Car radios are way more expensive because of the added selectivity, sensitivity and small size.
Tube numbers can be damn near identical and be very different inside. The 6*6 is an execption to the rule.
I'm guessing that the most likely tube failing is the 12AX7. The 6HU8 is probably a driver for the power tubes while the 12AX7 (sometimes 12AT7s) are preamplifiers. The crackle is often some kind of minor voltage fluctuation that would be picked up more by the preamp tubes.
If the crackle is on one channel you might want to just swap the 12AX7s around and see if the crackle changes channels. That may give you an idea of who's the culpret.
As why tubes turn microphonic - I really don't remember.
The next time I have a chance to plug the beast in, I'll try swapping tubes from channel to channel. I can't remember whether I did that the last time I was poking at it or not.
(no subject)
Car radios are way more expensive because of the added selectivity, sensitivity and small size.
Tube numbers can be damn near identical and be very different inside. The 6*6 is an execption to the rule.
I'm guessing that the most likely tube failing is the 12AX7. The 6HU8 is probably a driver for the power tubes while the 12AX7 (sometimes 12AT7s) are preamplifiers. The crackle is often some kind of minor voltage fluctuation that would be picked up more by the preamp tubes.
If the crackle is on one channel you might want to just swap the 12AX7s around and see if the crackle changes channels. That may give you an idea of who's the culpret.
As why tubes turn microphonic - I really don't remember.
-m
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