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Tube preamp kit for guitar?

PostPosted: Wed Sep 28, 2011 1:46 pm
by joeriz
Hello all,

Does anyone know if there are any good tube guitar preamp kits being sold? I've searched the web quite a bit but haven't really found much of anything. I'd be interested in something along the lines of a vintage Fender preamp clone.

Alternatively, has anyone here ever modified an old tube hifi preamp for guitar use?

Any thoughts?

Thanks,
Joe

PostPosted: Wed Oct 05, 2011 12:42 am
by Gingertube
You could try London Power in Canada. They have a number of different guitar preamps. BF fender is certainly one of them.
http://www.londonpower.com/
Also look at Ted Weber, not sure if he does just preamp kits or only full amp kits.
http://taweber.powweb.com/store/kits.htm

Probably lots of others but these are 2 I have dealt with and was happy with.

Cheers,
Ian

PostPosted: Fri Oct 07, 2011 7:15 am
by joeriz
Thanks very much. I checked with Weber and they do not offer preamp kits...full amps only.

The London Power kits look like a possibility.

Thanks again,
Joe

Re: Tube preamp kit for guitar?

PostPosted: Fri Apr 06, 2012 1:06 am
by Scott Novak
joeriz wrote:Alternatively, has anyone here ever modified an old tube hifi preamp for guitar use?


My first guitar amp was an old Heathkit integrated mono Hi Fi amp. Then I went through a number of solid state amps until I built a tube preamp from scratch. I do cringe at the thought of the solid state graphic equalizer that I used for tone control.

Schematics are available for most of the guitar amps around. If there is one in particular that you like, just copy the preamp section.

You can help it along and build regulated filament supplies for the tubes to reduce hum and keep a stable cathode temperature regardless of the line voltage.

Scott Novak

Re: Tube preamp kit for guitar?

PostPosted: Sat May 12, 2012 7:25 pm
by ChrisAlbertson
joeriz wrote:Hello all,

Does anyone know if there are any good tube guitar preamp kits being sold? I've searched the web quite a bit but haven't really found much of anything.

Joe



Joe,

Are you still looking? One thing to remember is that every full amp has a preamp. Just don't install the power tube and output transformer.

But if you like that Fender style tone in depends on the power section driving negative feedback to the preamp. A stand alone preamp would not sound the same way. So, what some people do is build a 5 to 8 watt amp run a dummy load across the speaker terminals.

Now for a more direct answer. Look here:
http://www.ax84.com/corepreamps.html
There are several to choose from.

Re: Tube preamp kit for guitar?

PostPosted: Wed May 16, 2012 8:07 am
by wyatt
ChrisAlbertson wrote:
joeriz wrote:Hello all,

Does anyone know if there are any good tube guitar preamp kits being sold? I've searched the web quite a bit but haven't really found much of anything.

Joe



Joe,

Are you still looking? One thing to remember is that every full amp has a preamp. Just don't install the power tube and output transformer.

But if you like that Fender style tone in depends on the power section driving negative feedback to the preamp. A stand alone preamp would not sound the same way. So, what some people do is build a 5 to 8 watt amp run a dummy load across the speaker terminals.

Now for a more direct answer. Look here:
http://www.ax84.com/corepreamps.html
There are several to choose from.


It's not just about leaving off the Pi and power amp, you also want the output impedance/voltage to be right.

Typically this means adding a cathode-follower final stage to designs like Fender's AB763 (Blackface) preamp.

Re: Tube preamp kit for guitar?

PostPosted: Wed May 16, 2012 9:23 am
by ChrisAlbertson
wyatt wrote:Typically this means adding a cathode-follower final stage to designs like Fender's AB763 (Blackface) preamp.



I think you are right. If the preamp is going to drive other equipment through a cable then it is good to have a driver from the cable. A cathode follower is good for that and adds nothing to the sound and has no gain. Any "left over" triode section can work.

Those schematics I linked to assume you would place the power section in the same chassis

Re: Tube preamp kit for guitar?

PostPosted: Wed May 16, 2012 9:59 am
by Scott Novak
ChrisAlbertson wrote:A cathode follower is good for that and adds nothing to the sound and has no gain. Any "left over" triode section can work.


While any triode will work as a cathode follower, a 6DJ8 has about the lowest impedance you can get in an audio tube and can drive cables much better. A 12AX7 on the other hand does not make a great cathode follower because of it's high impedance.

Also, when the load resistance is too low, the gain of a cathode follower drops way down below unity. People forget about the loading effects on a cathode follower.

Scott Novak