U47 Build using EF80

[Spencerleehorton]

HI All,


have put in the 1k 5w and changed the 10k to 25k trim, wound down the trim and now get about 183v at B+ connector for mic, haven't test just after the 1k 5w yet but wanted to get voltage down a bit further so gonna have to go up to 3k 5w and see what happens.
changed the 2k trim on the heater for 5k and it still sits at 6.3v on the lowest point? gonna have to do the same here  reckon.

polar pattern switch i have used a paper clip and a spray bottle top cut up, poked the paper clip through so to give something to click it across.
just gotta put a couple of pieces of flexible metal close to the end so when it is slide across they contact each other, and when slid back they disconnect.
obviously this is will all be mocked up out of plastic and metal at a later stage but for the moment it just needs to work any which way!!!

regards

Spence.

 

[gary o]

Sounds like a plan..... I like the cathode pot I usually put that on my mics can fine tune the thing and see whats going on..... your switch sounds nice too.

Re power supply is that the way to do it I really dont know would like to learn, I usually get powers supplies work as I want by trial & error I would probably mess with values of the last 3 resistors as you say you will have a trimmer there...... I was think about the G7 power supply in original form it supplies 160V B+ 7 looks like stays at 160V when mic is connected different to some other supplies like Maxex MK47, interesting as I say I dont understand be great if a power supply guru were to pop up now......would love to learn, as I say I may see if i can knock up a supply for my M269 for the heaters tho.....

heres schematics from M49B & M269 build threads  http://dl.dropboxusercontent.com/u/43869772/PSU249P.pdf

https://dl.dropboxusercontent.com/u/43869772/D-M269/M269_Schematic.pdf

 

[Spencerleehorton]

HI Gary,

yeah i have built several of those M269b and M269c, and i have several M49b and M49c here, only built 4 psu's for them.
M269c is an excelent mic and i ushally use that for vocals or the AKG C12, the M49c i have used for more pushed distorted vocal sound on some heavier tracks and sounds good but mainly M49c on guitar amps with ribbon mic or sm57.

regards

Spence.

p.s Happy new year!!!

 

[Spencerleehorton]

Hi guys,

right one step forward 2 back, have powered up psu and mic together and get 100v at B+ so nearly there, little more tweaking to get 105v.
heater giving 6.3v unloaded but when connected to mic i get 0.124v so somethings not right here.
Have re made switch and works nice.
Just the heater to sort out now.

regards

Spence.

 

[gary o]

Happy new year 

nearly there then looking forward to hear how she sounds.....

Spence did you buy the boards & build the M269s M49s Im interested in the PSU for M49B & M269 the one that has the choke all my haeter cathode connected mics MK47 M49B Sm269 sound good but have more noise than ela m251 M49C & others.

I have the M269 up & running but not as quiet as my Elam & 49C m269 doesnt have cathode connected to heater......I need to order a choke maybe

 

[Spencerleehorton]

HI Gary,

yeah i got some early boards from dan, great pcbs, all my pcbs are quiet and mics sounds great so no complaints, my C12 has the edge on the noise front, the c12 only really listens to whats going into the mic rather than the room sound, i find the m49 picks up the room personality more.i
I use my c12 with a reflector shield and pop shield as well to hone in on the vocal.
if your getting noise on your psu without choke then get a choke in there dude, that other thread you showed me he used a couple of them.
I will chat to my very knowledgable friend about the use of chokes and relay any theory for you.

regards

Spence.

 

[Spencerleehorton]

Happy New year everyone,

found that i didnt attach pin 6 from valve down to ground so will do that and test again tomorrow.
fingers crossed now!!

regards

Spence.

 

[Spencerleehorton]

Hi All,

all voltages working now, and mic getting what it needs for the heater, gonna go and test if it passes audio!!!

regards

Spence.

 

[Spencerleehorton]

HI All,

sounds fantastic!!!! slight hum which would be nice to get rid of, hum is around 120hz, if i cut at this frequency get rid of it.
Any ideas on how i should approach getting rid of this hum?
on drums sounds amazing, just couple of foot away in front, on vocals its amazing as well, nice big bottom end, clear and creamy top end, time to build a 2nd version with oil paper caps!!!! and more original resistors, also gonna put a relay in there for the polar pattern.

regards

Spence.

 

[gary o]

Brilliant  Re humm I use croc clips connect heaters the disconnect while mis is working to see if hum goes away to find if its the heater voltage thats humming

Could be electromagnetic can you move transformers around sometimes turning them 45 degree angle hum goes away....

just couple ideas good luck

 

[Spencerleehorton]

Hi Gary,

couple of things still to do with it: put a relay in connected to pin 7 so i can adjust at psu for polar patterns, heat sink on the LM350 which i've used for the heater supply, move transformers around in case to see if hum improves, plenty of room to move them so i'll move them to one end and turn them 45 degrees hopefully this will reduce the hum.
Have made some preliminary recordings but at the end of the day i'm not worried about it all too much yet as the capsule ain't that great and neither is the transformer but just getting it to work was the main aim and i've got there now, just some little tweaks to getting sounding a little better, then i will change the capsule and transformer for better ones.

regards

Spence.

 

[0dbfs]

Didn't read the whole thread but if you have it set up in a fixed bias layout and the heater ckt is using a regulator then you will most likely have residual 120hz in the heater ckt. Ie; if cathode ref point is derived from that it will be audible.

Check out the PSU Dany has for the M49 and M269 builds since that one is adequate for both fixed and auto-bias implementations with adjustable B+ and H+.

Cheers,
jb

 

[Spencerleehorton]

Hi Guys,

we seem to think its coming from the B+ rail, as when connected and mic turned up i turn the psu off and the hum goes instantly then i hear the valve power down, if it was on the heater rail it would keep humming and go slowly with the heater powering down.
my very intelligent friend who seems to be able to solve all of these riddles is onto it and going to use a better power rail to see if the hum goes.

regards

Spence.

 

[0dbfs]

My guess is that the 120hz ripple is on the heater since powering it down also stops the voltage going through the diode bridge / rectifier section of the H+ supply too.

The PSU smoothing caps hold the charge for a little while (on both B+ and H+) so takes a couple sec's for them to discharge fully. That's why it's not instant-off.

Ripple on either B+ or H+ is audible (H+ in a fixed bias setup) however the ratios of audio-signal to 120hz ripple (and noise-floor) are different so the B+ ripple is usually already down towards the noise-floor while the grid bias point is derived directly from the H+ supply and the difference between say about -1V at the grid and say 45V at the anode is significantly different in terms of "how loud the ripple is at the output" compared to the audio signal at those nodes.

Hope that helps.

Cheers,
jb

 

[gary o]

Spence you have already built the power supply JB mentions for either your M49B or M269 you could use the heater side of the supply to test this mic also try disconnecting the 6.3v while mic is on as you know will still pass audio as heater cools but in my case noise goes away

Obfs I made M269 & M49B circuits in last two days but using LM317 heater supply I made for a Elam both I knew I may have issues & did but not humm but white noise hiss... is this a result of the regulator I have been eyeing danys M49B PSU and want to build one waiting for choke to arrive .... I also tried reversing the heater polarity like in U67 a lot of the white noise went away tho Im not sure I understand whats going on...... I then built M269C & M49C they are silent..... I also built & re built Maxes Mk47 it too has the white noise mush its not terrible but its there is this just because of the heater cathode bias style.

 

[0dbfs]

Gary, Yeah.

The 49C version is autobias (B is fixed) and doesn't derive the grid bias from the H+ supply so that's the difference. The choke and filtering should sort that out. I'm putting together a pair of 67's right now and those also reference the grid bias against the H+ supply. I believe the 251 is also autobias.

The U67 uses a fixed bias derived from the H+ (actually H-) tied directly to the grid to get the negative voltage ref on the grid with the cathode @ GND instead of other fixed-bias implementations where the cathode is referenced to a + voltage and the grounded grid which makes G-negative-with-respect-to-K.

I've got a handful of EF800's so may check those out at some point. I would think that Dany's PSU2649assive will work great with a number of tubes with 6.3V heaters and be flexible enough to dial in the desired amount of underheating V depending on that tube's specified heater current. I believe the specified choke is rated @ 600 mA so if the heater starts drawing more than say 400mA'ish may be necessary to go up to slightly higher ratings and things...

Cheers,
jb

 

[Spencerleehorton]

Hi Guys,

ive used a LM350 regulator instead of the LM317, the LM350 is good up to 33v but i dont know if has introduced any noise into the circuit?
I will try my other M49/M269 psu's and see what they are like.

regards

Spence.

 

[gary o]

Thanks jb Im gonna have to re read this few times to get into my brain I have made six mic circuits this week attempting to find a favorite I did the U67 & was interested in its heater /bias scheme being different to the rest ..... I have noise issues with all the fixed bias circuits & none of self biased, I tried copying the reversed heater polarity with M49B & M269 & it kinda worked but need to understand..... but the noise issues are white noise is that what to expect ?

Thanks again Im learning great stuff.

 

[0dbfs]

Gary, Sounds cool. Also trying to better wrap my head around the U67 now too

The white noise is probably from the heater regulator if fixed bias comes from the H+. Self bias doesn't use the H+ so it may still have noise on it but it's not introduced into the grid in those cases.

Cheers!
-jb

 

[Spencerleehorton]

HI Guys,

Im obviously not getting something here as you seem to be saying to use the M49/M269 psu for the 6.3v correct?
I have tested the voltage on 3 of my m49/m269 psu's and the H+ is 24v-25v unloaded?
Im not getting how unloaded the U47 H+ supply is much less than this, if you could explain please.

regards

Spence.