Re: [Harp-L] Blackstone 1 amp (new post)

[MARK BURNESS <markwjburness@xxxxxxxxxxxxxx>]

Hi Geoff,

A single 6SN7 in push-pull (as opposed to "single-ended" like a champ), with a 
Phase Inverter tube (you have 2 preamp tubes, so I assume that it has a PI check 
to see whether 6SN7 pins 3 & 6 are linked together, or whether they have their 
own wires, each running to the Output Transformer), can make 6-7W under drive in 
PP class AB, 10W in class B (never used for instrument amps)....clean W will be 
less. I have just built a 6SN7 powered amp myself, for practice/recording/lined 
out performance, I incorporated a lower power design (half watt) to make it more 
suitable for apartment use, you can see/hear the amp at 
www.myspace.com/markburness.

I can't find any solid info regarding Blackstone, so I assume that it is/was a 
small scale producer. Subsequently, circuit info might be hard to find. You 
could ask over at the www.music-electronics-forum.com (there is a reference to 
RG Keen on a Blackstone page I saw, RG is an old hand at MUF so I'm guessing the 
builder frequented there, or the old Ampage, at some time), or you are welcome 
to send any digital pics to me for evaluation, in case you are worried about 
infringing any propietry designs (confidentiality assured)...if you're not 
worried about that (it's your amp & you should have a schematic), post links to 
them here.

On a practical note, I very much doubt that the amp is fixed bias, so you can 
change the 6SN7 for any other 6SN7 without any adjustments. Operating voltages 
will be fairly low, so  unless Blackstone used rediculously small W plate 
resistors (like 0.25W) you should have some flexibility with preamp subs too. 
Could be a cool little amp, if it sounds good, then it is good...schem could be 
moot.

Cheers, Mark.

 



________________________________
From: geoff atkins <geoffatkins@xxxxxxxxxxxxxx>
To: harp-l@xxxxxxxxxx
Sent: Saturday, 27 November, 2010 6:41:13
Subject: [Harp-L] Blackstone 1 amp (new post)


Does anyone please have circuit information on a "Blackstone 1" 
head amplifier, I'm guessing it was made within the last 10 years? 
I have tried searching the net with no results.

The box is Orange laquered pine, with finger-jointed corners, 
and 6mm thick transparent Perspex / plexiglass plates at each side.
The chassis is white powder-coated , black lettering. 
Internal wiring is exceptionally neat, as is the whole construction.
IMO it's too visually prominent for gigs, so it will be integrated 
in a new case with an old 12" speaker. 
Access is needed both sides of the chassis so that's a little tricky.

Rectification is solid state. 
The single input jack is probably low Z, a dynamic mic drives it fine.
The tube line up is two twin triode 12AT7s in the pre-amplifier, and a twin
triode 6SN7GT as mono output. All bases are ceramic.
There's a stand-by switch. Speaker impedance is switchable 4 /8 ohms, and it
also has a variable line-out jack. 
There are no effects such as reverb etc.
It was sold to me new as a "One Watt" amplifier, -the shop had 'lost the
paperwork' - but I suspect perhaps it is 5-6 Watts ?

Thank you for any info you may have,
Geoff Atkins