• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube amp for newbye

Hello,
I'm frarobertooo and it's the first time I post here and like quite every newbye I won't be probably clear in my request :) Please go easy on me!
Well, I have decided to build an amp for my Fender Rhodes with a stereo output of 50 watt or more. I have already some knowledge on electronic but this will be my first real diy project and sure I'd like to keep it simple ;)
So I was looking for an easy, clear, not necessarily cheap schematic with easy to find components. One of my problem is that I really don't know which tubes are regularly manufactured and which are hard to buy.
Could you please help me, also with a simple good link?
Thank you,
frarobertooo
 
Browse the internet tube stores like tubedepot.com and tubestore.com, anything that they sell will be mostly in current production.

A 50 watt per channel project based on vacuum tubes/valves will not be very simple.

If you can live with an 8 watt per channel output, search for Mikael Abdellah's SE KT88 schematic on this forum, that project is quite simple to execute. If you decide to build this amp, search for porkchop's post on his build of this amp, it is very informative and will help you with the project.

This project was my first vacuum tube/valve project.
 
Thank you for the answers!
In the last month I have surfed the web but I could'nt find a 50W DIY tube amp kit and my post was much like a last hope query :)
Now I'm pondering to build a solid state final amp (gaincone ones? Lynx v3.0?) with a tube preamp... is this total weird? I mean, in this way I should have some of the tube audio characteristics with the solid state power.
 
Thank you basstard (nice nick :)
Yes my Rhodes is mono... I'm a little bit confused but I'm slowly undestand what I need.

In the meantime I have found Schematics Heaven and throroughly surfed it. As usuall I have another lil' question:
In quite every schematic it isn't specified the transformer data: how can I determinate which is the right one? In example: In the Marshall 1987 Lead 50W there are 3 transformer but I have no clue of their technical data.

I know I know, I'm the newbye epitome but I really don't like to post several times in a forum with lots of questions...
 

basstard

Member
2008-01-19 12:33 pm
ok, so you can go mono and get no prob mate,,,
I don't know the frequencies these things generate but I'd say you'd better go for a bass amp. A bass can generate from say 20-30Hz up to 8-10KHz so if you get a decent cab that covers the whole range you can get covered almost all of the frequencies you need.
A guitar can generate frequencies from say 160-200Hz up to 10kHz so if you need lower freqs you're not sure to get them with a guitar amp,,,
Or else you could use a guitar amp and modify it to get more lows,,, depends on what you like best really.

In the specific schematic you posted I can only see the 6.3v indicated [that's for the filaments]. What I normally do, is see what voltage is indicated on the schematic just after the transformer and then I buy an adequate transformer that can keep also with the current drawn by the circuit.
This is what I do, maybe there's a more scientific way I don't know of.

If you need to be pointed to some transformer seller/manufacturer in italy just tell me.
 

Brett

Member
2002-01-07 6:02 pm
frarobertooo said:
Thank you basstard (nice nick :)
Yes my Rhodes is mono... I'm a little bit confused but I'm slowly undestand what I need.

In the meantime I have found Schematics Heaven and throroughly surfed it. As usuall I have another lil' question:
In quite every schematic it isn't specified the transformer data: how can I determinate which is the right one? In example: In the Marshall 1987 Lead 50W there are 3 transformer but I have no clue of their technical data.

I know I know, I'm the newbye epitome but I really don't like to post several times in a forum with lots of questions...
Ask around on one of the MI forums to see what voltage the B+ is: someone will know. Then look for an off the shelf power Tx to suit. The choke will simply need to be adequate depending upon the supply needs; again look at tube datasheets and look at the total current for the output stage as suggested by the tube manufacturer; they'll often be very close. The filament currents can be worked out form the tube datasheets.

Marshall PS and OPT's can be found aftermarket from places like Heyboer, but they're expensive usually.

Do not 'improve' the PS with a bigger TX, caps etc, or the OPT with a hifi specified design as part of the sound is due to underspecified components leading to PS sag under load and OPT's saturating. Either clone it and get as close to possible Marshall sound, or scratch build something else.

Unless you're playing loud metal with no FOH PA, I've never seen the need for 50W in reality.