Ciao Gluca
I have a small question about the 211 schematic. I see that you have about 400V at the plate, implying that the B+ should be still higher. Do the DN2540's survive this without a problem (as they are rated for 'only' 400V?) IF they survive and are reliable, well, that is good news!
Erik
I have a small question about the 211 schematic. I see that you have about 400V at the plate, implying that the B+ should be still higher. Do the DN2540's survive this without a problem (as they are rated for 'only' 400V?) IF they survive and are reliable, well, that is good news!
Erik
Yes I have.
Here it is the signal chassis and the PSU
I am using thyratrons now. There is a 3rd box for the filaments not shown. More pics of a Italian DIYers meeting we had last year are here ... the server can be slow.
Erik,
the DN2540 are rated for 400V Drain to Source and they actually see only 100V circa (top mosfet): my PSU is 100mA@500V. 500V-400V are left to the 211 to swing the signal towards the output.
The DN2540's are quite reliable as long as they are insulated, heatsinked and protected by a 2K resistor at the upper mosfet's drain: I had issues at higher voltages at the start-up. A simple resistor fix the problem.
The CCS can be replaced by a >150H choke but I had better result loading the tube with solid state.
Ciao
Here it is the signal chassis and the PSU
I am using thyratrons now. There is a 3rd box for the filaments not shown. More pics of a Italian DIYers meeting we had last year are here ... the server can be slow.
Erik,
the DN2540 are rated for 400V Drain to Source and they actually see only 100V circa (top mosfet): my PSU is 100mA@500V. 500V-400V are left to the 211 to swing the signal towards the output.
The DN2540's are quite reliable as long as they are insulated, heatsinked and protected by a 2K resistor at the upper mosfet's drain: I had issues at higher voltages at the start-up. A simple resistor fix the problem.
The CCS can be replaced by a >150H choke but I had better result loading the tube with solid state.
Ciao
Gluca said:
Hi , I know in Italy you have the people on tube diy love also before some factory with tube products , maybe fivre was famous in tubes .i have one question ? I found on fivre 6sn7 it has nice sound so after that I receive some of 6sn7 without brand name and logo on glass .this 6sn7 is nos and same sound and same building .but bit different .can you see the picture of these two kind of 6sn7 and maybe you have some information. You can see actual picture in my previous post and picture of 6b4g amp .
I've just done a type 10/VT25 DAC output stage . Pretty simple , I'm obtaining bias off the filament , it's run with DC with the negative end of the filament grounded so no need for a cathode bias network . Load is a Valab 200H choke , this is fed via a TVC directly from the balanced outputs of the CS4397 DAC chip , there are only three parts including the valve (excluding the psu) . As with all DHT valves for low-level use , a decent filament supply is required . I use passive LCLCL but Ronan Reg type circuits also work ok
316A
316A
hooman said:
You don't need one . It's really very simple . The transformer volume control input is connected directly to the +/- outputs of the DAC chip , output of the TVC runs between the type 10 grid and 0V . This could be substituted with a 220k grid leak resistor and run the input directly to the grid . Filament is run with DC , negative side connects to 0V rail . Anode load is the choke , I think my HT rail is 180V and the chokes' DCR 2.3k . I forgot there is a coupling cap from the anode , that makes 4 parts rather than 3
cheers
316A
Gluca said:
Yes LCLCL is the way to go . I do the beefiest current rated choke on the input (around 30mH) to meet critical inductance with >15,000uF followed by a lower (usually 2 x2mH in series as I have a stock) followed by a 47,000uF . Final choke a much higher value , either 2 x 30mH in series or a 280mH for lower current valves such as 10Y depending on what's on the shelf
Filament bias is very useful , I'm certainly not going to bother paying for a Blackgate or tricking out the ultrapath connection . Used this mainly on the medium mu types like 3C24 , with lower mu a resistor in series is added to bias up . The 10Y is ideal , nice easy-to-light 7.5V filament and a good few volts to get the bias . You are right it's asymetrical , the 'centre tap' never seems to be in the middle
Of course filament schemes like this need to be very good indeed , the filament should really be trated as another input and that final choke seems to really help isolating the signal from the filament supply as it's in the signal path . About the last thing you want to do is have the signal going through a wacking great bypass cap at the pins cheers
316A
Yeah that was me who posted Gluca's schematic in the other forum. I was saying that I got my inspiration to build an 801a preamp from his.
BTW, how do you tackle the delay turn on for that circuit? Being that they are mecury tubes, isn't it needed?
I did get a pair of 816's. If I decide to use them it will be for aesthetic reasons as I do like the blue glow. Its my wife's favorite color, so it ups the WAF.
BTW, how do you tackle the delay turn on for that circuit? Being that they are mecury tubes, isn't it needed?
I did get a pair of 816's. If I decide to use them it will be for aesthetic reasons as I do like the blue glow. Its my wife's favorite color, so it ups the WAF.
JoshK said:
I have two switches. The first turns on the MV rectifiers filaments (and the signal tube filaments as well). The other ignites the high voltage. I turn the 2nd on after 30 secs or more. I was in a rush to finish the preamp so it was the quickest way ... one day I'll build myself a proper delay circuit. Yes ... one day
Hi JoshK , I explain in my previous post a but schematic .do you remember our discus on vt25 and you r favorite tubes 801 ? but it was for power amps . after tow weeks, I have receive 801 tubes just in two . I send the picture of my 6b4g x8 to you before .JoshK in head of tubes diy us forum skills in tubes .
I would say that you should adjust the 'load' to emulate the tube's filament/cathode. For a 2A3 that would be a 1R resistor (2,5A through 1R = 2,5V filament voltage)
I have another remark and related question: filament biasing is indeed very interesting and 'KISS', still, where does one source all these chokes? I could certainly go the route of letting one wind them for me, but that is expensive...are there 'cheap' sources as well?
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