NAD: Laney AOR 100

Dopesick

Got this baby delivered last week and it is in startlingly good nick for such an old amp. Even the handle looks in pristine nick which I find a miracle with Laney.

Just wondering though...yes, these are 100w. Extremely loud. Thicker than three concrete elephants and just as heavy....I took it to band rehearsal last night. On Low output the preamp volume was dimed, but it was still clean.

Now I've been told it's extremely difficult to get a pure clean sound out of these amps especially at such a high setting on the preamp. Also when turning up the MV it was about 1 o'clock before I could get it to sufficient level (we do like to play at ear splitting volumes though).

Are my tubes on the way out? They light up and they certainly get hot (almost burnt my hand off when it was over) but I'm surprised how much I had to crank it to get it to the desired volume level. The lack of any distortion on the Low input as well is a little weird. Surely they must be louder/more aggressive than this?

Kitsune

Pics? I've been considering one of these for an age, mainly because of this:

John_A

Dopesick said:

Got this baby delivered last week and it is in startlingly good nick for such an old amp. Even the handle looks in pristine nick which I find a miracle with Laney.

Just wondering though...yes, these are 100w. Extremely loud. Thicker than three concrete elephants and just as heavy....I took it to band rehearsal last night. On Low output the preamp volume was dimed, but it was still clean.

Now I've been told it's extremely difficult to get a pure clean sound out of these amps especially at such a high setting on the preamp. Also when turning up the MV it was about 1 o'clock before I could get it to sufficient level (we do like to play at ear splitting volumes though).

Are my tubes on the way out? They light up and they certainly get hot (almost burnt my hand off when it was over) but I'm surprised how much I had to crank it to get it to the desired volume level. The lack of any distortion on the Low input as well is a little weird. Surely they must be louder/more aggressive than this?

Surely if you want distortion you would use the high input

ICBM

It's a long time since I worked on one, but that doesn't sound quite right - the clean sound is meant to be clean, but I think it will break up if you turn it up high.

Check that all the preamp valves are 12AX7 (ECC83) and no-one has deliberately reduced the gain by fitting either a 12AT7 (ECC81) or 12AU7 (ECC82). If they're all 12AX7s, substitute a known good one for each of them in turn and see if any of them is obviously low on gain.

ecc83

ICBM said:

It's a long time since I worked on one, but that doesn't sound quite right - the clean sound is meant to be clean, but I think it will break up if you turn it up high.

Check that all the preamp valves are 12AX7 (ECC83) and no-one has deliberately reduced the gain by fitting either a 12AT7 (ECC81) or 12AU7 (ECC82). If they're all 12AX7s, substitute a known good one for each of them in turn and see if any of them is obviously low on gain.

I found a shematic for a Mkll but the valves are not identified, some odd cathodes resistors though for 83s? 2k7, 10k!

No sense R for the OP stage but bias voltage on the grids is stated as -42V, seems a bit cool if 34s and 460 V on the OPT?

Dave.

ICBM

ecc83 said:

I found a shematic for a Mkll but the valves are not identified, some odd cathodes resistors though for 83s? 2k7, 10k!

This is normal in Marshall-derived circuits. 2K7 is the standard value for the first gain stage and 10K for the second gain stage in the 2203-type circuit. Soldano and then Mesa went even further, with 39K in the third stage (equivalent to the Marshall's second).

ecc83 said:

No sense R for the OP stage but bias voltage on the grids is stated as -42V, seems a bit cool if 34s and 460 V on the OPT?

Also normal for 100W Marshall circuits. They need to be biased relatively cool or they're very hard on the screens - I find just under 30mA is the 'magic' setting, ie 13.5W with 470V on the plates - the best tone and good reliability.

ecc83

What G2 feed Rs do they use? I just checked the HT-100 and S1 100 and they are 1k5. I'd bet the A100 is the same (can't find a map atmo) and I rarely had any great valve troubles. Biased at 25mA per 34.

Dave.

ICBM

Marshall used 1K, except on the ones that didn't have any at all! - 70s 50W models with the lower HT voltage - presumably they thought they didn't need them and decided to save 10p or whatever it was... I always fit them if I'm servicing one of these.