DIY Audio Projects Forum

I want to build a ul stereo amp like the lacewood2 or marblewood amp. I already have the hammond 270fx transformer, 275-0-275@150ma. 6.3v @5 amp, 5v@ 3a. This leaves me using a 5v rectifier. My questions are: 1) it looks as though I would have about 50ma of B+ to spare. Could I use that to supply a buffer, phono preamp and tone stack.
I am looking at buffer, phono preamp and tone stack designed by E.J. Jerrich. He lists them as requiring 250-300vdc@40ma. Would they be compatable? 2) is it feasable to use common ps and build buffer, phono preamp and tone stack on seperate chassis from main amp? Any thoughts? All suggestions would be greatly appreciated.

You can run transfomers at near maximum ratings
From exprience I had been running cheapo chinese transfomers slightly past ratings with more voltage drop on b+ but it dosen't heat up past 50c on 20c ambient so it will last long .

Transfomers last long up to 50c, 60c or higher then you risk damage. Its the temperature that matters.

Things don't get hot as long as you only get one set of winding near max power. Both 275v and 6.3v windings ran near limits then it could get very hot.

If running all on one power supply will cause heat problems and everything else would work I do have another power transformer. I could build a seperate ps for the buffer, phono preamp and tone stack. The 270dx is rated 550vct@90ma, 5v@2a and 6.3@3amp. Maybe a 5y3gt sovtek rectifier. Just trying to avoid extra choke. Nothing at this point is written in stone. I am open to all advice and opinions and appreciate it very much.

Hi, If you use solid stage rectifiers the loading will be less and the B+ higher. All my designs are SS rectified and when done right are extremely quiet and reliable. I am aware of the tube vs SS rectifier disagreements but I honestly can not hear the difference between well implemented versions of either type. YMMV.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

What you want to do is entirely feasible and can be made to work well.

That being said, Please allow me to provide another perspective. First, these two projects (power amp and buffer/preamp) will not be your last. The odds are that more equipment will be in your future simply because you'lI soon find that you want to try something else or compare different things for yourself rather than relying entirely on the opinions of others. Or it may be that, like so many of us, you soon find the process of building your own equipment to be incredibly addictive. Also, I have found that there is enormous satisfaction in the process of growing and evolving your systems; swapping out an preamp here, a tone stack there, trying different power amps, even trying specialized tone shaping circuits.

All of this will be much easier, and much more satisfying with each building block acting as a standalone entity in your system. They are some projects around the forum where preamps of various kinds have been married to power amps within a single chassis. However, I would put forth that such projects should be left for the future; after you have refined your wants and desires, and really decided what type of building blocks you want to integrate together.

So my advice to you would be to build the projects as separate units. At this stage, the flexibility preserved will be well worth the marginal extra effort and cost. It's just my opinion, of course. But at least please consider what I've said before you make your final decision.

And above all, enjoy the process.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog

All suggested replys are greatly appreciated. In the past I have used silicon rectification as well as tube rectification. I like both but am wanting to go with tube rect on this go around. I do have seperate pt's available.
I really like both the lacewood and marblewood amps Matt. I love the tube rolling ability with the marblewood and therefore will almost certainly go with that for main amp. That choice will definately require seperate ps to meet the demands of say 6l6 tubes.
This is my first time of multiple circuits. I have in the past built a few guitar and radio amps. Also several tube am radios from regens to superhets. Suffered a few failures along the way too. Age has taught me asking for help is much better than hard knocks lol.
Stand alone it will be. I will be ordering ot's and chokes soon. I will build amp first. You folks are the greatest.

From exprience valve rectifiers make your music slightly more warming even after regulation with solid state devices to reduce noise.

Matt and others, I think I am going to go with a 5ar4 rectifier on this build. Have gone with all other ps design for marblewood. Do you see any reason to not use this rectifier tube? Chose octal socket and using 5v winding for heater. Also, tube data lists limiting resistors for each plate. It looks like I would need 100 ohm for each plate. Does that sound correct and what wattage do you suggest?

If you know the maximum current in the build and you know the maximum power rating of the resistors then you can find suitiable resistance using i^2*R
http://www.sengpielaudio.com/FormulaWhe ... ronics.gif

Just keep in mind the extra voltage drop due to resistor and the rectifier internal impedance, this can be monitored by current in the build times resistance V=IR

I don't see any reason not to go with the 5AR4/GZ34.

Don't worry about the output curves on the data sheet. Just run both plates directly off the transformer and put a single dropping resistor downstream of the first capacitor like it shows in the schematic. You might also want to reduce the first reservoir cap from 47µf to 33µf. This will increase the conduction angle and soften the current spikes in the transformer secondary. Some rectifier data sheets make a big deal about total plate resistance, but modern transformers generally have adequate secondary resistance and so long as you don't use too large a reservoir capacitor, the rectifiers are fine. Especially in a low current design like this one.

The total current's vary based on what power tubes you use but worst case current, in my build with the 6W6s, was a little over 105mA. So with a 350Ω resistor like the one I used, about 4W. I used a 350Ω 5W power resistor for about 20% margin. My guess is that the GZ-34 will give you a final B+ about 10 volts higher than the 6CA4 in this design. As such you might want to lay in both 350Ω and 390Ω power resistors and see which one gives you better voltages.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog