The Fine Things are Always Hand Made
I am in the progress of correcting the Riders AW12 schematic to reflect the changes in the late version single dial units. (This while working to get mine operational).
I need someone that has a working unit to make a rear panel voltage reading for me. NO disassembly required!
There is a round 4 pin female jack on the rear panel of the chassis.
The top two holes are connected to the filament voltage and the bottom two holes are connected to the HV coming from the power supply and chassis ground..
With the radio operating at a normal volume I need the DC voltage reading from the chassis to the HV pin. Should be 250VDC or below.
Your help is greatly appreciated!
I have a late version AW-12 Deluxe with AVC which uses pin 6 of the cable from the receiver for the revised audio path from the 2nd AF 56 tube to the amp. (Initially, the Deluxe AVC used pins 1 to 5 - and pin 6 was unused.)
My records from when I restored mine years ago noted 270 volts from the field coil to pin 4 of the receiver cable which goes to the high end of the B divider in the receiver. My household voltage was 122 volts AC. The Scott owner manual says use the up (hi) position of the amp's hi-lo switch if line voltage is above 110 volts. So your 250 volt figure is about right ... and agrees with the Riders diagram for the "Scott Deluxe AVC Super 1933".
You didn't ask, but Pin 6 of my late AW-12 cable carries 370 volts, from a point ahead of the B+ field coil, thru a choke in the amp to pin 6 (and one end of the audio transformer) and through the cable to another choke in the receiver in route to the plate of the 2nd AF tube. Then from the 2nd AF plate back to the amp plug pin 3, I noted 340 volts at pin 3 and to the 1/2 MFD cap in the amp connected to the other end of the audio transformer. (That explains Norm's comment in another thread about the revised circuit protecting the audio transformer from the stress of high voltage. ) So if you use a Variac to provide about 115 volts, the pin 4 and 6 voltages would be about 250 and 350 volts, respectively.
My late AW-12 works very well - sensitive, good meter action, clear sound. I play it every couple weeks. In fact, my late AW-12 seems more sensitive than either of my two AW-15s. So, I think my AW-12 is operating correctly. My AW-15's do sound better, owing to the more powerful 2A3 output tubes, I suppose.
That 4 pin socket you mentioned next to the tone control was for a 4000 meter attachment, which evidently was never put into production.
I also have the model with pin 6 being used.
I noticed that the voltage on the plate of the 2nd AF is about 285 and the 1st AF it is about 203.
These are both higher than the troubleshooting info found in archives.
Does this sound about right or do I need to do some additional troubleshooting ?
I've shut down for the night but tomorrow I'll check the voltage on pin 6.
The voltage I have on the high side of the divider is 265 volts.
The AC line switch is in the 120V position.
Thanks for any advice !
Your late version Scott Alwave Deluxe with AVC was designed to operate nicely across wide variety of AC household voltages, which in those days might vary considerably during the day. Power company control is much better today, and seems to be consistently higher today. My house voltage is more like 125 volts, give or take a couple volts.
A point of clarification: The actual household AC voltage affects set voltage readings. The 120/110 HI-Lo toggle switch merely selects the power transformer primary between the full winding or the tap. It does NOT select the exact voltage to the primary of the power transformer. Use a Variac and accurate voltage meter to feed exactly 120 volts if you like. Otherwise, if the actual house AC voltage happens to be, say, 126 volts, readings of the various secondary windings will be higher, especially the high voltage secondary.
Say at 120 AC for house voltage, the high voltage circuit ahead of the power supply choke (first filter cap) the voltage is 400 volts. If then you increase the house voltage to 125, expect the high voltage at the first filter cap would increase to 417 volts. (125/120 x400 =417).
My notes from 1995 on my late version AW-12 Deluxe w AVC recorded set voltages thus :
430 before the amp's choke. 400 after the choke. And after the speaker B+ field coil, 270 volts to the voltage divider in the receiver. However, I did not record the actual house voltage or if I was using my Variac. But as the diagram for the diagram says 250 at the receiver's voltage divider, I was probably not using a Variac, the house voltage was probably in the mid 120's. Today, I set the Hi-Lo switch to Hi, meaning the dial light and tube filaments would dim down a bit, so 1) the tube filaments run a little cooler and the high voltage peak is reduced, especially during the initial surge the first few seconds.
Understood. I am using the switch in the high position. I'll check the line voltage a few times over the next days. Normally it runs 123-124.
Many thanks for the information on the voltages in the power supply. That provides a good reference point and I'll verify those in the next day or two but I expect they will be ok.
The voltage readings I am getting to the voltage divider (265 volts) in the receiver seem reasonable.
The readings that I'm getting on the 1st AF (203 volts ) and 2nd AF (285 volts) seem a bit high vs. the troubleshooting tables (1st AF @ 175 and 2nd AF @ 230) but I'm not sure this information in the table applies to this version.
Again, thanks for your expertise and sharing the information !
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