Impedance difference
Would you suggest then that the A470 and A420 are (somewhat) interchangeable? Would the impedance difference affect the operational curve of the plate(s)?
Things that make you go, "hmmm".
What makes the 420 your fav? Aside from the higher impedance, what makes it a good choice?
I wonder how the A420s would work in the ST-70...
Just thinking outloud...
Brian
Would you suggest then that the A470 and A420 are (somewhat) interchangeable? Would the impedance difference affect the operational curve of the plate(s)?
Things that make you go, "hmmm".
What makes the 420 your fav? Aside from the higher impedance, what makes it a good choice?
I wonder how the A420s would work in the ST-70...
Just thinking outloud...
Brian
Re: Impedance difference
hey-Hey!!!,
The impedance difference is enough to change the oeration slightly, and in a good direction I think. Try drawing half a 4k3 line( 2150 Ohm slope) and one at 3300 Ohms slope on the EL34 curves; the difference is slight.
Now for an AB amp there will be a further change to 1/4 of the a-a impedance as one power tube gets cut off, and that complicates things significantly to make a solid accounting of that effect. The higher load will have more power while both tubes conduct.
cheers,
Douglas
brosenau said:Would you suggest then that the A470 and A420 are (somewhat) interchangeable? Would the impedance difference affect the operational curve of the plate(s)?
Things that make you go, "hmmm".
What makes the 420 your fav? Aside from the higher impedance, what makes it a good choice?
I wonder how the A420s would work in the ST-70...
Just thinking outloud...
Brian
hey-Hey!!!,
The impedance difference is enough to change the oeration slightly, and in a good direction I think. Try drawing half a 4k3 line( 2150 Ohm slope) and one at 3300 Ohms slope on the EL34 curves; the difference is slight.
Now for an AB amp there will be a further change to 1/4 of the a-a impedance as one power tube gets cut off, and that complicates things significantly to make a solid accounting of that effect. The higher load will have more power while both tubes conduct.
cheers,
Douglas
Bandersnatch said:
Curious. I've got a set of Hammond 1620 which are 6600 ohms. I bought them for a PP EL84 project, where they seemed to function acceptably. I did notice they are "louder" than the set of Z565 equivalents which eventually replaced them. I always attributed this to the difference in impedance ratio (the Z565 are certainly a bit higher than 6.6k ohms on the primary for a given secondary load).
I'm sometimes wondered what tube they had in mind when they wound the Hammond 1620.
Just noticing something
I often use tube operated equipment (or pictures of them) on my desktop. After I booted up this morning, I was looking at a perticular model of CD player that uses tubes for its output stage. This model (and many others) also has output transformers.
Now, I'm sort of guessing that the typical outpuit impedance level of these devices is between 5 & 10K ohms at line level (between 0 and 2.5 volts).
My question is - why would these units utilize output transformers when they could simply use an emitter-follower buffer style connection?
Here's the web site for a unit in question...
http://images.google.com/imgres?img...+amplifier&start=108&gbv=2&ndsp=18&hl=en&sa=N
I often use tube operated equipment (or pictures of them) on my desktop. After I booted up this morning, I was looking at a perticular model of CD player that uses tubes for its output stage. This model (and many others) also has output transformers.
Now, I'm sort of guessing that the typical outpuit impedance level of these devices is between 5 & 10K ohms at line level (between 0 and 2.5 volts).
My question is - why would these units utilize output transformers when they could simply use an emitter-follower buffer style connection?
Here's the web site for a unit in question...
http://images.google.com/imgres?img...+amplifier&start=108&gbv=2&ndsp=18&hl=en&sa=N
Hey Burnedfingers,
It looks pretty similar to a driver board I had and researched. Have a look at this thread and see if it is the same.
Thread on mystery board
It looks pretty similar to a driver board I had and researched. Have a look at this thread and see if it is the same.
Thread on mystery board
Burnedfingers,
If those are 6DJ8 or relatives, it looks like the first GSI board by Andy Fuchs. Probably a later version of the NYAL board. Andy worked there back in the day. I have a simple schematic of it somewhere. You might try Andy at Fuchs Audio Technology, does guitar amps now but still might help, at least with some info. If not I'll try to dig up what I have, I have lots of info on his second mod., 12AX7s and 6CG7s.
Craig
If those are 6DJ8 or relatives, it looks like the first GSI board by Andy Fuchs. Probably a later version of the NYAL board. Andy worked there back in the day. I have a simple schematic of it somewhere. You might try Andy at Fuchs Audio Technology, does guitar amps now but still might help, at least with some info. If not I'll try to dig up what I have, I have lots of info on his second mod., 12AX7s and 6CG7s.
Craig
Burnedfingers,
All I ever had of that circuit was what Andy drew for me years ago. There were a few part(s) values on the schematic and not much more, I'll dig it up, it may have some value to you. We were conversing back and forth back in '90/'91 when I was in the Gulf playing war. I got a few of the newer boards and was asking about the old circuit. Still have one set of the newer boards.
Craig
All I ever had of that circuit was what Andy drew for me years ago. There were a few part(s) values on the schematic and not much more, I'll dig it up, it may have some value to you. We were conversing back and forth back in '90/'91 when I was in the Gulf playing war. I got a few of the newer boards and was asking about the old circuit. Still have one set of the newer boards.
Craig
ST-70 (needs & ideas)
I e-mailed them a few weeks ago. They no longer sell parts of the chasse any more - it just wasn't cost effective for them.
Just a thought though - I noticed a lot of hoopla about keeping the St-70 stable in regard to bias current. While the bias pots add versatility and variability (somewhat), wouldn't it be a good idea to throw in a couple of zener diodes to stabilize the current? It just seems like a cost-effective and logical solution...
B
I e-mailed them a few weeks ago. They no longer sell parts of the chasse any more - it just wasn't cost effective for them.
Just a thought though - I noticed a lot of hoopla about keeping the St-70 stable in regard to bias current. While the bias pots add versatility and variability (somewhat), wouldn't it be a good idea to throw in a couple of zener diodes to stabilize the current? It just seems like a cost-effective and logical solution...
B
Just finished my first Dynaco ST-70
I just finished my first Dynaco ST-70 last night. After a quick test, I discoverd that I missed a wire on the multi-terminal lug giving the bias circuit a proper ground. Now it sounds much better.
OK, it's official - I'm hooked!
I only modded the main cap and upgraded a couple of the electrolytics that looked old. Next, I'm going to mod the EL-34s to run in the more pure (but less powerful) mode.
I got such a rush from the clean sound, I could hardly sleep last night. It was almost better than...OK, it was a close second.
Have a great day!
I just finished my first Dynaco ST-70 last night. After a quick test, I discoverd that I missed a wire on the multi-terminal lug giving the bias circuit a proper ground. Now it sounds much better.
OK, it's official - I'm hooked!
I only modded the main cap and upgraded a couple of the electrolytics that looked old. Next, I'm going to mod the EL-34s to run in the more pure (but less powerful) mode.
I got such a rush from the clean sound, I could hardly sleep last night. It was almost better than...OK, it was a close second.
Have a great day!
Well, I can't see doing much else (besides flying) that give's me a warm fuzzy these days. It's good to have a hobby that keeps me home instead of gallivanting the neighborhood.
Incidentally, I was wondering how many people got into this trend and ended up building just about everything from kits or from scratch? I bought a nice little cathode-follower board that I'm going to turn into a pre-amp. I thought it would be a nice next project to accompany the amp.
B
Incidentally, I was wondering how many people got into this trend and ended up building just about everything from kits or from scratch? I bought a nice little cathode-follower board that I'm going to turn into a pre-amp. I thought it would be a nice next project to accompany the amp.
B
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