There is no need to follow this scheme specifically though. If your screen is connected to 0v at the PSU, and you do not experience any hum problems, all is good.

 

[gary o]

Hi Saxmonster sorry to confuse with my Ela M 251 questions I did NOT mod a Apex board I made mine from scratch personally I find it quicker & easier not to use a board for my own experiments... but from what I read here quickly you have instructions to mod a Apex board to C12 ish circuit but with the added cathode follower as you say prob best to stick to that one plan plus the transformer you have on the way wont be good for a standard plate out C12 or a Ela M251....I wouldnt worry to much about the look & color of components as long as you follow whats in your cake recipe you will end up with a better mic, as I think iot has been pointed out in this thread the capsule is a huge part of the sound of a mic it will make the biggest difference its the best place to spend your money, good luck have fun

 

[gary o]

Matador am I right in saying that the audio doesnt go thru the bypass cap but is effected by it..... what Im asking is quality of the capacitor is less important..... its the capacitance of the capacitor that is most important to the ears of the beholder..... thanks again

 

[pasarski]

Matador am I right in saying that the audio doesnt go thru the bypass cap but is effected by it..... what Im asking is quality of the capacitor is less important..... its the capacitance of the capacitor that is most important to the ears of the beholder..... thanks again

Audio definitely goes through and quality matters, what quality you like is a different story. I'm no expert but I assume low ESR is desired?