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Hello !
I bought a Lomo 19A9 and it`s not working probably. It got a very poor LF response. I measured the PSU and get 120VDC and 18VDC - I think thats way to much. Could it be the tube in the PSU ? It says 6X2N ( Cyrillic ) is there any US or European counterpart for this ? Any help would be much appreciated !
best regards -k.

You need to measure these voltages with the PSU under load (with the mic connected). 120V doesn't sound unreasonable for the HT voltage in a cathode follower mic. Edit: saw this:



Before you go checking anything, what is the history of the problem? Did the mic suddenly lose low-end? Any other problems? Make sure your PSU is set for the correct voltage (seeing as yours sound so high).

Hi Rodabod !
thanks so much for your reply !! I bought the mic like this - so I don`t know the history.
I just opend the mic. The capsule looks very clean but the mic has been modified - all the original parts are there but someone added a 47k resistor between pin5 and pin 6 - and a 330nf capacitor from pin 6 to ground. ? !
The tube says B519N/10 but I`ve also the original 6zh1p. Can I damage the capsule when it gets 120V instead of 50V ?
thanks again - k.

What country did you buy it from? Does it have a fixed mains plug or an IEC socket? Try and figure out if the supply is set for 110V or 220V. It sounds like it could be set incorrectly.

I can't comment too much on the mods as I don't have a great understanding of the circuit. All I know is that it looks like a plate follower. So the output is taken from pin 5. The valve is a pentode, so I think that's why pins 5 and 6 would usually be tied together in order to operate in triode mode. I'm not sure why yours would be modded to add a 47K resistor.

The capsule will hopefully be ok if it has been subjected to 120V as usually what happens is the diaphragm collapses and gets sucked onto the brass backplate. I would be concerned that your valve's heater has been fried if it has had 18V applied to it as that is surely too much. As I said before though, you need to measure these under load to get the correct readings.

I just measured the voltages with the mic connected - and get 50VDC + 6,3 VDC ! I think I will remove the modifications and then will see what it sounds like. Maybe I should replace the 25uF Capacitor. Does anybody know which voltage rating it should have ?
thanks k.

Don't mean to hijack your thread but since we're talking about 19a9 power supplies:

My 19a9 didn't come with an original tube power supply. It came with a supply that looks exactly like the supply that came with my 19a19. A newer smaller none tube power supply. It has the same cyrillic tag on the front. And strangely it has a 3 pin connection out of the PSU to the mic but the mic has a 4 pin connector.

The mic seems to work properly and sound good. I've not been worried because I figured that a tube in the power supply wouldn't make much of a difference in the "sound" of the mic. Am I right in that assumption?

Hi otisroom !
I was told the biggest difference lies in the output transformer which is settled in the PSU. maybe the 19A9 an the 19A19 got the same output transformer ?
On my 4pin cable pin1+pin3 are soldered together. so I suppose 3 pins are fine... How do the two mics compare in sound ? best. k

keeno wrote:Maybe I should replace the 25uF Capacitor. Does anybody know which voltage rating it should have ?

I'm not sure as my valve theory is a bit ropey. Obviously a 63V cap would work fine - I'm not sure what voltage will be there as I'm used to seeing an anode resistor. If you do replace it, use a decent quality cap like an Elna or Panasonic as it is in the audio path.

While you have the mic open, try to avoid touching near the Hi-Z areas (where the capsule interfaces with the valve) as finger grease/sweat and dirt can form a relatively low resistance across surfaces and lead to noise and level loss. Your mic is probably point-to-point wired though, so not really a worry. You may as well inspect the capsule for cracks, holes and any serious contamination too. If you still have trouble, then try inspecting all of the wiring including the power supply and the cables, and also try swapping the valves.

It has been a while. Apparently I never drew a schematic.
The western tube equivalent is the 6AK5.
I have a 22uF 63 volt electrolytic cap going from cathode (pin 7) to ground. If that is old, I would replace it.

Hi! I removed the modification and replaced the tube. Now the LF response is back and the mic sounds nice. Now I get 55VDC on the anode and 5,6VDC on the heater. Is that to low ? thank you all -k.