Coffeedj,
Thank you for starting this great project and sharing your findings.
Your schematic calls for a 80-90mA transformer.
Each of the channels draws 40mA, so a 80mA transformer gives no extra headroom.
May be it would be smart to specify at least a 100mA transformer in the schematic? I am sure that your guide will serve as a starting point for a lot of first time builders.🙂
Thank you for starting this great project and sharing your findings.
Your schematic calls for a 80-90mA transformer.
Each of the channels draws 40mA, so a 80mA transformer gives no extra headroom.
May be it would be smart to specify at least a 100mA transformer in the schematic? I am sure that your guide will serve as a starting point for a lot of first time builders.🙂
<<No single 12B4... has zero reaction into knocking the box its housed in.>>
You can't expect a tube to be silent if you tap the tube or even tap the box it's mounted on. Every tube with gain is going to have some response to vibration. The 12B4 is perhaps a bit more sensitive to vibration than average, but none of the ones I've tried has had problems like some 6DJ8, 12AX7, 6AQ5 or especially Type 27 samples that I've used in other preamps.
Dave
You can't expect a tube to be silent if you tap the tube or even tap the box it's mounted on. Every tube with gain is going to have some response to vibration. The 12B4 is perhaps a bit more sensitive to vibration than average, but none of the ones I've tried has had problems like some 6DJ8, 12AX7, 6AQ5 or especially Type 27 samples that I've used in other preamps.
Dave
bequerel said:
Good point. I'm using old stock transformers, which had about 50% headroom built in. My 80ma transformer doesn't even get warm. Changes made and posted.
Salas said:
I've wondered about using the Russian tubes. How do you compare these in quality of sound to the good USA 12AX7's or Euro ECC83s.
I did not feel any lack of transparency, but I have only used it in that phono and I haven't substituted 12AX7s or 83's there (would need some rewiring), so to know more. It has screen (pin9) between channels also and that helps in phono especially. Its only 6.3V for heaters (4,5). They will show 10-15% less mu than a strong 12AX7 in practice so there must be some care about level matching if comparing, among other considerations.
Attachments
Coffedj, looking at the your site leads me to believe you are going to sell Parts or a kit perhaps? If so, could you elaborate?
TubeMack said:
Thanks for asking.
Yes, I am trying to set up a website to sell parts and kits. Basically, I putting together (hopefully!!) a retirement business that can be run by one or two people. I've been collecting tubes and parts for years and one of the things I've noticed is that there is a need for quality kits or completed kits like the old HeathKit or Dynaco. Those vintagle products were not top-of-line, but they sure filled a hole for a lot of hobbyists and enthusiasts, and they lasted for years. Ebay testifies to their enduring value.
Most of the parts required for kits are readily available from places like Antique Electronic Supply, DigiKey, and other botique shops. That includes parts like resistors, capacitors, wire, fuses, sockets, and the like. The parts that are difficult to come by at a reasonable cost are Old Stock tubes, transformers and chokes, good looking chassis', and help to get the design completed when you get stuck. Getting a really good finished product look is difficult unless you are willing to spend a lot of time in your basement designing your own.
These areas are where I've been focusing my effort. I've set up a relationship with a Hong Kong transformer and choke expert to handle custom designs at a good price. I've been working with a local machine shop and local wood-working shop to make a series of enclosures that can look great sitting next retail products. Cost will be more than a Hammond enclosure, but these will have a signature look.
The designs will be simple to execute. I have a lot of designs to post up on the site (over time) and these will be within the capability of the average hobbyist to build. I've got a blog set up to provide technical help as needed. In addition, I'll be providing pre-drilled circuit boards for some of the interchangeable parts like power supplies.
The final important piece is excellent quality and pre-tested Old Stock tubes. These I have available directly, or through several relationships with suppliers that I have set up. With all the pieces in place, and a little work, the sound quality can be truly excellent--equal the quality of retail products costing thousands, or tens of thousands of dollars, but without fancy bells and whistles.
What is left to do is to finish website, get all data posted, etc. Since I'm still working a full time job it is a slow process, but bit by bit the pieces will appear.
Phono Stage to add to 12B4
The 12b4 design is done--next is the phono stage since I designed the power supply to add it. I will start a new thread in this forum.
My desire is to do a passive RIAA design with the third corner (at 50KHz) added. THis will be a new one for me. In the past I've copied the Hagerman Coronet design as one that works very well.
Please send recommendations.
The 12b4 design is done--next is the phono stage since I designed the power supply to add it. I will start a new thread in this forum.
My desire is to do a passive RIAA design with the third corner (at 50KHz) added. THis will be a new one for me. In the past I've copied the Hagerman Coronet design as one that works very well.
Please send recommendations.
Thats wonderfull! How long before the items related to the B124 are ready? I'm going to go ahead and start a 12B4 build. My first road block is a total lack of a nice wood base as i'm planning for something a little more elegant than the standard homebrew look! I'm ready for a prototype chassis now!😀
Coffeedj,
I see that the heaters in your 12B4 schematic are referenced to ground.
Would it be smarter to lift them to eg. 30V by means of a voltage divider?
Reason I am asking is that I have seen a lot of other schematics where this has been done to reduce the heater/cathode potential.
I see that the heaters in your 12B4 schematic are referenced to ground.
Would it be smarter to lift them to eg. 30V by means of a voltage divider?
Reason I am asking is that I have seen a lot of other schematics where this has been done to reduce the heater/cathode potential.
bequerel said:
That is not a bad idea, but it is not necessary in this design. The 12B4 has a max Plate voltage of 550V--we are running at 120V. Typical cathode voltages for a 12B4 are in the 20-30V range in TV operation whereas ours is 11.2V The innards are huge (single plate) with lots of space between components. For other tubes like the 6AQ5, where a 6V6 is crammed into a 7-pin tube, it makes a lot of sense.
Another upside of this low voltage and heater-starved design is that once you find the "best" 12B4 tube--it will last for decades.
TubeMack said:
I just spoke to the custom woodworker/furniture designer and he is working on completeing a design. I'll post as soon as I know.
OK, Lots of questions!
1. Have you considered putting together a recommended parts list of "Mid-grade" componets for the newer DIY guys? Also, some of these items, like the Large surplus heater supply caps may be hard for some to source.
2. You mentioned you already had plate chokes, but I can't find them on your site.
3. Earlier you stated:
"Alternatively, I'm putting together a design using .440H chokes in a triple and quad PI filter design that should be awesome. I use these for guitar amps because they have incredible speed; DCR is 16 ohms. I'm going to get some boards made to standardize the placement and methodology."
Should I just hold off until you have these boards? Do you have a time frame? I'm ready to start buying some of my needed items at this time? I'm bored!!!
BTW I hope any new PS design still ultilizes that 5U4 GB for the rectifier. A choice I was happy with!!
4. Will you offer a PT, and if not can you or someone else here recommend a MID to Upper grade unit? I feel this should be the first purchase no?
1. Have you considered putting together a recommended parts list of "Mid-grade" componets for the newer DIY guys? Also, some of these items, like the Large surplus heater supply caps may be hard for some to source.
2. You mentioned you already had plate chokes, but I can't find them on your site.
3. Earlier you stated:
"Alternatively, I'm putting together a design using .440H chokes in a triple and quad PI filter design that should be awesome. I use these for guitar amps because they have incredible speed; DCR is 16 ohms. I'm going to get some boards made to standardize the placement and methodology."
Should I just hold off until you have these boards? Do you have a time frame? I'm ready to start buying some of my needed items at this time? I'm bored!!!
BTW I hope any new PS design still ultilizes that 5U4 GB for the rectifier. A choice I was happy with!!
4. Will you offer a PT, and if not can you or someone else here recommend a MID to Upper grade unit? I feel this should be the first purchase no?
TubeMack said:
I'll answer questions in the reverse order, but to report to the group I just finished doing a listening test using my multi-(power)amp to drive Lowther PM2As. You can see the multi-amp on my web site. This pre-amp is truly awesome! Full on volume, I can't hear anything coming out of the super-efficient Lowthers. I thought at first there was something wrong with the hook up. Even running the 6DQ6B tubes, which require 23 volts P-P at the input to drive them, it rocks. [As an aside I really like the 6DQ6B--it sounds better in SE Pentode mode than either the 6V6 or 6L6.] Anyway, the only possible change would be to use ultra-grade chokes. I've got some on order from Hong Kong, but those will take about 3-4 months to arrive.
With respect to the power supply, give me a few days to complete proving the design and post it as an option. For this one I will have the power chokes available for sale, and I'm going to size it to a standard Hammond transformer #272BX. This is the best value transformer they make. It requires using a 2 diode rectifier and tying the 5.0v + 6.3V together for the DC heaters. If you want to use a 5U4 you can go to the 270FX instead. ALternatively, if you are not going to do a phono stage, the #272BX can work with a 5Y3 and DC heaters with a little more ripple. The Hammond transformers can be bought from AES (www.tubesandmore.com). I always buy all my transformers in January when shipping is free. By June I'll have custom power transformers made by my Hong Kong supplier. If anyone knows a cheaper place to buy Hammond transformers, please let all of us all know.
Plate Chokes: I haven't got ANYTHING listed on my site for sale because I'm too interested in design and HATE working on the website. I'll get going on it 🙄 though. In the meantime, once I get the parts list completed I'll post it and people can email me for parts. I'll put together a mid-parts level Parts List, with recommendations for upgrades where it makes sense.
Thanks for pushing me to get this done!
PS: I'm going to try to lay in a supply of DC heater caps also.
Attachments
More on the power supply & testing
I waxed eloquent about the low henry multi-stage PS design and realized I better be able to support the statement with good data. In the past I've tested using resistive loads, but that is always cumbersome when checking out performance paramements.
I threw together a Hi-Voltage Current Sink that can dump up to about 350ma of current--that's enough to test almost any SET based amp, and most medium power P-P amps (at least one channel at a time.)
Here is the schematic if anyone cares to build their own. I'll be using this to test the limits of my PS and then publish the results.
CHeers.
I waxed eloquent about the low henry multi-stage PS design and realized I better be able to support the statement with good data. In the past I've tested using resistive loads, but that is always cumbersome when checking out performance paramements.
I threw together a Hi-Voltage Current Sink that can dump up to about 350ma of current--that's enough to test almost any SET based amp, and most medium power P-P amps (at least one channel at a time.)
Here is the schematic if anyone cares to build their own. I'll be using this to test the limits of my PS and then publish the results.
CHeers.
coffeedj said:
Hey coffeedj!
Thanks to you too, The 12B4 must be a lucky one if knowing you... 🙂
I've follow this and Marks 12b4 projects, and had get the most of the parts over time. I`m glad that you can supply with chokes and others ((haven`t ever seen a choke in real life, but I`m sure can solder 🙂). The pictures (do you have a few more?) on your web are good to have, and comments too 🙂
I like the tips too, with strong and weak signal separated, layout...
Thanks for all.
Cheers Jan Jensen
Low Henry Power Supply
I've finished the testing and design on the Low Henry Power Supply. Results are quite a bit better than I expected. Impluse response is excellent, using a 10ma torture test. This power supply should be scalable from 30ma to 500ma.
The design results are too big to post, but the whole design and final power supply will be posted on my web site in the next couple of days. In the full document, I go through the derviation of appropriate ripple for this 12B4 line stage. It turns out that with 0D3 voltage regulators, 10mv of ripple from the power supply is more than clean enough to give no detectable hum. The ripple output (before regulator tubes) will be less than 1mv at the expected current draw, so final B+ may be clean enough as is for phono-stage supply.
Cheers,
I've finished the testing and design on the Low Henry Power Supply. Results are quite a bit better than I expected. Impluse response is excellent, using a 10ma torture test. This power supply should be scalable from 30ma to 500ma.
The design results are too big to post, but the whole design and final power supply will be posted on my web site in the next couple of days. In the full document, I go through the derviation of appropriate ripple for this 12B4 line stage. It turns out that with 0D3 voltage regulators, 10mv of ripple from the power supply is more than clean enough to give no detectable hum. The ripple output (before regulator tubes) will be less than 1mv at the expected current draw, so final B+ may be clean enough as is for phono-stage supply.
Cheers,
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