MoJo Brit 800 Build: At My Wits End!!!!

[sluckey]

I guess this was too vague.

...Lower the value of that 220K resistor that's connected to the bias diode until you have -60V at the output of the diode. I'd start with a 100K and then adjust up/down until I had -60V.

[pompeiisneaks]

It is so mind boggling to me to have someone come to a forum asking for help to then go on being rude to people and acting like they know already how to resolve the problem. Your skill with electronic circuits in general doesn't directly easily apply to tubes, OR you're not as skilled as you think you are.

I'm pretty new to this, only been doing it for a few years and see many of your assumptions are way off base. I also see you being testy to people that know about 100 times what you do about this subject.

How would you feel as a certified aircraft mechanic to have me coming and asking you for help and telling you that i know how planes work because I once flew on one, and have done flight sims...

And then being testy to you because you don't answer my non clear, uninformed questions perfectly and immediately out of the goodness of your heart for free?

I think you should ask yourself why you think people would want to help someone that doesn't respect the time and effort they put in for free, to be berated for not doing it 'right'?

~Phil

[Stevem]

First off a kt77 is much more like a 5881 in terms of its 25 watt rating.
Second, the tube data sheet for a kt77 with about 400 volts on its plate and screen calls for -31 volts with a 25% up or down range.

I would want you to get at least a - 38 volts to show up on pin 5 of each output tube socket before you even try to pop the output tubes back in.

Next the filament voltage of 5.6 vac is not good!
With the output tubes yanked out you should have very close to 6.8 volts, that’s over 20% low !

A acceptable voltage range is 6.3 + or - 10%.

[ViperDoc]

I had the exact same problem when turning the key on my Tweed Super: insufficient bias voltage. I had no sound and lowered heater voltages across the board. Once I got the voltage range correct and properly adjusted the bias, all was well.

Another thing to look for is an incorrectly wired bias adjustment pot. Mine was wired backwards once on a PR build in the source diagram and it limited the bias adjustment too much and I risked frying those output tubes. Correctly wiring the adjustment pot saved my bacon.

[nflrage]

It is so mind boggling to me to have someone come to a forum asking for help to then go on being rude to people and acting like they know already how to resolve the problem. Your skill with electronic circuits in general doesn't directly easily apply to tubes, OR you're not as skilled as you think you are.

I'm pretty new to this, only been doing it for a few years and see many of your assumptions are way off base. I also see you being testy to people that know about 100 times what you do about this subject.

How would you feel as a certified aircraft mechanic to have me coming and asking you for help and telling you that i know how planes work because I once flew on one, and have done flight sims...

And then being testy to you because you don't answer my non clear, uninformed questions perfectly and immediately out of the goodness of your heart for free?

I think you should ask yourself why you think people would want to help someone that doesn't respect the time and effort they put in for free, to be berated for not doing it 'right'?

~Phil

Don't think your comments are appropriate...I am frustrated that this doesn't work and I've got 20 different replies that are giving assumptions/advice and not answers. Same as in your analogy, if you asked me how to change a spark plug in a reciprocating engine, I would assist with step-by-step directions, not just tell you "I think you need plugs and a socket wrench". I do know how circuits work but when you do not obtain the readings you are expecting it gets a bit weird. I do appreciate the help but wish it were a bit clearer.

[nflrage]

First off a kt77 is much more like a 5881 in terms of its 25 watt rating.
Second, the tube data sheet for a kt77 with about 400 volts on its plate and screen calls for -31 volts with a 25% up or down range.

I would want you to get at least a - 38 volts to show up on pin 5 of each output tube socket before you even try to pop the output tubes back in.

Next the filament voltage of 5.6 vac is not good!
With the output tubes yanked out you should have very close to 6.8 volts, that’s over 20% low !

A acceptable voltage range is 6.3 + or - 10%.

This is some strong guidance...I will make the changes tomorrow on the bias resistor.

[sluckey]

This is some strong guidance...I will make the changes tomorrow on the bias resistor.

Hopefully you'll get on the correct resistor this time.

[pompeiisneaks]

It is so mind boggling to me to have someone come to a forum asking for help to then go on being rude to people and acting like they know already how to resolve the problem. Your skill with electronic circuits in general doesn't directly easily apply to tubes, OR you're not as skilled as you think you are.

I'm pretty new to this, only been doing it for a few years and see many of your assumptions are way off base. I also see you being testy to people that know about 100 times what you do about this subject.

How would you feel as a certified aircraft mechanic to have me coming and asking you for help and telling you that i know how planes work because I once flew on one, and have done flight sims...

And then being testy to you because you don't answer my non clear, uninformed questions perfectly and immediately out of the goodness of your heart for free?

I think you should ask yourself why you think people would want to help someone that doesn't respect the time and effort they put in for free, to be berated for not doing it 'right'?

~Phil

Don't think your comments are appropriate...I am frustrated that this doesn't work and I've got 20 different replies that are giving assumptions/advice and not answers. Same as in your analogy, if you asked me how to change a spark plug in a reciprocating engine, I would assist with step-by-step directions, not just tell you "I think you need plugs and a socket wrench". I do know how circuits work but when you do not obtain the readings you are expecting it gets a bit weird. I do appreciate the help but wish it were a bit clearer.

I think my comments are very appropriate. I'm the forum admin/moderator and it's my job to try and keep people civil. So far your tone has been way less than civil. Just because YOU think a reply is 'advice/assumption and not answers' doesn't mean it isn't. The best attempts were made with the minimum information given. If you want to continue asking people to help but make sure they fit your narrow definition of 'proper help' then you're not going to last long online my friend.

~Phil

[bepone]

Don't think your comments are appropriate...I am frustrated that this doesn't work and I've got 20 different replies that are giving assumptions/advice and not answers.

i'm reading the topis and see the problem. it is impossible for you to fix that, sorry all answers you get allready. you need to measure current through the output valves, and reduce it with the bias voltage (put more negative, bias is the "regulator for the flow through the valve") and some of your problems can be fixed. but others will permanently remain..

[Colossal]

Thread locked

[pompeiisneaks]

Other than the abusive post, I'm thinking leaving this thread as a cautionary tale for those that think coming to a forum and acting like a jerk is the right way to do it... will not be the right way to do it.

I do now understand why his username was nflrage

username checks out.

If others think I should just nuke the thread, I can.

~Phil