After my recent fiasco of the non arriving but take my money amplifier from J. Sound Lab and not being able to find anything I can afford or "like", I am going to build my own 300b SET integrated amplifier. I have decided on the schematic (J E Labs 300B SE), that I am going to use. I am given to understand that there are other designs that may be better but I really would like to keep it simple as this is my first big project. Being a bit in the dark I have a few questions that I would really appreciated getting some feedback on...
I was thinking of using 10mm black acrylic for the top and bottom plate with a dark mahogany frame. Will the acrylic be able to take the heat generated from the valves?
Should I use Teflon or ceramic valve bases and is there any brand that I should keep clear of?
Which OP transformers to Use? I have looked at the Sowter SA08, the SA07, Audio Note group B and the Transcendar Transformers TT-017-OT. I am really in the dark here and I don't want to pick the wrong one. I have heard good things about all of the above. The Sowter SA08 I think might be overkill but I am probably justifying picking the cheaper SA07. I am note sure if the Audio Note reputation is swayed by the Brand Name. The spec looks decent on the Transcendar though they are the most reasonably priced of the lot and I think the lightest in weight.
Any help would be great!
I was thinking of using 10mm black acrylic for the top and bottom plate with a dark mahogany frame. Will the acrylic be able to take the heat generated from the valves?
Should I use Teflon or ceramic valve bases and is there any brand that I should keep clear of?
Which OP transformers to Use? I have looked at the Sowter SA08, the SA07, Audio Note group B and the Transcendar Transformers TT-017-OT. I am really in the dark here and I don't want to pick the wrong one. I have heard good things about all of the above. The Sowter SA08 I think might be overkill but I am probably justifying picking the cheaper SA07. I am note sure if the Audio Note reputation is swayed by the Brand Name. The spec looks decent on the Transcendar though they are the most reasonably priced of the lot and I think the lightest in weight.
Any help would be great!
top plate: somehow the heat needs to get out, and a metal chassis or top plate is so much easier to work with. Copper is easy to make black, but it's expensive.
transformers: Sowter give enough data to enable a sensible decision, and will provide more if you ask. If Audio Note and other options provide the same data, you can compare, otherwise you have to trust to reputation. I trust Sowter's no-nonsense approach, but they are not cheap.
Given you have enough data, you then have to decide on your priorities, because every transformer is a compromise. To some extent you should take into account the kind of speakers you will use, and whether you will be using global feedback. The relationship between valves, transformer and speakers is quite complicated, especially in the bass region. OTOH, it is unlikely that enough data will be available to support a fully reasoned decision, so you may as well not bother.
If you are choosing between transformers of equal quality, dc current rating, bandwidth and power rating, then the biggest is probably the one to go for. This is because full-power bandwidth is not the same as that quoted for small signals. If you want full, articulate bass, you need a transformer that remains as linear as possible at low frequencies at high power. The bigger the core, the better in this respect. If I were uncertain or befuddled, that's how I would decide.
You've been sensible to choose a simple circuit and concentrate on the quality of the transformer.
transformers: Sowter give enough data to enable a sensible decision, and will provide more if you ask. If Audio Note and other options provide the same data, you can compare, otherwise you have to trust to reputation. I trust Sowter's no-nonsense approach, but they are not cheap.
Given you have enough data, you then have to decide on your priorities, because every transformer is a compromise. To some extent you should take into account the kind of speakers you will use, and whether you will be using global feedback. The relationship between valves, transformer and speakers is quite complicated, especially in the bass region. OTOH, it is unlikely that enough data will be available to support a fully reasoned decision, so you may as well not bother.
If you are choosing between transformers of equal quality, dc current rating, bandwidth and power rating, then the biggest is probably the one to go for. This is because full-power bandwidth is not the same as that quoted for small signals. If you want full, articulate bass, you need a transformer that remains as linear as possible at low frequencies at high power. The bigger the core, the better in this respect. If I were uncertain or befuddled, that's how I would decide.
You've been sensible to choose a simple circuit and concentrate on the quality of the transformer.
For the whole amp or just the transformers? If it is the latter then no more than £500
Well, that allows lots of possibilities for top-shelf iron, like Hashimoto, James, Electra-print, Tango, Tamura, etc.
What's the budget for the entire amp?
On another note, have you considered any other 300B SE designs?
Are you planning on using an 83 rectifier? You may want to consider a non-mercury rectifier like a 5AR4, GZ34, GZ37, 5U4 Etc. Any of these should work as well with little (or none) power supply tweaking, and eliminates bringing mercury vapor into your living room.
http://www.diyaudio.com/forums/tubes-valves/50440-using-83-a.html
Several years ago I snagged a pair of Transcendar TT-015's on eBay for about $110. (3K-100mA-15W SE) This was before they began jacking the starting price up. I made a lash-up with an external Kepco lab supply and was impressed with the sound quality. But I got busy with something else and never made a finished amp. Maybe someday. But even at todays price, they're still a good deal.
Attachments
Last edited:
Boywonder- I will be using 5U4G as I have several SED and Faico versions of these. The faico version are virtually identical- I can hear no difference and the faico is a fraction of the price
Hollowsate- Cheers for sharing your experience and yes they are a bit more pricey now.
Plasticisgood- Thank you for you rational input. I did wonder about copper. At work (teflon extrusions) our electrical engineer pointed out to me that copper is good blocker of RF. I think you are probably correct on the sowter transformer. I have looked at James as well. But I keep coming back to sowter. I need to decide which to go for the SA07 or SA08. Again showing my ignorance but trying to be sensible- the SA07 seems to show a flatter response but I am wondering if the overkill of the SA08 might be better in the long run. IE- Better to spend once on the expensive transformer than to spend less then end up buying the one I really wanted but talked/justified myself out of. I did not; but should have guessed that like with valves, circuit design and even caps there is no one ultimate perfect one for every job. Like you say- it is a compromise.
I need to think more on this and spend more time comparing the stats.
Hollowsate- Cheers for sharing your experience and yes they are a bit more pricey now.
Plasticisgood- Thank you for you rational input. I did wonder about copper. At work (teflon extrusions) our electrical engineer pointed out to me that copper is good blocker of RF. I think you are probably correct on the sowter transformer. I have looked at James as well. But I keep coming back to sowter. I need to decide which to go for the SA07 or SA08. Again showing my ignorance but trying to be sensible- the SA07 seems to show a flatter response but I am wondering if the overkill of the SA08 might be better in the long run. IE- Better to spend once on the expensive transformer than to spend less then end up buying the one I really wanted but talked/justified myself out of. I did not; but should have guessed that like with valves, circuit design and even caps there is no one ultimate perfect one for every job. Like you say- it is a compromise.
I need to think more on this and spend more time comparing the stats.
I remember a fire at work where there were acrylic turnings in the tray of a lathe and hot metal chips had landed on top. Plastic has a tenancy to crack where cut or drilled unless you use special tools for cutting, would require rubber washers under the screws or bolts to keep from over compressing the transformer mounts. I would have serious reservations from the flammability, if a component fails you could loose everything!
The best OPTs I have used out of Lundahl, Audio Note and O-netics is O-netics. Bud Purvine makes them in the USA in small quantities. There may be a waiting list but it's worth finding out what the situation is. hpurvine@gmail.com I'd prefer these to Sowter. I'd also seriously consider James and Hashimoto instead of Sowter.
But I'd put my resources into the input section. I'm using 4P1L in filament bias into either Lundahl LL1692A/18mA or Hammond 126C interstages. This is a cheap and wonderful directly heated tube. If you're anywhere near the London area you can come and have a listen. I'm in Hammersmith.
Andy
But I'd put my resources into the input section. I'm using 4P1L in filament bias into either Lundahl LL1692A/18mA or Hammond 126C interstages. This is a cheap and wonderful directly heated tube. If you're anywhere near the London area you can come and have a listen. I'm in Hammersmith.
Andy
Hi Andy, thanks for the offer but I am over 100 miles north. I am interested to know why you do not rate sowter as highly as others? I did look at Audio Note with interest. It is a big choice I have to make as there is about £200 difference which goes along way when making an amp even more so when each transformer is just shy of a weeks wages for me.
Last edited:
I've never owned a Sowter transformer - I'm just thinking of value for money here. What I have owned and listened to are:
LL1620/80mA - using this now because I need the 80mA
LL1623/60mA - similar to above
LL1682/50mA - scaled down version, LL1620 probably better sounding.
Audio Note Trans-152 - comparable to the LL1660 but no better, probably better at 5K than 2.5K
O-netics - commercial SE OPT - best sound of all the above, but smaller and not as powerful in watts. If you want to run the 300bs at 70mA you need to go up to the next model, which is the Level 1 I think. Goes up in price to levels 2 and 3.
The point I'm making is that you should not put all your money into the OPT, thinking that this will "make" the sound. It won't. The input stages will really make the sound. What you don't want to do is use generic indirectly heated tubes with resistor plate loads and cathode resistors with bypasses and couple them up with capacitors. That will kill any possibility of a really great amp. So reserve a good part of your budget for interstages. If you want a 2-stage amp, use a high mu valve into a really good interstage. If you want a 3-stage amp then use all directly heated tubes. This will make a big difference in itself. Think about it - why do you imagine a 300b will make all the difference? It has a mu of about 3. Spare a thought for the input stage which has a combined mu of 70 to 100. Why go out of your way to use a DHT in the output and overlook the importance of directly heated tubes in the input? Where I would put my money is LL1692A for the input stage - under £200 a pair - and a pair of Hammond 126C in the driver stage - £60 a pair. Use 4P1L in filament bias for both stages. Here's a rough schematic. The input stage is the same but substitute a LL1692A/18mA or a LL1660/18mA and run it at 15 or 16mA. This is what I'm using and it's the best 300b amp I've built or heard.
LL1620/80mA - using this now because I need the 80mA
LL1623/60mA - similar to above
LL1682/50mA - scaled down version, LL1620 probably better sounding.
Audio Note Trans-152 - comparable to the LL1660 but no better, probably better at 5K than 2.5K
O-netics - commercial SE OPT - best sound of all the above, but smaller and not as powerful in watts. If you want to run the 300bs at 70mA you need to go up to the next model, which is the Level 1 I think. Goes up in price to levels 2 and 3.
The point I'm making is that you should not put all your money into the OPT, thinking that this will "make" the sound. It won't. The input stages will really make the sound. What you don't want to do is use generic indirectly heated tubes with resistor plate loads and cathode resistors with bypasses and couple them up with capacitors. That will kill any possibility of a really great amp. So reserve a good part of your budget for interstages. If you want a 2-stage amp, use a high mu valve into a really good interstage. If you want a 3-stage amp then use all directly heated tubes. This will make a big difference in itself. Think about it - why do you imagine a 300b will make all the difference? It has a mu of about 3. Spare a thought for the input stage which has a combined mu of 70 to 100. Why go out of your way to use a DHT in the output and overlook the importance of directly heated tubes in the input? Where I would put my money is LL1692A for the input stage - under £200 a pair - and a pair of Hammond 126C in the driver stage - £60 a pair. Use 4P1L in filament bias for both stages. Here's a rough schematic. The input stage is the same but substitute a LL1692A/18mA or a LL1660/18mA and run it at 15 or 16mA. This is what I'm using and it's the best 300b amp I've built or heard.
Attachments
Last edited:
Bluebell Audio sells the 126C for £27.10. I get my Lundahl transformers from Thomas Mayer. http://vinylsavor.blogspot.co.uk/2012/03/filament-bias-part-1-concept.html The link to his site explains filament bias and why it's a really good idea for directly heated tubes like the 4P1L.
Andy
Andy
Last edited:
Thanks Andy for the schematic and the links. Thank you ixe13 for the ebay heads up. I am still getting the parts together for the monoblocks but the OP transformers will have to wait as the exhaust decided to fall off the car on the way back from work the other day- Great. So I do not think I will be putting any money down untill next month. I will keep you posted. All the best, Richard.
... really would like to keep it simple as this is my first big project. Being a bit in the dark I have a few questions that I would really appreciated getting some feedback on...[/SIZE][/FONT]
I was thinking of using 10mm black acrylic for the top and bottom plate with a dark mahogany frame. Will the acrylic be able to take the heat generated from the valves?
Should I use Teflon or ceramic valve bases and is there any brand that I should keep clear of?
....
Here is some advice that is not "trendy" but 100% based on good engineering
1) Use a conventional tube amp chassis. Yes the kind they have been using for 60+ years. This is a plain aluminum box. Hammond makes some good ones like these:type_Document_Title_here
The 17 x 10 x 3 part is $40. (be sure and get the cover plate as you need metal on all six sides.) These are cheaper brands but Hammond is the "standard".
2) Buy BELTON sockets. They are the best quality. Don't care about other's claims about gold plating or other voodoo magic. They use a very high quality glass filled plastic and the shape of the contacts is good and that is what matters most.
Attach the sockets to the chassis in #1 with a pait of #6 or #4 machine screws and star washers. I use blue locktite on the nuts. Tubes mostly cool by radiation, not conduction.
I always take the time to build cabinets for my amps. Even in the 1950's when they made cars with no seat belts just to save a buck they still covered the tubes. Cover the chassis with wood, plexiglas or whatever. It is purely cosmetic and does not matter.
What matters is that inside the chassis where the high voltage wires live, all six sides of the box needs to be made of conductive materials and connected to ground.
For transformers: Hammond 1630sea might work. They are massive at 11 lbs each. price is $125 with free shipping from STF elect. the big Hammonds have a very impressive sound
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
- Home
- Amplifiers
- Tubes / Valves
- Which OP transformer and materials?