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Plexi 50 board

1/6/2004 2:27 PM
Sacha	Plexi 50 board Hi folks, I'm looking to build my own Plexi 50 and found some pre-assembled boards, but here's the most interesting I found : http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2370523276 I wrote to the seller and here's his reply : ====================================================== Sacha, The regular 1987 twin bias board is $65US.The twin bias config is found on most hi-end, hi-fi equipment and boutique guitar amplifiers.It means that instead of having a 'single' trim pot which feeds a single bias voltage to both of your output tubes you will have 'two' trim pots...one for each tube for the ultimate in control when biasing your amp.With only one trimmer both your tubes will be conducting different currents (so much for the matched tubes theory!!!) Now you can bias each tube to identically matched currents by adjusting the individual bias voltages. By 'balancing' the dc idle current in the output tubes and transformer you will also cancel AC ripple thereby eliminating hum while also cancelling any magnetic flux bias in the transformer that can suck power.It is my best selling board. Options:I can change the plate load resistors to 220K for a bit more drive or change the .002 uF coupling cap in the treble channel to a .022uF for less hi end(popular mod).I can change all the caps from paper in oil to Mallory 150 series or all the resistors to metal film or carbon comp.etc etc..... I also sell a "Tube Sag Simulator" for $15. This small simple circuit mounts on the inside of the chassis (2 kepnuts & bolts) and simulates the compression/sag of the tube rectifier found in the JTM45 and comes with an easy to follow wiring diagram. If you buy a board, just stay in touch and we can discuss all sorts of mods for your amp like a pentode/triode switch,master volume control,parallel input mod or an effects loop (tube or solid state)....or even installing a reverb ??......I have all sorts of documentation I can send you for free no problem.I have attached a picture of the dual bias Plexi 1987 Superboard. Hope I was of some assistance Thanks...Martin ====================================================== What do you think ? Looks like a nice board for the price!

1/6/2004 2:27 PM

Sacha

Plexi 50 board

Hi folks,

I'm looking to build my own Plexi 50 and found some pre-assembled boards, but here's the most interesting I found :

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2370523276

I wrote to the seller and here's his reply :
======================================================
Sacha,
The regular 1987 twin bias board is $65US.The twin bias config is found on most hi-end, hi-fi equipment and boutique guitar amplifiers.It means that instead of having a 'single' trim pot which feeds a single bias voltage to both of your output tubes you will have 'two' trim pots...one for each tube for the ultimate in control when biasing your amp.With only one trimmer both your tubes will be conducting different currents (so much for the matched tubes theory!!!) Now you can bias each tube to identically matched currents by adjusting the individual bias voltages. By 'balancing' the dc idle current in the output tubes and transformer you will also cancel AC ripple thereby eliminating hum while also cancelling any magnetic flux bias in the transformer that can suck power.It is my best selling board.

Options:I can change the plate load resistors to 220K for a bit more drive or change the .002 uF coupling cap in the treble channel to a .022uF for less hi end(popular mod).I can change all the caps from paper in oil to Mallory 150 series or all the resistors to metal film or carbon comp.etc etc.....
I also sell a "Tube Sag Simulator" for $15. This small simple circuit mounts on the inside of the chassis (2 kepnuts & bolts) and simulates the compression/sag of the tube rectifier found in the JTM45 and comes with an easy to follow wiring diagram.
If you buy a board, just stay in touch and we can discuss all sorts of mods for your amp like a pentode/triode switch,master volume control,parallel input mod or an effects loop (tube or solid state)....or even installing a reverb ??......I have all sorts of documentation I can send you for free no problem.I have attached a picture of the dual bias Plexi 1987 Superboard.

Hope I was of some assistance Thanks...Martin
======================================================

What do you think ? Looks like a nice board for the price!

Replies:

Sacha Cmon! I'm sure someone can help!... -- 1/6/2004 7:01 PM