• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Schematic for 2A3/300B SET OTL amp

Status
Not open for further replies.
Jump to Latest
#21
Assembling the parts

Well I've made up my mind. This is the way to go. I'll find a suitable chassis and some greenlee punches and go from there. At this point I don't have a clear understanding of the DC filament PSs but I'll cross that bridge when I get there.

Ray - Approximately what are the dimensions of your chassis? I want to make sure I get boxes that are adequate in size. Thought about polished stainless plate on a hardwood case, but punching the holes might be challange.

I need to choose the right tube sockets, lots of price variance in that area. I don't want to cut corners. Looks like 300Bs are gonna set me back 800 to 900 dollars.

I liked your toroidal covers, where did you find those?

Rick
 
#23
Hi Rick, good call; I don't think you'll be disappointed.

Here's the chassis I used;

4308T DIY chassis Full Aluminum Enclosure / mini AMP case/power amplifier box | eBay

Some more info you'll need; there were some design updates introduced after the book publication so you'll need an updated schematic. I'll scan my copy in and send it to you in the next day or two.

There's a schematic of the revised output stage for the DC version in my picture library. Swapping in TL783 devices for the LM317 is a recommended upgrade.

I guess you're aware that the amp gets quite warm, both the tunes and the filament supplies get hot.

You'll notice from my picture library that I use PCBs, one for the input stage and one for each 300B as well as some for the capacitor bank in the CLCLC B+ supply. I can probably help you out with these - drop me a PM if of interest and I can detail.

BTW, I use Teflon CMC tube sockets.

Ray
 
#24
Nearly forgot about the toroids. These were custom wound by Canterbury Windings here in the UK, they are a small specialist company who do an excellent job. The toroids were potted into plastic enclosures by them. I'm sure they'll be somebody who can do similar on your side of the water.

It's a shame you live in 110V land as I have a pair of potted toroids that I've recovered from my previous AC build that I plan to sell on but sadly they only have a 230V primary.

One other thing on toroids, each DC filament supply should have at least its own secondary winding or if you want to push the boat out a transformer per supply.

Ray
 
#26
Transformers

I've seen the 50VA 2x6volt toroids for around $15.00, not expensive and I've bought a couple of toroidals from them before. Machine wound and seem like good quality. I would like to find some covers though, what comes to mind is to cut the bottoms off of some aluminum or brushed stainless water bottles. I can paint or powder coat the cans if aluminum. PVC pipe caps is another option either for a mold or the covers themselves.

Look forward to seeing the updated schematic. Time to go shopping.

Regards,

Rick
 
#28
Trip up to N. Atlanta

deafbykhorns said:
Shoot me a PM if interested later this month, I may be coming up to N. Atlanta to ride some single track MTB after Christmas so we may cross paths......
Click to expand...

Let me know if your coming this way. I can put you in touch with a friend who knows the routes in the mountains, from mild to murderous.

I used to to road biking in the mtns but have had to slow down after an accident.
 
#29
nautibuoy said:
Nearly forgot about the toroids. These were custom wound by Canterbury Windings here in the UK, they are a small specialist company who do an excellent job. The toroids were potted into plastic enclosures by them. I'm sure they'll be somebody who can do similar on your side of the water.

It's a shame you live in 110V land as I have a pair of potted toroids that I've recovered from my previous AC build that I plan to sell on but sadly they only have a 230V primary.

One other thing on toroids, each DC filament supply should have at least its own secondary winding or if you want to push the boat out a transformer per supply.

Ray
Click to expand...

Hello Ray - I've ordered some cmc sockets, when they arrive I'll look on ebay for a Greenlee Chassis punch. If I use off the shelf transformers, it looks like I'll need to use one per circuit. By reading the forum, it looks like Tent Labs is an option for the DC Circuit. Those are fairly expensive, is there a schematic posted where I can build the DC supplies myself?

Regards,

Rick
 
#30
Hi Rick.

I sent you a private message a couple of days ago about the amplifier schematic and some other stuff that might help you but haven't heard back?

Did you contact Andrew about his filament supplies for the 300Bs? Andrew hasn't published the schematic for his supply.

An alternative to the Tentlabs boards, well regarded and at a lower price, is the Rod Coleman DHT filament supply;

Rod Coleman DHT Filament Regulator

Make sure you read the notes, especially about the supply transformers.

Ray
 
#31
One thing that is very helpful with Andrew's psu is the fact that they don't need to be adjusted. This is different with the Coleman's and could become a bit of a hassle in the case of the 300B OTL.
The idle current of each 300B is always fluctuating for some tenth of volts which is ok and normal in this configuration but needs a rock stable DC for the filaments that doesn't move so that it cannot become part of the regulation process. Andrew's boards are excellent in this respect.

Wolfgang
 
#32
Andew

nightsky said:
One thing that is very helpful with Andrew's psu is the fact that they don't need to be adjusted. This is different with the Coleman's and could become a bit of a hassle in the case of the 300B OTL.
The idle current of each 300B is always fluctuating for some tenth of volts which is ok and normal in this configuration but needs a rock stable DC for the filaments that doesn't move so that it cannot become part of the regulation process. Andrew's boards are excellent in this respect.

Wolfgang
Click to expand...
 
#33
Andrew's Power Supplies

nightsky said:
One thing that is very helpful with Andrew's psu is the fact that they don't need to be adjusted. This is different with the Coleman's and could become a bit of a hassle in the case of the 300B OTL.
The idle current of each 300B is always fluctuating for some tenth of volts which is ok and normal in this configuration but needs a rock stable DC for the filaments that doesn't move so that it cannot become part of the regulation process. Andrew's boards are excellent in this respect.

Wolfgang
Click to expand...

That's good news, I am buying the boards from Andrew along with the caps. Ray is providing a couple of other boards.

Regards,

Rick
 
Status
Not open for further replies.
Top Bottom