Another meter question.

[Thermioniclife]

Hello all, I'am working on a pair of Monamour's and getting a hinky reading on one. I got to the meter test section and this is what I have. we will call one amp good and the other bad. The meters were packed with a note that said disregard the parallel 9.09 ohm resistors.
On the good amp at 50ma setting it reads a little over 50, at the 60ma setting a little over 60ma.
On the bad amp at 50ma setting its reading almost 60ma and at 60ma setting about 68ma.
So I then clip leaded 3 9.09 resistors on the bad amp and the numbers seem to be where they should be.
I then disconnected the meters and measured .9 ohms on both of them Hmmm.
I then whipped out my LCR meter,
Bad
.6 uH
.763 Rs
.77 DCR
Good amp
.6uH
.729 Rs
.74 DCR
I then measured the filament voltage and got
Good
2.33 Vdc
Bad
2.36
with 121 Vac on the mains.
The only real difference seems the LCR meter reading on DCR and Rs about .03 ohm.
I know I have some 1 ohm .5% resistors somewhere ( I need to use a shovel and rake to go through my inventory. )
and am planning to install them on the ground for the 2a3 cathodes and measure across them. If both amps are running at the
appropriate current I guess I will use the 9.09 resistors on the bad amp. Does that sound like a plan?

 

[Paul Birkeland]

You certainly can give that a shot.  On the first run of MonAmour meters, the meters we purchased were not compensated from the factory, but between now and then they are compensating them.  If you are getting the correct reading with some resistance added, that is a very reasonable modification to make. 

Also keep in mind that the filament voltage is the DC component plus some ripple, hence the reason why it appears low when checking with a meter. 

 

[Thermioniclife]

Thanks for the reply PB, If one meter is wonky I do not mind and will install the resistors and call it a day. But I think I need to confirm the the cathode current in both amps to sleep at night. The thing got me worried was the seemingly similar measurements with my
Fluke 87, but the LCR meter showed that .03 DCR  between them, do you think that that discrepancy is significant enough to make a
difference?  I just found the 1 Ohm 3 watt resistors ( a miracle in itself). Ok thanks again.

 

[Paul Birkeland]

The DC voltage between 4 pin socket pins 1 or 4 to ground divided by the cathode bias resistance indicates operating current.

 

[Thermioniclife]

Thanks PB I will check it out.

 

[Thermioniclife]

Hey PB. So I got a chance to mess around with the Monamours today. I Measured the cathode current 3 different ways and both amps
seem to be very close. Dc volts divided by measured resistance to ground as you suggested, disconnected meters and measured current
directly with my dmm and measured Dc volts across 1 ohm resistor. Both amps are running 53ma on the 50 ma setting and 64 ma on the 60 ma setting. I do not think I will ever acquire a pair of vintage 2a3's and just run the EH tubes I received with the kits. I will install the 9.09 parallel resistors on the amp with the wonky meter. My question is does the 53 and 64 ma cathode currents cause any alarm to you? Thanks.

 

[Paul Joppa]

The current difference is small enough to ignore, and the Sovtek/EH/JJ/etc. tubes can handle quite a bit more than 60mA. Plus, as the tubes age and lose emission, the current will slowly drop.

 

[Paul Birkeland]

There will also be a little bit of variation depending on your line voltage as well.

 

[Thermioniclife]

Thanks fellas, I will move on with the build, appreciate the responses.

 

[Thermioniclife]

Monamours up and running and singing beautifully. The low end is fantastic and of course the mids and highs are sweet. units are on my bench in nearfield with a pair of Paradigm Atoms 86Db sensitivity and they are plenty loud. Still have to put a finish on the bases then its into 18' X 19' living room with a pair 95 Db Tektons.
Great job Bottlehead. Thank You.