No power to phono section of Fisher 500C?

nj pheonix · Oct 5, 2018

dcgillespie said: ↑

Mike -- What you have is conflicting evidence, which is not uncommon in the initial stages of troubleshooting. In the current example, you state that (relative to ground) there is -25 vdc at pin 4 of V17 while 0v at pin 5, and 0v at pin 4 of V16 with pin 5 of that socket confirmed as grounded. And, you've stated that neither tube is glowing. In taking these as absolute facts, then either:

1. One of the items in my post 16 must be true, or if not, then

2. One or more of the facts as given are in error.

There can be no other possible outcomes here if the facts as stated are true. What happens so often however, is that something you think is true, is in fact not true.

Think of it this way. If the product of a multiplication problem is 20, and one factor is 5, then the other factor must be 4. What's happening here however is that we're saying that the product is 20, one factor is 5, but the other factor is (say) 6, which cannot be true. Either the product is incorrect, or one or both of the factors are incorrect -- one or the other, but as is, something presented as true is clearly not true.

For the case at hand, IF there actually is -25 vdc at pin 4 of V17 as stated, and IF there is 0V at pin 5 as stated, then either:

1. The tube or tube socket's pins are dirty, or

2. The tube is bad (as in an open heater), or

3. The receptor pins in the socket are broken (as in breaking the circuit).

The only other possible scenario if there is -25 vdc on pin 4 of V17 and 0 v on pin 5, would be the case of pin 5 of V17 somehow being shorted to ground. But if that were the case, and the tube's and socket's pins are all good, and tube is good, then its heater would be glowing wildly, since it would be receiving twice the normal working voltage. But you stated that the heaters are not glowing. So once again, the facts as offered don't fit. Maybe you have multiple bad tubes that you are assuming as good, but are not, or various other possibilities.

It sounds rediculously elementary, but assume nothing, and retest everything. The answer lies in going back and finding out what you think is true that is not. Once you find that, then you can find the answer to the problem. That is the only way to solve problems that otherwise would seem to defy explanation, like the one you have in front of you.

Dave

Dave
Click to expand...

Listen to Dave, Mike .
I have been where you are.
I believed what i stated but I found my method or recording was wrong .
It happens.

Mikeorg · Oct 5, 2018

OK "WE" you and me got the 12AX7's glowing, turned out it was ether a cold solder on V16 or V17 or a dirty pin or loos pin's~I tightened all of them~!!! Thanks I'm going to check voltage and see where we are. Thanks Again! Oh not to mention a bad tube

dcgillespie · Oct 5, 2018

So glad you found it Mike! And, welcome to the wacky world of troubleshooting, where even the simplest of problems can be so evasive to solve. When the puzzle pieces don't fit, always assume nothing, and go back and recheck everything. It's the shortest path to getting the issue resolved.

Congrats!

Dave

audmod01 · Oct 7, 2018

Kudos on your success. It is surprising how often we can misinterpret what we are observing. Sometimes it helps to let it rest a while before going back to recheck.

Joe

Log in or Sign up

No power to phono section of Fisher 500C?

nj pheonix AK Subscriber Subscriber

Mikeorg New Member

dcgillespie Fisher SA-100 Clone Subscriber

audmod01 Super Member

Share This Page

Log in or Sign up

No power to phono section of Fisher 500C?

nj pheonix AK Subscriber Subscriber

Mikeorg New Member

dcgillespie Fisher SA-100 Clone Subscriber

audmod01 Super Member

Share This Page

Useful Searches