Valve Condenser Cardioid Mic RV15 Red5 Audio

[trancedental]

A Red5 Audio RV15, I was hoping to use this as donor for a DIY clone, the PSU looks like the usual non pattern switch Alctron / Apex type, however the microphone PCB size spacing is too narrow at 30m width, 85mm length & screw spacing is 25mm. So too small for the Groupdiy mic PCB projects.

I think I could try some mods, although there are some SMD components included on the PCB, I'm assuming it's a Apex 460 / 450 circuit as the through hole components are familiar, 3 x 1uf / 450V, 2 x 220uf / 16v electro's, 2 x 100K & 33R, 47R, 3W? resistors, 1uF / 250V film cap.

The usual C9 / C10 caps on the secondary transformer outputs are SMD ceramics, with added resistors & other components.

I've tried old USA 6072a & Mallard M8137 / 12AT7 valves so far, looking to buy a better capsule, maybe a 47 type instead of the 67 type installed.

I'm not sure if I can get a PCB transformer upgrade so the original will stay.

 

[Khron]

Why is there a Schoeps-oscillator-looking group of components in there, i wonder? Those two grey inductors, the little SOT23-package (likely an NPN transistor) and a couple light-grey capacitors (C0G / NPO pF-range ceramics)...

Are they taking the heater voltage, and using that circuit to create the capsule bias voltage? As opposed to a resistive divider off the tube's B+ supply...

 

[trancedental]

Hi Khron,

Compared to most MIC tube / 460 mic types this one is a mystery, I'll have another look at those parts on & try & get readings & codes. There's no schematic online either.

Both ceramic caps are 290 nf, both resistor codes are 561 = 560R, inductors have no codes.

Wired in series, cap - resistor - inductor to the output + PCB part values on picture.

PCB through hole part values added.

 

[trancedental]

2nd section of SMD part values & picture. I haven't managed to get the capsule PCB apart so far!

All parts BOM

BOM RV15
Electro
1uF / 450V X 3
22ouF X 2
100nF 250V Film
100K X2
47R
33R

SMD
108G
1M
560R X 2
220nF X 2
170uF
630pf
35pf
2.4nF

Zener? X 2
Diode Code 682
G1 3pin transistor
Inductor? X 2

 

[kingkorg]

That thing looks like it has a lot in common with AKG Perception mics. The transformer and capsule seems to be the same. I find that very interresting!

 

[trancedental]

Thanks kingkorg!

AKG Perception 820 Tube has got some at least, similar construction, the inside layout, head-basket, body & the bottom 7pin connector. I don't even remember that AKG mic actually being released?

Now to find a schematic.

 

[Drosselmeier]

 

[Khron]

Why is there a Schoeps-oscillator-looking group of components in there, i wonder? Those two grey inductors, the little SOT23-package (likely an NPN transistor) and a couple light-grey capacitors (C0G / NPO pF-range ceramics)...

Are they taking the heater voltage, and using that circuit to create the capsule bias voltage? As opposed to a resistive divider off the tube's B+ supply...

View attachment 89907View attachment 89908

My point exactly...

 

[trancedental]

The Golden Age TC1 looks very similar as does the Record MTC-120.

TC1 schematic & AKG P820 pics.

 

[Gus]

In the 820 I see two bridges and four other diodes that look like they might be in series so maybe 4 Zeners to regulate.
Uses caps at the diode bridges, nice
Ferrites, nice