Why is my Audio Research SP6-b noisy?

I have an Audio Research SP6b pre-amp and it is very noisy-has a very loud hiss.I do have it hooked to a very large
pair of altec lansing VOT horn loaded speakers.I have used
4-5 amps and it stills has the hiss.Is this normal?
I know the horns amplify the hiss because when I hooked it
up to my klipsch speakers it was not as noticable.
Any suggestions.I just replaced the tubes.It does it with
the new tubes and old tubes.Go figure.
Anyone else have this problem?
The usual cause of hiss and related noise in a tube preamp is tubes that need to be replaced, or re-biased. This type of noise will be particularly notable with horn speakers, which are very efficient. Maybe some owners of SP-6b preamps will have some other advice to offer.
Sdcampbell I think hit it on the head for you though, have the bias checked, you did not mention which amps. or how long you have been using the VOT's, as it may be a differnce that you have noticed more when switching to these from another speaker. Also, is this with or without a source, which source, is it obvious with a source?
The previous posts are correct...it likely needs new tubes.
That being said, I will also say that I owned an SP-6B
a number of years ago, and despite it's exalted reputation,
I found it lacking, especially in the relatively high
noise floor. I later owned an SP-14 which I found superior
in most regards. In it's day (late 70's) the SP-6 series
was quite good, but more recent designs substantially
better the SP-6's.
All the above are correct, I would like to add that a lot of noise is can be generated by the power supply. In such power supply there is the infamous capacitors that go weak and tend to 'dry' up, thus allowing the line frquency (X2) to not be filterd out as the designed. Check with Leonard at Audio Research, this preamp is a very quality piece and will give great to excellent results when operating as designed. Hope this helps.
vett this is my typical experince with tubes + horns, which are very sensitive. The only tube preamp that I found quiet enough was a Golden Tube SEP-2 or SEP-3. All the others that I tried were so noisy & microphonic (including some very pricey & popular preamps) that I "just said no" to tubes. Try some quality solid state instead.
Thank's for the responses.I have new tubes in it and no
difference.The unit does sound incredible though.I
will talk to Audio Research.
steve, do i assume correctly that you first noticed the hiss when you started using the horn speakers? if that is so, then you are the victim of their efficiency. i've noticed the same thing with an sp10 which is very sensitive to tube noise. one way to solve the problem is to attenuate the output of the preamp. for example in order to get remote control, i inserted a passive volume control (think placette or crook) and this did the job quite nicely. there are probably other ways of attenuating the output of the preamp but i'm not a technician and can't help you.
Output caps in both the phono and pre-amp stages can cause noise.