With the tube line up that you gave, I pulled up this schema of a 5 incher of that older tube vintage with a fist full of dual triodes inside, as yours also does, with the sole exception of the final vertical amp stage and down in the Hoz timebase circuitry.
In your case expect the 5Z3 for the LV power supply tube vice the 6X4 and the CRT high voltage being via using your 2X2's in a voltage doubler circuit vice the shown 1V2.
At any rate, I have marked up the Hoz deflection plates and their triode driver tubes in orange markup and the vert plates and their corresponding driver tubes in green.
Take note at top center that there is the utilization of isolation and peaking coils (red box mark up)in the plate circuitry of that pentodes ( it would be a triode in your case) vert amp circuitry in order to clean up the frequency response and extend the overall high end bandwidth of the vertical circuitry.
Now I am wondering if that just might be what you are encountering on your unit. They sometimes seem to make those coils different looking in their casing configuration on some units as well as the use of color dot markings. Possibly that is what you have. They also are susceptible to the weird formulations of protective over coatings that they used on some units , in the respect of their reacting with exposed copper wire and a resultant corrosive action eating up the copper wire ends, with an eventual open circuit.
Checking your unit, see if your suspect "mystery component" is connected to a plate connection of either a 6SL7 or 6SN7 tube. Also run a continuity check on the device to see if there is resistance present. In the specific case of these two units that this schematic references, they are wound upon fixed resistors with their casing serving as a coil form. In the case of a coil winding opening up, the base resistor value would still be readable. On your unit, should the device be a coil on its own dedicated coil form, you would be reading an open circuit path should the winding have failed.
Next info from you.... would be if a trace is possible on the CRT face. BUT if there was a condition of mass circuit imbalance within the H - V deflection plate driver circuitry, it is possible that the beam could be so over deflected in one direction that even the centering controls could not bring it back onto the faceplate.
With some reverse engineering on your part of tracing down the wiring from the deflection plates back to the tube that they connect into you can initially see which of the two 6SN7's or 6SL7's are dedicated to vert and hoz deflection plate drivers, and then the others would be for the vertical amp and preamp stage as shown at the top left area or for the hoz timebase and sync circuitry as shown at the bottom left area.
Also, since I see that you listed a 6SJ7, that pentode could equally be dedicated in its function as sync / hoz osc function on the hoz timebase circuitry, such as the 6DT6 is on this schema OR up at the vert power amp circuitry up where the 6AF11's pentode section is shown being used.
as I initially mentioned.
Feed back time .......
For smoother inter-referencing, since this schema is merely a tad wider than the page width of display and will only upset overall width a bit, I'm just going to tack it on the end . Since its being hosted off site, it will not present a hindrance to this sites B/W except for that instant while being called up and viewed, and even at that, it is only constituting of a mere 145K.
73's de Edd
http://img521.imageshack.us/img521/9637/5intubedscopeschemayd2.gif
: I,m trying to restore a Millen Synchroscope that was built for the MIT radiation lab dated 4-30-45. There is no model # I can find on it except for serial #123. I've tried milleninfo@jamesmillenco.com to no avail. It has a 5" CRT and a 150vdc meter on the frt panel. It looks a lot like the RCA scopes of the time and uses Radiotrons: (1)5Z3,(1)6SL7,(1)6SJ7,(5)6SN7,(2)2X2 and I believe an EX905 CRT. There is a ceramic component with a single orange dot on it that appears to be an open resistor that comes off the plate of one of the 6SN7's. Does anyone have information on a schematic for this or possibly a similar RCA scope? Thanks, and I really appreciate this website lots.
Walt.....Mc Crystal ( and at what frequency are you resonating today ?....hi hi )
With your supplied info, and comparing to the supplied schematic, looks like the possible equivalency of your 6SN7 could be assumed to be the the V5B section of the 12AU7 which goes on to feed the differential pair of deflection plate drivers of V6 A-B.
Your plate resistor being in the order of R46 a 10k resistor. Does the resistor that you found seem to be original, as that seems to be a high wattage rating for using for that positions application. Also see if that triode section is using a cathode resistor (R47 equivalent), and , if so, its value.
The specs on a 6SN7 have a cutoff on the plate dissipation at 1 watt, so no more than ~3 ma would be wanted flowing through that plate-cathode power loop (hopefully not experiencing your worst case 325 V mentioned...but they would like to see ~250Vdc on that tube, with a 300 V MAX spec. ) BUT, if you saw a cherry red plate...you DID exceed it with that opted choice of low value of plate resistor. After you do zero in on a final ? value of plate load resistor, put a series milliameter in line and see what current the circuit is then actually consuming.
Also, check the B+ supply line coming from the main B+ and see if it is initially dropped with a
feedline resistor somewhere in the line prior to the point where your "resistor" is supposed to be receiving its B+.
On this circuit, note that the B+ has been initially dropped down by R45 (3.9K). Also the cathode circuitry has R47(1K) in the power loop.
Also check your unit and see if that plate circuitry that you are working with is coupling into the deflection plate driver circuitry as you see this one doing with C28 (.1ufd).
You might compare this specific portion of circuitry to be roughly akin to a push- pull audio output circuit stage.
The preamp being on the left and the phase inverter being the next stage and the pair of outputs
being at the end. The difference, with the output transformer being replaced with a set of load resistors at R52-53, in order to have a varying voltage level developed across them to be fed on up to the H deflection plates. The interest there, being on more of a swinging electrostatic voltage rather than a swinging power level. Plus, there is a lot of DC coupling involved, since the precise DC aspect of the carried signal is equally of importance as the AC component. BUT FINALLY....... the signal handling in this circuitry is a recurrent sawtooth waveform rather than an audio signal !
ZUJ 'ing.....standing by
73's de Edd
: Edd- I suspected that the open component was a wire-wound resistance/inductance, size-wise it looks around 5 watts,but I wasn't sure what value to plug in to the 6SN7 plate circuit. Orange is 3 but then again maybe not a value mark for this device. I tried a 150 ohm w/w resistor,but the plate of the tube began to glow red. I shutdown the scope and tacked in a 2k w/w resistor and got a wisp of a green trace on the screen(none before). It appears that it's working the horizontal circuit as that tube is on the same side of the scope as the horizontal controls. I'm going to try a 10k w/w resistor with a sliding tap so I can adjust and observe the results,it is a low voltage device(325v). The HV is there,but I dont have a measuring tool other than a sparkplug test indicator. Thanks for your help.
“the green powder fell out”….aaah-haa...... sounds like the old corrosively aggressive copper sulphate syndrome.
That mentioned shortcoming on positioning should be a DC ranging imbalance capability in the hoz driver circuitry just prior to the hoz deflection plates.
Possible, resistive values shifted , imbalanced tube mu , or possibly old leaky paper caps, if any are involved in that circuit.
Glad you were able to find out what you have so far. You might pull out ALL of the ~20 meg resistors that you can find and build a 10/1voltage divider in order to extend your instrumentations DC metering capabilities on up into the multi KV range. Probably best to initially test it on an ~ 250 VDC value and tweak in the bottom resistive legs end value to get a 25Vdc readout.
That should give 10KV capability on an otherwise metered 1 KV scales range limits, a cushioning value above what will be expected for being that CRT’s supply.
Then move on over and sample and evaluate your CRT’s hi voltage health. Run the trace intensity from min to max while monitoring HV value and see if that supply regulation is stable enough.
Otherwise, you would be seeing the focus drifting.
BTW....ever surmise out the justification for the analog DC metering on the front panel of that unit ???
ZUJ’ ing
73's de Edd
: Sir Edd- I mapped out the circuit around the 6SN7 (a picture always helps) to see where it comes from and where it goes and then decide what it does.It looks like it's the Horizontal Deflection Oscillator,between the sweep frequency selector switch RC network and the CRT plate drivers. The RCA receiving tube manual shows expected voltages and currents to be higher for oscillator duty than if it was class A amplifier duty for the 6SN7GTB and these coincide with voltmeter readings taken.I jumpered in a 10K plate resistor and measured 17.6 mA plate current (too high),then 33K of plate resistance brought it down to 7.7mA (more reasonable) Next I chipped into the(original) open plate resistor/inductor at where the leads entered the device and found my open at the point where the green powder fell out. I got to the remaining conductor end and measured 26K ohms. I now have a working sweeper although the trace isn't well centered(the horizontal position control is all the way to the right) and the Intensity control doesn't vary brightness very much. I may be looking at a HV issue but at least it's now working. Thanks for your ideas and schema to get me headed in the right direction. The belly of this thing is rather overwhelming if you try to take in the whole thing at once and not just focus on the stage requiring attention.
adouglas at gis.net