How much of a beginner? If you have never done any construction, then obviously go with something a good deal simpler. If you are that new, then you shouldn't be considering a 30WPC stereo amp anyway. If you've had some solid state experience, and don't burn up components while soldering, and can figure out where to put the parts on the circuit board, it should be doable.
This particular design doesn't operate at extreme voltages, which is a definite advantage. You shouldn't consider something like an 845 SET that runs 1.0KV for a first project.
If you are a very new beginner, then perhaps something like that Tube Lab Simple SE would be more suitable.
Fyi, take a look at my post in Swap Meet, I still have a couple of those chassis available, perfect retrofit for ST-70 iron! Also associated parts for toobe amp DIY. More room on this chassis, looks great, and it opens more options.
As far as the ST-70's quality, the weak points are the driver circuit (awful) and the power supply.
If you get those two things straightened out, and you strap the output tubes for triode, you get a very good quality PP amp. I'll say 76.5% of the total potential for tube amps, not too shabby.
The good part of the ST-70 is that arguably it is the best iron that Dyna made, and isn't too bad at all. Some people like the SCA-35's iron better, but it is much lower power.
Nothing wrong with upgrading a ST-70, but it's sort of like asking "how good is this old Chevy?" If you upgrade the old Chevy enough, at what point is it a very low % Chevy and it becomes something else? Which, of course is fine... and you have to start with something and stay within a budget, so it is a good place to start and get a decent result.
🙂
_-_-bear
As far as the ST-70's quality, the weak points are the driver circuit (awful) and the power supply.
If you get those two things straightened out, and you strap the output tubes for triode, you get a very good quality PP amp. I'll say 76.5% of the total potential for tube amps, not too shabby.
The good part of the ST-70 is that arguably it is the best iron that Dyna made, and isn't too bad at all. Some people like the SCA-35's iron better, but it is much lower power.
Nothing wrong with upgrading a ST-70, but it's sort of like asking "how good is this old Chevy?" If you upgrade the old Chevy enough, at what point is it a very low % Chevy and it becomes something else? Which, of course is fine... and you have to start with something and stay within a budget, so it is a good place to start and get a decent result.
🙂
_-_-bear
I wonder if those folks are really hearing the iron, or if it might be the tubes? It's my belief that the 6BQ5 is the most dynamic pentode ever made.
I was walking out the door when responding to the last posts and did not read properly...
Your suggestion to use triode rather than U/L makes sense and will be easy to implement. Construction has not commenced yet. I am hoping to start the power supply next week. I hope that fixed bias and adjustable current sinks will make experimenting/adjusting for best performance easy.
As for Eli's suggestion of 7591, I have a quad ready to go and have sketched out a drawing of a (lockable) switch arrangement to be able to switch between 6L6 types and 7591. Also have a few quads of 6BG6GAs and adaptor bases, so plan on experimenting a little.
Regards,
Chris
I've read lots of high praise for your El Cheapo, for which I can find lots of info, but I can't seem to find much on the Grande version. Is there a dedicated thread/web page for this design? I love things that are El Cheapo!
I'm slowly working my way through that thread you linked and it looks like a really interesting project. It might be a stretch for me and would probably take some serious time/effort/thought but it could be a lot of fun.
Since you said you are starting construction soon I'm assuming you are not waiting for the Tubelab board to come out; are you doing the entire thing P2P?
I've reverse engineered a Z-565 and a couple A-470's. The Z-565 is superior iron.
diytube.com :: View topic - Z-565 Windup
diytube.com :: View topic - The A470 OPT, an interesting work of art.
Cheers!
No, I am not waiting for the Tubelab board. I am going to construct in modules on vero board and point to point. At this stage a power supply board with the B+ regulator and the +/- 155V, a board with the mosfet source followers and a bias board. Probably a turret board or tag strips for the ancillary components.
Construction will be mono block in aluminium chassis. Will post on the 6L6 thread when construction begins.
Cheers,
Chris
Construction will be mono block in aluminium chassis. Will post on the 6L6 thread when construction begins.
Cheers,
Chris
That (very long) thread goes through the design of an amplifier from the conceptual stage up to a working amp. There were a few places where the circuit went through some changes, but that is part of the design - build - test - listen - modify cycle. Like most projects it went through periods of serious activity, then it went dormant. Then it woke up again, and went back to sleep.
It looks like Chris is getting back to his build. Last September I built a breadboard with two tested and working driver boards and two dual octal tag boards for the output tubes. It sits on the shelf and screams at me to fire it up, but that hasn't happened yet. After the Simple P-P stuff is done, I will plug it in.
There is (or was) one in existence. I was getting stupid amounts of power (60 watts) but I was "bending" the tube specs a bit. Listening tests were very promising. The modifications to the basic build were fairly easy (you leave stuff out). I am planning to build a complete amp based on this concept, which will be documented and posted. Building seperate mono blocks would be fairly easy. A single stereo amp using one power transformer to run two boards poses a bigger challenge. There will be a seperate thread about this amp in the Tubelab forum. Stay tuned.
I did some experiments along those lines a while back. There was a thread here too. It drew no interest so I didn't take it much further. The Simple SE doesn't have a phase splitter on the board. I hacked up the board several different ways to make one. These modifications all worked, but weren't exactly "Simple".
It is a really easy thing to do if you use an external phase splitter. There are two ways to do this. If your source can handle running into a transformer, you can use a transformer to do the phase splitting. My Phono stage does not like the $11 Edcor WSM15K/15K connected to its output, but the CD player doesn't mind. I have also used an external phase splitter circuit to drive the Simple SE.
The Simple SE board can be connected to a single P-P output transformer and an external phase splitter (transformer or active) to make a P-P amp. No modifications to the Simple SE board are needed. Power output depends on tube choice. I would expect 20 to 30 WPC in triode, 40 to 70 in pentode.
Again a mono block version using the Allied 6K7VG transformer is easy. Finding one power transformer big enough to run two channels would be tough.
I made myself a guitar amp using a preamp board with a phase splitter on it. It is connected to an unmodified Simple SE board running cheap 6L6GC's in pentode mode and it cranks out about 60 watts. It has performed flawlessly for about 2 years despite my numerous attempts to blow it up! It really screams too. The power supply on the Simple SE runs the preamp too.
I have been down this road too. It is (or was) a fairly common thing to buy an old Camaro, strip out the old drive train and replace it with modern components. Then you realize that the old drum brakes can't stop a 450 horsepower car, so you replace them. Then comes the steering, then....... At some point you will have a very nice Camaro, but it isn't a 68 Camaro anymore, and it costs more than a brand new one. Finding a decent 68 Camaro to start with isn't cheap any more.
I bought a Dynaco ST 70 at a rummage sale for $40. It actually worked too. I planned to to the rebuild thing, but the project never got started. I realized that I enjoyed making my own designs more than tinkering with someone elses. I sold it to another forum member who planned to do the same. I don't think he ever got started either. Like the old Camaros, the price of decent Dynacos has gone up. It may not be economical to rebuild, and like the old Camaros, you are still dealing with 40 year old iron too. Also like the 68 Camaro it is possible to build an entire "Dynaco ST 70" with all new parts.
Tubelab. You got rid of a working stereo 70 that you paid $40 for?? Madness. At the very least you got some great transformers for a song. A working Stereo 70 should be (notice I said should be) worth at least around $240 which is the approximate value of the three transformers if working. You can design and build your own nice amp with that iron if you want to.
from what I've read the shortcomings of the ST70 are undertated power transformer and poor quality output transformers (the bullk of hte cost of an amp).
What problems does the 1.5H choke pose problems over say a 7 -10H choke?
What problems does the 1.5H choke pose problems over say a 7 -10H choke?
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I PAID $40 for it. I didn't sell it that cheap! It was a few years ago and I sold it for a reasonable price at the time (don't remember the exact deal).
Dynaco ST 70 iron is regarded as good sounding, but easy to damage if overstressed.
there are several companies selling aftermarket "replacement" power iron for the ST-70, bulked up considerably. A good thing.
the output iron is good.
in input/drive circuit is not good.
the PS "choke" is a goof, as is the amount of PS capacitance. Of course the choke is better than a resistor in the same place, imo.
Oh, the "76.5%" is rounded up... 😉
the output iron is good.
in input/drive circuit is not good.
the PS "choke" is a goof, as is the amount of PS capacitance. Of course the choke is better than a resistor in the same place, imo.
Oh, the "76.5%" is rounded up... 😉
My ST-70 has Uncle Ned's driver board and Sheldon Stokes' PS board. It sounds pretty fine to my ears.
I'm curious on this one too. I used EDCOR in my Simple SE and so far have been really pleased/impressed but that is my only experience with OPT's. The EDCOR offerings seem like they would save you some decent money compared to the reissues at Triode Electronics.
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