Fisher FM-50B Tubes

[PJ62]

I am total tube noob, and just acquired said tuner. The unit runs, but doesn't sound all that great. The tubes are all different, seem to be low end brand-x usa and japan. Should I look for better tubes to improve the sound? There are 2x 12ax7/ecc83, 2x 12at7/ecc81, 1x 6aq8/ecc85 and 4x 6au6 tubes. Which tubes or areas do I spend money on, and which do I keep what I have? A cursory check of the internet shows that everyone likes Mullards and Telefunkens, but where? The tuner tubes, the MPX unit, the output 12ax7? Any advice apprecitated, thanks!

[Steve O]

At first blush, I'd say that your tuner need a good alignment and maybe some caps replaced before you consider tube rolling. The differences various tubes make in the sound of a properly operating tuner are subtle. The difference an alignment makes is not subtle even with non-audiophile approved tubes.

Bottom line if this were mine: restore and align before rolling.

[PJ62]

Thanks for the info. When I picked up the tuner, the fellow offered to sell me a "matching set of Fisher brand tubes" to go with it for big money, which I politely declined. I think he pulled the original tubes and stuck in junk (almost all have the brand names worn off). I guess my question now is, is it wise to adjust and align the tuner using a set of used tubes of unkown quality that I know I'm going to replace?

[Fisherdude]

... I guess my question now is, is it wise to adjust and align the tuner using a set of used tubes of unkown quality that I know I'm going to replace?

And the answer would be no.

Aligning is the last thing you do after you're reasonably confident that everything else is working ok. If you do an alignment, and then change tubes or other components, you will probably throw the alignment off again.

Since you're pretty sure he replaced the original tubes with assorted used tubes, you need to have the tubes checked. If any test as weak or below acceptable readings, replace the weak tubes and then see how it works. Btw, I assume you're using a decent antenna, and/or you are sure you don't have any reception issues at your location.

[Holst]

And the answer would be no.

Aligning is the last thing you do after you're reasonably confident that everything else is working ok. If you do an alignment, and then change tubes or other components, you will probably throw the alignment off again.


If I recall my Fisher's correctly, just changing that 6AQ8 will make a pretty big difference in alignment.