Just purchased a 68 Fender Bassman

[Bluesbishop]

Hey Everyone!
I just bought this '68 Fender Bass on ebay: http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 3725216214

It claims to have the AA165 circuit instead of the more common AB165 circuit, can anyone tell from the picks of the board?
Any mods anyone would recommend? I'm a HUGE SRV and Page fan, wouldn't mind setting this up to use KT66's

Thanks for any input!

Ken

[VelvetGeorge]

Sweet! Those amps are workhorses.

You might want to do the blackface conversion. It's cheap and sounds great. Let me know if you need some info.

George

[Flames1950]

Hey BluesBishop, I replied over at PlexiPalace too, but I'll repeat here.
It's not an AA165, but an AB165--the little terminal strip between the power tube sockets and phase inverter are the giveaway. I can't tell from the pic if the 220K resistors that should be hooked up there are gone or not. A clearer pic would help to see if any other mods have taken place too, there are at the very least many replaced caps in there. (Hint--I put the SoZo's that George can sell you in my '68, they sound great!! A little fatter than the Orange Drops.)
The only change I like to make to an AB165 is to add a 100uF filter cap inside the chassis, these were a bit underfiltered and can ghost note the hell out of you when cranked. And you'll wanna crank it--they have a real nice overdrive with either a Fender guitar or a Gibson. A little bluesier than the typical EL34 Marshall overdrive, big meaty sound.

[Bluesbishop]

Thanks guys for the input! When I get the head, I'll take some photos so I can get a better idea what's going on. God, If we could only find Old Marshall this cheap!


Thanks


Ken

[flemingmras]

Thanks guys for the input! When I get head, I'll take some photos.
Thanks


Ken

PLEASE DO!!!

Jon

[Bluesbishop]

Ok Jon...That was GET the head, NOT get head! ....Jeez! ROFLMAO!!!



Ken [/b]

[flemingmras]

You KNOW I had to do that. ROCK N FUCKIN' ROLL!!!

Jon

[Bluesbishop]

Well, my '68 bassman arrived today. The Tag says AB165, NOT AA165.
Took everything apart, all tannies are orginal, has new tubes ( ruby 6l6GC) and EH in the preamp.

All the caps on the boards have been replaced, I've taken some photos that I'll post, but my camera is terrible...be warned

Any feedback on how everyhting looks would be appreciated

Ken

[Flames1950]

Recapped......good.
It is wired as an AB165, not an AC568.......good. (I really like the crunch of my '66 AB165, with Gibsons or Fenders.)
Plate resistors changed out......at least it will be quieter (so many Fenders have noisy plate resistors that it's almost a necessity to change them out.)
How's she sound?? I'm puzzled by the seller's "plenty of headroom" claim, all of these I've tried are pretty crunchy.
On my '68, which I rewired to AA864 spec, I wasn't happy with the three-gain-stage Bass channel sound, even with a guitar tone stack (the two-gain-stage Normal was picture-perfect blackface clean.) I actually went back to the AB165's third gain stage (with the funny interstage feedback loop) which was just what the doctor ordered, both crunchwise and EQ-wise.

[flemingmras]

Yeah my Pro is the AA165 schematic, which I'm not too fond of. If I had a spot to mount a mid pot I'd swap it with the AB763 schem.

Jon

[Bluesbishop]

Well, I wish I could tell you how she sounds...but I only have a 16ohm cab right now, and I'm alittle paranoid to run it 16ohms. I'm going to order a avatar G12H cab loaded with G12H30's this weekend, so I'm hoping to have the cab by next weekend!

This may be a silly question, but do I need to run it at 4 ohms, or can I run it at 8ohms? I was think of ordering two 8ohm cabs, and keeping one for at home, thew other for practice, and both for shows.


Flames, can you send me the mods you've done? I like the idea of one channel more fender and one channnel very JTMish. Speaking of JTM, have you ever run KT-66's in your bassman?

Ken

[flemingmras]

On your 16 ohm cab...is that a 4X12 cab?

If it is, you can make it a 4 ohm cab by wiring all the speaker terminals in parallel with each other(i.e. all the positive terminals go togehter as do all the negatives). This will drop your load impedance down to 4 ohms.

Jon

[Flames1950]

Fenders are much more tolerant of impedance mismatches than Marshalls, eight ohms shouldn't be a problem with it. I ran mine through an eight ohm cab for about ten years.
A lot of what I did to mine required gutting the board and re-routing the wires underneath it, because the AA864 has wires under the board in different places than the AB165.
As an alternative, I finally ordered some of George's board material and made my own turret board for my '68, which made things a lot easier to experiment with. But it really was worth it in the end, the Normal channel was picture perfect Fender blackface, and the Bass channel sounded like my AB165's Normal channel (more crunch -- the AB165 routes both channels through the extra gain stage, instead of just the Bass channel. Why would you route the bass channel through an extra gain stage anyway?? ) Probably have to re-think some of the cathode resistor/cap combos to get it more JTM45-ish, although maybe just changing the first stage 1500 ohm cathode resistor to an 820 ohm would be enough. I also scrapped the "Deep" switch and copied the bright switch wiring from the other channel, that Deep switch is utterly useless.
Bottom line for me? I like the Normal channel as is on these. I'd copy the tone stack values from the normal channel, or from a JTM45, your choice, and install those values in the Bass channel. Wire a bright switch instead of the Deep. If that's enough, cool; if you need more balls on the Bass channel, try lowering the cathode resistor to an 820 ohm. The 25uF cathode bypass cap Fenders use should still be plenty big; Marshall's 250-330uF caps were way overkill.

[Flames1950]

Oh, I forgot -- SoZo caps sound KILLER in place of those Orange Drops!!

[flemingmras]

I ran my Pro through a 12 ohm out-of phase load once fully cranked with no problems. When I tried out my '73 cab this is how it was wired. Note the speaker on the far right wired out of phase. Three speakers in series with one of them crossphased, all three in parallel with the 4th!!! What the fuck!!!???

Jon