ELA M 251 (non export) build with a 5718

[Spencerleehorton]

Hi oneroom studio,

As it turns out now I have another m269/m49 psu to build so I'm gonna build a second m269c and use the ac701 for that. And stick the 6072 in this Elam 251.
Does everything else look ok that I've put to use?
Gonna check these relays switch correctly before I wire it all in.
Also I have 9:1 ratio Sowter TXF that I'm thinking of using.
Gonna build my own body from some 50mm brass tube then gonna nickel plate.
I have a cheap r47 microphone parts capsule that I was going to use which should hopefully do for the time being until I have some funds for a suitable replacement.
Will update once I get some time to complete.

Regards

Spence.

 

[duantro]

Lowfreq - I used a 30M, and I haven't noticed any strange low frequency issues. I would be surprised if the grid resistor was the issue in your case. The first thing I would do if I had too much low end would be to decrease C1. The C12 had a 0.5mF cap on the output, so a 3u3 might be overkill in your case.

Spencerleehorton - Unfortunately, you won't be able to swap out a 6072/12AY7 and an AC071 in the same mic. These tubes have to be biased differently. In the original AC701-based 251, the plate resistor was 200K and the cathode resistor was 3k6. For an Export (6072) version of the 251, you'd want a 100K plate resistor and a 1K8 cathode resistor.

Hi, I'm wanting to do this with an Ac701k also. I plan to use a 200K plate resistor (instead of the 100K in the schematics here), a 3k6 cathode resistor (instead of  1K8 ), and 8M2 for R4 ( instead of the 30M). Also I'd need to set Heaters to 4V. Any suggestions on how to adjust 4V for heater and still get functioning relays? Possibly tap relays  into 6v somewhere before trimmer brings heaters to 4V? Or maybe use lower voltage relays like  769-DS2E-S-DC3V (http://www.mouser.com/ProductDetail/Panasonic-Industrial-Devices/DS2E-S-DC3V/?

 

[Banzai]

Don't worry about the relays, they'll work just fine with lower than rated voltage.

Use DS2Y-S-DC5V and hit them with 4V.

http://www.mouser.ch/ProductDetail/Panasonic-Industrial-Devices/DS2Y-S-DC5V/?qs=sGAEpiMZZMs3UE%252bXNiFaVCLW1ZA8WQBLG5bZLeo7zPc%3d

Any suggestions on how to adjust 4V for heater and still get functioning relays? Possibly tap relays  into 6v somewhere before trimmer brings heaters to 4V? Or maybe use lower voltage relays like  769-DS2E-S-DC3V (http://www.mouser.com/ProductDetail/Panasonic-Industrial-Devices/DS2E-S-DC3V/?

 

[duantro]

Don't worry about the relays, they'll work just fine with lower than rated voltage.

Use DS2Y-S-DC5V and hit them with 4V.

http://www.mouser.ch/ProductDetail/Panasonic-Industrial-Devices/DS2Y-S-DC5V/?qs=sGAEpiMZZMs3UE%252bXNiFaVCLW1ZA8WQBLG5bZLeo7zPc%3d

I guess that will work, I just had already ordered the 6v versions so was wondering about a workaround for using them.

Any suggestions on how to adjust 4V for heater and still get functioning relays? Possibly tap relays  into 6v somewhere before trimmer brings heaters to 4V? Or maybe use lower voltage relays like  769-DS2E-S-DC3V (http://www.mouser.com/ProductDetail/Panasonic-Industrial-Devices/DS2E-S-DC3V/?

 

[Banzai]

The 6V ones will work too. They're specified to switch at 70% or less (= 4.2V), so you can use them if you have to.

The 5V relays will work at 3.5V or below.

Good luck!

 

[duantro]

I've got it put together with the ac701k. The 6v relays seem to be working. As is, the heater, while  loaded, will adjust down to 4.3v. Should I add resistance in the H+ side of the psu to get it closer to 4v? It also has a lower audio output than I think is normal, and Omni setting is even quieter (and thinner) than cardiod and fig 8. I'm thinking I have a bad connection somewhere around the middle relay and will check it out soon.

 

[Matt Nolan]

I've got it put together with the ac701k. The 6v relays seem to be working. As is, the heater, while  loaded, will adjust down to 4.3v. Should I add resistance in the H+ side of the psu to get it closer to 4v? It also has a lower audio output than I think is normal, and Omni setting is even quieter (and thinner) than cardiod and fig 8. I'm thinking I have a bad connection somewhere around the middle relay and will check it out soon.

Omni will be quieter than Cardioid, and thinner than Card and Fig-8. I would have expected the Fig-8 level to be around the same as the Omni though.

 

[duantro]

I had a minute to look at it, and after checking some connections, It is working now! 6v relays are doing their job with 4.3v. I will take it to my studio and see how it sounds.
Edit: I changed r9 to 470r to be able to drop Heaters to 4V.
The Beesneez 251 body Is remarkably heavy. Going to take a solid Atlas stand to keep it in place!

 

[digitall2000]

Hi OneRoomStudios
I was wondering when using the 5718 did you follow the schematic for the 701 tube (200k Plate Resistor)?
I'm assuming that 'cause the non export tag
Or did you use the schematic for the 6072?
What was your plate voltage 100v, 120v?

thanks lance

 

[Lowfreq]

A few posts back he mentions that he's using a 100k plate resistor, as am I in my 5718 loaded m251.

I used a trim pot for my cathode bias and I ended up with it around 2k26, so a little different than OneRoomStudios, but I doubt that it'll be that much of a difference anyway. I've also used a 47uf capacitor here instead of the 20uf. It seems to be a good balance of controlling the low end of the CT12 capsule, although I may try a 100uf at some stage to see if it gives me a bit more bottom without getting tubby.

I've gone for a 1gig grid to ground resistor as opposed to the smaller values, and the mic seems pretty quiet.
I'm also using a 1uf output capacitor which is closer to the AC701 schematic than the 3.2uf of the 6072 schematic

I've got my voltage at 120v and everything seems to be running well.

Hopefully that helps.

 

[JessJackson]

Hows it sound?

 

[Lowfreq]

It sounds good, but quite a hard sound on vocals, especially compared to my U47 clone, which kinda feels more like a warm hug.

I feel like I could still substitute the 47uf to something larger to see if I can get some of the low end back on the 251, but it's working on acoustic guitar really well. I also find acoustic guitars can get quite boomy, and this is probably one of my only mics that I don't find myself reaching for a high pass filter.

 

[klausheyne]

RE: Underheating of impedance converting tubes:

I've experimented for 30 years with AC701 tubes and found what Neumann and Telefunken confirm in their internal communications (but not always backed up on their schematics):
4.00 VDC nominal, (+) 0.05VDC (1.25%),  (-) 0.2 (5%) max deviation. You go higher, you stress the tube, you go lower, you stress the tube, plus increase the noise floor.

On EF86 I've settled for 6.15VDC for the longest, least stressy operation (all voltages measured at the tube).

For what it's worth.

 

[micaddict]

Thanks, Klaus.
Yes, the AC701 doesn't give you much room to play.
And they're too expensive to screw up with. 

So what about the 5718 (OP)? Do you have experience with it? Like the EF86, that would be a 6.3 V tube. Some datasheets speak of a max 5% deviation (under- or overheating), but that seems like stretching it, especially for overheating.
Would you aim for 6.15 V here, too?

 

[klausheyne]

While I have no experience with the 5718, I run EF86 penthodes as well as  medium-mu dual triodes like 6072 at 6.15VDC in microphones.

 

[Mikael-ange]

Resurecting this thread, I have a question about using a 5718 into it.
Do you guys directly solder the tube in place of the 9 pins tube socket, or do you use turret and solder the tube on those?
Or maybe separate acrylic board (for exemple) connected to the various point on the tube socket pcb?
I trying to do it in a way that doesn't involve desoldering half the component for acces when doing tube change.
Thank a lot

 

[OneRoomStudio]

I'm not sure what happened to the pictures at the beginning of this thread other than them being almost 10 years old(!), but here's what I did (sorry for the poor quality pics, my camera back then must not have been very good and I no longer own that mic):

I don't know if you can tell from the pictures, but the grid wire actually passes through a hole and gets wired straight to the front capsule wire (as well as 150M resistor and 1nF cap).

 

[Mikael-ange]

I'm not sure what happened to the pictures at the beginning of this thread other than them being almost 10 years old(!), but here's what I did (sorry for the poor quality pics, my camera back then must not have been very good and I no longer own that mic):
View attachment 114797View attachment 114796
I don't know if you can tell from the pictures, but the grid wire actually passes through a hole and gets wired straight to the front capsule wire (as well as 150M resistor and 1nF cap).

Thanks a lot
Don't be sorry about the picture, as you said; those are 10 years old.
Yes I can see the grid wire going direct to the capsule connection.
I think I will try first to make a tube support that go into the 9pin tube socket first, before doing it the way you did it for the reason mentioned on my previous post.
But anyway, thanks for the pics and sharing even after 10 years.