Weber 18 watt tmb noise and bias

[Structo]

Richie knows these amps very well, I would listen to him.

Not to discount others opinions here, just say'in.

[M Fowler]

My advise just plain sucked and was wrong, I'm embarrassed can I start over

[Phil_S]

+1 on what Tom says about Richie.

As for the B+ supply, dropping that will require a "trick" like a zener on the center tap. I don't like tricks like that because they generate a lot of heat. My suggestions for dropping B+, in no particular order are:
-Use a real tube 6CA7 instead of the copper cap rectifier.
-Make sure you are using the 125V primary connection on the PT.

If you haven't already made a change, I think you are confused about the cathode bias resistor. 500r is too big. Follow what Richie says!

[Randy Magee]

If you used the Weber PT, which B+ leads did you use? From the voltage readings you're getting, it sounds like you used the reds instead of the red/white leads which are the lower voltage leads...

[Richie]

I was just adding in my 2 cents. you guys were doing fine.
And i agree, i'd just wasn't going to bring up anything about the copper cap, not touching that one with a ten foot pole...

As for what you are calling the bias resistor.. using a 150ohm for the pair.

And you have a 500ohm there now?.. the plate voltage will rise quite a bit.

The value of the cathode resistor will make the plate voltage change.
The plate voltage will be much higher using the 500ohm.
Using the 150ohm for the pair, the plate voltage will go lower as the tubes are running hotter,conducting more.


I know Phil S made a typo- meaning 6CA4.. not 6CA7. easy to type stuff thinking of other things.. Done it myself many times.
The 6CA4 is the rectifier tube used in the marshall 18 watters.
Or EZ81.

I know the weber layout /schem is a bit different. And different in values in parts of the amps power section compared to stock marshall 18 stuff.

So there may be some difference in the voltage between sections in the power supply stages.
I think most 18w that use a 1.5k resistor, see a difference of about 15 to 17 volts between the high B+ and the Screens. Or plate and screens.
Cathode voltage can vary in the ballpark of around 10v. using aroung a 130ohm cathode resistor. The tubes used or selected you may also see some slight differences in the voltage on the cathode. All tubes or pair will not be exact, but fairly close.

If you were to use a 125 ohm or 120 ohm cathode resistor, the ballpark cathode voltage would drop some. If you went to a 180 ohm, then the cathode voltage would go up. Probably around 12 to 13v.

Just guessing here so don't take it as exact.. but will be close.
Hopefully this helps you see how these interact.

[Smitty2]

I had to take a couple days off but am back to it now fellas. I will be digging in in the morning and yes I thank you Ritchie and the rest of you for your input. Btw there is no white 125v on this transformer just red and red and white and i am using the red and white it is a *eber w02530 tranny I do not really want to use a diodes to drop the voltage on the center tap nor the secondaries.. I can Lower the 500 ohm 10w resistor All the board caps that came in the kit are 150v and higher ?? I think I should lower these to 25-50uf 50v except for the one big one, correct ? I am more use to fender designs I do not like the fact that *eber kits are poor designs with very little in depth instruction. I never got a spec sheet for voltages and the extra resistors were either the wrong value OR missing altogether. I built this kit exactally to the lay out sheet they provided. I have a actual tube rectifer on the way. Do I need to use the 5v tap for the tube cause the print nor layout specify ?? One thing for sure is I am going to dig in and get this right this week... So thanks to all and hopefully I can get her right with all your input, but I am sure Ill be back asking some questions thanks guys