Renron said:
Isn't the input impedance defined by R1 in the circuit (1Mohm?)
According to the wiki http://en.wikipedia.org/wiki/Valve_amplifier valves in general have very high input impedance (near infinite)
Brit01 said:
Brit01
This is not true, the table can be read for either input or output tube positions. You just look at different columns for the information you need. When looking for input tube positions, find the tube of interest, then the B+ you are planning to operate at then read off the Rk (cathode resistor) values to set the current recommended in the first stage. For the output position you can do similarly to select the output stage Rk's. For linestage applications you will be interested in the Zo (among other things, gain as well probably). Note - you ideally want the next stage's input impedance (ie your power amp) to have at least 10x the Zo of the tube you are selecting. For example in my case, my Millenium's input impedance is 2k, so I need to choose valves preferably under 200 ohms Zo in this circuit. The 6DJ8 with 150V B+ delivers 199R Zo at 10mA current. There are a few other tubes which offer similar Zo as well, or slightly higher. For those with valve power amps, this is less of a concern as their input impedances are usually significantly higher.
Of course JB doesn't list all dual triodes in the guide (there are thousands!). The circuit values for these I think can be calculated if required - see details within his cookbook on how.
In any case it seems you have got yours working well which is great to hear.
Hope that helps clarify things.
Hi Kendrick,
Thks for the advice. I have a table in his manual that says it lists some triodes for the input position on the 5687 board.
I found another JB table, much more comprehensive, listing the Zo also. Maybe this is the one you are referring to.
So I have a B+ of 250V.
R15: 80K
R16: 100K
Rk on both tubes: 470 ohms
6N1P input tubes
5687 output (276 Zo ?)
I am intending for now (later with a valve power amp hopefully) to use it with a SS power amp and am thinking the imperdence is very low then.
Do I need to increase the cathode resistors to reduce current??
I do have a line level control on my power amp but I noticed during testing I still have to really keep the line level very low. Too much power from the Aikido.
I think you meant 'input impedance'
No offence, but I think you are wasting your time. It is well documented that valves have a very high input impedance and the circuit itself sets R1 to 1Mohm. I doubt a 20Mohm DVM is going to able to measure it in any case...
Further I wouldn't try measuring impedance with the circuit on using a DVM. You'll be injecting a DC voltage from the DVM to measure the impedance - god know what that will do to the circuit, worse your audio system if it's still connected at the time...
What's the real question driving this investigation avenue???
Bottom line is any DAC will be able to drive a quartet of 6SN7s in an Aikido as there will easily be the 10x ratio of DAC output impedance to Aikido input impedance.
No offence, but I think you are wasting your time. It is well documented that valves have a very high input impedance and the circuit itself sets R1 to 1Mohm. I doubt a 20Mohm DVM is going to able to measure it in any case...
Further I wouldn't try measuring impedance with the circuit on using a DVM. You'll be injecting a DC voltage from the DVM to measure the impedance - god know what that will do to the circuit, worse your audio system if it's still connected at the time...
What's the real question driving this investigation avenue???
Bottom line is any DAC will be able to drive a quartet of 6SN7s in an Aikido as there will easily be the 10x ratio of DAC output impedance to Aikido input impedance.
Howdy Brit
True but depends on the power amp. You should be OK given the Zo above.
Have fun.
Right. Unfortunately as I bought the 9 pin boards I don't have the reference to the 5687 tube in them. Nevertheless...(if you want to PM me and send me the book I can check the values for you)Brit01 said:
Until I see the book listing the 5687 I can't be sure you've got this right. However the likelihood of both Rks being the same are almost nil. Looking at my data sheets for the 6N1P at 250V shows an Rk of 221R flowing 5mA. Please re check.Brit01 said:
Zo sounds about right, grunty output tube but need to see the sheet (or calculate it myself - call me lazy!)Brit01 said:
Brit01 said:
True but depends on the power amp. You should be OK given the Zo above.
Yes, but why would you? Follow the Aikido guide and be happy. You want the tube to operate in its most linear part. Deviating from the guide is possible but should be done with caution.Brit01 said:
Try a different tube compliment in the input stage. At that B+ you've got a gain of 17.7 with a 6N1P. A 6CG7 drops it to around 10dB, the 5963 similarly. I really like the NOS RCA 5963s - try some and see what you think. 7dB drop is a fair whack. I'd also bypass the power amp attenuator. It's just another quality eating component in the signal path.Brit01 said:
Have fun.
Silver Stealth said:
Kendrick-----AKA----SS,
"I think you meant 'input impedance'"
Of course, you are correct. Thanks for the correction.
"No offence, but I think you are wasting your time. It is well documented that valves have a very high input impedance and the circuit itself sets R1 to 1Mohm. I doubt a 20Mohm DVM is going to able to measure it in any case..."
No offense taken, I sincerely appreciate that you are willing to share you knowledge and experience with us noobs.
Learning is never a waste of time though.
"What's the real question driving this investigation avenue???"
I am building a kit from Dantimax (Relvol1) and the input impedance is asked for with determining the value of a input resistor...Or none at all.
BTW my DVM goes up to 40M ohms.
My Dantimax kit is a 100K remote attenuator.
Again, thank you VERY much for helping us out with your experience and knowledge.
Ron
Don't have a soft copy right now.
But here is a link to one of the tables:
http://www.tubecad.com/2006/05/blog0064.htm
It shows the 6N1P with a Rk of 221 ohms an Zo of 422 at 250 B+.
And 5687 with a Rk of 198 ohms at B+ 250 and Zo of 276.
So you recommend changing the Rk to 221~ and 198~ respectively?
Keeping the Rk's as suggested in the table will keep it in the linear range right? If this is the case then I need to change out the 470 ohms for the above values.
I have a Carver TFM-55. I think it had a input Z of 50K.
I've been actively searching for a good deal on some new tubes such as the 6N6P/6H30.
I will check out the 5963.
Thanks a lot
Brit01 said:
Hey Brit
You got it! The Zo is only of interest in the output tube position - as you said you'll get 422R Zo with that combination and B+ you are proposing. Change the Rk values to the 221 and 198 respectively and happy days! ;-)
It won't matter if you don't match these Rk values exactly, just get close. Then when it's running measure the voltage drop across the Rks to verify how much current you are actually flowing through each tube. Probably worth archiving that info for when you want to do other changes later on.
Must try that 5687 some day.
Renron said:
Howdy Ron
So you've got one of these units at http://electronics.dantimax.dk/Kits/Selectors_-_attenuators/index.html - looks good.
As its got a constant input impedance of 100k it should work with any upstream DAC or CDP. (Remember as Ollebolle posted a few pages back, DAC/CDP feeds the attenuator which then feeds the Aikido circuit). Even if you had a valve or Aikido output stage on your CDP (!!!) the 100k value of the attenuator will mean you won't have any drive problems into the Aikido (good to know when you make the next one for your CDP!!!)
As the Aikido input R1 is 1Mohm it will work just fine (10x 100k = 1Mohm so it meets the 10x guideline).
FYI - I used the V03 kit from www.diyclub.biz with R-2R resistors selected by relays. I think this is 50k.
As JB would suggest, go about slinging some solder and let us know how it sounds!
OK now that is strange.
I changed the resistors.
200 for Rk of 5687 and 230 ohms for Rk of 6N1P BUT then my B+ dropped to 210V.
Didn't think the B+ would change by altering the cathode resistors.
Now I need to increase C1 on the psu to increase the B+ I guess. I only have a 0.47 cap. This is all I needed to get 250 B+ with the 6X5 rectifier.
I changed the resistors.
200 for Rk of 5687 and 230 ohms for Rk of 6N1P BUT then my B+ dropped to 210V.
Didn't think the B+ would change by altering the cathode resistors.
Now I need to increase C1 on the psu to increase the B+ I guess. I only have a 0.47 cap. This is all I needed to get 250 B+ with the 6X5 rectifier.
Brit01 said:OK now that is strange.
I changed the resistors.
200 for Rk of 5687 and 230 ohms for Rk of 6N1P BUT then my B+ dropped to 210V.
Didn't think the B+ would change by altering the cathode resistors.
Now I need to increase C1 on the psu to increase the B+ I guess. I only have a 0.47 cap. This is all I needed to get 250 B+ with the 6X5 rectifier.
Brit
Not unexpected - vs the 470R you were using you are now asking for more current through both input and output stages. Depending on how robust the power transformer is you will get some drop in B+. Might be worth checking also that the sum of currents doesn't exceed what a 6X5 can deliver.
I can see that the 6X5 can produce 70mA DC output current and the peak plate current is 210 mA. My tranny is rated at 200 mA also.
Loads of headroom here.
I'm only running a 0.47uF cap. I believe the Hytron can take up to 16uF.
I will try 5uF to increase the B+ and see where I go from there. Nothing in stock now. Have to pay a visit to the shop
Loads of headroom here.
I'm only running a 0.47uF cap. I believe the Hytron can take up to 16uF.
I will try 5uF to increase the B+ and see where I go from there. Nothing in stock now. Have to pay a visit to the shop
Silver Stealth said:
(good to know when you make the next one for your CDP!!!)
I am using a Denon DVD1600 for audio input at the moment, it has a feature to turn off the video portion of the player so there is less interference (noise). Cool huh? My next player will be the new OPPO Blue Ray player.
FYI - I used the V03 kit from www.diyclub.biz with R-2R resistors selected by relays. I think this is 50k.
I looked into that one but was leery of the price/quality of the unit. I looked around the net but didn't see many reviews of that product. How do you like it? Does it have a digital readout?
As JB would suggest, go about slinging some solder and let us know how it sounds!
You Betcha! I'll get right on it! With Pleasure!
Thanks for the help SS
Ron
Brit01 said:I can see that the 6X5 can produce 70mA DC output current and the peak plate current is 210 mA. My tranny is rated at 200 mA also.
Loads of headroom here.
I'm only running a 0.47uF cap. I believe the Hytron can take up to 16uF.
I will try 5uF to increase the B+ and see where I go from there. Nothing in stock now. Have to pay a visit to the shop
Good idea, 0.47uf won't be offering much assistance (more a bypass cap at that value!)
You can see in the data sheet at http://www.r-type.org/pdfs/6x5gt.pdf that for instance running 25mA you get 310V out vs 280V at double that current (50mA). As your tranny is more than capable, it's obviously the tube characteristic that governs this. Note the output is flatter with increasing current if using a choke input (8H), maybe only 5V difference between these two currents. Your local transformer manufacturer may be able to make one up for maybe $20-30.
You asked about the V03 kit...
The nice thing about the VO3 kit, is that when you buy the AO3 case (or the cheaper unit they offer in steel ilo aluminium, the display drops straight into the cutout. Gives the project a very OE high class look. Nice blue lighting. PM me and I can send you a pic.
The unit defaults to input 2 and -88dB attenuation. This is OK but it would be good to be able to change these values, alas you can't. I'd also like to be able to dim or turn off the display, also not available. Finally I'd like it to have a 'home theatre' through - which it doesn't (may rig up a four pole relay to achieve this). Having said that it does work quite well. 4 input switch is also quite handy. Plastic remote is fairly cheesy and now rattles with some loose stuff inside but many would learn these functions to their universal remote anyway. You can buy a metal one on their site if you wish at around $30US.
The base of the AO3 case is pretapped for many boards to screw straight into. IEC and RCAs are already cut out too.
I have always found finishing a project neatly to be difficult unless you have a full workshop and loads of time. Most metal workers aren't interested in one off cases and if they are, the price rises accordingly. The local electronic stores here generally only have rack mount type cases - not really nice enough IMO for such a worthy pre as the Aikido!
The nice thing about the VO3 kit, is that when you buy the AO3 case (or the cheaper unit they offer in steel ilo aluminium, the display drops straight into the cutout. Gives the project a very OE high class look. Nice blue lighting. PM me and I can send you a pic.
The unit defaults to input 2 and -88dB attenuation. This is OK but it would be good to be able to change these values, alas you can't. I'd also like to be able to dim or turn off the display, also not available. Finally I'd like it to have a 'home theatre' through - which it doesn't (may rig up a four pole relay to achieve this). Having said that it does work quite well. 4 input switch is also quite handy. Plastic remote is fairly cheesy and now rattles with some loose stuff inside but many would learn these functions to their universal remote anyway. You can buy a metal one on their site if you wish at around $30US.
The base of the AO3 case is pretapped for many boards to screw straight into. IEC and RCAs are already cut out too.
I have always found finishing a project neatly to be difficult unless you have a full workshop and loads of time. Most metal workers aren't interested in one off cases and if they are, the price rises accordingly. The local electronic stores here generally only have rack mount type cases - not really nice enough IMO for such a worthy pre as the Aikido!
SS,
PM sent for photo, thanks for the offer.
I agree that presentation is difficult without a complete machine shop at one's disposal.
By profession I am a termite. I make little pieces of wood out of big pieces of wood. Metal fabraication was my fathers profession and he was superb at it. Too bad I didn't have the opportunity to be his student. I cant' ask him about metalworking now...... but I have some tools I don't know how to use!
It sounds like the V03 is a good quality kit and about the same price as I paid with out a remote or PS. Very nice it to have a prefab case/chassis. I looked it up at DIYGENE. Did you upgrade to the AE resistors? Id so what's the difference and how does one know it makes a difference?
Ron
PM sent for photo, thanks for the offer.
I agree that presentation is difficult without a complete machine shop at one's disposal.
By profession I am a termite.
I make little pieces of wood out of big pieces of wood. Metal fabraication was my fathers profession and he was superb at it. Too bad I didn't have the opportunity to be his student. I cant' ask him about metalworking now...... but I have some tools I don't know how to use! It sounds like the V03 is a good quality kit and about the same price as I paid with out a remote or PS. Very nice it to have a prefab case/chassis. I looked it up at DIYGENE. Did you upgrade to the AE resistors? Id so what's the difference and how does one know it makes a difference?
Ron