tube 414 revisited

[pucho812]

It's baaaaacccccccccccck.

O.k. you guys may or may not remember a thread I started a good while ago
http://www.groupdiy.com/index.php?topic=19965&highlight=tube+414

well I finally was able to procure the mic into the shop again , this time the conditions are as long as I need it as it is not in use at the moment.

So back to making a schematic and board artwork.:twisted:

So far the mic itself has the standard 414 capsule

it's attached to a 5840 submini tube(A Dave Royer fave). there are 2 resistors and a cap in circuit and that's in. The mic transformer is in the PSU. and it all comes out to a 6 pin connector. Shouldn't take long at all to get that drawn. Then the Psu is simple.

At any rate this makes a perfect candidate to use with maybe a ck12 from peluso or maybe a china mic.

 

[jackies]

Sweet!
The board you making will fit into 414 body too?
:thumb:

 

[pucho812]

[quote author="jackies"]Sweet!
The board you making will fit into 414 body too?
:thumb:[/quote]

Um no. I have no real plans to make board art work available to the masses. If anything recreate the board artwork as it is which yes fits the 414. However there is so little in there that one could bread board it without issue.

 

[ruairioflaherty]

Hey Pucho,

I'm pretty interested in this mod. I have a 414 that I'm less and less in love with as the years go by. Something puzzles me though, you describe a regular 414 as being bright - I've owned 3 of the B-ULS model and I haven't found them to be bright. They are certainly darker than a U87, an AT4050 or many of the Chinese mics I've heard for example. I have used a couple of EBs and the newer XLS models which I did find to be brighter.

Is there any way that you can set this mic up alongside an unmodded 414 and make some quick samples? I hate when people ask for sample to prove that gear x or y is worth building but in this case the mod requires pretty invasive work on a reasonably valuable mic and I would probably be slow to move unless I thought the mod addressed some of the issues I perceive with a regular B-ULS. Those issues IMO - I don't like the vague top end and the cloudy and slightly nasal mids (less of a problem in omni). I never use the pad or roll off switches so I've no problem removing these.

Does anyone have an opinion on the merits (or lack of) of the rectangular basket design - resonant nightmare or genius? I don't have any mic building experience to comment but I have been using 414s on a weekly basis for about 12 years so I can field any questions about applications of the sound of the stock mic.

Sorry for the ramble, it's been a long ass work day.

Cheers,
Ruairi

 

[rodabod]

[quote author="pucho812"]there are 2 resistors and a cap in circuit and that's in.[/quote]

Can you give us the values? That'll give a clue as to whether it's a plate-out or a cathode follower.

 

[zebra50]

Hi Roddy,
Good to see you - been busy or away?

[quote author="ruairioflaherty"]Does anyone have an opinion on the merits (or lack of) of the rectangular basket design - resonant nightmare or genius?[/quote]

Gus should have some opinions on this - he built a 'square' mic some time ago to good effect, although I can't find the thread right now. Look at old ribbon mics - Many of those have semi-parallel chambers.

Stewart

 

[rodabod]

[quote author="zebra50"]Hi Roddy,
Good to see you - been busy or away?[/quote]

I was away in the US for a couple of weeks (mainly Chicago and New York) and have been recording/mixing a fair bit. And outside of this I've got to work too!

My Thiele with Lomo 19A19 circuit is almost finished, so I'll report back on that.

[quote author="ruairioflaherty"]Does anyone have an opinion on the merits (or lack of) of the rectangular basket design - resonant nightmare or genius?[/quote]

It's not actually a box profile - more a wedge. I reckon AKG knew what they were doing probably. I like the 414.

 

[ruairioflaherty]

[quote author="rodabod"]
[quote author="ruairioflaherty"]Does anyone have an opinion on the merits (or lack of) of the rectangular basket design - resonant nightmare or genius?[/quote]

It's not actually a box profile - more a wedge. I reckon AKG knew what they were doing probably. I like the 414.[/quote]

I'm with you Roddy, in general I have been a 414 fan over the years. Maybe not the perfect mic on a given source but very good on almost everything - I like them on snare, OH, some voices, sax, bass amp (really good at this!) and lots of acoustic instruments like mandolin etc.

I have a feeling the 414 limitations are electronics first, capsule second but I could be wrong on that. I'm very curious to hear this capsule and basket with a simpler set of electronics. I normally cringe when I hear phrases like "lifting a veil" etc but I actually think there's more potential in the capsule and basket design than is currently being tapped.

Am I right in saying this mod would be reasonably reversible? It seems like it to me.

Cheers,
Ruairi

 

[rodabod]

The most work might be fitting a new multi-pin socket. The micro-switches may be tricky too.

From experience with condenser mics, the vast majority of the character in my opinion is from the capsule.

 

[Gus]

I would guess it is a CF to a 2:1 or 4:1 transformer with a pattern control.

Is the pattern control a pot or a switched one?

 

[pucho812]

[quote author="Gus"]I would guess it is a CF to a 2:1 or 4:1 transformer with a pattern control.

Is the pattern control a pot or a switched one?[/quote]

It's a 5 position switch in the PSU which gives you the exact same polar patters as found on the 414. mic has no roll off or pad.

 

[skipwave]

So capsule polarization is not done by grid leak voltage. I think my guess in the old thread could be right, lower cathode R than the Royer plan for lower output impedance.

Supply HT volts?

 

[Gus]

Why not floating grid caused charge voltage?

My guess at the circuit.

Floating grid to capsule backplates(both backplates connected together), charges the backplate maybe 50VDC

Front of capsule to ground

Rear of capsule maybe via a resistor(is there a .01uf etc film cap attached to the resistor at the capsule side?) open for cardiod(EDIT more likely at 1/2 or the same voltage as the backplate, open for cardiod without the back skin connected is harder to do but worth it if you can) , ground omni, 100VDC 8, <50VDC >0VDC wide cardiod, >50VDC and <100VDC hypercardiod. Why not just use a 100K pot?

I am guessing 50VDC and 100VDC because a Royer PS like used in the 2001 mod gives around 100VDC and 50VD is 1/2 and an OK charge voltage.

select cathode resistor for the tube used to get it at about 1/2 of the B+ underload.

How close am I?

 

[CJ]

I threw this down to better visualize what Gus was sayin.

This is Not the actual circuit, just a starting point, Rev A, if you will.
I do not know where the other end of the cap goes.

OT:
Tony is still idle, so no news on the Stephan Paul mic.

 

[Gus]

I like the drawing

Most likely a 5 way switch with maybe 100K or greater same value between OR the values sum up between P3 and both ends to be equal
1)B+ for 8
2)Hyper
3)cardiod (1/2 supply)
4)wide Cardiod
5) Omni ground
wiper to resistor to cap to back

The otherside of the cap at the backside should go to ground and the resistor maybe 22meg(red red blue) or greater

The trick looks like getting the capsule voltage to 1/2 the supply voltage. I guess you adjust the cathode resistor value.

Cap to a nice Ni transformer

IMO no need for a PCB I would use perf board and a tie wrap(s) with a grommet(s) to hold the tube to the board.

I am not sure about the power supply. I see 6.3VAC and 125VAC. If so maybe the power supply has a higher B+ voltage like 120VDC

 

[ioaudio]

i made a 414 mod, but unfortunately didnt have a camera at that time.
the costumer brought a brass ck12 and a original t14/1 transformer and a empty 414buls housing. i used a ec71 tube in a elam251 type circuit , no problem to fit the small t14/1 inside the mic housing.

 

[Gus]

A guess at voltages and schematic

Add maybe 100K resistors between the 5 way switch connections

Added a cardiod only switch

http://twin-x.com/groupdiy/displayimage.php?pid=2680&fullsize=1


Any thoughts?

 

[CJ]

Lets test this M I X pic link:
Oh goody!
Thought ot might be protected.

 

[Marik]

[quote author="CJ"]Lets test this M I X pic link:
Oh goody!
Thought ot might be protected.

[/quote]

Ah, this is a C12A. With original brass CK12 just awsome. I also saw with a Teflon capsule--piece of crap (in comparison, of course) :razz: .

 

[Gus]

To be clear The schematic is a guess at what the Royer tube mod to the 414 is with a cardiod only switch added. It has two resistors in the body like the pictures of the Royer 414 mod.