500B Snap, crackle, pop
- Thread starter Rockyhill
- Start date
Perfect!
Dave
Dave
I cleaned the PI pots as best I could; it's not easy getting Deoxit into them. Turned the shafts dozens of times. Adjusted them and buttoned things up. Powered up the receiver and waited. No popping for perhaps a minute then it came back in the Right channel. Still intermittent. Since it took a bit of time to begin does this sound more like a tube as the cause? If so, where should I focus? I have 4 spare GE12AX7 I can roll in.
Yeah it sounds like a tube. Start with the phase inverter tube (V-12). Then work backwards (V-10) And also the REMOTE CONTROL DUMMY PLUG! These tend to be forgotten during cleaning.
Swapped V11 and 12. Still pop in right channel. Then swapped V9 & 10. Pop in right channel. I also wiggled the plug quite a bit while powered up expecting some noise but heard nothing. Could it be the FM a/o phono tubes? I wonder if it's the PI pots that just aren't making noise until all tubes are warmed up and fully conducting. I will order replacements.
Last edited:
petehall347
the brandy coffee man
give the tubes a wiggle gently .. worked for me 45 years ago ..i was 11 then .. damn i am getting old ... transistors came along ... i need to go back to valves as we call them .
good luck with fix ... crackles are bad connections mostly . its just a matter of finding them .
good luck with fix ... crackles are bad connections mostly . its just a matter of finding them .
If the noise is present with the volume control full down, then the problem must be located in either the driver or output stage of the channel affected. If you've eliminated the phase inverter pot, the tubes in question, and cleaned the sockets appropriately, then it must come down to a component in the power amplifier section of the bad channel. Next test: see if it makes the noise with the driver tube removed.
Dave
Dave
Thanks Dave. I did a series of tube swapping to locate the culprit (drivers out/power in, drivers in/power out & moving tubes from channel A to B and vice versa). I determined it's one of the 7591 tubes (I didn't test by only having one tube in for a given channel as I thought that would not be a good idea). I suspect it's the tube that's been in position V15, as I have noticed that tube has always measured differently than the others when I set the bias, pre and post IBAM. These are EH tubes bought "matched" from from a source other than Jim McShane as he was out of stock at the time.
I have a set of GE 7591 tubes that came with the receiver. Can I use two of the GE's in place of the 2 suspect EH's and leave the other 2 EH's? Or should I replace all 4 with the GE? I have never used the GE's in this receiver other than for perhaps 30 seconds when I first powered up after the rebuild.
petehall347
the brandy coffee man
i would clean the pins of the suspect ones first and try again just to rule that out .
While it's not always best from a pure performance standpoint, if the tubes you are using can all be biased properly, it makes no difference who manufactured them or when/where they were made. Best performance will always be had from a matched quad.
Glad you found it!
Dave
Glad you found it!
Dave
I rolled in the GE 7591. IBAM measurements below. They sound pretty darn good. And no popping sound anymore.
Long term solution is to get a matched quad; also want a matched quad of 6BQ5 for the ST-35 so I got to start saving my pennies. Fortunately the annual "spendathon" is almost behind me (all 4 of us have birthdays around Christmas, plus my anniversary, and my mother's birthday. Yikes!)
Long term solution is to get a matched quad; also want a matched quad of 6BQ5 for the ST-35 so I got to start saving my pennies. Fortunately the annual "spendathon" is almost behind me (all 4 of us have birthdays around Christmas, plus my anniversary, and my mother's birthday. Yikes!)
Looks great!! Glad you got it all sorted out now.
Dave
Dave
