Lomo 19a19 schematics

[Tillmann]

I have a Lomo 19A19 tube mic that is in very good cosmetic condition, but it doesn't seem to be working correctly. It sounds very harsh in the mid range, yet it is still quiet. The capsule looks almost new and I think that perhaps either the tube/valve is bad and needs to be replaced, or that I need to build a new power supply for it. The PSU seems a bit underbuilt for my liking.

I was wondering if anyone knew where I could find a schematic for the mic and perhaps for the power supply so that I could build a new one? Also, I was wondering if someone knew where I could locate some new tubes for the mic?

These sound very good when they are working properly. I need to get this back in order. Any help is appreciated.


Cheers,

T!

 

[rodabod]

Aaron,

I'd do a few things - firstly check that none of the components got shaken loose when it was in transit - re-seat the valve. Look in the PSU and check for any obvious parts that are looking loose or have dodgy looking joints (nothing wrong with dodgy looking joints, we just don't want them in the PSU).

See if you can get a volt meter on the cable connectors either at the PSU or at the mic and try to get a reading for the heater and HT voltage. Try not to kill yourself though.

As far as getting schematics is concerned, I'd maybe try asking Greg at Electrical Audio. They have a lot of Lomos, and he seems very knowledgeable.

Here's a nice pic from Staurn Sound just for the hell of it:

http://www.saturn-sound.com/images/lomo%2019a19%20-%20inside%20views.jpg

 

[gang of elk]

According to this link, http://www.microphones.ru/LOMO/LOMO_19A19.html, there's not a western equivalent for this tube (6S31B-R), is this possible?

I have a pair of these too, not sure what tubes they use, never cracked them open, I'm paraniod of damaging the pressed-on grill cage. Did you have any problems disassembling yours?

As for replacing the tube, I saw a pic somewhere that demonstrates how the capsule carrier pivots out of the way to provide access to the base of the tube. Looks like that should help minimize the fiddling, at least a little bit.

Curious about this tube, I too could use at least 1 to keep as a spare.

 

[Tillmann]

[quote author="rodabod"]Aaron,

I'd do a few things - firstly check that none of the components got shaken loose when it was in transit - re-seat the valve. Look in the PSU and check for any obvious parts that are looking loose or have dodgy looking joints (nothing wrong with dodgy looking joints, we just don't want them in the PSU).[/quote]

The first thing that I did was take it apart before I ever tested it. It looked fine as far as general condition is concerned. Very nice actually. However, it fits together rather interestingly. Each screw is slightly different in size and/or length and must fit with it's corresponding hole. It's kind of funny actually, however you have to be careful and gentle. They're not of a precision build like a Neumann, but they use some good key parts. Also, mine looks much different inside than the one you had a link to. I'll try to get some pics soon.

The valve attaches via wire leads rather then fixed metal pins, so there really is no re: seating to be done, if I recall correctly.

[quote author="rodabod"]
See if you can get a volt meter on the cable connectors either at the PSU or at the mic and try to get a reading for the heater and HT voltage. Try not to kill yourself though.
[/quote]

I'll try this later in the week. I tested the thing out in Berlin last week on 220V and now I'm back on location in the States working (110V mains), so I don't have any kind of a bench. Actually, right now I don't have any furniture at all for that matter, but that's another subject- however I'm still deeply concerned about my microphone, even though I've been sleeping on the floor for a week now! :green: That could perhaps be the very definition of madness. :razz:

I'll contact Electrical too and share whatever I find with y'all.


Cheers,

T!

 

[Tillmann]

[quote author="gang of elk"]I have a pair of these too, not sure what tubes they use, never cracked them open, I'm paraniod of damaging the pressed-on grill cage. Did you have any problems disassembling yours? [/quote]

I wouldn't be afraid. Just pay attention as you disassemble it and be gentle and it should be fine. As to the tube, I wouldn't doubt if there's not a western equivalent. However, there were a lot of these tubes made. They were used in a lot of the Soviet mics as far as I've heard.

[quote author="gang of elk"]
As for replacing the tube, I saw a pic somewhere that demonstrates how the capsule carrier pivots out of the way to provide access to the base of the tube. Looks like that should help minimize the fiddling, at least a little bit.
[/quote]

Do you have the pic? I've made some inquiries elsewhere about tubes. I'll keep you in the loop.


Cheers,

T

 

[gang of elk]

found that pic..

http://www.vintageloop.com/LOMO_19a19.html

 

[Gus]

Clean the cable connectors the pins and sockets can cause strange problems.

lomos I have seen two connector styles one was a green mil looking one the other a silver one. Had problems with the green ones.

What style body 19a19? there are two different bodies I have seen

 

[rodabod]

One of the connectors I saw used looked like a NATO connector. We use them for satellites. Rugged stuff!

 

[gang of elk]

Gus speaks the truth. :idea: These connectors (for 19a19) gave me grief! BOTH were picking up heavy RF due to poor connector contact. Turned out to be the flat inner surface on the of the threaded collar, which on these mics (or at least on mine) is the only shield contact point from cable to mic body. I burnished that surface and problems disappeared.

This connector is for a 19a9 and is much more substantial feeling and easier to use. No problems from this one.

 

[Tillmann]

I'll open it up and snap some pics ASAP. To be continued:

T

 

[rmburrow]

I wouldn't be afraid.  Just pay attention as you disassemble it and be gentle and it should be fine.  As to the tube, I wouldn't doubt if there's not a western equivalent.  However, there were a lot of these tubes made.  They were used in a lot of the Soviet mics as far as I've heard.



Do you have the pic?  I've made some inquiries elsewhere about tubes.  I'll keep you in the loop.


Cheers,

T

Check and clean all of the cable pins and connections first.  Oxidation and current don't mix.  Also, oxidation of copper can rectify...this mixed with audio equals distortion big time..

Measure the heater voltage and the HT...if the heater voltage going to the valve is 6.3 volts or thereabouts, there are workarounds if you cannot get another valve.  Since the valve is subminiature and must be soldered in, a triode connected 5840 comes to mind...also the 5703 subminiature triode, the 7586 nuvistor, etc.  Most likely you may need to try several valves and select for lowest noise.

Be careful around the HT...