Source for GR80 tube in Neumann Gefell CMV 563 power suppl..

Archived from groups: rec.audio.pro (More info?)

In article <ltis119p8k8annp4oi5011e582gk80k86p@4ax.com>,
<spambegone_bdb@cox.net> wrote:
>I need to find some replacements but my Google searches have come up
>with nothing.
>
>It appears to be a shunt regulator tube. Anybody know about these and
>where to find 'em?

Are you sure of that number? I have never heard of a GR80, but the
VR80 is a very common shunt regulator. What voltage is supposed to be
across it?

I will say that gas regulator tubes don't fail very often. They are
usually one of the last places I look when output voltages are wrong.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

In article <nc0t11dsnkt44h5ac8dhkc1tvj51906ppa@4ax.com>,
<spambegone_bdb@cox.net> wrote:
>GR80 is the designation on the only schematic I've been able to find
>for the power supply (which actually appears to be in Russian, Polish
>or some Slavic language).
>
>There are 2 of these GR80 in series. One end ties into the B+ line
>after the first 16UF cap and 20k dropping resistor. The other end
>ties to ground.

Does the schematic say what voltage should be across the pair? Have you
measured what IS across it? Is it lighting up nice and blue?

> A one megaohm quarter-watt resistor connects from the
>junction of the two GR80 to ground.

Is it good? That's to get the top one in the pair to fire off
reliably. If it's open, you may have trouble getting them to fire.

> There are 2 more dropping
>resisitors and 16UF caps that follow this arrangement.
>
>I believe the B+ voltage to the mic should be around 125 vdc, but it
>currently measures over 250 vdc.

So you know that the pair should have something more than 125V across
it but not TOO much more than 125V across it.

Are either one of the things firing? If you swap the two, do they fire?

Are they 9-pin minis or octals?

You can easily replace both of them with a zener diode string and probably
reduce your noise floor considerably too. But it won't be authentic.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

<spambegone_bdb@cox.net> wrote:
>On 24 Feb 2005 21:02:22 -0500, kludge@panix.com (Scott Dorsey) wrote:
>
>>In article <nc0t11dsnkt44h5ac8dhkc1tvj51906ppa@4ax.com>,
>> <spambegone_bdb@cox.net> wrote:
>>>GR80 is the designation on the only schematic I've been able to find
>>>for the power supply (which actually appears to be in Russian, Polish
>>>or some Slavic language).
>>>
>>>There are 2 of these GR80 in series. One end ties into the B+ line
>>>after the first 16UF cap and 20k dropping resistor. The other end
>>>ties to ground.
>>
>>Does the schematic say what voltage should be across the pair? Have you
>>measured what IS across it? Is it lighting up nice and blue?
>
>Schematic gives voltage coming off rectifiers as 200 vdc. B+ at the
>microphone end of the pi network = 120 vdc.

I got that, but how much voltage are you supposed to be losing in the
20k dropping resistor? Let's say you lose 20V through the dropping
resistor, that would mean the pair should have 150V across them which
would mean 75V each.

You could sub with three 50V zener diodes and see what the output voltage
was with 150V across the regulator string. That would at least tell
you how close you were to that estimate.

>>Are they 9-pin minis or octals?
>
>They're 7 pin minis.

Pin 5 is plate, pin 7 is cathode? Sounds like an OA2-family tube to
me. Check the OA2 in your handbook.

>>You can easily replace both of them with a zener diode string and probably
>>reduce your noise floor considerably too. But it won't be authentic.
>
>Hmmmmm, interesting. Probably preferable to be non-authentic and
>working than *dead* authentic.
>
>How would you calculate the values of the zeners? Trial and error
>starting with stacking 4 X 50 volt zeners?

If we knew what the operating voltage of the GR80 is, we could make a
good stab at it. I'll bet 80V just given the name and the fact that
should be in the general ballpark.
>
>
>Here's the setup:
>
>200 v coming off rectifiers ------> 16uf cap to ground ---> 20k series
>resistor------> GR 27-50 shunt regulators to ground ---> 16k series
>resistor ---->16uf cap to ground ----> 10k series resistor ---> 16 uf
>cap to ground ---> to microphone.

Also be sure to calculate the maximum power at 100V (the difference between
the voltage across the zener string and the supply) through a 20K
resistor with V^2/R so you can size the zeners properly. I figure
you can get by with one-watt zeners.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

Great tips Scott and Bruce. Thanks!!! I'll check it out as soon as I
get the ps back and I'll post the results.

..

On Fri, 25 Feb 2005 16:13:07 GMT, bruce seifried
<vze2qwtg@verizon.net> wrote:

>Here's my guess at what's probably wrong:
>
>Having had many CMV563 power supplies cross my bench, one thing I notice
>frequently is corrosion on the pins of the regulator tube(s). Most
>CMV563s use the later N61 supply, which has the single GR28-20 or
>STR125/60 tube, rated at 125 volts. The older D102 supply uses two GR80
>tubes, which are indeed 80 volt tubes. A faulty connection at the pins
>will most likely allow the supply to float at full unregulated voltage,
>which in the case of the D102 is around 200 volts. Try cleaning the pins.
>
>The other possibility is that the 1 meg resistor at the junction of the
>two tubes has opened. This will most likely prevent the tubes from
>conducting, with the same end result.
>
>Although it's possible you have a bad tube, I've never seen one go bad.
>
>bruce seifried
>eclair engineering