Awesome preamp man! I've been thinking this would make a great preamp tube for sometime.
I'd also be curious to see it replace the 5687/6H30 in the Raven PP preamp. You would need two valves each side but it would make a serious line stage there too.
I'd also be curious to see it replace the 5687/6H30 in the Raven PP preamp. You would need two valves each side but it would make a serious line stage there too.
Hello,
You can get them from Big Bear Audio in the UK. You can request to get it gapped to any current. I wanted to use if for other purposes as well with other DHTs so got it at 40mA. You can get a 30mA one if you prefer.
Yes you can wire it in Alt V mode for differential output, haven't tried though.
Thanks
Ale
Actually I was suggesting replacing the 5687's with 4P1L in a raven like topology. Mostly for sh**s and giggles. You could just use alt v as you said for differential drive though.
Been following this 4P1L and the 26 tube thread for a while.
A friend gave me a butt ugly + I mean ugly 26 preamp, but is the sound ever Swwweet.
I.ve done some tweaking and some mods, I can read a meter + solder.
Maybe it's time to attempt a built. Over at Bottlehead they are now offering a 4P1L kit preamp at a very good price, it's not as elaborate as the builds here. But maybe this might be a good place for me to start, as my first build.
They also have a 300B preamp that looks pretty interesting.
The real thing that sucks is my system has been in storage for far to long, looking forward to getting it back up and running soon. :O(, :O(
A friend gave me a butt ugly + I mean ugly 26 preamp, but is the sound ever Swwweet.
I.ve done some tweaking and some mods, I can read a meter + solder.
Maybe it's time to attempt a built. Over at Bottlehead they are now offering a 4P1L kit preamp at a very good price, it's not as elaborate as the builds here. But maybe this might be a good place for me to start, as my first build.
They also have a 300B preamp that looks pretty interesting.
The real thing that sucks is my system has been in storage for far to long, looking forward to getting it back up and running soon. :O(, :O(
Well, you read it all here first! Anatolyi and others here have been building 4P1L line stages for years.
I can't see how Bottlehead are dealing with microphonics - nothing obvious above the top plate. Maybe there's decoupling below the plate. If they haven't dealt with it properly they're in for a lot of complaints!
I'm also a bit sceptical about just using a L200C regulator. It would have been nice to see filament bias. The glow tube is good - we've all been using those!
Smash DHT Preamplifier Kit Specs | Bottlehead
Totally agree with Andy. You get what you pay for....or less...
Ktuuri,
I would suggest to make the effort to built it yourself ( you have plenty of information on this thread) using the appropriate parts and you will be rewarded by a fantastic sound.
You have the option to buy the kit and then modify it ( added cost) or just built your own ( recommended). I am sure that you'll get enough support to be able to cope with the difficulties of this built.
Good luck,
Radu
Ktuuri,
I would suggest to make the effort to built it yourself ( you have plenty of information on this thread) using the appropriate parts and you will be rewarded by a fantastic sound.
You have the option to buy the kit and then modify it ( added cost) or just built your own ( recommended). I am sure that you'll get enough support to be able to cope with the difficulties of this built.
Good luck,
Radu
I don't see how they have done it either. But I know how, I have seen how many of you have dealt with it and had great success.
That might sound like a good idea. I know there is alot of support if I take this on. I do like to do a little wood work, so making a chassis or two would be no problem, I have all the tool for that as well.
Maybe it's time!
Thanks Guys!🙂
It probably is a good place to start. You get a good looking, well laid out chassis, all the switches, plugs, pots, sockets, caps, resistors, power transformer etc. Bottlehead won't put out something bad. In fact their kits are very well thought out and the builds are supplied with excellent manuals and even a dvd I believe.
I'm sure you could shoehorn seperate transformers and Rod Coleman's regulator...AFTER you have built it stock...that will also teach you something about the worth of the alterations you may or may not make.
Whatever you do. Take your time...and don't try to rush things. Build nice or build twice.
I have always chosen to build my own stuff...with some major frustration along they way...and some ugly looking stuff...some good as well ofcourse...and have often thought that it would have been much cheaper and good looking to have gone the Bottlehead route. Also they have a great little forum/community going.
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Hi,
Looks good, I will build one!
Are you sure the output impedance is 425 ohm? It should be around 80 or so...
Howdy,
I'm trying to filament bias a 4P1L with the Coleman DHT Heater but things don't work out. Filaments are in parallel for 2 volt, 15 ohm bias resistor, input to the DHT Heater 16 volt, output 2.0 volt. When I raise the input voltage to the DHT Heater, its output voltage follows and can't be adjusted by the pot. At the risk of burning out the filament I shut off. When testing with an external resistor only, output voltage adjusts normally when Vin-Vout > 4 volt. Might the onboard power resistor of 1.0 ohm be a wrong value?
I'm trying to filament bias a 4P1L with the Coleman DHT Heater but things don't work out. Filaments are in parallel for 2 volt, 15 ohm bias resistor, input to the DHT Heater 16 volt, output 2.0 volt. When I raise the input voltage to the DHT Heater, its output voltage follows and can't be adjusted by the pot. At the risk of burning out the filament I shut off. When testing with an external resistor only, output voltage adjusts normally when Vin-Vout > 4 volt. Might the onboard power resistor of 1.0 ohm be a wrong value?
Hi Vincent,
Why? At very low frequency you see Ra||Rp reflected in the secondary. That is Ra=(1k6 || 1K2)/(4.5)^2. This is lower than 80 and you still need to add the RS=277ohms, however at higher frequencies, the Lp=2*pi*f*L. L=50H approximately and this impedance is complex. Lp is now in series with the Rp. If you want to avoid the complex algebra involved, you can simulate this in LtSpice and you will see that is higher than 420 ohms
cheers
Ale
Why? At very low frequency you see Ra||Rp reflected in the secondary. That is Ra=(1k6 || 1K2)/(4.5)^2. This is lower than 80 and you still need to add the RS=277ohms, however at higher frequencies, the Lp=2*pi*f*L. L=50H approximately and this impedance is complex. Lp is now in series with the Rp. If you want to avoid the complex algebra involved, you can simulate this in LtSpice and you will see that is higher than 420 ohms
cheers
Ale
Attachments
Hi Disco,
Can you please confirm wiring in place? Is it different from my diagram in the link above?
What is the voltage you measure across the filament resistor?
thanks
Ale
You're referring to the diagram in #410?
Plus and minus of the power supply go to the DHT Heater input.
The 15 ohm is series connected to the tube and this string goes to the DHT Heater output, floating.
The voltage over the 15 ohm varies with the input voltage (!)
Plus and minus of the power supply go to the DHT Heater input.
The 15 ohm is series connected to the tube and this string goes to the DHT Heater output, floating.
The voltage over the 15 ohm varies with the input voltage (!)
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I am going to use 4P1L ( triode connected) with interstage transformer as a part of a driver for GM-70 SE. Input tube is 3A5 paralleled.
Fixed bias for all tubes, for now. For heating I'll use modified and additionaly filtered good quality switching power supplys.
So, I want to thank all of you for very nice job on 4P1L. That helped a lot. Looking forward to complete my project.
Keep up the good work.
Fixed bias for all tubes, for now. For heating I'll use modified and additionaly filtered good quality switching power supplys.
So, I want to thank all of you for very nice job on 4P1L. That helped a lot. Looking forward to complete my project.
Keep up the good work.
Yes, from a filament bias perspective. The preamp is this one:
4P1L DHT Preamp Siberian (Gen3) finished! | Bartola Valves
Basically you need 16V at the input of the Coleman regulator, then 10.4V on the output to get about 8.7V across the filament and 1.6-1.7V across the 4P1L filaments when it's set to 550mA or so.
Ale
If the Coleman reg is going to each side of the filament that's wrong. You need to think of the filament as extended by the cathode resistor. The coleman reg goes from one end of the filament to the end of the cathode resistor, which is ground.
Tricky... this is what I tried:
but this floating setup is missing the 32mA HV current 😉
An externally hosted image should be here but it was not working when we last tested it.
but this floating setup is missing the 32mA HV current 😉