I'm restoring a pair of Allen Organ mono amps. These employ an unusual
circuit (no bias adjustment and no apparent cathode resistors) and I'm
waiting on the factory to send me a schematic.

In the interim I replaced ALL of the coupling and bypass caps and reformed
the electros without the power tubes in place.

The tube compliment, per amp, is:

(4) 6L6GT
(2) 5U4G (regulated screen grid)
(1) OC3
(2) 6SN7
(1) 6AU6

When I stick in the power tubes and measure the idle current it's about 2.5
amps @ 120 VAC. That seems way too high to me. I'm thinking it ought to be
about 1/2 of that. The unit is fused at 5A. I didn't leave the amp on very
long at this point. The circuit is simple and I couldn't find any defects,
gross or otherwise.

I'm thinking about installing 10 ohm resistors on the 6L6 cathodes to
measure current.

Does this amount of quiescent current seem too high to anyone else?

Thanks in advance.

"Jon Yaeger" wrote

I'm restoring a pair of Allen Organ mono amps. These employ an
unusual
circuit (no bias adjustment and no apparent cathode resistors) and
I'm
waiting on the factory to send me a schematic.

In the interim I replaced ALL of the coupling and bypass caps and
reformed
the electros without the power tubes in place.

The tube compliment, per amp, is:

(4) 6L6GT
(2) 5U4G (regulated screen grid)
(1) OC3
(2) 6SN7
(1) 6AU6

When I stick in the power tubes and measure the idle current it's
about 2.5
amps @ 120 VAC. That seems way too high to me. I'm thinking it
ought to be
about 1/2 of that. The unit is fused at 5A. I didn't leave the
amp on very
long at this point. The circuit is simple and I couldn't find any
defects,
gross or otherwise.

I'm thinking about installing 10 ohm resistors on the 6L6 cathodes
to
measure current.

Does this amount of quiescent current seem too high to anyone
else?

Thanks in advance.


How and where are you measuring the ac current?

How did you estimate "about half of that"?

If measuring primary current, you should take into account estimated
efficiency of PS (70%?) and, if cap is first filter element, the
current gulping which makes the rms current much greater than the
average current and so could be confusing either your reading or
your estimate (or both).

Is it your normal practice to measure the ac input current? Never
thought to bother until I started messing with SMPS where PS
efficiency becomes the primary concern...usually I just measure the
output of each supply, installing temporary sense resistor where
necessary. If you measure the dc resistance of the OPT, then you can
use that as a sense resistor, measuring the drop across each
winding. Only if this shows a problem should you need a sense
resistor to individually test the two valves sharing each primary
winding.

cheers, Ian

in article , Ian Iveson at
wrote on 6/13/05 9:49 PM:

"Jon Yaeger" wrote

I'm restoring a pair of Allen Organ mono amps. These employ an
unusual
circuit (no bias adjustment and no apparent cathode resistors) and
I'm
waiting on the factory to send me a schematic.

In the interim I replaced ALL of the coupling and bypass caps and
reformed
the electros without the power tubes in place.

The tube compliment, per amp, is:

(4) 6L6GT
(2) 5U4G (regulated screen grid)
(1) OC3
(2) 6SN7
(1) 6AU6

When I stick in the power tubes and measure the idle current it's
about 2.5
amps @ 120 VAC. That seems way too high to me. I'm thinking it
ought to be
about 1/2 of that. The unit is fused at 5A. I didn't leave the
amp on very
long at this point. The circuit is simple and I couldn't find any
defects,
gross or otherwise.

I'm thinking about installing 10 ohm resistors on the 6L6 cathodes
to
measure current.

Does this amount of quiescent current seem too high to anyone
else?

Thanks in advance.


How and where are you measuring the ac current?

How did you estimate "about half of that"?

If measuring primary current, you should take into account estimated
efficiency of PS (70%?) and, if cap is first filter element, the
current gulping which makes the rms current much greater than the
average current and so could be confusing either your reading or
your estimate (or both).

Is it your normal practice to measure the ac input current? Never
thought to bother until I started messing with SMPS where PS
efficiency becomes the primary concern...usually I just measure the
output of each supply, installing temporary sense resistor where
necessary. If you measure the dc resistance of the OPT, then you can
use that as a sense resistor, measuring the drop across each
winding. Only if this shows a problem should you need a sense
resistor to individually test the two valves sharing each primary
winding.

cheers, Ian


I have a decent variac with a voltage and current meter. The current
displayed is total AC current @ 120 VAC.

The "about half of that" is based on the quiescent current of a "typical"
amp with (4) 6L6 or similar.

Jon

It wouldn't hurt to put some cathode resistors in there to see what the
current is. But you probablly ought to wait until you have a schematic
in hand, unless you are willing to trace and draw it all out.

"Jon Yaeger" wrote

How and where are you measuring the ac current?

How did you estimate "about half of that"?

If measuring primary current, you should take into account
estimated
efficiency of PS (70%?) and, if cap is first filter element, the
current gulping which makes the rms current much greater than the
average current and so could be confusing either your reading or
your estimate (or both).

Is it your normal practice to measure the ac input current? Never
thought to bother until I started messing with SMPS where PS
efficiency becomes the primary concern...usually I just measure
the
output of each supply, installing temporary sense resistor where
necessary. If you measure the dc resistance of the OPT, then you
can
use that as a sense resistor, measuring the drop across each
winding. Only if this shows a problem should you need a sense
resistor to individually test the two valves sharing each primary
winding.

cheers, Ian


I have a decent variac with a voltage and current meter. The
current
displayed is total AC current @ 120 VAC.

The "about half of that" is based on the quiescent current of a
"typical"
amp with (4) 6L6 or similar.


Thanks.

Ian