Matchless DC30 screen grid and bias resistor values?

[Ledvedder5150]

I've read that the 3W 100 ohm screen grid resistors in the DC30 causes the EL84's to run too hot. This apparently wasn't as much an issue with NOS tubes, but causes new production tubes to burn up much faster. Has anyone increased them to something like 470r or even 1k?

Also has anyone changed the 10W 62r or 68r bias resistors to drop the bias a bit?

[Stevem]

Is this the model with the high and low power switch?

[FUCHSAUDIO]

I use 470's in Blues Juniors and most EL-84 amps in general. A few tech friends go as high as 1-K. 100-Ohms is dangerously low, especially with modern tubes.
Matchless has been known for years as a company that runs power tubes to insane currents. Raise the screens, if it's cathode bias, change that resistor too.

[Ledvedder5150]

Yes, it has the half power switch.

[Stevem]

Go with 470 screens and up the cathode resistors by 10%.

JJ brand outputs are the most durable I have found in terms of holding up to running hard.

[Ledvedder5150]

Go with 470 screens and up the cathode resistors by 10%.

JJ brand outputs are the most durable I have found in terms of holding up to running hard.

So you think 75r/68r in place of the 68r/62r?

[Roe]

100R screen resistors are perfectly fine, provided proper resistance between the screens and mains filter cap (e.g., 420R to 780R, depending on voltage)

[Ledvedder5150]

100R screen resistors are perfectly fine, provided proper resistance between the screens and mains filter cap (e.g., 420R to 780R, depending on voltage)

How can I confirm that? This is the layout. Unfortunately, I don't have a schematic.

Dizzy30Ceriatone.jpg

[pdf64]

…
How can I confirm that? …

With a meter set to measure resistance.
One probe at one choke terminal, the other at the other.
Amp deenergised and isolated from the mains.

[Ledvedder5150]

…
How can I confirm that? …

With a meter set to measure resistance.
One probe at one choke terminal, the other at the other.
Amp deenergised and isolated from the mains.

I'm getting about 160r.

[pdf64]

There you go, try adding a resistor in series with the choke. 330ohm or 470ohm, probably needs to be at least 5W.

[Roe]

100R screen resistors are perfectly fine, provided proper resistance between the screens and mains filter cap (e.g., 420R to 780R, depending on voltage)

How can I confirm that? This is the layout. Unfortunately, I don't have a schematic. Dizzy30Ceriatone.jpg

neither a layout nor a schematic will help unless they specify resistance between the screens and mains. Just add a 330-470R 5w resistor in series with the choke in order to reduce the screen voltage and current

[Ledvedder5150]

There you go, try adding a resistor in series with the choke. 330ohm or 470ohm, probably needs to be at least 5W.

Does it matter which side of the choke?

[pdf64]

No.

[Ledvedder5150]

I measured my bias today. Looks like I'm getting 46.5mA, which is 126% dissipation.