Cool! That would be great!
Well, I have a paair of 100K stepped attenuators and I was planning to use those, but would they work OK? Would I still need to eliminate the 47K input resistor? Should I add a resistor in parallel to get back to ~50K for the input?
Also, could you let me know how much you paid for the Tribute autoformers? I saw the price of the S&B and I thought I'd comparison-price shop for the future.
I've looked at that and it seems pretty nice.
Hmmm. an interesting consideration...
Kofi
Kofi Annan said:
Depends on the type of attenuator, or whether they are constant impedence or vary according to the setting. You want the input impedence high enough so that your source is happy (10-20k is ok for most CD players, though the higher value might sound a bit better), but low enough so that any electrons collecting on the control grid have an easy enough path to ground. That depends on the tube and operating conditions. You might get away with 100k just fine. Try it, it's not a big enough difference to suddenly send things over the edge. Or, yes, you can put a 100k in parallel to get to 50k (nothing magic about 47k, it's just a common value around 50k).
Sheldon
dear experts
I have a D3a / 300B amp with a interstage transformer. The D3a is in triode mode. Is it useful to try the d3a as a pentode in this application ? Or can you say on forehand that the sound will be worse ?
Is hanging a CCS under the cathode of the d3a a useful idea ?
These could also be questions our worldpeacekeeper
could be interested in
regards
I have a D3a / 300B amp with a interstage transformer. The D3a is in triode mode. Is it useful to try the d3a as a pentode in this application ? Or can you say on forehand that the sound will be worse ?
Is hanging a CCS under the cathode of the d3a a useful idea ?
These could also be questions our worldpeacekeeper
could be interested inregards
Attachments
Hi Jaap (and others as well),
Kinda nice to see an old doodle I drew up years ago pop up once again. Now to adress your question... A pentode has a very high source impedance, which may even be considered to be infinite in "quick and dirty" type calculations. If you connect a choke (being the primary of the interstage) to an AC source with infinite impedance, you'll get a response that starts at 0 (or minus infinite dB) and rises with 10dB per decade ad infinitum. You made a mathematically perfect differentiator. Of course, in reality the tube has a finite impedance and there are more impedances as well which play a role, but generally an interstage transformer will deliver better bass when driven by a low impedance source such as a triode.
Or, you could also load the interstage with a resistor at either the primary or the secondary side (i'd opt for secondary). This makes the -3dB point well defined, and guarantees a more constant gain figure above the -3dB point. As you have a 1:1 interstage, the minimum value for the load resistor can easily be determined: it is the voltage swing required to fully drive the power triode, divided by the standing current of the driver tube. Experiment with values going up from there. As you already have the tubes wired up, I'd suggest just doing the experiment and let your ears decide what they like best.
Regards,
Jurgen
Kinda nice to see an old doodle I drew up years ago pop up once again. Now to adress your question... A pentode has a very high source impedance, which may even be considered to be infinite in "quick and dirty" type calculations. If you connect a choke (being the primary of the interstage) to an AC source with infinite impedance, you'll get a response that starts at 0 (or minus infinite dB) and rises with 10dB per decade ad infinitum. You made a mathematically perfect differentiator. Of course, in reality the tube has a finite impedance and there are more impedances as well which play a role, but generally an interstage transformer will deliver better bass when driven by a low impedance source such as a triode.
Or, you could also load the interstage with a resistor at either the primary or the secondary side (i'd opt for secondary). This makes the -3dB point well defined, and guarantees a more constant gain figure above the -3dB point. As you have a 1:1 interstage, the minimum value for the load resistor can easily be determined: it is the voltage swing required to fully drive the power triode, divided by the standing current of the driver tube. Experiment with values going up from there. As you already have the tubes wired up, I'd suggest just doing the experiment and let your ears decide what they like best.
Regards,
Jurgen
It is nice to "meet" the designer of that doodle. What does it sound like Jaap and or Jurgen?
Maybe we should split Jaap's amp thread from Koffi's? (Even though Koffi might be interested)
Maybe we should split Jaap's amp thread from Koffi's? (Even though Koffi might be interested)
Re: dear experts
Konnichiwa,
While the ultimate answer broadly relates to personal preference, in a limited sense.....
No footballing way.
Basically, pentodes like strictly resistive loades, triodes just love reactive loads.... (okay, it's the exec summary, reality is slightly more complex, I know, so don't beat me too much.)
Depends upon use. In your case, most likely no.
Do us a favour (nothing personal - general - if I may be forgiven). A lot of good material is referenced in one of the local sticky thread. Applying oneself to the context is highly utilitarian and on top of it very spiritual....
Sayonara
Konnichiwa,
Jaap said:
While the ultimate answer broadly relates to personal preference, in a limited sense.....
No footballing way.
Basically, pentodes like strictly resistive loades, triodes just love reactive loads.... (okay, it's the exec summary, reality is slightly more complex, I know, so don't beat me too much.)
Jaap said:
Depends upon use. In your case, most likely no.
Do us a favour (nothing personal - general - if I may be forgiven). A lot of good material is referenced in one of the local sticky thread. Applying oneself to the context is highly utilitarian and on top of it very spiritual....
Sayonara
Hello (jurgen) Timpert, bas H and the rest of the world,
The Timpert amp sounds really good. They should of course, I built them as monoblocks with each two powertransformers, and four chokes. Add to that a big Amplimo toroid OPT and a Tribute IT and you will realize that transport is out of the question. I will have to live with that amp the rest of my life I suppose.😀
The Timpert amp sounds really good. They should of course, I built them as monoblocks with each two powertransformers, and four chokes. Add to that a big Amplimo toroid OPT and a Tribute IT and you will realize that transport is out of the question. I will have to live with that amp the rest of my life I suppose.😀
Hi,
Sorry about the slightly off topic reaction, but I just felt the urge to respond. Perhaps a little vanity thing going on here...
Jurgen
Sorry about the slightly off topic reaction, but I just felt the urge to respond. Perhaps a little vanity thing going on here...
Jurgen
Konnichiwa,
You typhically want to "underheat" valves at the datasheet limit.
If you do, they live longer (400%) and vary less in terms of Gm etc. over their life. The datasheet limit for 6.3V Valves is 5.7V.
In my case the 5.5V winding on the lady day transformer gave me nearly 6V under load, so even a little high. Get the transformer wound any way you like, just make sure to heat valves at the lower datasheet limit (+/-5%).
Sayonara
Kofi Annan said:
You typhically want to "underheat" valves at the datasheet limit.
If you do, they live longer (400%) and vary less in terms of Gm etc. over their life. The datasheet limit for 6.3V Valves is 5.7V.
In my case the 5.5V winding on the lady day transformer gave me nearly 6V under load, so even a little high. Get the transformer wound any way you like, just make sure to heat valves at the lower datasheet limit (+/-5%).
Sayonara
Woo hoo!
Got the power transformers from Jack yesterday. They're pretty damn huge. My wife picked up the package and broke eight vertebrae! Ouch!
Pictures to follow...
Kofi
Got the power transformers from Jack yesterday. They're pretty damn huge. My wife picked up the package and broke eight vertebrae! Ouch!
Pictures to follow...
Kofi
Good to see you back in action. As you have no doubt found, Jack's bark is much worse than his bite, so to speak, but you can be sure he won't undersize a transformer. And you can be sure it won't run hot. So get going. I'm curious to hear this thing, if only via hearsay, which you must deal in often.
Sheldon
Sheldon
Agreed. I said, "I know you don't approve of this design" and he said, "well.... I forgive you." <sniff>.
And how! They're the size of the Space Shuttle!
Me too, but I still have a lot of parts to cobble together. Its gonna be a while, but I'll note progress as I make it. Next step: Lundahl OPTs.
Kofi
So...
I'm thinking that I'll go with the TJ "Full Music" mesh plate (well, punched plate) 300b gold for the tubes, but I'd be willing to hear impassioned recommendations for 300bs as long as they don't break the bank.
Well?
WELL???
Kofi
I'm thinking that I'll go with the TJ "Full Music" mesh plate (well, punched plate) 300b gold for the tubes, but I'd be willing to hear impassioned recommendations for 300bs as long as they don't break the bank.
Well?
WELL???
Kofi
OK, so its been a while.
Mrs. Annan and I are saving some cash for an important event so I need to carefully, but deceptively, buy parts over time and have them shipped to a non-disclosed location and smuggled north.
Anywayze, I'm thinking my next purchase should be the choke load, so that's the next step, but I'd still like to know if anyone has had any positive / negative experiences with the TJ Fullmusic 300b. If so, which one should I try for? Does the gold pinned job sound better? Meshplate?
Anyone know any smugglers?
Kofi
Mrs. Annan and I are saving some cash for an important event so I need to carefully, but deceptively, buy parts over time and have them shipped to a non-disclosed location and smuggled north.
Anywayze, I'm thinking my next purchase should be the choke load, so that's the next step, but I'd still like to know if anyone has had any positive / negative experiences with the TJ Fullmusic 300b. If so, which one should I try for? Does the gold pinned job sound better? Meshplate?
Anyone know any smugglers?
Kofi
Anyone on the opinion of the TJs? Kind of interested in these and I'm looking for anyone with good / bad experiences.
Kofi
Kofi
Would this link help MrAnnan?
http://www.enjoythemusic.com/magazine/equipment/1201/300b/
Ciao
Gianluca
http://www.enjoythemusic.com/magazine/equipment/1201/300b/
Ciao
Gianluca
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