AKG C414-E1 pattern remote control

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Conviction

Well-known member
Joined
Mar 27, 2013
Messages
318
Location
Sweden
Hi all,

I recently picked up an AKG C414-E1 complete with the pattern remote control. It's in great condition, barely used.

Out of curiosity, I checked the polarization voltages and discovered that the node for the backplate (negative/positive, -60/0/+60) was extremely low - and I can't really tell any difference between the patterns.

In figure-8, my voltmeter is showing a maximum of -16.5VDC.

The output voltage from the selector switch(es) corresponds with those stated in the schematic. Nothing wrong there.
However, after R6 & R7, the 27M resistors decoupled with 22nF(see schematic and parts list), the voltage drops down to -16.5VDC.

Is this due to loading? I thought a VTVM would take care of that.
First I used my Fluke DMM, then an old Simpson 260 VTVM.

Please excuse my ignorance  :-X


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These voltages are at very-high source impedance - so you need to take into the equation the input impedance of your meter, or you'll get way too low readings

Jakob E.
 
> Simpson 260 VTVM

I can't find any confirmation the 260 was made as a VTVM. All I see are passive VOMs.

"Fluke DMM" covers a lot of turf. Some have "low" input Z to bleed stray leakage in Power circuits; others are high Z.
__________________________

R6 R7 are 27 Meg.

Unspecified VTVM is 11 Megs. (Possible 1Meg to 50Meg and specialty types.)

So you expect to read 11/38 or 0.289 of the voltage supplied to R6 R7.

(There is another >150K in the line but this is small next to 27 Meg.)

0.287 * 60V is 17.36V. You observe 16.5V. The 5% difference will not funk-up the sound; and is probably explained by "small errors" in VTVM and resistors.
__________________________

Simpson 260 are usually 20K/V on VDC. Now you need to say your DCV range. If we ass-ume 250V, 250V*20K/V is 5 Meg loading. From 60V 27 Meg we would expect 9V. The 500V range is 10 Meg, but reading 16.5V on a 500V range seems odd. Even with mirror scale, it peeps like "high 15V", not any point-something.
 
PRR said:
> Simpson 260 VTVM

I can't find any confirmation the 260 was made as a VTVM. All I see are passive VOMs.

"Fluke DMM" covers a lot of turf. Some have "low" input Z to bleed stray leakage in Power circuits; others are high Z.

Sorry  :-X It's a 303. I accidentally wrote the numbers from this page: http://www.simpson260.com/303/simpson_303.htm
I'll update as soon as I can confirm the range (and voltage - might be a memory error there).

The 303 is not mine, but belongs to an elderly fellow down at the workshop.

The Fluke is a 789 process meter.

 
> It's a 303.

http://www.simpson260.com/downloads/simpson_303_user_manual.pdf

What can you work out, knowing the specs?

 
PRR said:
I can't find any confirmation the 260 was made as a VTVM. All I see are passive VOMs.
The 260 had a few add-on piggyback adapter modules available. The model 651 was a battery powered DC VTVM and used a 1AG4 pentode.

Gene
 

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PRR said:
> It's a 303.

http://www.simpson260.com/downloads/simpson_303_user_manual.pdf

What can you work out, knowing the specs?

10 megs for all ranges! The guy at the workshop told me it was 1 meg. I guess he was wrong.

This means your calculations based on an 11 meg unspecified VTVM is in the ballpark. Even more spot than assumed.
 

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