EHX Hot Tubes (1979 version) - supply voltage?

[anotherjim]

I seem to remember coming up with 6mA per inverter for 4069U @9v... but...
4049U has fatter N channels.
Different fabs/processes give different channel Ron ranges. But there are fewer different types in new stock.
In the Hot Tubes, 2 out 4 inverters have pull-off input resistors so they don't idle at maximum shoot thru'.

On the PCB, double layer boards excel in hiding the story of how things connect. The diode has to be parallel protection as the anode is definitely on the ground plane. Big electro will be main 9V and small electro maybe Vref network for the opamp.
FB1 is a fusible? Or a tiny ferrite inductor (never seen one like a mlcc cap)?... or they planned a fuse/ferrite but fitted a zero-ohm link instead?

[Rob Strand]

The diode has to be parallel protection as the anode is definitely on the ground plane.

Maybe not as obvious as it seems as you could have a series diode on the negative side, sort of like a Boss ACA type setup. AFAIK, those Electroharmonix supplies are linear (ie. with a transformer) but are regulated and supposed to put out 9.6V.

(The Snarling Dogs pedals were supposed to be clones by I think they were running for 5V or so.  Some people have criticized them as not being proper clones.)

Interesting, found something.  Here's a trace of the nano bass-balls power supply

https://mimmotronics.com/blog/emergency-room/er15/



So series diode in the negative rail.  Presumably the pattern is copied across at least some of the nano pedals.
R1 is 47 ohms; the resistor is between the ferrite bead (FB) and the electrolytic filter cap and doesn't seem to be on all pedals. 
The ferrite bead (FB) isn't shown either but is between the 100pF cap (C20) and the resistor R1.

I'm not sure the battery -ve is correct on that schematic.  (Based on the additions below the battery -ve connects to the circuit side ground via the input jack.  It does not pass through the diode.)

I can add a few of details about the nanos.

After looking at some nano pedals:
- The diode drop is only present on the DC jack supply.
  The battery power does not pass through the diode.
- If the +ve rail resistor is present both the battery and DC PSU pass through the resistor.
- The battery -ve is switched through the input jack.
  The DC jack power is not switched via the input jack.

So,
- the pedals provide a nominal 9V for both DC jack and battery power; provided the EHX power supply is used.
  If you use an adaptor which is exactly 9V the circuit will see 8.4V or so.

- if the +ve rail resistor is present it will drop the voltage of both the battery and DC PSU

- Some pedals use an SMD diode instead of a 1N4004 power diode.   That means if you daisy chain pedals off the same PSU the power for all pedals could pass through the SMD diode.  Which isn't a good idea.

[anotherjim]

^ Thanks Rob, that does make more sense with what we can see.

[Rob Strand]

^ Thanks Rob, that does make more sense with what we can see.

The annoying thing is we still don't know the voltages on that unit.

My best guess from the PCB pic is the +ve rail series resistor (R22) has marking 1500 which would make it 150 ohm.

You would assume the LED current doesn't pass through R22.   The 18mA published current is likely
include the LED current.   So the current through R22 might be around 14mA as the low estimate
to 18mA - 2mA (LED) = 16mA as a high estimate, so maybe 15mA ballpark.

Drop across R22,  15mA * 150 = 2.25V   ;  not unreasonable but assumes 150 ohm is correct.
So Vdd = 9 - 2.25 = 6.75V.

I doubt the supply on the original (non-nano) Hot tubes is that low, it's probably 8.4 to 9V.
And.. that's going to make the supply current go up a lot from the nano's 15mA/18mA.

[aion]

Just to put a bookend on this - I was able to measure an original Hot Tubes from 1978 and the IC power pins had a supply voltage of 8.14V. Thanks for the lively discussion, I learned a few things!

[Rob Strand]

Just to put a bookend on this - I was able to measure an original Hot Tubes from 1978 and the IC power pins had a supply voltage of 8.14V. Thanks for the lively discussion, I learned a few things!

Thanks for posting the result.

[mdcmdcmdc]

Looks like this has been settled, but if there's any other info/readings you want from an original, I'm back home and happy to crack it open.