Bassman AB165 Advice

[GCastor]

I am thinking of buying a silverface Bassman AB165 that has been modded to AA864 specs on the normal channel and a JTM style circuit on the bass channel. Unfortunately I am not able to play this thing before I purchase it. The seller says it has some popping and hissing noises due to moisture absorption into the circuit board, that apperantly all old fender amps get. I have never heard of this before, and everytime I have heard of a similar problem, it was usually due to a faulty component (usually high voltage resistor).

Has anyone heard of this moisture absorption stuff? Would this be something to avoid or just pick it up and try and fix it?

Thanks

[Sonny ReVerb]

The old Fender boards were made from a material they called 'fish paper'. They were prone to moisture absorption, especially in damp or humid conditions. Do a search for 'fish' and 'moisture' and you'll find some discussion on the topic.

http://en.wikipedia.org/wiki/Fishpaper

http://www.oliner.com/fishpaper.htm

[GCastor]

So I would need a new board and all new components to eliminate this?

[Ace Carson]

I think the optimal way for this case would be to disassemble the amp, make another board and in the meantime test the caps for leakage and the HV resistors for correspondance to the R value labeled. There simply might be no need for anything new except the board.

[M Fowler]

The whole basis for these old Fender Amps, especially silver face, is don't pay too much as they generally need lots of work.

If your into designing or modding then the mojo chassis/head cab or combo cab is a better way to go. Buy or make your own boards get the triodestore magnetic components package tranny set and you will have a better than old Fender amp.

My 2 cents, Mark

[GCastor]

I could probably get this one for $450, and would like to put as little work into it as possible.

[jhaas]

According to the Fender Field Guide at Ampwares, the average price paid over the past 14 years is $435. So it doesn't sound like $450 is a "steal", but there are a lot of variables, of course.

[GCastor]

Ive been watching craigslist and ebay and unfortunately the prices on these are rising. $450 wouldnt be a steal but probably just a fair price, considering my original plan was to get an AB165 and do a similar mod.

I dont have a lot of experience working on tube amps, but have decent soldering skills and a technical background, how big of a job is it to replace the "fish paper" board. Can you order a replica with eyelets and simply move the old components to the new board? If this is the case it doesnt sound like too bad of a job.

[crbowman]

Often times popping and hissing in old Fenders can be eliminated by swapping out the 100K CC plate resistors with something newer and more robust like RN65s or equivalent. I've heard about the problems with moisture and the fish paper boards but have yet to see an example where this was actually the REAL problem and I've played, owned, and or serviced LOTS of 'em. The infamous brown caps are also problematic as most of them develop voltage leaks over time. Basically there are a lot of variables in the old Fenders that can cause this behavior (tubes?) and few of them are really very expensive to fix. Could be something really simple......or...not.

[GCastor]

assuming all components test good.

[GCastor]

Thats really what i was trying to get a feel for, if someone just told the seller that this was the problem, because i had never heard of it (which isnt saying much) and he went along with it, or if it was more likely a component issue. The amp was gone through when the mod was done, but who knows if the old CC resistors were replaced with new CC resistors and they accumulated moisture or drifted in value again.

[crbowman]

Ken Watts at Watts Tube Audio does a replacement board for AA864 for $40.00.
http://www.turretboards.com/TURRET_EYEL ... MPLIER.htm

So you could probably rebuild the entire board for $100.00 bucks or so.
Plus, their are plenty of guys on this forum who could help you source anything you need. All in all, not a SUPER deal money wise, but could be a good fun learning experience.
About 15 years ago I bought an old blonde 6G6-B Bassman that had been cannibalized for parts and spray painted black. I built about a half dozen different circuits in it before I finally just restored it. Learned a TON and had a lot of fun with it over the years. Still have it too.

[Structo]

I think unless the cabinet is in very very good condition and the amp besides having some component changes, is not worth that money.

A lot of times you see good condition amps like that for around $400.

Because if you have to replace the circuit board, and replace the components, you just defeated the vintage mojo of the amp.

So you are basically using the cab, chassis and transformers to build a new amp.

If he replaced the blue molded caps then that would decrease the value considerably.

[GCastor]

Thanks for the help!! I am probably just going to find a nice clean silverface AB165 locally that I know exactly what has been done to it and go from there.

Peace

[solderstain]

I think unless the cabinet is in very very good condition and the amp besides having some component changes, is not worth that money.

A lot of times you see good condition amps like that for around $400.

I agree - that's too much for a modded amp. You can find intact ones for $500 or less if you're patient. Hold out. Don't be in a hurry, unless you're looking for a project amp, and if so, I'd probably offer around $300 to $350 for an amp that's been modded like you describe, and even then only if I can get a GOOD look inside and if the iron is original.