Anyone have the schematic for a Rode classic?

Anyone have the schematic for a rode classic?

I also need the schematic ! ... 
Thx
Guy

Yes, I owned one of the original Rode NT Classics for years, and was never able to locate a proper schematic...would love to see what made that mic tic...nice clean detailed top-end...one of Rode's best efforts, IMHO...

Here you go

Part 2

Part 3

Part 4

Thanks mate Any chance for Classic 2 sch?

I don't have that one, sorry.  I don't even remember where I got the first one, I remember having to help my brother with an issue on his Classic 1 and I'm sure some kind soul here stepped up and provided it.

We should probably repost in the tech docs section.

Thanks for that ruairioflaherty !

Helpful this old thread - thanks. Just looking at that schematic, and the grid leak resistor to ground is shown as 200M........ can this possibly work given the cathode circuit shows 2.7k to ground and 1.35V? At Rg = 200M would the 6072a not just cut-off or be very current starved?

Is it a schematic typo or can it really work?

Thx

T

The +1.35 V across 2.7 kΩ means that plate current is 500 µA - entirely reasonable for its grid voltage being about -1.5 V - also reasonable for the large value of Rg.

Thank you. Yes, on the face of it. However for the grid to be at -1V or so, leakage current would have to be be about 5nA. Which seems far too small? On the face of it, any reasonable 'normally used' value for leakage current would force the grid too negative and the valve into shut off or starvation. And so the enigma.

I think its unusual, and intriguing if it works. Might lead somewhere I suppose. Once signals get going, grid-cathode would act as a diode rectify the grid signal and change bias depending on level?

T

Look close at the power supply schematic.
A quiz
What do you see that you often do not see in other power supplies?

HPF?

Someone doesn't quite understand here. Valves in class A like this have zero grid current, it is not like a transistor! the Cathode is biased positive by the cathode resistor drop, so the grid is negative to the cathode by this voltage. 200MOhms for a grid resistor in this circuit is perfectly reasonable, and the Lo cut is provided by the input capacitor(s) time constant with this resistance, the reeds setting the frequency. Simple enough.

Gus said:

Look close at the power supply schematic.
A quiz
What do you see that you often do not see in other power supplies?

Click to expand...

Positive supply for the relays doesn't work as it is drawn ? ;-)

T

davezawadi said:

Valves in class A like this have zero grid current

Click to expand...

Thx - not quite zero though. Reputable reference suggests c 500nA typ for triode with mu c 60. And suggests grid leak bias R c 5-10M. Whereas 200M would require c 5nA leakage to work and that seems a stretch?

T

Gus said:

Look close at the power supply schematic.
A quiz
What do you see that you often do not see in other power supplies?

Click to expand...

The heater is supplied by a current source / regulator.

As to the 200M grid leak resistor, I just read about a backwater called 'contact potential bias'. If I understand it right, there always exists a potential difference between cathode and grid because (intentionally) these are coated with different material having very different work functions. Like two dissimilar metals in contact I suppose. Apparently, even with zero anode potential, a heated cathode can cause a floating triode grid to go a volt or more negative relative to cathode. So if Rg is big enough a triode might 'self bias' due to contact potential. And if that bias happens to allow the valve to conduct it will. Point is that such bias doesnt depend on either Rg or Rk, just on the valve so long as Rg is big enough...... I think?

If so, I wonder if this part of the mojo?

T