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Discussion Starter · #1 · (Edited)
I've been after a vintage Bassman for a while, but not willing to pay some of the prices out there, particularly since I am theoretically moderately handy with a soldering iron and understand capacitor discharge. So, yesterday, I finally scored one for a not-crazy price with the understanding that it needs the standard restoration (power filter caps, etc.) before plugging it in at all. But ...

... it seems to me someone already had a pass at it. It has the 3 prong power cable grounded to chassis well and correctly, that was expected. But while most of the filter caps are obviously original, one has been obviously replaced and none of the originals show any leakage.

So, thoughts? Should I just tube it, plug in, and see what happens or should I (order, wait for delivery, and) do the filter caps before even seeing if it works at all?

Some pics to support my observation below. I have more zoomed in pics if they would help with comments.









It is the AB165 circuit which some people say is "sought after" and lots of other people say is crap and should be changed closer to AA864 (particularly the output section feedback and inverted output transformer hookup; and the weird hum-control/half-a-tube-bias circuit). I have no idea either way, never played a vintage Bassman myself, but I expect I will be modding it to AA864 at some point just for the sake of hearing what all the hoopla is about :).
 

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I'm guessing the amp was previously assessed and given the "minimum required" servicing for safety & functionality, hence the grounded AC cord, single cap replacement, and nothing else (except maybe proper biasing). If it was me, I'd certainly feel comfortable plugging it in to see how it sounds...
 
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You can indeed plug it in and test it. If you want the security of a reliable rig when on a gig, I'd fully service it. There's tons of these Bassman amps out there. In my opinion it does not qualify as a collector piece. If you want to play it, Service it. Those old 2 in 1 Whale cathode caps on the main board and bias board would be gone PDQ if it were mine. All new e-caps and resistors in the b+ power supply. F&T there for sure. New metal film resistors in there. The caps are dated 1967 BTW. Just my .o2 c.
 

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Discussion Starter · #5 · (Edited)
@StevieMac @Lincoln @keithb7 : thank you very much for your comments and encouragement. I got my confidence up a bit, tuned it on, and ... nothing happened. Nothing at all. Checked voltages on filter caps, nothing. Sigh. Let's check the fuse, what the heck. Hey, the fuse is blown, that's not a good sign, but let's try a good fuse. Turn it on and ... we have a working 1967 Bassman Amp :).

In a half hour basement (bassment?) levels checkout, everything sounds great. I still don't know if it sounds like a Bassman, but it does sounds like pretty classic Fender cleans on all inputs and both channels. The bass channel is fine for guitar, a bit bassier than normal channel as expected, but sounds great with a strat. The BRIGHT switch does its job, but the DEEP switch seems to act like a bright/tinny switch (will have to check if something's been modded or broken on that path). Both sets of bass and treble controls seem to do their jobs. Couldn't turn it up to any kind of a breakup, way way too loud for the basement. The fuse held fine, so a bit of a mystery there as to what caused it to blow in the past in the first place.

Now that I have a baseline (a bassline?) of functionality, I will take @keithb7's advice and cleanup anything that could/should be cleaned up/replaced on a near 50 year-old amp. As part of that, I'll check out if any mods might have already been done. Then, I'll see if AA864 changes are in order. Pretty happy with the deal and the sound :).
 

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A fuse blows when a component like an electrolytic cap, is failing. Allowing electrons to flow freely to ground. This pulls too much amperage and the fuse melts. It does its job very well. Once. What some people do next is try same fuse. It works for a while then blows again. Then they up the fuse. And it works again...Until the failing cap blows up. Smoke ensues. If you are lucky, transformer doesn't fry. Don't fall into this amp death trap. Service it now. A blown fuse is a big clue that it's due. Order caps asap.
 

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Discussion Starter · #7 ·
Good call. Aluminum electrolytics do fail short, not a great situation for power supply (power to ground) bypass. Ordering now.
 

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If the amp has been used regularly the power supply caps will fare better than one that has sat for long periods of time. I used to replace all power supply caps without a second thought, now I only replace if the amp hums or I see bulges on the rubber caps. It wouldn't hurt to replace all but it really isn't life or death. If the amp doesn't blow fuses, then they're probably good. I've done more than a few of these, the 864 is a favourite but the Ab165 has it's charms. Definitely a very cool amp. Enjoy!
 

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Definitely replace them. I have done quite a few, and while theoretically, filter caps don't affect tone, every one I have done sounds better after. Spragues have gotten stupid expensive and the F&T's are fine. For 100$ or so, you will have peace of mine and it will be good for another 50 years.
As for the whole Blackface thing, to me its a bit of hype. Unless you are cranking it, I don't think you will notice any difference. You want overdrive? Use a pedal. They take pedals very well.
But....if you do ever play in a really loud band, there is nothing like the sound of a Blackface Bassman cranked wide open through that 2x12 cab.
I think that's the only area where BF's sound "better" than SF's....cranked open, getting that tube distortion.
 

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At about $10 per cap, in a non-collectible amp, why the reluctance to change caps? I am curious. If I'm in there, and I know they are old, I replace them. - Cheers.

Capacitor - F&T, 350V, 100µF, Axial Lead Electrolytic
Like I said, it's not life or death if they test good and the amp shows no symptoms of bad caps. After almost 30 years of repairing amps I've developed somewhat of an experience and knowledge base and try to be minimally invasive but not at the expense of amplifier performance. It's definitely your call whether you replace them all, I just choose not to and I've had no issues that I know of.
 

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Looks like you got a great amp .
About 25 years ago I spent too many hours tracking down some ghost notes in that model Bassman.
Turned out the cause of the ghost notes was the two feedback resistors that go from plate to grid on the output tubes.
Clipped them and the problem disappeared.
 

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Discussion Starter · #13 ·
Looks like you got a great amp .
About 25 years ago I spent too many hours tracking down some ghost notes in that model Bassman.
Turned out the cause of the ghost notes was the two feedback resistors that go from plate to grid on the output tubes.
Clipped them and the problem disappeared.
Wow, that sounds like a pretty difficult root cause diagnosis! Impressive! And very good to know.
 
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