Replacing the 6au6

[2string1]

I just noticed the Fisher branded 6au6's in my 500B are 6au6A for some reason. It say's on the chassic 6au6. Did it originally come with 6au6A's Well I just bought the 6au6. Will they be ok in the 500B?

 

[Patrice B]

Were your original 6AU6's shot? In the case the answer is no, no reason to replace them...

 

[Patrice B]

Just for the record:

I acquired a Fisher 101R mono tuner back in september. Now fully rebuilt and aligned...

Yesterday, strangely, I heard rushing noise for about 45 seconds before the FM station finally came in! Not normal as usually it was around 10-15 seconds max.

Inspection of voltages, testing tubes: the last IF 6AU6 ramps up slowly on my tester, I mean around 30 seconds to reach the 90% range. This is after the tube being idle on the tester for around 1 minute from cold.

Today, I've bought two spares (6AU6WA) and replace the offending one. Sure, the Heathkit multiplexer hooked to the Fisher wasn't sounding as good as before: the stereo separation was screwed... Bear in mind that this 6AU6 is feeding the MPX out and is probably also part of the detector stage.

So, to resume, the old 6AU6 taking centuries to reach operating point is back. I'll wait until it dies completely as I don't want to spend money again for a new alignment.

 

[jaymanaa]

Depending on intended uses, military or other high reliability tubes are not always screened for noise. This is seen a lot in computer tubes. The 5963 comes to mind, a computer version of the 12AU7. A very good tube, but you have to weed out the noisy ones, same as the red base 6SN7 and 6SL7 varieties. Not saying they are overly noisey, just not always "low noise" as many tubes designed specifically for Hi-Fi.

 

[Patrice B]

Just for the record:

I acquired a Fisher 101R mono tuner back in september. Now fully rebuilt and aligned...

Yesterday, strangely, I heard rushing noise for about 45 seconds before the FM station finally came in! Not normal as usually it was around 10-15 seconds max.

Inspection of voltages, testing tubes: the last IF 6AU6 ramps up slowly on my tester, I mean around 30 seconds to reach the 90% range. This is after the tube being idle on the tester for around 1 minute from cold.

Today, I've bought two spares (6AU6WA) and replace the offending one. Sure, the Heathkit multiplexer hooked to the Fisher wasn't sounding as good as before: the stereo separation was screwed... Bear in mind that this 6AU6 is feeding the MPX out and is probably also part of the detector stage.

So, to resume, the old 6AU6 taking centuries to reach operating point is back. I'll wait until it dies completely as I don't want to spend money again for a new alignment.

Update: It wasn't the 6AU6 going south... It was the ECC85 (6AQ8).

Anyway, replacing 6AU6's could lead to realignment.

 

[larryderouin]

Patrice; I've had good results using a 6DT8 in place of the 6AQ8. According to sources I've read, the DT8 is the recommended sub for the AQ8. Even better is the price. About $4. for the DT8 vs. $18.+ for the AQ8.

I have 1 spot where the DT8 doesn't work well. That's in a SANSUI 1000A in the multiplexer. For some reason it doesn't like the DT8. Put a weak aq8 in and it works better than a new testing dt8. Go Figure.

Larry

 

[Patrice B]

Patrice; I've had good results using a 6DT8 in place of the 6AQ8. According to sources I've read, the DT8 is the recommended sub for the AQ8. Even better is the price. About $4. for the DT8 vs. $18.+ for the AQ8.

I have 1 spot where the DT8 doesn't work well. That's in a SANSUI 1000A in the multiplexer. For some reason it doesn't like the DT8. Put a weak aq8 in and it works better than a new testing dt8. Go Figure.

Larry

Thanks, good to know for the next time.

The ECC85 (siemens) wasn't too expensive neither: 14 CAD.

Patrice