Buzz in sound from video - a porthole

[Rcr1961]

Mike,
V7 is the last IF amp, a 6AU6 sharp cutoff pentode, the 6BA6 is the same but
is remote cutoff.
When I got the set I completely re-restored it ( had to make it pretty and to my liking ) when I first powered it up the sound alignment was far off from
the picture, after I corrected that I had the same buzz problem you now have.
I was thinking of modifying the bias on the last IF the keep it from getting
cutoff but, then it dawned on me that a less invasive way would be to just swap a tube with the characteristics that I wanted. This worked out far better that I had hoped !!!.

Hope you have the same results.

Bob R.

Originally Posted by kramden66

Bob R thanks , whats supposed to be v7 , what is originally there ?
v7 according to that service manual i posted a link to ?
this too is a 24g26 , i don;t remember a buzz in the one you got from me but i guess there was.

thanks old coot and the rest , i haven;t had time to do anything with it yet
mike

[earlyfilm]

Originally Posted by kramden66

. . . . . . perhaps this means something , the buzz control when turned hits a point where the sound goes out and comes back . . . . . .

Yep!

It means that in all probability the slider in the buzz control is not making contact with the resistance element and when that happens, it opens the cathode on the audio detector and your sound goes out.

This either indicates a dirty control or a bad control.

It is also possible and quite probable that the sweet spot on the buzz control is in that open spot.

To test the control:
Put an ohm meter on both ends and it should read 600 ohms. Put an ohm meter on the cathode end and on the slider and when the control is rotated, it should vary between 100 and 600 ohms with no open spot.

James

[kramden66]

Thanks old coot for bringing up the continuity on the quad coil - - it is open so now i have to find something to replace it with , Bob R i can try the 6BA6 but if the quad is open i don't know if it would make a difference , well maybe it will , i will try it just because it is easier to do then changing the coil and then have to change the coil more then likely if i can find a substitute
mike

[kramden66]

couldn't find a replacement that was suitable so i decided to look at the quad coil , the first couple of wraps of the fine wire toward the top didn't look so great so i looked further and there was a break , so i repaired it omitting a couple turns but it has continuity now , so i have to try realign the sound , it was previously working without the quad hooked up and now that it is the whole circuit has changed so alignment will have to be done.
mike

[wa2ise]

You might need a little more capacitance if you can't get it to align. But if the coil has many turns and you took away maybe 1% of them, you should have enough adjustment range to get it aligned.

[kramden66]

yes what little came off shouldn't effect it , i could have spent hours trying to re attach it but it is so small and at the top it shouldn't make any huge differene

[kramden66]

Well just thought i'd let all know that after repairing the quad and doing the adjustments the sound is nice , thanks for the help.

[old_coot88]