On that topic, I saw the weirdest thing ever. Somebody had set bookshelf speakers up on plant stands--effectively cutting off cabinet space that could have been used for quality bass. Why does better marketing usually result in lesser quality?
I have debunked the theory that Teflon silver caps have to be used in the signal path of tube amps to sound great.... Tube amps can be made on a budget that sound great! It is more than just the components, it is the design electrically as well as physical layout.
It is more than just "Tube amp", it is what topology of tube amp......
One of the advantages of "PP triode connected output tube amps" is the fact that the speakers are connected through the transformers to the tubes. The speakers impedance is directly reflected to the output tubes so as the impedance goes up, the output gain goes up also. SO why is that a big deal? With solid state the output impedance is very low and the amp does not care about speaker impedance. When the impedance increases, the output power is decreased P=V^2/R. If the gain of the output section is a reflection of the speaker impedance the gain goes up compensating for the change in impedance. Don't take my word for it, do an A B comparison for yourself.
It is more than just "Tube amp", it is what topology of tube amp......
One of the advantages of "PP triode connected output tube amps" is the fact that the speakers are connected through the transformers to the tubes. The speakers impedance is directly reflected to the output tubes so as the impedance goes up, the output gain goes up also. SO why is that a big deal? With solid state the output impedance is very low and the amp does not care about speaker impedance. When the impedance increases, the output power is decreased P=V^2/R. If the gain of the output section is a reflection of the speaker impedance the gain goes up compensating for the change in impedance. Don't take my word for it, do an A B comparison for yourself.
K & K has a nice kit for the ST70 (you provide a used ST70) for <$300 USD.
details here:
K & K Audio - Lundahl Transformers, audio DIY kits and more
details here:
K & K Audio - Lundahl Transformers, audio DIY kits and more
The Bob Latino ST70 's seem to be popular.
You don't need a "kit" per say, you can order transformers and fill in the blanks for the rest of the parts. That will give you more choice and flexibility on the final project.
You can build a juicy tube amp for $500.
Get the iron from Hammond or Edcor, purchase resistors and capacitors in "kits", you will save money had have parts left over for other builds or changes.
You don't need a "kit" per say, you can order transformers and fill in the blanks for the rest of the parts. That will give you more choice and flexibility on the final project.
You can build a juicy tube amp for $500.
Get the iron from Hammond or Edcor, purchase resistors and capacitors in "kits", you will save money had have parts left over for other builds or changes.
I hope it isn't offensive that my Parallel LM1875 has a dial for that feature that took only 8 minutes to install and the whole thing cost only $34.
Bismar,
Those Mark III's you would need 2 so costs would add up. Maybe find used over there with good transformers for rebuilding.
Are you handy with tools, and working with metal and wood, as that could save you money by building your own chassis and speaker cabinets?
Can you get Hammond transformers over there for affordable prices, or do you have to ship from the US?
If so get some Hammond (12 lbs. ea so need to make a sturdy base/ chassis for these) 1650R OPT's as they can be had for $105 in the US. With a 100W rating and 5K input they will give you a great bandwidth (Frequency response range in the power range you would use, which is less than half the 100W rating)
One AnteK Toroid 325-0-325 PS trans for $40 as you could use SS diodes to save $ and have great solid bass. Just use ICL's (Inrush current limiters) to help the tubes, caps etc last. $10
PS cap board & kit $77 ( may save by wiring caps on perfboard etc.)
Pick one of the affordable Driver boards of your choice for ST-70. You can get them with a kit of parts for about $100.
All the above are wired up per std ST-70 schematics along with instructions from board kits
Other parts like the 4 Octal 8 pin tube sockets, RCA inputs and speaker terminals , wire etc. Maybe $50. Might be able to add a volume control for $10-20 but a nice line stage preamp may be better and could actually be added to your homemade chassis for say another maybe $50 if you use the amps PS.
For Phono you would have to build or buy a suitable preamp.
Base-chassis could be built for maybe $50 or less if you get scrap materials to build with.
Tubes if you start with affordable EL34/6CA7 /KT-77 or 6LGC/KT-66 types could cost you $100-120
Maybe as low as $650 plus shipping if you want 35-40 W/CH to start and KT-88's could be rolled in later for a different sound and 50W/CH.
For an upgrade add an Edcor 2H low DCR (18-21 ohms) choke with 300-400 mA capacity @ $31-37
Should work with and sound fantastic with a wide range of new and used speakers out there.
Randy
Those Mark III's you would need 2 so costs would add up. Maybe find used over there with good transformers for rebuilding.
Are you handy with tools, and working with metal and wood, as that could save you money by building your own chassis and speaker cabinets?
Can you get Hammond transformers over there for affordable prices, or do you have to ship from the US?
If so get some Hammond (12 lbs. ea so need to make a sturdy base/ chassis for these) 1650R OPT's as they can be had for $105 in the US. With a 100W rating and 5K input they will give you a great bandwidth (Frequency response range in the power range you would use, which is less than half the 100W rating)
One AnteK Toroid 325-0-325 PS trans for $40 as you could use SS diodes to save $ and have great solid bass. Just use ICL's (Inrush current limiters) to help the tubes, caps etc last. $10
PS cap board & kit $77 ( may save by wiring caps on perfboard etc.)
Pick one of the affordable Driver boards of your choice for ST-70. You can get them with a kit of parts for about $100.
All the above are wired up per std ST-70 schematics along with instructions from board kits
Other parts like the 4 Octal 8 pin tube sockets, RCA inputs and speaker terminals , wire etc. Maybe $50. Might be able to add a volume control for $10-20 but a nice line stage preamp may be better and could actually be added to your homemade chassis for say another maybe $50 if you use the amps PS.
For Phono you would have to build or buy a suitable preamp.
Base-chassis could be built for maybe $50 or less if you get scrap materials to build with.
Tubes if you start with affordable EL34/6CA7 /KT-77 or 6LGC/KT-66 types could cost you $100-120
Maybe as low as $650 plus shipping if you want 35-40 W/CH to start and KT-88's could be rolled in later for a different sound and 50W/CH.
For an upgrade add an Edcor 2H low DCR (18-21 ohms) choke with 300-400 mA capacity @ $31-37
Should work with and sound fantastic with a wide range of new and used speakers out there.
Randy
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Current feedback is not used in mainstream products mainly due to being more sensitive to the speaker and room dynamics being part of the feedback loop. You are correct that accomplished by a different method, a similar result for improved sonic performance. More than one way to skin a cat...
Current feed back in solid state amps does have some limitations, "The principal advantages of current drive are seen to be an elimination of performance dependence on voice coil resistance ( which is thermally modulated) and also coil -inductive effects, which give rise to high frequency distortion, along with nonlinear electo-magnetic damping due to BL variations. The technique is similarly insensitive to the lumped series elements of the amplifier-loudspeaker interconnect. However, it is often necessary to lower the system Q caused by the loss of amplifier generated dampening, either by open loop compensation, by special drive-unit design, or by motional feedback, where the latter is regarded as the optimal method at low frequencies."
from Distortion Reduction in Moving -Coil Loudspeakers Systems Using Current Driver Technology, Mills and Hawksford 1989
In a tube amp it just a matter of reflected speaker impedance through the transformer on the output tubes......
No special feed back loops, no real change to dampening, however global negative can be used to lower the distortion.
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Jim McShane sells parts kits for "El Cheapo" builds. The builder supplies "iron" and case work.
That's a frequency response plot for a bass/midrange driver. The impedance curve will reflect both the drivers and the crossover used.
Just now I imagined: LM675 non-inverted, set to very low gain, with 47k to 100k feedback resistor for no current noise, run from reg/capmulti power, and enclosed into global negative feedback with a tube so as to override the solid state sound. A similar prospect can be done with TDA7293 by shorting the inputs to create a unity stable fet buffer with enough power to drive inefficient speakers. The low loss outputs of these two hybrid prospects is especially good for driving ported bookshelf speakers.
My opinion on Hybrid amplifiers: There isn't a circuit more cost efficient than the triode if one wants a tube amp sound. Fully solid state circuits can do it, but a totally effective tube emulation is several complex dodges stacked and instead of finding one tube, there are scads of little bits to find, which can be expensive, and energy consumption of such devices is usually inferior to the triode. Therefore, I do believe that any sensible tube hybrid amp will contain small signal triodes.
All of the other matters are all adjustable (at either amp or speaker) or at least less complex.
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Sorry I am posting in a hurry, but the OP flag says he is from Australia. Suggestions about power supplies, transformers an shipping need to be considered. That is 240 volt mains and very expensive shipping for transformers and speaker drivers.
For OP, if you can get speakers that are 3dB more sensitive (92 dB), then you can get away with half the amplifier power. Tube amps of 10-14 watts are great for a beginner. Getting 30 watts becomes more expensive and complex (but still achievable). I think if you can get a few dB more sensitive speakers, the 10-14 watt options mentioned are all great.
Trouble with speakers is trying to get more than two of the four parameters (small, cheap, efficient, bass extension).
Good luck with the project, plenty of helpful people on this forum who will be willing to assist you!
Chris
For OP, if you can get speakers that are 3dB more sensitive (92 dB), then you can get away with half the amplifier power. Tube amps of 10-14 watts are great for a beginner. Getting 30 watts becomes more expensive and complex (but still achievable). I think if you can get a few dB more sensitive speakers, the 10-14 watt options mentioned are all great.
Trouble with speakers is trying to get more than two of the four parameters (small, cheap, efficient, bass extension).
Good luck with the project, plenty of helpful people on this forum who will be willing to assist you!
Chris
Agreed! Shipping costs can eat you alive, without a trek from North America to Australia.
Chris, do you know if Triad brand magnetics are readily available in "Oz"? These days, they are manufactured in China and favorably priced. The power trafos I suggested for "El Cheapo" have dual primaries, which makes them useful in both "120" and "240" V. zones.
Hi Bismar. I built a st-70 kit from Bob Latino earlier this year. Everything included, you just need solder and soldering iron. Mine cost almost AUS $1200 (with options like vol. control, 240 volt transformer & upgrade caps) delivered to Northern Territory, Australia. Yes, it's over your budget but there's no guesswork involved, you won't need to mess around trying to find all the parts you need and the finished amp will look and sound great. There's no point trying to save a few $ on a cheap amp if you're not happy with the end product. Mine is in a big room and has no trouble making my (and my neighbours) windows rattle. Plenty of power even for not-so-efficient speakers. Just my two cents worth, and no; Bob Latino didn't pay me to write this! Good luck with your build! All the best, Pete.
Thanks guys, you've given me a lot to think about.
Quick query about the ST70 amps, can i replace the A470 OPT with a hammond 1650R?
The A470 afaik is 4300 ohms and the 1650R 5000 ohms.
Also what would be the equivalent of the PA051, the power transformer for the ST70?
I'm investigating the possibility of buying transformers locally.
Quick query about the ST70 amps, can i replace the A470 OPT with a hammond 1650R?
The A470 afaik is 4300 ohms and the 1650R 5000 ohms.
Also what would be the equivalent of the PA051, the power transformer for the ST70?
I'm investigating the possibility of buying transformers locally.
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In the Netherlands there is a kit sold under the trade name VELLEMAN having four parallel push-pulls EL34 with fixed bias and the chassis is chrome plated it looks very impressive.The output power is 100+ watts per channel In the U.K. the agents are MAPLIN and in Australia they do have agents as far as I know. Buy any electronics mag from the U.K. and their ad should be in there. This is sufficient to fill a medium sized hall. even with very inefficient speakers. They do offer a repair service if you encounter problems
That higher primary impedance on the 1650R will result in a bit lower distortion and will be happier with 6L6GC & KT-66 type tubes. Actually more ideal for sonics!
Here's the spec's you want if you build with a tube rectifier. It is an upgraded trans compared to the original so you can run the big KT-88 tube by adjusting the bias. Go to dual 5AR4/GZ34 if you are going to use the big tubes too. That will really make a solid PS if you want tube rectified. That's why all the manufactures of the bigger amps back in the day made mono blocks like the Dynaco Mark III's or simply went to SS diodes.
PA060 S Dynaco ST70 Upgrade Power Transformer Replacement MADE IN USA
If you want SS diodes instead use ICL's as I mentioned and 320-0-320 V for the same B+ as SS drops less voltage. along withe the same or greater mA capacity.
Make sure the heater outputs have the same Amperage or a bit higher won't matter.
Use this diode mod with Quieter faster UF4007's for a few cents more. It saves the tube rectifier which is under a lot of stress in this amp and many others. Also new production tubes are weaker. It doesn't affect the sonics and keeps the slow warm up of the 5AR4/GZ34 too.
If you can find a Toriod like the Antec I mentioned for less $ that would be great too. Just need a bias tap for the 55V. You could always use a separate small transformer for that.
I figured Hammonds might be sold over there as a few builders from your country use them.
Hammond Mfg. - Electronic Distributors - Australia & New Zealand
Randy
Here's the spec's you want if you build with a tube rectifier. It is an upgraded trans compared to the original so you can run the big KT-88 tube by adjusting the bias. Go to dual 5AR4/GZ34 if you are going to use the big tubes too. That will really make a solid PS if you want tube rectified. That's why all the manufactures of the bigger amps back in the day made mono blocks like the Dynaco Mark III's or simply went to SS diodes.
PA060 S Dynaco ST70 Upgrade Power Transformer Replacement MADE IN USA
If you want SS diodes instead use ICL's as I mentioned and 320-0-320 V for the same B+ as SS drops less voltage. along withe the same or greater mA capacity.
Make sure the heater outputs have the same Amperage or a bit higher won't matter.
Use this diode mod with Quieter faster UF4007's for a few cents more. It saves the tube rectifier which is under a lot of stress in this amp and many others. Also new production tubes are weaker. It doesn't affect the sonics and keeps the slow warm up of the 5AR4/GZ34 too.
If you can find a Toriod like the Antec I mentioned for less $ that would be great too. Just need a bias tap for the 55V. You could always use a separate small transformer for that.
I figured Hammonds might be sold over there as a few builders from your country use them.
Hammond Mfg. - Electronic Distributors - Australia & New Zealand
Randy
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Looks like Digikey has OPT's for a reasonable price. May have a suitable PS trans from another manufacture.
If your handy this might be doable , sound great , and be affordable with your own chassis. Uses Eico HF-89 Schematic , which was a well liked amp using the popular Mullard 5-20 circuit.
diytube.com :: View topic - Overhaulin' the ST70
If you don't want to go that way boards are available again for 2 mono amps with everything mounted on the circuit board for an easy build. Of course you have to source the parts and build two chassis etc. There is BOM on the site and manual for it with parts list too.
http://www.diytube.com/phpBB2/viewtopic.php?t=5117
Randy
If your handy this might be doable , sound great , and be affordable with your own chassis. Uses Eico HF-89 Schematic , which was a well liked amp using the popular Mullard 5-20 circuit.
diytube.com :: View topic - Overhaulin' the ST70
If you don't want to go that way boards are available again for 2 mono amps with everything mounted on the circuit board for an easy build. Of course you have to source the parts and build two chassis etc. There is BOM on the site and manual for it with parts list too.
http://www.diytube.com/phpBB2/viewtopic.php?t=5117
Randy
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Hi Bismar. I can send you the complete parts list etc that came with my amp kit if you like.. It may make life a little easier if you're building a st-70 type amp. A couple side notes.. Bobs chassis is stainless steel which is a pain to modify (but looks great). Having the inputs at the front isn't a great idea. The power trafo is bigger than the original so running kt-88's /6550's is no problem. I've run it loud for hours and doesn't get very hot.
All the best, Pete.
All the best, Pete.
Hi guys thanks for your input.
I'm leaning towards getting a ST70 kit without the transformers, and purchasing the Hammond 1650R for the OPT.
In regards to the power transformer, i think i will stick with the laminated core types even though its probably has a high cost.
Seeing as the two OPT will use 200W at max capacity, what kind of laminated core transformer should i be looking for?
I'm after something that digikey stocks to minimise shipping costs.
I'm leaning towards getting a ST70 kit without the transformers, and purchasing the Hammond 1650R for the OPT.
In regards to the power transformer, i think i will stick with the laminated core types even though its probably has a high cost.
Seeing as the two OPT will use 200W at max capacity, what kind of laminated core transformer should i be looking for?
I'm after something that digikey stocks to minimise shipping costs.
A PS with those spec's I gave, for SS or use the link to Triode's as that's an upgraded one as it's an upgraded one with higher mA capacity than the original which has been said to be fine on the forms with KT-88's. If you can find one with a higher rating in mA capacity like 350-400 mA that would be fine too. You will only be using half of the OPT's capacity too at the most.
Using the toriod PS trans. would probably entail extra costs as you would probably want a cover for it and have to buy a bias PS trans.
Original copy of chassis in SS can be had from dynakitparts.com verse Triode Electronics which isn't quite original. Just depends what you want.
Dynakitparts has original cages other parts too.
Randy
Using the toriod PS trans. would probably entail extra costs as you would probably want a cover for it and have to buy a bias PS trans.
Original copy of chassis in SS can be had from dynakitparts.com verse Triode Electronics which isn't quite original. Just depends what you want.
Dynakitparts has original cages other parts too.
Randy
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Transport costs for the transformers is going to eat some cash. I have had good results with Edcor output transformers. They also make power transformers. If you can find a power transformer from them that will work, you can combine shipping with their very well priced output transformers. http://www.edcorusa.com/c/8/class-x
Have you decided on a speaker design yet? If you are competent enough to build speaker boxes, then you will be able to make an amplifier chassis. That opens you up to not having to use a kit. Several people posting on this forum make excellent designs with printed circuit boards (e.g. tubelab and pete millet) that may offer better performance than the ST70.
I do not know about triad availability here. I have had Edcor ship here and I have had the opportunity to pick up transformers from USA and Asia while travelling with work. All my amps have Edcor output except my 6L6 PP amp with Tamura. Power trafos are cheap Chinese or Hammond.
Ebay Australia may throw up some transformers that are salvageable.
Chris
Have you decided on a speaker design yet? If you are competent enough to build speaker boxes, then you will be able to make an amplifier chassis. That opens you up to not having to use a kit. Several people posting on this forum make excellent designs with printed circuit boards (e.g. tubelab and pete millet) that may offer better performance than the ST70.
I do not know about triad availability here. I have had Edcor ship here and I have had the opportunity to pick up transformers from USA and Asia while travelling with work. All my amps have Edcor output except my 6L6 PP amp with Tamura. Power trafos are cheap Chinese or Hammond.
Ebay Australia may throw up some transformers that are salvageable.
Chris
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