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Hello, I am new to this forum and to amp building from scratch.

I recently assembled a Get Set Go 300b on Turret boards, and a have run into several issues I have not been able to address.

First and foremost I have 370v dc coming from the power supply after the 10 resistor r18. I am not sure how critical the voltage is here, but concerned it may be to high, as my kit version of this same amp was 335v.

Second, I have been unsuccessful eliminating the hum that is coming from the filament supply. I was able to reduce the noise by increasing the 4700uF 16v cap to 10kuF 16v capacitors but I still have too much noise, and when I measured the voltage to the heaters I see 6.2vdc. I double checked the resistor across c-12 and c-14, and verified is 1.5ohms.

The power supply I am using is the Dynaco PA-774 , I am also using solid state rectification.

Any help is appreciated, Dave Harris

I figured out what was causing the hum, now the amp is dead silent.

I am still curious about the heater and power supply voltages.

Dave

With SS rectifiers, you will see a B+ around 370V, so that is all good. The regular GSG 6AX5GT tube rectifier has a healthy voltage drop - great for 6B4Gs, but undesirable for the new 300B types. Your filament voltages are higher due to the larger caps (i.e. that FWB rectifier is more efficient). Just increase those dropping resistors by 1 ohm - you can just add a regular 1 ohm power resistor in series or change them to 2.5 ohms or two 5 ohms paralleled.
Post pix when you can!

Shannon

Thanks, I appreciate the info, I will post pics once I get a few items cleaned up.

Thanks, Dave

Turret board

Under the hood.

Chassis rear

Front

This is my first attemp at engraving. I think it turned out good, but I have alot to learn.

The 2 tops shown here are spares that were previously damaged, perfect for practicing.

I'd like to hear about your engraving method, especially if it's DIY friendly (ie no CNC). Looks great to me.

Shannon

separks wrote:I'd like to hear about your engraving method, especially if it's DIY friendly (ie no CNC). Looks great to me.

Remember those mall tables in the late 70's early 80's where a guy with an engraving copier effortlessly transferred something on to brass or two-toned-layered-plastic with a copy machine?

I've looked for those and they disappeared from existance

Sorry to disappoint, I did this with the CNC router I use to build my horns.

Dave

Dave welcome to the dark side :-)

I thought the tube forum was the bright side.

I guess its just the better sounding side.

Dave