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AMPEG SVT 2-PRO Smelling and Peaking like mad!

J

jimmykebab

Feb 12, 2008
31
0
#1
My Ampeg SVT 2-PRO has gone a bit mental. I took to to a tech who said I need new tubes (worn out after 1 year and not played on loads 120 hours - but I didn't let them cool before moving/ventilation inlet has been covered by a case).

So I got myself a matched sextet of the same tubes used by ampeg and fitted them (all seem well seated), the amp is still peaking like a ****er to a point where gain in down at 1/4 or 9'o'clock and I'm using the master right up, which is no good as I have no 'headroom' left before the thing peaks out.

Anyway, last night I used it and it started to smell a little, I'm worried.

My tech is away for 2 weeks now and I really need to use that amp.

Any ideas?

Could leads be an issue?
 
#5
Gotcha!

Allow the unit to warm up at proper AC line voltage for at least 20 minutes. With no input signal present, adjust each
control so that only the associated green LED is lit. The controls may be slightly interactive. If neither LED is lit, the amp
is overbiased. This will result in some distortion in the power amp and a generally thin sound. If the green and red LED are
lit, the amp is underbiased and too much current is flowing in the power tubes. This will give a big, full sound but will also
reduce the life of the power tubes.
 
#7
Replied to your PM.... but hadn't read this thread yet

The peaking thing is probably independent of the bias and smell issue... well maybe not the smell...... but probably the bias.

if you biased according to the lights, odds are that you are in the range.....even if not "perfect". Yes there is a chance of it being way off, but probably it is close. A meter will give the real answer.....

OK... "smell" has a lot of options. What does it smell OF?

There is the normal smell of hot wood, dust, and tolex etc, with overtones of "that bar smell"...... If it's just more of that, and everything else seems normal, no sweat, likely.

if you smell that "something is really hot that shouldn't be" smell, a roasting plastic, acrid smell.... Then I *might not* want to run it without a check-over.

if you look at the tubes in a dark area, and see ANY dull or brighter red color on the power tube plates (not the filament light), turn off and wait for tech..... the bias lights are telling evil lies.

As far as the peaking.... was that the original problem? it sounds like one of the later stages of the peak light circuit has a problem, which may or may not be part of the smell issue.

if that were the ONLY problem (peak light gone crazy) and the amp seemed to be OK at your normal settings, I'd use it and ignore the light until it's fixed.

Actually, for any of the above, I'd have it on the bench for a look-see, but I have unfair advantages.............
 

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