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Thank you very much for your reply Shockwave, yeah the unit had ruined the tube completely so I am working on it now without a tube installed, weird thing is that I tried replacing the resistor, diode, zener diode without a change, I do know when it was on its way out I had -24 at pin5 on the...

As a starting point I guess, does anyone know what I should have on this blue wire coming from the transformer? I am starting to wonder if the transformer doesn't have issues or somthing, since there were so many versions of the JB 150 it makes it hard with the schematics. Thanks

Hi guys I am about ready to pull my hair out over this modulator, last week it hot plated a tube popped a fuse so I went ahead and replaced the HV capacitors and the 100 uf 200vdc capacitor for the bias. When it first screwed up I put a voltmeter on pin 5 on the 8417 tube and watched the...

Ok, thank you

Hi guys I am a little confused on this old carbon resistor here, what exactly is the rule of thumb here, which is the first band ? The red ? If calculated like that this would be a 2.23 ohm resistor however it is reading 23.75 K ohms. If calculated the other direction it should be a 24K ohm...

Played with it a bit last night, I removed that disc cap coming off that coil tuner which allowed a -102 vdc of bias to pins 5 on the drivers, tested it out for a bit then put my better driver tubes in since I had trust it wouldn't red plate them, it ran stable but of coarse it wasn't putting...

Yes, that looks like this is exactly how this amplifier is setup, the cathode gets grounded when the relay is keyed. The wire coming off of that coil tuner has -104 vdc on it before that disc capacitor but after that capacitor it is actually +2 vdc until the radio is keyed then it only goes to -...

Oh yes, absolutely I do know about that! I am actually good and careful with that subject and even though there are bleeders I check each and every time for present voltage

I would be very good at the sheet metal work, have alot to learn on the electronics part of it

Probably so linearone, if I knew as much about them as you guys do anyways, but I don't but would sure like too. I just get a kick out of fixing these old boxes that are older than I am ! I enjoy it once and if I get it figured out anyways and learn somthing in the process, however I am having a...

Hi, I very well may try coming off the ac heater voltage with the diode and cap like you mentioned for the screen and try that out and see what happens! I was messing around with it a bit last night and noticed I have a - 104 vdc of negative bias on the wire coming directly off of that input...

But that -48 volts of bias was also under modulation I forgot to mention that but you said with that high of screen voltage the negative bias would have to be 10 times higher than the -16 volts and that's nowhere close, is it perhaps possible to use the screen voltage off of the final tubes for...

I tried it and grounded the screen grid pins and it worked but I was lucky to see 100 watts out of it so I wired it back up the way it was before and will start over. Ya know one thing I noticed last night after I keyed it down enough times and got it to start cherrying the plate I heard the...

Pin 3 the screen voltage has 510 VDC on it

However, what do you think about that burnt resistor, did you happen to see that ?

That's ok Nomadradio, I thought that seemed kinda odd That's why I wanted to confirm that with you before I tried that procedure, yeah you may have very well seen higher voltage on Pin 3 earlier in this thread, I will check it out tomorrow and go from there ! Thank you very much for your help !

There is also this 1/4 watt resistor right underneath the preamp relay that looks kinda burnt I am not sure what it is for but I do know the preamp works in this box, just somthing I thought I would mention, but yeah let me know if it is ok to disconnect that coil from pins 5 and 9 if so I will...

Hi, this is the only wire feeding pins 5 and 9 on the driver sockets and it is coming from that input tuning coil or is it a bias adjustment coil ??? Is it safe to go ahead and disconnect there from that disc capacitor and put that wire to ground then as it connects all 4 pins in that driver...

10-4 Nomadradio I will definitely try this and get back with you with the results, I am also thinking about installing a metal mesh screen between the drivers and final tubes on this because they are very close together, like alot of you have done on the Maco 300