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I have a Fisher 400, which is technically a receiver, but this is a general question about tube tuners (or the tuner sections of tube receivers).How often should a tuner be aligned, and what exactly does this procedure involve? How do you know when it's "time" ?
My tuner sounds fantastic sometimes, horrible at others. On the same station. Source is a roof-mounted Yagi. Wonder if it's just a matter of interference, or the signal being "better" at different times of the day.
Follow Ups:
Check the antenna connection - I know my Fisher 500 has a local and dx connection (the local has a resistor across it) - try the dx if you are experiencing a weak signal.Also check for bad connections or weak tubes in the front end - if the tubes are good make sure the pins are clean and the sockets are still good - this can give rise to intermittent issues when the receiver heats up and things move a little bit.
First of all check out WHEN the tuner sounds bad. If it happens regularly after it has been on for a period of time, then there may be an internal, heat-related problem. If it happens at certain times during the day, it's probably signal related. Typically, FM reception is worse during the day.Most every tube tuner I've worked on (many dozens) could benefit from an alignment, but many only marginally. I've come across more problems resulting from someone being inside the set and screwing some adjustment up - worst case breaking a tuning slug. Proper way to align a tuner is to use a generator with sweep capability, so you can actually "see" and optimize the IF and demodulator passband shape. I've also come to realize that to get the last "ounce" of performance, you should "tweak" the IF's for minimum HD distortion but this requires an HD meter. I typically aligh the front end (RF section) by ear as the adjustments are very broad.
Aligning the multiplex section is a whole other issue, and you must have a top-notch generator to do so. I've found the problem with tube multiplex decoders to be lack of stereo separation above 1khz (the only audio tone many generators use). Separation can fall drastically above this.
If you have (access to) a tube tester, I suggest testing all of the tubes both for quality and interelectrode leakage (which can be a problem with 6AU6's, a typical tube in the IF stage).
Charles King
Also tell us. There may be a pattern,consider joining our yahoo group.
It could even be a PSU problem with mains if getting through!?
I too use a toob rcvr, it's a tweaked /modded Kenwood simulcast 9wpc item. Mines in tuner only mode.
To what extent has the 400 been restored / serviced? It's a stereo FM/FM only model IIRC. Does it have a signal strength meter for FM?
does that show any change - when it is crap?
Which Yagi? FM only? Range and KW output of the station?
Listening, out.
WarmestTimbo in Oz
The Skyptical Mensurer and Audio Scrounger'Still not saluting.'
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