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#107
03-06-2010, 02:00 AM
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OK... I did a round of readings. To tell the truth, I'm not sure what the difference is between "filament" and "the rest". But this is what I have so far:
6A8: pin 1 - nothing pin 2 - nothing pin 3 - .2 - .5 VDC pin 4 - .01 - .02 VAC pin 5 - 1 VAC pin 6 - 3 VDC pin 7 - 7.13 VAC pin 8 - .9 VAC 6K7: pin 1 - 0 pin 2 - 7.12 VAC pin 3 - ? pin 4 - 88.6 VDC pin 5 - 3 VDC pin 6 - n/a pin 7 - 0 pin 8 - 3 VDC This is with the tubes in. Should I do it without? I'd better wait till it cools down... 
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#108
03-06-2010, 03:55 AM
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You should be getting something like:
6A8 Pin 1:nothing Pin2: 6.3v AC Pin3: about 200v DC Pin4: at least 100v DC Pin5: not much of anything Pin6: probably nothing here, either Pin7: 6.3v AC Pin8: 4.3v DC 6k7 Pin 1: nothing Pin2: 6.3v AC Pin3: 250v DC Pin4: 102v DC Pin5: 3.4v DC Pin6: nothing Pin7: 6.3v AC Pin8: 3.4v DC These are just kinda what I threw together looking at the tube datasheets and a similar schematic. I'm probably pretty wrong with the 6A8, but there should at least be high voltage on pin 3. Basically, those high voltages are the ones you will need. To properly measure the filaments, set your meter to AC volts, and put your meter leads on pins 2 and 7 of those tubes. Next time you make measurements, pull the 6A8 and 6K7 tubes and see if the B+ voltages come up. I've had radios with bad tubes that would drag B+ down. I see that the 6k7 tube is getting some voltage on pin 4, with 88v. Since that 88v comes off the line from the power to the 6k7's plate, you should be getting something on pin 3 as well.
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#111
03-06-2010, 01:31 PM
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From the schematic here is what you should have on the 6A8 and 6K7:
6A8 Pin 1 0V Pin 2 to Pin 7 6.3VAC Pin 3 262VDC Pin 4 102VDC Pin 5 Not shown but should be negative DC Pin 6 190VDC Pin 8 4.3VDC 6K7 Pin 1 0V Pin 2 to Pin 7 6.3VAC Pin 3 251VDC Pin 4 102VDC Pin 5 3.4VDC Pin 6 not used Pin 8 3.4VDC Pretty close to what Leadlike came up with. The voltages you got on pin 3 of the 6K7 and 6A8 are somewhat in line with what you should get. The voltages on pin 8 of both tubes are good. What you show on pin 6 of the 6A8 in post #107 is way low. Measure the voltage you have on capacitor C13 (junction of C13 and 40,000ohm R3). If this voltage is really low then either there is a short around there or R3 is open. If this voltage is high (around 390V) then you probably have an open winding on the oscillator coil L5 and/or L7.
__________________
Sean - WØKPX
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#112
03-06-2010, 01:48 PM
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That pin leads to the switch that changes bands. I don't see any visible short... But... the wires leading to the OSC Conv. are the only wires that I did not replace on the radio. I didn't want to disturb those coils and they looked fair. Maybe they are bad. Most of the wires in this radio had the insulation crumbling off, some bare. I think the simple thing to do first is to replace those wires and check the connections on the switch while I do it.
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#114
03-06-2010, 03:36 PM
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I just let it warm up for about 5 minutes and turned the tone all the way up. I was able to hear 1 station distantly on AM. But I have to turn up the volume about half way and the hum on the speaker is pretty loud. I can tell, this radio could get quite loud when turned up.
It's starting to happen.....
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#117
03-06-2010, 08:03 PM
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Pin 4 on the 6K7 is low. It is tied directly to pin 5 of the 6A8 and they should both have 102VDC. These points get fed from the B+ through the 8800 ohm resistor R9. R7 and R8 along with R9 create a voltage divider to supply screen voltages for the 6A8, 6K7, and 6J7.
When you get the voltages within reason maybe you can tweak the I.F. transformer adjustments to see if that helps. It is best to have a signal generator for this but you can get close enough by tuning in a station and then slowly adjusting the screws that appear to be on the bottoms of the transformers. I would suggest going in the order of C27, C24, C19, C17 as shown on the underside view in the service info. You would adjust each for maximum signal.
__________________
Sean - WØKPX
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#118
03-06-2010, 09:18 PM
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Are you sure it's pin 4 on the 6K7 to pin 5 on the 6A8? I can change it but it's pin 4 to pin 4 now and maybe my eyes are playing tricks, but I think the schematic says 4 to 4 to R9. You are the boss though... just checking.
Last edited by de.facto7; 03-06-2010 at 09:24 PM.
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#120
03-06-2010, 09:26 PM
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looks like pin 4 to pin 4 to me, too-I'm using the Nostalgia Air schematic of the A64, which NA claims is the same as your A66.
http://www.nostalgiaair.org/PagesByM...4/M0007754.pdf Either way, that 8800 ohm resistor is really the only offender that could be causing this low voltage.
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