Hi Guys,
I have been looking around here to get started on a valve amp. But I want an integrated amp and not just a pre-amp. Output power should be ~20 watt.
The designs I have looked at so far are using tubes that are rather expensive. I guess thats kind of the deal if you want more than just a pre-amp. But maybe there are design that use some that go for below $100 per tube for the output stage?
I am Australia based and one of my main vendors I am dealing with buying components has a large and costantly growing choice of tubes. But I feel its kind of limited here compared to what is available in the US.
I have been looking around here to get started on a valve amp. But I want an integrated amp and not just a pre-amp. Output power should be ~20 watt.
The designs I have looked at so far are using tubes that are rather expensive. I guess thats kind of the deal if you want more than just a pre-amp. But maybe there are design that use some that go for below $100 per tube for the output stage?
I am Australia based and one of my main vendors I am dealing with buying components has a large and costantly growing choice of tubes. But I feel its kind of limited here compared to what is available in the US.
Have searched for EL34 or 6L6?
https://www.tubedepot.com/products/jj-e34l-el34-power-vacuum-tube
https://www.thetubestore.com/psvane-5881-6l6gb
https://www.tubedepot.com/products/jj-e34l-el34-power-vacuum-tube
https://www.thetubestore.com/psvane-5881-6l6gb
Wow, that looks interesting! Guess I just need to search for some circuit designs that use them. Next challenge will be transformer.
You mentioned you are in Australia. There are some creative solutions from 'down under' like using 100v line output transformers as OPTs ...
100V Line Output at OPT
... and using cheap TV tubes ...
EL36 SE
If working to a budget is your goal, then it can be possible to create something under $100 I think, with an eye on auction sites and creativity.
What are you hoping to build?
100V Line Output at OPT
... and using cheap TV tubes ...
EL36 SE
If working to a budget is your goal, then it can be possible to create something under $100 I think, with an eye on auction sites and creativity.
What are you hoping to build?
I find the Eico HF-87/89 really good for a first project, you can get very decent results using 6L6s instead of the original EL34s. I built one, works great. 6H9->6SL7, 6H8->6SN7, 6P3S-E -> 6L6/5881.
Besides some exotic types, most of the AF power tuber cost less than $100 here in Europe. But if you wanna go really cheap, I'd vote for series heated, P-type TV tubes. E. g.: According to the RCA datasheet, a pair of cheap PL84's can put out 25 watts, and even more, if we follow the designs of some Hohner musical instrument amplifiers. The caveat might be that suitable OT's aren't stock types.
Best regards!
Best regards!
Oh, up to ~120 watts are possible with still bargain tubes: A pair of GU-50's 😉 ! But it'd require a surely non-bargain OT and an even so PT.
You see what I mean: An amplifier's total cost isn't a matter of the power tubes, at least not in first line, but of the 'iron'.
Best regards!
You see what I mean: An amplifier's total cost isn't a matter of the power tubes, at least not in first line, but of the 'iron'.
Best regards!
Probably true, but 25W OPTs don’t cost significantly less than 8 watt ones do. Save ten bucks for 1/3 the power - WOW - I can put that into retirement savings and be rich in 1000 years. The same bargain tubes (XL86/PL84, or $3 TV sweep tubes) will drive either. Jump up in power to say 70, 100 watts, and things get expensive fast. And 5 watts single ended isn’t necessarily any cheaper ($5W SE OPT>> $25W PP OPT, frequency response being equal). Easier to understand and build yes, but cheaper no - unless you’re willing to live with say 80 to 100 Hz low end to get the price of that gapped trafo down. I would dare to say that about 20 watts PP is a sweet spot considering what quality output iron costs, and the fact that cheap tubes can be used. It’s also in the realm of using 120/240 or 240/240 volt isolation trafos for power (to get 320-ish volts, and perhaps 160 for g2 at the same time), eliminating the need for that to have a premium added onto the price.
Push come to shove the cost of OP valves isn't the main cost when building a valve amp. The OPT's are the highest priced components, your talking roughly £100 each for budget 25w PP OPT's. Next is the mains tfmr, however if your time rich but skint you can buy a cheap used toroid for roughly £30, pull off the secondary/s then wind on your HT winding and heater windings for about £20 worth of copper wire.
Another big cost is the chassis, but if you have time and can use your hands to fettle metal, that's another X amount of dollars saved. Washing machines from a scrapyard are good sources of wire, that leaves you OP valves. Stick with EL34's or 6L6's or at a push 807's, there are cheaper valves but valves like TV valves are not for beginners to be honest.
Lastly if your gonna build an amp, choose wisely, just because you can find a schematic it doesn't mean it'll work if you build it: do your research.
Good luck, Andy.
Another big cost is the chassis, but if you have time and can use your hands to fettle metal, that's another X amount of dollars saved. Washing machines from a scrapyard are good sources of wire, that leaves you OP valves. Stick with EL34's or 6L6's or at a push 807's, there are cheaper valves but valves like TV valves are not for beginners to be honest.
Lastly if your gonna build an amp, choose wisely, just because you can find a schematic it doesn't mean it'll work if you build it: do your research.
Good luck, Andy.
And nobody says you have to run EL34’s on 400 volts either. They run just fine on 300-340 if you only require 20 to 25 watts. Then you don’t even need to rewind a cheap toroid for power - use it the way it comes. Slap on a 6.3 volt winding out of bell wire and call it good.
A Rowe R-4359A jukebox amp may be a consideration. Output and power supply PP iron usually goes for $200-$300 on Ebay. The stock amp is rated for 50 watts from a quad of 7591s and a couple 12ax7. The output secondaries are a bit goofy but if my measurements are correct the primary is around 4500 ohms with 8 and 2 ohm usable secondaries.
One day if we have a little time, I would like us to take up the thread on this one and in particular on the opts and the different ways of wiring them.
I've tried half a million combinations and ended up getting lost, I really like these amps and it would be great to cross read on how to use the opts.
@Andy: It's just Ebay so it all depends on whether the specific vendor is willing to ship. The current selection is kind of rusty.
@huggy: I hear that. From what I can tell the oft quoted wiring directions are incorrect. 100 VAC on the primary returns a little over 4 VAC between the highest voltage secondary terminal E1 and ground terminal E4. A voltage ratio of just under 25 means between 4k:8 and 5K:8. Terminating E1-E4 with 8 ohms and measuring the wide band primary impedance with a DATS V3 gives comparable results.
@huggy: I hear that. From what I can tell the oft quoted wiring directions are incorrect. 100 VAC on the primary returns a little over 4 VAC between the highest voltage secondary terminal E1 and ground terminal E4. A voltage ratio of just under 25 means between 4k:8 and 5K:8. Terminating E1-E4 with 8 ohms and measuring the wide band primary impedance with a DATS V3 gives comparable results.
Rowe R-4359A transformers | | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | |
| OPT L | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | |
OPT L | Terminal | E1 | E2 | E3 | E4 | E5 | E6 | 70V | 70V | Prim 1 | Prim 2 | Prim CT | | | | Condition | | |
| Colour | Yel | Grn | Brn/Wht | Wht | Blu/Wht | Grn/Wht | Blk | Gry | Brn | Grn | Red | | | | | | |
| Vac to E4 | 4.202 | 2.102 | 0.263 | 0.000 | 0.525 | 1.052 | 9.400 | 9.400 | x | x | x | | | | 100 VAC 60 Hz Brn Grn Primary | | |
| Ohms to E4 | 0.4 | 0.2 | 0.1 | 0 | 0.1 | 0.1 | 3.5 | 4.3 | x | x | x | | | | | | |
| Ohms to Pri Red | x | x | x | x | x | x | x | x | 74.6 | 55.7 | 0 | | | | | | |
| | | | | | | | | | | | | | | | | | |
OPT R | Terminal | E1 | E2 | E3 | E4 | E5 | E6 | 70V | 70V | Prim 1 | Prim 2 | Prim CT | | | | | | |
| Colour | Yel | Grn | Brn/Wht | Wht | Blu/Wht | Grn/Wht | Blk | Gry | Brn | Grn | Red | | | | | | |
| Vac to E4 | 4.210 | 2.103 | 0.263 | 0.000 | 0.526 | 1.054 | 9.420 | 9.420 | x | x | x | | | | 100 VAC 60 Hz Brn Grn Primary | | |
| Ohms to E4 | 0.3 | 0.2 | 0.1 | 0 | 0.1 | 0.1 | 3.6 | 4,2 | x | x | x | | | | | | |
| Ohms to Pri Red | x | x | x | x | x | x | x | x | 73.8 | 55.7 | 0 | | | | | | |
| | | | | | | | | | | | | | | | | | |
Power | Terminal | AC Line | AC Line | AC Line | 5 VAC | 5 VAC | HV Pos | HV CT | HV Neg | 6.3 VAC | 6.3 VAC CT | 6.3 VAC | VAC | VAC CT | VAC | | | |
| Colour | Blk | Blk/Yel | Blk/Red | Yel | Yel | Red | Red-Yel | Red | Grn | Grn/Yel | Grn | Brn | Brn-Yel | Brn | | | |
| VAC | 0 | 120 | 0 | 0 | 5.42 | 330.5 | 0 | 334.8 | 3.348 | 0 | 3.35 | 27.53 | 0 | 27.55 | | | |
| Ohms | | | | 0 | 0.1 | 39 | 0 | 42.2 | 0.1 | 0 | 0.1 | 1.2 | 0 | 1.2 | | | |
Re: Amp on a low budget --
I think the biggest differences in expense come from the metal and magnetics.
If you build a stereo push-pull EL34 amp with 450V B+ that requires a power transformer capable of delivering 300mA of plate current, that transformer will cost significantly more than a power transformer for a PP EL84 amp capable of delivering 300V B+ at 200mA plate current.
If you build an amp with a 450VDC B+, you'll need to use 500V rated capacitors or series-connect 300V capacitors. However, if you build a PP EL84 or PP EL86 amp with a 300V B+, you can safely use 400V rated capacitors, which saves some money.
The output transformers are the key ingredient. Member kodabmx likes to put together amps with repurposed toroid stepdown power transformers used as OPTs. That can save a lot of money right there.
The cost of tubes is significant, but audio types all seem to cost about the same. A JJ EL84 costs about $20 each these days (kind of expensive), while a Russian 6P14P-EV can cost even more than that. The generic Russian 6P14P costs about $15 these days. Russian 6P3S-E are going for $25 each (prices for those have gone UP). The bargain used to be the generic Russian 6P3S (no "-E"), but those cost $15 each these days. Still a good deal for what you get (use it like an old 6L6G with no more than 350V on the plates, not like a 6L6GC). The cheapest EH EL34 tubes cost about $30 each. I would call all of these kind of expensive.
kodabmx and Lingwendil have posted some compelling designs that could be built cheaply. Eli Duttman's "El Cheapo" amp is also a classic, but will only yield 10W per channel at most using UL wired 6AQ5 outputs.
I think the biggest differences in expense come from the metal and magnetics.
- The chassis
- The power transformer
- The two output transformers for stereo
If you build a stereo push-pull EL34 amp with 450V B+ that requires a power transformer capable of delivering 300mA of plate current, that transformer will cost significantly more than a power transformer for a PP EL84 amp capable of delivering 300V B+ at 200mA plate current.
If you build an amp with a 450VDC B+, you'll need to use 500V rated capacitors or series-connect 300V capacitors. However, if you build a PP EL84 or PP EL86 amp with a 300V B+, you can safely use 400V rated capacitors, which saves some money.
The output transformers are the key ingredient. Member kodabmx likes to put together amps with repurposed toroid stepdown power transformers used as OPTs. That can save a lot of money right there.
The cost of tubes is significant, but audio types all seem to cost about the same. A JJ EL84 costs about $20 each these days (kind of expensive), while a Russian 6P14P-EV can cost even more than that. The generic Russian 6P14P costs about $15 these days. Russian 6P3S-E are going for $25 each (prices for those have gone UP). The bargain used to be the generic Russian 6P3S (no "-E"), but those cost $15 each these days. Still a good deal for what you get (use it like an old 6L6G with no more than 350V on the plates, not like a 6L6GC). The cheapest EH EL34 tubes cost about $30 each. I would call all of these kind of expensive.
kodabmx and Lingwendil have posted some compelling designs that could be built cheaply. Eli Duttman's "El Cheapo" amp is also a classic, but will only yield 10W per channel at most using UL wired 6AQ5 outputs.
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Wouldn't be able to get a Rowe R-4359A jukebox amp here in AUS. But there are a lot of good suggestion here.
I am totally new to valve amps and don't know the basics. From what I learned is that I need an Power Transformer and an OT (that means Output Transformer). So my guess is, it will be 2 OTs and one power transformer.
These OTs are supposed to decrease the high voltage coming from the tubes down to "speaker level"? It also seems that I can pass signal between 100 to 400V through the tubes?
I am totally new to valve amps and don't know the basics. From what I learned is that I need an Power Transformer and an OT (that means Output Transformer). So my guess is, it will be 2 OTs and one power transformer.
These OTs are supposed to decrease the high voltage coming from the tubes down to "speaker level"? It also seems that I can pass signal between 100 to 400V through the tubes?