AB165 mods...or why must learning be painful?

[jaysg]

I've been cleaning up what I thought was an AA165. I had trouble biasing it last night and remembered that they used up old tube charts...wasted time.

Here's the oddity, the guy is bassist. He has a pile of quirky bass amps, and changing it for the best guitar tone isn't the plan. I've modded the bias but I don't know whether or not to change the output to BF. Is all that feedback and 'wrong' coupling better for bass?

[rhinson]

I've been cleaning up what I thought was an AA165. I had trouble biasing it last night and remembered that they used up old tube charts...wasted time.

Here's the oddity, the guy is bassist. He has a pile of quirky bass amps, and changing it for the best guitar tone isn't the plan. I've modded the bias but I don't know whether or not to change the output to BF. Is all that feedback and 'wrong' coupling better for bass?

yep. esp the fb loop as is. leave it alone. i still like it best for guitar as is---with just a couple of minor changes (fb loop cap and lower snubbers in the earlier stages). i think it sounds pretty good----jut my tastes perhaps.

rh

[jaysg]

...esp the fb loop as is. leave it alone. i still like it best for guitar as is---with just a couple of minor changes (fb loop cap and lower snubbers in the earlier stages). i think it sounds pretty good----jut my tastes perhaps.

rh

Hi Robert, thanks for the reply

If you mean the stage 1 snubbers on the plate resistors, I saw recommendations to clip them out. In this amp, they're both .01uF. How much smaller on that .1uF in the feedback loop?

[rhinson]

...esp the fb loop as is. leave it alone. i still like it best for guitar as is---with just a couple of minor changes (fb loop cap and lower snubbers in the earlier stages). i think it sounds pretty good----jut my tastes perhaps.

rh

Hi Robert, thanks for the reply

If you mean the stage 1 snubbers on the plate resistors, I saw recommendations to clip them out. In this amp, they're both .01uF. How much smaller on that .1uF in the feedback loop?

for bass just leave everything as is. for guitar (keeping everything else the same---no bf sf conversion) i'd keep the snubber at 470pf - 2200pf in the bass ch and keep the guitar ch as is ---but it is to taste. just experiment with the .1 in the feedback loop----i've done several but honestly can't recall what i did---may have left it for the tightness it gives. this is where the eico 1140 comes in handy rh

[David Root]

I have one too, a late '67, almost an early SF. In fact it has what appears to be an original blue/silver SF grille cloth, but not the SF aluminum trim, it's a BF with SF grille.

I have seen it said that to mod an AB165 for guitar, keep the AB165 preamp circuit as is and change the power end to AA864 specs.

Anyone done that? Does it rock?

[cpollack]

I have an AB165 (late, also with the silver/blue grill cloth and aluminum surround), and play bass through it. I did some minor preamp mods, but left the power section alone. I think the 220K feedback resistors in the PI help with bass. I did change the bias from a balance to overal level control and bumping up the PS caps to 100 or even 220 uF tightens up the bottom and lets it get a bit louder. It's actually a very nice sounding bass amp and loud enough for small gigs. The usual cab I use with it is a '70s Fender 2x15 slant with JBL D140s.

It does a nice spanky BF Fender sound with guitar, too (think the intro to "Yellow Ledbetter"). My Strat loves it; my LP Jr. hates it.

[rdjones]

I've been cleaning up what I thought was an AA165. I had trouble biasing it last night and remembered that they used up old tube charts...wasted time.

AA165 stickers were used for quite a few AB165s, 6 months or more.
I have one here.

Here's the oddity, the guy is bassist. He has a pile of quirky bass amps, and changing it for the best guitar tone isn't the plan. I've modded the bias but I don't know whether or not to change the output to BF. Is all that feedback and 'wrong' coupling better for bass?

Generally yes.
But "it depends" a lot on style both playing style and music.
The fact that he has a pile of amps indicates he's searching for tone, so having the signature Fender scooped/bright sound can be a good benchmark.

rd

[jaysg]

50W clean at 400Hz and 63W clean at 100Hz....who knew? I'm impressed.

[rdjones]

50W clean at 400Hz and 63W clean at 100Hz....who knew? I'm impressed.

400Hz is close to the center of the Fender tone stack scoop.
Amp appears to be 'happy'.

rd