No bias Raw voltage.

[TonyM]

Hi
Started a new build its based around Patrick Turner's Re-Engineered 40w Marshall.
As the Hammond 290EEBZ PT has no CT I've implemented a full wave bridge rectify with a 50r 50w inrush resistor to the first node.
The choke is a Hammond 5H @ 500mA 26ohms and the OT is a Hammond 1650ka, 50w 3400ct.

Ive tapped the HT for bias voltage, typical 220k to reversed diode to 2 x 10uf 160v caps and the 15k resistor, at this point I've added a dual pot bias adjustment, as per Rob Robinette, 33k bias range adjustment. But I'm only getting -27v.

In the meantime I've tapped the 50v secondary winding which gives me -69v and I can adjust the bias.
Also when try take  reading across the 1 ohm resistor on the cathode of the EL34 I only get -10mv.

I get a very low hum from the speaker but no real output

I can't figure it, any thoughts.

[Merlin]

Since there is no centre tap you need a cap-coupled bias supply.

[TonyM]

Thanks for your response. I had a malfunction of my tablet and only part of the message  was posted but I've updated the  message.

So with the bias diagram, the 220k and a cap on the rectify B+. what would be a recommended cap for that cap?

[Merlin]

A 630V plastic cap would be suitable.

[TonyM]

Any idea why I might not be getting a proper reading across the 1 ohm cathode resistor.

Both resistors are connected to pin 1 & 8 on each tube. The resistors are showing a correct resistance.

With 460v on the plates and 418v on the screens.
The grids show -40 and I use the OT drop voltage method. My valve dissipation is 16.20w and 16.42w.

[Merlin]

Only just saw the other half of your original message, you might as well use the 50V winding for bias then.
I don't know why you're not getting the correct reading on the 1 ohms resistors, it kinda sounds like you accidentally grounded pins 1+8 somehow?