|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
72.201.10.143
...please correct me if my informaton is incorrect,which tube diode (used as a rectifier in a full-wave supply) would not be damaged by use with a large power supply transformer with a secondary having less than 100 ohms resistance? I am told on the tubediy that to go with a power transformer with a lower DCR secondary requires going to SS (FRED's), that tube diodes will not last. I really would prefer not to go to SS in the PS, but I do want full wave rectification of a low DCR power tx.
Can anyone give me clarity on this topic? Thanks very much. :)
"It ain't a comeback until it's left the shop" Jimmy Dunne, the first man to drive a VW Beetle faster than 200 mph, and he has the forehead scar to prove it; I will always honor him for taking a chance on me when I wanted to be an engine mechanic.
Follow Ups:
as usual:) If you are going down this "low DCR" path because you want to try it out, great. But if you just want to build good sounding amps without a lot of wasted time and money I'd say don't bother. As you can tell the preacher don't know the whys. Plenty of other time proven designs where the whys are already known. It is one thing to try skinning the cat another way for the heck of it. Quite another to reinvent the wheel. So ask yourself just what you are trying to do and why.You can make a good sounding amp with either a cap or a choke input filter and with either tube or silicon rectifiers. The general feeling is choke input and tube rectifiers are worth the extra cost and lower B+.
....to go ahead with winding my own lower DCR chokes, but I'm just going to use the regular choke input critical inductance formulas; I have all the glassware tubecad software, hopefully in there somewhere should be power supply design help. I'll breadboard it, measure ripple and play a little, and when I'm satisfied go ahead. I really like these Lundahl interstage transformers; I am seriously thinking of just using an interstage tx to go from the guitar amp overdrive/tone section then through a clean drive tube and use the interstage to then drive the 300B for the single ended output. I'll also use a phase splitter tx to drive the PP pair of 300B's for the gig boost stage for the additional 4x12" gig speaker cabinet.This whole low DCR thing in the end has just petered out; I really appreciated the post of the fellow who pointed out that Dennis has been doing this as a full time job for years, without some sort of rationale how are we part timers possibly to get anything accomplished?
It certainly makes sense to have a lower DCR choke for a choke input filter, and keep it low DCR within reason, but beyond that it does seem just out of proportion and a ton of bandwidth for...nothing tangible. I have been debating explaining to Jeff that I can tell he's autistic like me, but I don't want to hurt his feelings. I can see all the signs though: fanaticism around an internalized idea that can't be expressed in a way anyone else can understand, the lack of a pause button along with a tendency to emotionally over-react to things that are taken the wrong way to start with (I have really been working on this pause button thing myself; email and internet forums are brutal places when you don't take the time to think through what you're saying), the tendency to make everything black and white, accidentally offending other people when you absolutely don't mean to but are just thinking out loud (without first pushing aforementioned pause button), etc, etc.
I will in the future devote some play time to my shot-in-the-dark "ratio rules" to see if there is some possibility of acceptably reducing ripple while at the same time maintaining very low DCR, H and C, but you're absolutely right - there are so many issues in an amp that wasting time on this goose chase is just silly. I bought a 193...4? I forget - it's now in some stack around here - RCA tube handbook, and I was so impressed by all the very cool information in it - these guys knew their stuff!! I found some great ideas in there that I think will apply wonderfully to my next version of Max's guitar amp - who woulda thunk?
The fact is, this realization came to me about the same time your post, Max's 6L6 triode-strapped single ended guitar amp sounds FABULOUS with a plain old RC high DCR power supply and cheap tx's for both power and output, so why in the world am I getting hot and bothered about low DCR? In fact, I replaced the cheap 125 series Hammond output tx with a decent one from Angela, and Max complained, told me he liked the tone better with the cheap Hammond! So I put it back in, and he's happy again. So there you go.
Thanks for all your advice, I have really appreciated every bit of it. By the way, do you have a suggestion for what driver tube I should use to drive the interstage tx to drive the 300B single ended? You see, the way I'm doing it is this: I'm using the 12AX7's and 12AU7's for overdrive distortion and tone controls and reverb, but I want the final driver/interstage tx/output tube SE stage to be clean. In this second version I'm changing from the 6L6 to the 300B for the output tube; want that DHT true-triode magic. I'll keep Max happy by modding the overdrive stages for as much distortion as he could possibly want (I'm not only going to have positive feedback to the grid, I'm also going to play with cathode feedforward overdrive), but I want the output stage triode clean; this way I can switch the preceding stages so he can go super clean or super distorted or any variation in between; by keeping the single ended output stage clean I can then add a gig boost stage without losing tone. Sorry for how long this is; I got on a roll!! I am just fanatically in love with the sound of harmonic distortion in a guitar amp through triodes....and that's not ALL autism.
Best!!! Charles
"It ain't a comeback until it's left the shop" Jimmy Dunne, the first man to drive a VW Beetle faster than 200 mph, and he has the forehead scar to prove it; I will always honor him for taking a chance on me when I wanted to be an engine mechanic.
You'll have to use choke input or limit the input cap size. Use Duncan Amps PSU designer to make sure peak current stays within rating of recitifier tube(parallel tubes if you REALY want low supply impedance).
...that kills the tube diodes!!! I didn't understand that. I also now see why it's probably better in the overall picture to go with a center-tapped secondary and two diodes for full wave instead of a non-center-tapped secondary and a four diode bridge; otherwise the power goes through two diodes in series. It doesn't hurt the tx to have the power go back and forth between two halves of the secondary; it's just more wire to get to the same desired resistance.I don't have a problem parraleling the power tubes; in terms of the whole cost of a really good amp (in this case seriously over the top guitar amp, but same deal) it's only an extra thirty or forty bucks including sockets. I'll save that winding my own chokes.
Cool. Thanks. The clarity I get from helpful people like you is just precious; now I know precisely how to proceed. Now that I finally have a digital camera I will get some pictures posted of Max's first guitar amp; it looks god-awful but sounds like heaven. :)
"It ain't a comeback until it's left the shop" Jimmy Dunne, the first man to drive a VW Beetle faster than 200 mph, and he has the forehead scar to prove it; I will always honor him for taking a chance on me when I wanted to be an engine mechanic.
This post is made possible by the generous support of people like you and our sponsors: