Admiral 20B1 Combo restoration

[Kamakiri]

Try swapping around a couple of your 6SN7s just for grins. How are your resistances at the tube pins?

[SwizzyMan]

OK I think my agc circuit is a bit off and this may be my sync issue. At the junction of the .5 uf agc filter and the 47k agc dropping resistor the voltage when a signal source is connected should be -5 volts but I read -4.17 volts instead. The problem is that I replaced that resistor and that capacitor. Also I am using only one lead of the antenna connection since the other one broke off yesterday but I had the same issue before the lead broke. What do I do? replace all the agc resistors? I know that the tubes involved in this circuit are in fact good.

[EdKozk2]

Hi Swizzyman,
Do you have a scope to check the waveform at pin 1 (grid) of the 6au6 sync sep?
It should look similar to the waveform at the output of L16 ( where the syn signal is removed from the 6AC7 video amp output). Make sure inductor L16 is not open. The output signal of your 6AU6 syn seperator pin 6 should only
be a pulse without any video image information. If you don't have the enough of a pulse signal going into the sync phase splitter then you will never get the
horizontal or vertical oscillator to lock in. The vertical pulse is the summation of all horizontal pulse after passing through the intergator network R59 thru R61 along with C41 thru C43.
If you don't have a scope, check L16 just in case. It should be a low resistance.
Sam's says to measure the 6AU6 AGC voltages from pin 7 (cathode) to other pins.
pin1 (-6.8vdc)
pin5 (-140vdc)
pin6 (+115vdc)

Ed

[SwizzyMan]

Replaced some of the resistors in the agc and the big 1 watt 2.2k filter resistor which checked at 113k. Now it is even harder to maintain vertical and horizontal hold! What is going on? I am out of ideas now.