I,m new at posting a thread ! Here goes ...... I have a nice D&A Phantom three stage amp that I,m freshening up ! All is finished but one problem in the keying circuit ! This is the triple stage version ... 4 - 6LQ6,s driving 6- 6MJ6,s with the 6AQ5 tube keying circuit , 2 relay version . I cannot find a schematic anywhere that shows this 6AQ5 tube circuit ! The problem is I did not pay attention to which pin on the 6AQ5 tube socket that the negative side of the 10uf 150v capacitor gets soldered to !!! I believe that I have it narrowed down to Pin 4 (6vac) or pin 5 ( 450vdc ,Plate) ... If I,m correct, this capacitor comes into play with SSB . I have powered this amp up on am only (capacitor not soldered to the tube socket, SSB switch is off) into my Ameritron 1500 dummy load with 4 watts of drive. I have 900+vdc and 450+vdc from the power supply and the amp loaded up 500+ watts with a 4 watt dead key ! Looking like I,m good to go aside knowing where to solder this 10uf 150v cap to the 6AQ5 tube socket !!! Any help would be appreciated , Bruce
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Need help with a D&A Phantom amplifier ....
- Thread starter allrpm
- Start date
The negative goes to pin 5 and the plus through the SSB switch to the hot side of the relay. Here is the Raider:
I thank you very much for your time DrAudio , I thought it might be Pin 5 . Pin 5 has 450vdc on it and the SSB switch has 450vdc on the off side of it, I don,t understand why the capacitor is only rated at 150v ? This capacitor was blown apart when I removed it !!! Your thoughts ? Bruce
It is odd that they only use a 150 volt cap but it's not a component that fails very often on D&A amps. When I replace one I always use a 10uF - 450V just because. Caps are inexpensive so might as well upgrade it when replacing.
That schematic has one difference. It shows the heater wiring for a 12AQ5 tube. The 6AQ5 will generally have the green/yellow striped wire feeding the correct voltage to the tube's heater. The 12.6-Volt green wire-to-green wire voltage from each transformer's heater winding is split half-and-half between pairs of the large tubes. The green/yellow striped wire is the center tap of the 12.6-Volt winding. In the diagram above, that would be the wire feeding the 6.3-Volt pilot lamp.
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nomadradio, thank you for commenting in this thread, this amp has the green wire with the yellow stripe on pin 4 of the 6AQ5 @ 6.3vac ..... I have read an older thread of yours discussing the solid green wire (12.6vac) from each of the 3 transformers feeding the 4- driver and the 6- final tubes in groups of 4 (10 tube , 4+4+2) . Pin 5 in @ 12.6v on a pair and out on Pin 4 @ 6.3v with a jumper to another pair in on Pin 5 @ 6.3v and Pin 4 to ground ! I was confused at first as to how 12.6v can go in and 6.3v comes out of the same tube, but the amp works ! I enjoy working on the old tube stuff, been doing it for years and still learning thanks to forums like this and people like you and DrAudio out there waiting to jump in and help someone in need !!!! Thank you , Bruce
Update : Amplifier is up and running great on AM and SSB , thanks to DoctorAudio and nomadradio! One a last question if I may ..... on the 6 - 6MJ6 final tube sockets there is a heavy bare wire with a Z-14 choke and an adjustable pot similar to the grid tune circuit .... what is this adjustment for ?
That is equivalent to the "Load" for the driver section when the amp is on "high". I guess one might call it a Cathode tune but electrically it's on the output side of the tapped driver tank coil. D&A put the "Tune" cap for the driver section on the front but probably for space reasons (and the tapped driver tank being on the side) put the load inside. It can be adjusted for maximum peak but be very careful.
He's right. A control that's marked "Load" sets the peak power. That means a modulated signal from the radio.
The driver "Tune" control at the outer end of the front panel must be peaked with the plates in between the max and min extremes. Plates farthest apart is minimum capacitance. And when they are fully meshed together, that's the max end. But there is no mechanical end stop. This control rotates freely 360 degrees.
There are two ways to see if the control is properly peaked, and not just stalled at one or the other full extreme of its value. Eyeballing the cap's plates on the inside of the front panel is one way.
The other way can be done with the cabinet in place. Turn the Tune knob a full turn. If you see only one peak in that full turn, this is not really a peak. It's the extreme setting of that control.
Doesn't tell you WHICH extreme this is. Only tells you the cover DOES have to come off so you can see which extreme made it look like a peak on the meter.
It's not really a peak if it occurs at one or the other end of travel.
And if what you have is that single "false" peak on the driver Tune knob, the driver coil gets adjusted to bring that control's proper peak back between the control's extremes where it belongs.
Never mind how that's done. I've gotten windy enough for the moment.
73
The driver "Tune" control at the outer end of the front panel must be peaked with the plates in between the max and min extremes. Plates farthest apart is minimum capacitance. And when they are fully meshed together, that's the max end. But there is no mechanical end stop. This control rotates freely 360 degrees.
There are two ways to see if the control is properly peaked, and not just stalled at one or the other full extreme of its value. Eyeballing the cap's plates on the inside of the front panel is one way.
The other way can be done with the cabinet in place. Turn the Tune knob a full turn. If you see only one peak in that full turn, this is not really a peak. It's the extreme setting of that control.
Doesn't tell you WHICH extreme this is. Only tells you the cover DOES have to come off so you can see which extreme made it look like a peak on the meter.
It's not really a peak if it occurs at one or the other end of travel.
And if what you have is that single "false" peak on the driver Tune knob, the driver coil gets adjusted to bring that control's proper peak back between the control's extremes where it belongs.
Never mind how that's done. I've gotten windy enough for the moment.
73
Ok ... I started all 4 caps at half mesh, marked the knobs with a paint stick at 12 o'clock for a visual aid with the cabinet on. I have removed the cabinet put an eyeball on the caps .... here are the results with the amp loaded up modulating 500watts , top tune (by ma meter) is 3/4 open mesh (min.), top load (on left) is 1/2 mesh, Driver tune (bottom left of band switch ,no stop) is 3/4 closed meshed (max.), Driver load (bottom right of band switch with a stop) 3/4 closed meshed (max.) toward the stop. So...... with that said, this internal trimmer can be adjusted ( I know I,ll be playing with high voltage) for max power out on high ?
Ah, trimmer cap?
Is it directly under the six final tubes, with a wire leading to the driver Load control?
Or is it at the rear of the cabinet under the deck?
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Is it directly under the six final tubes, with a wire leading to the driver Load control?
Or is it at the rear of the cabinet under the deck?
73
It's the 'coarse' driver Load control. It's adjusted for best peak power with the front-panel driver Load control at half setting. Makes the one on the front panel the "fine" driver Load.
73