65' bassman 100w head

[Mixfly]

So I'm the noob here. I love to play and I can't help but fiddle with everything I play through.

Long story short: I was given a 65' bassman head. The first thing I did was open it up.

I found that the caps had leaked and the tubes were looking pretty rough. Both the tubes and caps seem to be original. I know it sat in a closet in a theater in Texas for around 20 years, but not much else.

I want to play this amp but other than changing the caps and tubes I have no idea what else to check. I'm pretty good with a DMM and a soldering iron, but I've never worked with tubes before. So my questions are these:

1.) What brand of caps with sound the best (I play country and southern rock)

2.) What brand of tubes work best with this amp

3.) what should I check other than the tube and caps before I plug it in.

I'll take any advice, but this is an un-modified all original amp that probably hasn't had anything done to it since it left the factory. also, what do these amps go for in good original condition?
If I don't like it when I replace the caps I'll probably sell it.

[ChrisAlbertson]

I'd only replace the electrolytic caps. The others don't really degrade in storage. You can't hear the brand of electrolytic filter caps. If any caps effect the sound it will be the coupling caps and even then the effect is subtle, more subtle then changing strings on the guitar

How do you know the tubes are not good? Dirt on the glass has no effect on the sound. I'd try the old tubes.

The safest way to power up an old un-known amp is with a variac and start with a low voltage just to see that nothing is shorted or open.

My guess is that the amp will make noise with no work on your part but I'd suspect any electrolytic that are 50 years old.

But I just built a small EL84 powered amp and put 45 year old tubes it it that were salvaged from a 1960's hammond organ and they work fine.

[EWBrown]

REplace ALL the electrolytics, and if it has 60s vintage silicon rectifiers in the PSU, those should be replaced with something newer, like uF4007s or 1N5408s. Also be suspicious of 50 year old "paper" capacitors, like "Black Beauties", etc, these can and will go bad and the plastic bodies can crack. "Orange Drop" caps of the same capacitance and voltage rating will be very good. I wouldn not bother with any "fancy" or "boutique" coupling caps here, they won't add anything significant to the tonal qualities of your amp.

Old, used tubes can still work just fine. A couple years ago, I pulled 67 12AX7s out of a nearly 50 year old Schober Organ, and after testing them all on a Hickok 6000, I found only two which were weak or bad.

I've also pulled myriads of 6L6GCs, 6CA7s, 5BQ5s and 6V6GTs (and smaller tubes) out of old "carcasses", and most of them were still perfectly good and usable.

The organ itself is way beyoond repair, after thirty-some years of bad storage in three different states, the keyboards, and PC boards are corroded beyond all hope, and the many generations of bugs and mice which made it a home only added to the corrosion, and seriously rusted the power supply chassis and transformers . I was able to rehab the 6.3V, 14A filament transformer, but the power transformer and filter choke were beyond redemption.

/ed B

[Mixfly]

Well I found a kit that had everything I needed (cap wise) and ordered it. Sprague and Orange Drop should be fine right? I'm planning on trying the stock tubes first, then changing them if needed.

I've been looking for a schematic for this amp thats clear and not a bad scan or someone's sketch. Surly someone has redrawn this schematic. I don't really need it, but it would be nice to have.

If anyone knows of one please let me know. It's the AA165 circuit.

[EWBrown]

Bad scans and scribbled schematics seem to be the norm for most Fender tube amos.

This typically bad scan of an AA165 Bassman is over at Schematic Heaven:

http://schematicheaven.com/fenderamps/b ... _schem.pdf

Fwiw, 7025S are just "FANCY" 12AX7s / ECC83s

Another "feature" of many Fender schematics is that many of them built-in intentional minor errors, used to confound "copycats" but not the savvy techs.

/ed B

[soundmasterg]

I'd recommend to replace the electrolytic caps only in the amp, then set the bias and see if it works. If it does, then use it that way and don't replace the signal (coupling) caps. The blue "molded" mallory caps that came in that amp are highly sought after these days and sound very good, and very rarely go bad. Putting Orange Drops in place of those will actually degrade the sound of the amp a bit, and will degrade the value of the amp a lot. If you do decide to replace the coupling caps in the amp and put the Orange Drops in there instead, I'd recommend to save all the old coupling caps in a baggie and sell the amp with those included in case the new owner wanted to have them put back in. Do not save the electrolytic caps however...just the coupling caps. The electrolytic caps are polarized also and will only go in one way. If you put them in backwards, they will explode. The only place in the amp that they go in backwards is in the bias circuit. You should be fine if you keep track of the polarity of the new ones and the old ones and put the new ones in the same.

Greg