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It's a 1972 AA270, new tubes, new PS caps, plays nice and quiet, but no vibrato. What I see is that the neon bulb will flash once or twice, then give a couple of weak flashes then nothing. Is the LDR (optocoupler) at fault? Yes I have swapped tubes....Thanx
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Yeah, that's what I would try replacing, first.
About 10 years ago, when my guitar buddies and I used those early/mid 70's silver faced Fender tube amps, and the vibrato or reverb went out, we alway had good luck with the old "hit-the-top-of-the-amp-really-hard-with-your-fist-a-few-times" technique. :-)
Of course, you can't pick a good-condition early/mid 70's Twin, Super etc. for $400 these days. Those Fenders were a great deal, especially if you could convert the guts to black face as they sounded amazing and were plenty loud enough to play w/ a drummer. Anyway, now that a lot of these amps are fetching "vintage" prices, its probably best to avoid this highly technical method of repair. :-)
Good luck and enjoy the amp. Those TR's are terrific!
OK, I'm not a gittar player, but it interesting to see the battle of the black was better vs the silver. Seems to me the iron is the same, basing that on the fact that anyone who sells genuine Fender parts sells the same iron for any era. Part numbers didn't change as far as I can tell. Were the circuit(s) better pre CBS? Or were CBS parts just cheaper. My friend plays an acoustic thru the amp, with lots of reverb dialed up. I've thought of upgrading the amp section coupling caps to Solen or better. I have the Groove Tubes book amp which has tons of schematics. What would be a good vintage chassis number to look up? Hope that made sense.....
If you peruse the schematic of the CBS era amps versus the blackface Leo-era amps, it becomes obvious. CBS techs tried to make many models more linear by increasing the plate voltages and fudging with cathode current and global feedback. In general the results were a very sterile, loud amps, with no life. Nearly every SF amp I've worked on for ppl & ppl that have silverfaces with this problem convert them back to blackface standards. This usually means dropping voltages on the pre-amp tubes, reducing the global feedback, and other such things. It's easy to do, just wire the SF to BF circuits. And keep the old parts in case you decide to sell it. For some reason, most guitar amps will hold better value in genreal, if sold as ORIGINAL. I think that's because there are a lot of ppl out there that tried to hot-rod or revert SF amps and totally mucked them up, to a point where it would be hard to get the thing back to original reliable status.One other note, after many misguided attempts, it's usually NOT a good idea to do wholesale coupling cap and/or resistor changes to these older vintage amps. You will almost always lose some of the original tone. I've tried using new, modern made caps and they tend to make the amp sterile. I only replace caps (expcept the electroltytics, which I always replace if more than 10 years old), if it needs to be replace. And usually with Sprague Mylar caps. My BF Princeton still has the original blue coupling caps in it & still sounding pretty good. Oh yeah, carbon comp (yeah, I know, how primitive) where there is carbon comp OEM. You can use fancier parts in newer amps which were voiced with more modern parts. Like Trainwreck, Buddah, etc.
Edits: 02/05/10 02/05/10
I'm not much of a technition but I think you can get a lot of milage by upgrading the caps. I'm sure there's a few other parts to swap out to make the amp exactly "blackface" but I believe doing the caps gets you most of the way there.
FWIW some of the early and mid 70's silver face models, like the Deluxe, are already really close to Blackface. I have a 76 Deluxe Reverb, which I think is the last year Fender made these w/o the dreaded pull switch, and I think it sounds great as is. The only change I made to it was to install a new speaker, but that was only because the original one developed a tear.
Good luck.
Some silverfaces had different iron than their blackface counterparts. Off the top of my head, I believe that the silverface Super ran heavier iron and higher voltage than the blackface. CBS tried to make this amp, and other silverfaces, more linear than the older ones. In the process they lost all life in the amp. Many ppl revert this and other silverfaces back to blackface standards (Champ comes to mind, also), for a that "Fender tone" they are used to.
A good book on all the model Fender amps made is "Fender Amps." By John Teagle and John Sprung. Hal Leonard Publications, 1995.
yer replies!!!!!!!!!
Should note that early Kauffman & Fender amps, "one-off" amps, and anything post-1995 will not be covered under this title.
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