DSL100HR Red Plating!

At idle what is the DC voltage across the cathode resistor?
The single resistor is 320 ohm for both tubes?

We need to clarify the speaker load because it's not really clear.
If you measure only the speaker cab with the ohmmeter what is the reading?
 
Hi amp mad scientist,
Plate to ground 466.3 vdc
Cathode to ground 33.2 vdc
Actual resistors 320.6 ohms. 2 resistors in series to make 320 ohms. Used for both tubes.
I am using a reasonably new single 8 ohm eminence speaker.
 
MarkA said:
Hi amp mad scientist,
Plate to ground 466.3 vdc
Cathode to ground 33.2 vdc
Actual resistors 320.6 ohms. 2 resistors in series to make 320 ohms. Used for both tubes.
I am using a reasonably new single 8 ohm eminence speaker.
Click to expand...
wait did you measure this cathode voltage with amp 4 ohm out connected to 8 ohm speaker?
Should have, because 2 tubes removed.

33.3 vdc
--------- = 0.104 A
320 ohms

.104 A X 466.3 V = 48.5 VA
(volts X amps does not =watts, but that's another subject)
(volts X amps = VA, which is "apparent" power, not true power)
two tubes, 24.25 VA per tube

Now, what is the max watt rating per tube?
What output tubes are you using?

Svetlana EL34= 25 W max per tube
If all the numbers given are correct:
You are running the tubes at 97%..................... not 85%.

However, between 90-100% is correct for class A operation.

However there is a couple errors in this calculation.
We are measuring plate and screen current added together, not plate current alone.

At idle what is the DC voltage drop across the 1K screen resistor?
Or is the screen resistor 1K?
Now you can calculate how much current the screen is drawing, and subtract that from the cathode current, leaving just the plate current - minus screen.
 
Last edited:
I am running a pair of el34s.
1k resistors on the screens.
Unfortunately I won’t be into the amp for about a week, however the el34 data sheet states:
Plate current max 100 ma
Screen current max 14.9 ma
Assuming an equivalent relationship through the operating characteristics:
14.9/114.9 = 87% plate and 13% screen
So using your calculation of 97% dissipation:
.97 * .87 = .844 or 84.4%
Actual measurements of the current would be more accurate, but I don’t think this is too far off.
 
MarkA said:
I am running a pair of el34s.
1k resistors on the screens.
Unfortunately I won’t be into the amp for about a week, however the el34 data sheet states:
Plate current max 100 ma
Screen current max 14.9 ma
Assuming an equivalent relationship through the operating characteristics:
14.9/114.9 = 87% plate and 13% screen
So using your calculation of 97% dissipation:
.97 * .87 = .844 or 84.4%
Actual measurements of the current would be more accurate, but I don’t think this is too far off.
Click to expand...
The last thing I don't understand, is where G2 is connected (besides the PI output caps) on each tube.
Is there a resistor to ground on each G2?
 
The 2 220 k resistors on the board I added connect between the pi coupling caps and the grids. These are tied to the ground side of the cathode resistor. Please see the attached generic schematic
 

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