I have a Pilot Radio model T-301. I replaced the caps and it still has a hum. I looked at the filter caps and to my surprise about 105 volts DC and 4 to 5 volts ripple.
So I looked around a bit to see if someone before me mis-wired the thing in the second of the filter and various field coils. But I have to admit the schematic is not very clear to me. But it may very well not be wired correctly as I see a black wire coming from the Power Amp plate to a coil and then a red wire going from that coil to a 120 uF cap, and then from that node another black wire to a 170 Ohm coil and then on the other side of that a red wire to the final filter cap (50 uF.)
So should not these coils be wired opposite phase? Can I trust the color of the wires to indicate polarity? What would happen if I changed them just to see? Would it hurt the set? Thanks for reading.
Edward
:I know there has been some discussion about hum in previous posts and as I am finding, it seems to be a recurrent theme.
:
:I have a Pilot Radio model T-301. I replaced the caps and it still has a hum. I looked at the filter caps and to my surprise about 105 volts DC and 4 to 5 volts ripple.
:
:So I looked around a bit to see if someone before me mis-wired the thing in the second of the filter and various field coils. But I have to admit the schematic is not very clear to me. But it may very well not be wired correctly as I see a black wire coming from the Power Amp plate to a coil and then a red wire going from that coil to a 120 uF cap, and then from that node another black wire to a 170 Ohm coil and then on the other side of that a red wire to the final filter cap (50 uF.)
:
:So should not these coils be wired opposite phase? Can I trust the color of the wires to indicate polarity? What would happen if I changed them just to see? Would it hurt the set? Thanks for reading.
:
:Edward
http://hertzmail.com/Riders-vols/Riders%20Volumes%201%20-%2023/
and down load all of volume 15 and it is there under Pilot T-300/ 3001
Thanks,
Edward
:Edward, can you point us to a schematic for this set?
:Doug
:
::I know there has been some discussion about hum in previous posts and as I am finding, it seems to be a recurrent theme.
::
::I have a Pilot Radio model T-301. I replaced the caps and it still has a hum. I looked at the filter caps and to my surprise about 105 volts DC and 4 to 5 volts ripple.
::
::So I looked around a bit to see if someone before me mis-wired the thing in the second of the filter and various field coils. But I have to admit the schematic is not very clear to me. But it may very well not be wired correctly as I see a black wire coming from the Power Amp plate to a coil and then a red wire going from that coil to a 120 uF cap, and then from that node another black wire to a 170 Ohm coil and then on the other side of that a red wire to the final filter cap (50 uF.)
::
::So should not these coils be wired opposite phase? Can I trust the color of the wires to indicate polarity? What would happen if I changed them just to see? Would it hurt the set? Thanks for reading.
::
::Edward
I see nothing abnormal about the set , but will clarify for you:
....just follow the bouncing ball....er...red line
Marked up Reference source is at :
http://img82.imageshack.us/img82/7309/pilot300tf1.jpg
In consulting that, we see the initial derivation of the raw B+ at the cathode of the 35Y4 routed over to the right until it gets to the initial 50 ufd of capacitive filtering at that input filter and then thru the GREEN combined filter choke / field coil of the speaker (Two for the money..honey..a good inductive filter for the power supply and the production of magnetic flux for the speaker). Hmmm..... now whats that there also...some RARE supplemental info at the top, as to the use of #29 wire with an end DC resistance result of 170 ohms. Me thinks that would be 2012 feet of wire. Now just how many turns would that make on an incrementally increasing size of winding within its bobbin on the field coil ?
So after the passage through that stage of inductive filtering it is met with a suppplemental hefty 120 ufd of capacitive filtering and then ready to meet with the greatest task of the day, the provision of that B+ that you see routed up to the BLUE audio output transformer along with the feed to the screen grid of the same output tube circuitry. The remaining B+ is then further routed over to feed all of the other circuitry of the set.
The only other thing of note in the circuitry is the routing of the secondary of the BLUE output transformer over to the right to the FUSCIA voice coil winding of the speaker. With one little variant, they incorporated a GRAY hum bucking winding into the field coil. Now I certainly don't see is as being as important on this set , with its hefty 50 / 120 ufd filtering values, as was on some of the golden oldies with their mere 8 and 16 ufd 's of capacitive filtering. At any rate, if there was a degree of hum being produced in the speaker from power supply derived ripple, the procedure was to place a minute winding upon the field coil (GRAY) and extract a specific required voltage level (HUMMM...chum ) to then place in series in the feed from the BLUE AF out secondary to the FUSCIA speaker voice coil. The idea was for an introduction of that voltage in 180 degree phase shift relationship with that feed of signal with the hum present that was going from the AF out to the speaker. If the two levels are coincident but 180 deg out of phase the hum is cancelled. If too little...less than optimum results ..if too much ... less than optimum results. That precise level being established by either the turns ratio or its degree of coupling to the field coil bobbin.
Another secondary problem can be the potential situation of a parts replacement wherein either the GREEN field winding or the GRAY
hum bucking coil has one connection incorrrect, where the effect is reversed and you get twice the hum...no extra charge . Whereupon one needs to correct that problem by wire swapping on one unit to get back the proper cancelling / nulling out phasing relationship.
Questions ??
73's de Edd