keeno wrote:Now I get 55VDC on the anode and 5,6VDC on the heater. Is that to low ?

Sounds ok to me. It's not uncommon to run valve heaters slightly lower than specified. I run that valve's heater at 5V in another mic of mine. Incidentally, I bought a Mullard M8100 as an equivalent for this valve.

Incidentally, regarding the circuit, I was chatting to someone else who owns this mic who was saying that the plate resistor and coupling cap from the plate are inside the power supply. The rekon that the plate resistor would be in the region of 100K (have a look if you are curious). With that in mind, and looking here, I'm guessing the bias voltage (across the 910 Ohm resistor) will be in the region of 1V, so a low voltage rating could be used for that cap. You could measure this to be sure though.

This is the one I drew a while ago. Sorry for the chicken-scratch. I would ignore the pin numbers (1-5).

Hi!

Roddy let me know about this thread. I was going to reply to his message but it makes sense to do it here - it's a good way of introducing myself.

I've done a bit of work on a 19a9 but there seem to be some differences of opinion on circuits and so the design may have evolved. The hand-sketched schematic that Roddy posted was from my mic.

A couple of points - there can be problems with grounding on the connector if it is old and worn. Also, the 6Z1P is not quite exactly a 6AK5 at the low current region in which mics tend to operate. I've been looking at these two tubes quite closely recently and unfortunately they are not perfectly interchangeable.

Clearly there are two different supplies kicking around - tube and sand-state. The 56K looks like it's there as a bleeder to keep techs alive! 22K plate resistor is lower than I had guessed, and the output cap & transformer are the 'wrong way round' in that most designs have the cap then the tranny, but the DC is still blocked so it may well be so. 30uF / 27 seems odd for the cap. I would have chosen something of lower capacitance and higher voltage.

There are pictures of the 'tube' supply here.
http://www.prodigy-pro.com/forum/viewto ... light=19a9

Roddy's comments on the mods are sound - someone had converted to pentode-operation.

Hope that helps.

Cheers!

Stewart
xaudia elektrik
York, UK

Is there a exact replacement for the 6z1p ? or who makes the best ?
I thought about trying a Telefunken 5654 ?

The best replacement would probably be another 6Z1P. The mic was, after all, designed with this tube.

Are you having trouble finding one? I have some NOS. (New Old Stock).

Thank you very much for your offer ! I got some 6z1hp too, but I am unsure of the quality. Are there different manufactures with different quality standards ? In the Powersupply I found a 6x2p - should I replace this like with like or could I try something like a EAA91 ? thanks k.