tizman, happy that you have discovered the measuring problem. However, your chokes are rated for 1.5Amp whereas your load is only 60ma until choke/s are loaded by at least 50% of it's rated current it will not regulate properly. Also quality of the last cap in a clc...filament supply effects sound quality (my own experience). For the people who don't have proper choke or SS supply like Rod's they can put a 100 turn air core coil in-between
DC supply and filament for some isolation (and for better sound). 1.9 volt is more than 5%--- not good I think. For your final build you should proceed with Rod's supply.
Regards
DC supply and filament for some isolation (and for better sound). 1.9 volt is more than 5%--- not good I think. For your final build you should proceed with Rod's supply.
Regards
minhaj: The proposed filament supply is capacitor input. My understanding is that a certain minimum current draw is only required if the supply is a choke input supply. I had a look online, but I can't find any information that indicates that the chokes in a supply after the first input capacitor require a minimum current to operate.
You are correct, tizman. It was my bad, sorry. Any progress?
Once your amp is up and running please try L as your last component in the supply and tell us if that makes any change sound wise.
Regards
Once your amp is up and running please try L as your last component in the supply and tell us if that makes any change sound wise.
Regards
It's coming along nicely. The CLCLCLCLC filament supply is working properly, and I included a 5 Watt wirewound rheostat for adjusting the voltage. I have laid out the chassis and should start drilling and affixing transformers soon. I am expecting a pair of inexpensive output transformers in the mail soon that I want to compare to a similarly priced new pair I already have, and a few vintage OPTS.
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Best of luck. I built all my DHT amps on bread-boards first. Once I made all the necessary changes and the circuits are optimized I moved onto the final casings. Making the signal tubes work properly specially in input position is not an easy task. Please keep us posted, and good luck once again.
Regards
Regards
Type 30 into EL84 or 6V6 with 5V4 - top plate
Here is the completed top plate of the amp that this thread gave birth to. I ended up using the 30 because I have many, and because this build is intended mostly as an investigation of what a DHT to IDHT amp sounds like. I haven’t permanently installed the OPTs as I want to swap a few different very small and very inexpensive ones in to see if these small OPTs do a good job when used only above 600 HZ or so. I will use my 01A and 26 tubes in a dedicated preamp in the future. The circuit and power supply are not installed yet, and not entirely finalized. The photo shows the amp with all tubes in but, in use, either the 6V6 or EL84 will be used, and not both. The 5V4 is for a bit of delay on the onset of the B+ as it is indirectly heated. The top plate of this amp is the bottom plate of an old console amp that was badly corroded. I used a wire brush on a drill to strip off the corrosion, and this is the end result. Patina galore. Not for everyone I suppose, but it works for me.
Here is the completed top plate of the amp that this thread gave birth to. I ended up using the 30 because I have many, and because this build is intended mostly as an investigation of what a DHT to IDHT amp sounds like. I haven’t permanently installed the OPTs as I want to swap a few different very small and very inexpensive ones in to see if these small OPTs do a good job when used only above 600 HZ or so. I will use my 01A and 26 tubes in a dedicated preamp in the future. The circuit and power supply are not installed yet, and not entirely finalized. The photo shows the amp with all tubes in but, in use, either the 6V6 or EL84 will be used, and not both. The 5V4 is for a bit of delay on the onset of the B+ as it is indirectly heated. The top plate of this amp is the bottom plate of an old console amp that was badly corroded. I used a wire brush on a drill to strip off the corrosion, and this is the end result. Patina galore. Not for everyone I suppose, but it works for me.
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Good work. How thick is the top plate? You may like to put a piece of cork sheet inbetween sockets and top plate for type 30 tubes, if you have not used already. Also you may try isolation for the transformer, it may help 30's microphony. Waiting for your sound impression.
Regards
Regards
Minhaj: The transformer came from an old radio, and was vibration free in that application, which had more current draw. That said, I will still put something rubbery and flexible where it makes contact with the chassis. Thanks for reminding me. The chassis isn’t particularly thick, but it is steel and rigid. There are a lot of heavy things bolted to it underneath, and more will be added. The entire top plate will be attached to a thick wooden frame with rubber bushings as insulators. The 30 sockets are screwed into a steel electrical cover plate with a layer of rubber foam glued to it, and that plate fits into another identical plate that is pressed up against the top plate with a layer of Green Glue in between the electrical plate and the top plate. So, there is the plate that has the sockets attached to it, then a layer of foam, then another plate, then a layer of Green Glue, and then the top plate. The plate with the sockets attached to it is not in contact with the top plate. The entire assembly is loose so that when you push down on the socket from above, the socket moves a bit, as it does when you push the socket up from from underneath. See the attached amateurish drawing for more details.
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Looking good! Nothing wrong with using repurposed materials, aka junkbox builds.
I've also tried the 30 in the SET I have breadboarded. Tapping on the tube, it is more microphonic than most of the tubes I've tried. I don't find it to be a problem in practice, however. At least not in a breadboard setup. Vibrations from music, or even tapping on the table, don't seem to cause any problems.
Oddly, I recently picked up some 26 globes and they're actually less microphonic than the ST versions I've been using. Perhaps this is just differences between individual tubes, though. Most people find the globes to be more problematic.
Another wonderful DHT I've used, which was actually developed to be non-microphonic, is the 864 / VT-24. Its GT shape looks rather generic next to the ST and globe DHTs but it sounds great - kind of a cross between the 26 and the 01A in my setup.
I've tried several DHT input candidates. I'm sure the primary tube I'll use is the 26 but the 864 and 30 sound great too, just a slightly different tonal balance / presentation.
I'm heating them with a little, under $10, Meanwell 3.3v DC SMPS. After some experimentation I figured out that I can use any of them without changing the voltage adjustment on the Meanwell by using a 3-way switch. The switch would add different value dropping resistors for the 864 and 30, while the 26 needs no resistor. Pretty cool.
I'm debating whether I want to incorporate the ability to switch tubes when I build the amp. The plate supply and bias is the same for all of them so the heater voltage is the only variable. Downside is that 864s and 30s could burn up their filaments if the switch wasn't in the right position.
I just ordered some Edcor OTs but, since the wait time is so long, I'll probably build it with the little OTs I'm using on the breadboard and then add the Edcors later. The Edcors should have better bass extension.
Since you're using your amp for higher frequencies only, I suspect the smaller OTs you're using now might actually sound just as good, if not better.
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FlaCharlie: In order to avoid killing tubes by forgetting to flip a switch (or someone else flipping a switch) I have taken to just putting in a dedicated socket for each tube type. All tubes can have their own biasing and plate resistor that way, and the dropping resistor on the filament can be on the socket. This doesn’t need to take up much space on the top plate because you can only use one tube at once, so the sockets can be very close to each other. Then you only have to worry about plugging tubes into the wrong socket.
Yeah, you could still plug one into the wrong socket since they are all 4 pin tubes with the same pinout. The only difference is the heater voltage.
It's a great way to have the option of using either 6V6s or 6BQ5s, though.
Labelling the tube sockets should help. A switch is trickier, and I have killed a few tubes in amps where I have used one, so I'm not doing that again for sure.
Assuming an adequately specified power transformer, the octal socket could also be used for EL34, 6L6 etc. However, I'm not sure if the 30 has what it takes to drive these other tubes. In my particular set up, with a XTA DP200 feeding the amp, I can increase the gain as required, but I haven't looked into the 30 driving other tubes with a typical line level output from the upstream component. I'm going to start with a resistor on both the plate and the cathode of the 30. A choke on the plate, a CCS or the Bartola gyrator will have more drive than a plate resistor. Something to look into...
FlaCharlie: What operating point did you try with the 30? I have 300 volts or so available from the B+ and want to start with a resistor on the cathode and plate for now. I'm curious if varying the operating point can reduce microphonics as well.
I'll probably start with 280 Volts B+, a 49K plate resistor and a 3K resistor on the plate. It's pretty bog standard, but I can always switch it up later.
You can measure vibration in terms of frequency, displacement, velocity and acceleration. For your given electrical and mechanical environment which is strong and which is week it is difficult to know/measure. Which tube including its construction is sensitive to which aspect of vibration is also unknown to us.
Tizman.....if 12ax7 in grounded cathode config can drive El34 or 6L6 then 30 also should be doing the job. 49K plate resistor at 3ma current will drop 147 volt so plate will be at 133volt and 3K cathode resistor will give you -9volt at the grid...I think for start up config it is fine. At this moment your challenge is to make the amp hum and microphonic free. Once it is done you always may fine tune for sweet spot etc. I have one request please run it with full frequency se transformer also because otherwise you will not be knowing if there is any problem in 30Hz to 500/600hz region.
GOOD LUCK. You will be successful soon.
Regards
Tizman.....if 12ax7 in grounded cathode config can drive El34 or 6L6 then 30 also should be doing the job. 49K plate resistor at 3ma current will drop 147 volt so plate will be at 133volt and 3K cathode resistor will give you -9volt at the grid...I think for start up config it is fine. At this moment your challenge is to make the amp hum and microphonic free. Once it is done you always may fine tune for sweet spot etc. I have one request please run it with full frequency se transformer also because otherwise you will not be knowing if there is any problem in 30Hz to 500/600hz region.
GOOD LUCK. You will be successful soon.
Regards
I'm quite happy with the 6N6G outputs, which I find fascinating. They're real triodes that are very easy to drive and they're internally biased so you just ground the cathode pin. Maximum power output (5.2w) is about the same as a 6BQ5 (5.7w) or 6V6 (5.5w). But, at those power levels, the 6N6G only has 5% distortion while the 6BQ5 has 10% and 6V6 has 12%.
The EL34, in pentode and with a similar B+, will get you twice as much power but that's also at 10% distortion. But twice the power only gets you an extra 3db, and that's at full output. In normal use, and at similar levels of distortion, the difference would be negligible, IMO. The 6L6 puts out even less power than the EL34 under the same conditions.
My input tubes are choke loaded (Hammond 156C), battery grid biased and plate voltage is regulated. I've used them with a combination of either a 0A2 regulator tube and a "9v" battery (which measures ~9.75v) or a 0B2 and 3 AA batteries, which measure ~4.55v.
I'm currently using the 0B2 setup. With the 30s installed I'm getting ~99v plate to ground. The DCR of the 156C is listed as 3.7k but they measure ~3.45k. The filament is at 1.8v.
I just tried the 0A2 setup with them, which resulted in a plate to ground voltage of ~140.5v. They were considerably more microphonic at that operating point. The 26s are quieter with the 0B2 setup too, so that's what I'll be using.
If microphonics continue to cause you problems, maybe consider using the 864 / VT-24. But, as I said, I don't consider it a problem if it's not audible under normal listening conditions. Lots of tubes will ping if you tap them, even many indirectly heated ones. So, I just don't tap them.
FlaCharlie: Did you do anything special in order to shield the plate chokes from the circuit? I have left room under the chassis for the pair of 156C that I have.
It's all still breadboarded - clip leads running every which way. The plate chokes are sitting upside down about 1" to 2" away from one of the output tubes and 3" to 4" from one of the input tubes. I'm always amazed that it's as quiet as it is.
I'm sure when I build it that I'll try not to put them super close to anything but I never actually shield anything. Sometimes I do use shielded wire but nothing beyond that.