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 41 
 on: July 11, 2019, 01:29:27 pm 
Started by afterlifestudios - Last post by afterlifestudios
Thanks Klaus.  Both these NGís have the bulb socket in parallel (not series) with the b+, and someone (two separate people) deliberately made the effort to do so.
I just thought before I put it back to stock (where it truly does just indicate if thereís AC making it past the switch), Iíd try to decipher the reason for the mod. It doubt it was bulb scarcity. The socket was not changed on one NG, and the other was changed to bayonet base and came with 4 spare ne51 (neon) bayonet base lamps.  Also, running an incandescent bulb in parallel off the b+ would pull too much, so these were meant to be neon I think. 

My thoughts are the possible overvoltage protection that neon provides, but I donít have the math to back that up.

Or maybe they wanted an indicator that shows youíre getting at least (n)VDC.  n being whatever the firing point of the neon bulb is.  Maybe thatís just a more useful indicator?

But if no one has seen this before, and nobody chimes in with strong support and reasoning for this mod, I will revert to stock.

Update:  Dennis from Tab Funkenwerk informed me that Oliver had come across a similar mod a couple of times and always reverted it to stock, sighting the impedance and need for purity of the b+.

So it's unanimous.  I'm heating up the soldering iron...  Thanks Klaus and Uwe.

 42 
 on: July 11, 2019, 12:12:57 pm 
Started by afterlifestudios - Last post by klaus
They probably did this because:

1. Original Neon bulbs of the kind used in Neumann NG supplies are hard to find and now quite expensive.

2. DC bulbs are the norm for powering pilot lights in power supplies, so techs are familiar with it, even without a schematic (before they became widely available on the internet).

As mentioned by several posters: power supply pilot lights just indicate that power is getting to the unit, nothing else.
That does not mean that it's always done intelligently: early N52 supplies used a pilot light feed in series with the heater voltage output: when the lamp's filament broke, the mic no longer received heater voltage.

 43 
 on: July 11, 2019, 01:01:32 am 
Started by afterlifestudios - Last post by afterlifestudios
Is it possible that the mod is for over voltage protection?
Or is that the same thing I already asked above?
Just trying to figure out why two separate techís did this mod...

 44 
 on: July 10, 2019, 09:00:14 pm 
Started by afterlifestudios - Last post by afterlifestudios
Thank you Uwe. I will remove the modified b+ lamp wiring (green twisted wires in photo) and connect the lamp socket to the AC110 as the schematic shows.   I have 110v neon bulbs but they were not firing, which is how I ended up discovering this.  They would only fire if the PSU was not under load (mic not connected), because they were getting a LOT more voltage.

Does anyone have simple layout diagram or photo of how the AC lamp sockets were originally wired?  As I mentioned, BOTH my NGís have this b+ indicator lamp mod so I donít have a normal one to copy.


 45 
 on: July 10, 2019, 08:33:15 pm 
Started by afterlifestudios - Last post by uwe ret
The heat shrink tubing and the two square 1kΩ/5W power resistors are clear evidence that the power supply shown in the photo has been serviced and modified.

None of the various implementations of NG-style power supplies ever utilized the neon indicator bulb (or anything else) for voltage regulation/stabilisation. The current to fire the small indicator bulb is far to small to be of any effectiveness for voltage regulation, that task was accomplished via a type 150B2 gas discharge tube in early regulated supplies.

If you cannot source a neon bulb, to avoid potential heat damage from incandescent bulbs I recommend a light emitting diode (LED) to illuminate the indicator. With a suitable current limiting resistor a wide range of desired brightness can be achieved. There even may be available LEDs operating of 110Vac, just like the original Neon bulb.

 46 
 on: July 10, 2019, 06:58:32 pm 
Started by afterlifestudios - Last post by afterlifestudios
I was surprised too.  But thatís what Iím saying: It is positioned after rectification and is being feed DC.  A wire comes from the last 40uf cap and brought back to the indicatotor bulb socket. Then the other side of the indicator socket is brought back via another wire along that same path to ground at the mic connector.  It doesnít exactly look stock.

Photo attached.

What are the odds that two separate previous owners in 2 separate countries did the same mod using the same method and layout etc?

Should I rip that stuff out and wire it as per the schematic?

 47 
 on: July 10, 2019, 06:36:19 pm 
Started by afterlifestudios - Last post by klaus
I cannot see how the pilot light in NG supplies could act as voltage stabilization: it's positioned on the AC side, pre-input transformer, rather than the DC side with its five heavy-duty filter caps. 

All of my official Neumann schematics for the NG and NG 1/2 show only AC bulbs, all positioned before rectification.

 48 
 on: July 10, 2019, 05:45:37 pm 
Started by afterlifestudios - Last post by afterlifestudios
Well.  I just discovered that the indicator lamp sockets in BOTH of my NG PSUís are run off the 105v DC.  Not the 110vAC like the schematics Iíve seen show.  So perhaps the neon IS part of the DC stabilization.

(Both u47 systems were bought at different times from different people in different places. One is Tele badged, the other is Neumann, so the chances that this was a mod done by the same person is extremely slim. And all the wire used corresponded with the rest of the PSU.)

I do not have a schematic that shows this arrangement.


 49 
 on: July 07, 2019, 03:28:50 am 
Started by RuudNL - Last post by RuudNL
Thanks Klaus! That is a great and simple solution.

 50 
 on: July 06, 2019, 05:35:37 pm 
Started by RuudNL - Last post by klaus
You gave the hint for the solution in your last sentence: simply* extract one from a Tuchel broadcast connector, and install it in the mic! The contacts used in U87/U67 head assemblies are actually the same as used in Tuchel-brand broadcast mic cable connector females.

* You need to use a trick to extract the pin from the connector without damaging its anchor: push the little barb/anchor which blocks the pin from coming out of its position inside the plastic connector IN, i.e. towards the center, as you lift it out. Use a very small screwdriver blade to do this:  ≤ 1.2 mm. Once out, reestablish the angle of the barb, so it again will seat properly in the Neumann head without being pulled out when removing the capsule head

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