Starting with the M269 sounds like a good idea to me.  Just pick a different tube and then adjust for the other factors.
Can try something simpler like the M49C circuit. Big LPF for smooth highs (680-1000pf plate to ground). 200-400M grid resistor for solid lows.

5840 works well with BV8
0.7-1mA bias
22-47uf bypass cap

Can use stock China supply with minor mods. Disconnect pattern switch entirely. Drop B+ to 120V. Raise heater to 6.7V with diode. If using decent cable, drop to 6.3V with 2Ω resistor. Can leave at 6.7V if using China cable ;D


Delta Sigma

...I suggested that he might like to try out one of my end address RF bias mics....
A Lo-Z condenser mic with an LDC capsule - so should be OK outdoors...

Oh man, this is beautiful! I've been meaning to tackle your whole RF thread (super interested in the project), but still haven't found the time. Seeing your finished product really makes me want to prioritize that thread!

Can try something simpler like the M49C circuit. Big LPF for smooth highs (680-1000pf plate to ground). 200-400M grid resistor for solid lows.

5840 works well with BV8
0.7-1mA bias
22-47uf bypass cap

Can use stock China supply with minor mods. Disconnect pattern switch entirely. Drop B+ to 120V. Raise heater to 6.7V with diode. If using decent cable, drop to 6.3V with 2Ω resistor. Can leave at 6.7V if using China cable ;D

Any ideas on how to implement a more complex filter? Is the 67/269 filter out of the question with a BV.08?
Neil Fitzpatrick

mjrippe

Here's a link to my end address LDC mount ... (mounting holes are for an BM800 body)...

https://www.shapeways.com/product/EFE6MUJYM/34mm-ldc-mic-bracket?optionId=123657963

Very nice!  And inexpensive as well.  My only thought is that a hemisphere or cone shape over the base (point toward back of capsule) would reduce parallel surface reflections, but how to get it inside the basket???

mjrippe

Can try something simpler like the M49C circuit. Big LPF for smooth highs (680-1000pf plate to ground). 200-400M grid resistor for solid lows.

5840 works well with BV8
0.7-1mA bias
22-47uf bypass cap

Can use stock China supply with minor mods. Disconnect pattern switch entirely. Drop B+ to 120V. Raise heater to 6.7V with diode. If using decent cable, drop to 6.3V with 2Ω resistor. Can leave at 6.7V if using China cable ;D

Ok, this is sounding good, lots of details and simple is better for starters.  Perhaps it is time for some perfboard.

rogs

Oh man, this is beautiful! I've been meaning to tackle your whole RF thread (super interested in the project), but still haven't found the time. Seeing your finished product really makes me want to prioritize that thread!
Very much an experimental project -- and not expensive to try! 
Always interested to see what other folk discover, with their own versions.....
www.amx.jp137.com - A DIY RF condenser mic project

rogs

Very nice!  And inexpensive as well.  My only thought is that a hemisphere or cone shape over the base (point toward back of capsule) would reduce parallel surface reflections, but how to get it inside the basket???
That's the tricky bit - getting it into the head basket! 
You might get away with a small cone - providing the centre 'peak' was no higher than 10 - maybe 15mm - above the existing base?....
www.amx.jp137.com - A DIY RF condenser mic project

kingkorg

Very nice!  And inexpensive as well.  My only thought is that a hemisphere or cone shape over the base (point toward back of capsule) would reduce parallel surface reflections, but how to get it inside the basket???

I have one simmilarly modded end address st51. This should be addressed, however i couldn't eliminate effect totally. There is also ring around the capsule which is the part of the grille construction, it affects the response as well.

It's a couple of db boost in 3-5K range. Doesn't sound bad, might be useful for live, but good to be aware of it.
« Last Edit: April 05, 2021, 04:28:10 PM by kingkorg »

mjrippe

I have one simmilarly modded end address st51. This should be addressed, however i couldn't eliminate effect totally. There is also ring around the capsule which is the part of the grille construction, it affects the response as well.

It's a couple of db boost in 3-5K range. Doesn't sound bad, might be useful for live, but good to be aware of it.

See, this is the kind of info that is super helpful!


 

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