I know this ship has sailed, but after hearing the sjs modified Rui Lourenco preamp in my system I had to try to build one.
The wood and metal work is what I am best at, but apart from building various clones (I still use a Velleman K4040 clone) I am pretty much a novice here. I am struggling my way into PSUD2 and LTspice (I hate computers, and they seem to reciprocate the feeling!), but I have a couple (!) of questions for you all.
Firstly, the 10 ohm filament resistor; the Vishay/Dale flat wirewounds seem to be unobtainable, so what is a good replacement non-inductive resistor, or resistors if I parallel them? I have read the whole 381 pages of this thread, but can't remember where I saw alternatives recommended.
And valve sockets for the AZ1; there are a couple (from Langrex), one ceramic and one bakelite (that one looks used although he calls it NOS). Would it make much difference, or are there better alternatives? Without spending Yamamoto money!
I am in the UK, so US sales tend to cause problems, but I will go there if it's the only way.
And I haven't even started on the valves, apart from a cheap AZ1 to get me going. Any advice on the 26s would be appreciated, or even if anyone has some to sell.
The OP txs are Lundahl 2745/8mA, but the rest of the iron is Hammond, to keep costs down. They are all on the way.
Any help and advice greatly appreciated.
The wood and metal work is what I am best at, but apart from building various clones (I still use a Velleman K4040 clone) I am pretty much a novice here. I am struggling my way into PSUD2 and LTspice (I hate computers, and they seem to reciprocate the feeling!), but I have a couple (!) of questions for you all.
Firstly, the 10 ohm filament resistor; the Vishay/Dale flat wirewounds seem to be unobtainable, so what is a good replacement non-inductive resistor, or resistors if I parallel them? I have read the whole 381 pages of this thread, but can't remember where I saw alternatives recommended.
And valve sockets for the AZ1; there are a couple (from Langrex), one ceramic and one bakelite (that one looks used although he calls it NOS). Would it make much difference, or are there better alternatives? Without spending Yamamoto money!
I am in the UK, so US sales tend to cause problems, but I will go there if it's the only way.
And I haven't even started on the valves, apart from a cheap AZ1 to get me going. Any advice on the 26s would be appreciated, or even if anyone has some to sell.
The OP txs are Lundahl 2745/8mA, but the rest of the iron is Hammond, to keep costs down. They are all on the way.
Any help and advice greatly appreciated.
I'm in London UK. I have all the parts for building 26 preamps - valves, sockets, resistors, caps, interstages, plate chokes etc. I've built several over many years, so have the circuit diagrams as well. Also some finished and semi-finished ones. Email me on performanceandmedia (at) gmail (dotcom). I have too much stock anyway, so glad to supply future builders.
Hi Richard,
The easiest Ayrton-Perry (non-Inductive) wirewound is the Mills MRA. Available in UK/EU easily at:
Mills | Hifi Collective
At lower price points the Welwyn W24 wirewounds get quite close, for lower cost. They are not Aryton-Perry though.
CPC is the lowest cost UK source for these.
The easiest Ayrton-Perry (non-Inductive) wirewound is the Mills MRA. Available in UK/EU easily at:
Mills | Hifi Collective
At lower price points the Welwyn W24 wirewounds get quite close, for lower cost. They are not Aryton-Perry though.
CPC is the lowest cost UK source for these.
Thanks Andy, I'll email you.
And thanks Rod; I already use Mills MRA from hifi collective in my speaker crossovers, which sound pretty good in there. I see they do 51R. I guess paralleling 5 would do the job. And I'll probably use Mills for R1 on your regulator.
But I did rather like the look of those stacked flat Dales. A bit silly really, as they will be inside!
Now I have to work out how to draw circuits in LTspice; and I got rather excited the other night when I discovered I should be able to model speaker crossovers too!
And thanks Rod; I already use Mills MRA from hifi collective in my speaker crossovers, which sound pretty good in there. I see they do 51R. I guess paralleling 5 would do the job. And I'll probably use Mills for R1 on your regulator.
But I did rather like the look of those stacked flat Dales. A bit silly really, as they will be inside!
Now I have to work out how to draw circuits in LTspice; and I got rather excited the other night when I discovered I should be able to model speaker crossovers too!
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Mills or Welwyn resistors are entirely good ones, I use them in R.C (Hi Rod! ) regulators.
But Mills -even 12W MRA12- are a bit undersized resistors. I have some items with lengthened resistance -and dark brown body- even so I use them at 70-80% dissipation. My rule of the thumb: use it at half dissipation.
In my heater bias preamps/VAS stages (#26, 10Y, 801, 841) I use non-inductive (NH type) 50W DALE resistors WITH -enough large- heatsink!
Most of heater biased tubes heater current is about 1-1.25 A and bias voltage 8-10V, so dissipation of heter bias resistor is over 8-10W.
IMHO conventional cooling is insufficinet in most cases (too high resistor temperature), therefore I use heatsinks.
) regulators.But Mills -even 12W MRA12- are a bit undersized resistors. I have some items with lengthened resistance -and dark brown body- even so I use them at 70-80% dissipation. My rule of the thumb: use it at half dissipation.
In my heater bias preamps/VAS stages (#26, 10Y, 801, 841) I use non-inductive (NH type) 50W DALE resistors WITH -enough large- heatsink!
Most of heater biased tubes heater current is about 1-1.25 A and bias voltage 8-10V, so dissipation of heter bias resistor is over 8-10W.
IMHO conventional cooling is insufficinet in most cases (too high resistor temperature), therefore I use heatsinks.
Mills or Welwyn resistors are entirely good ones, I use them in R.C (Hi Rod!
But Mills -even 12W MRA12- are a bit undersized resistors. I have some items with lengthened resistance -and dark brown body- even so I use them at 70-80% dissipation. My rule of the thumb: use it at half dissipation.
In my heater bias preamps/VAS stages (#26, 10Y, 801, 841) I use non-inductive (NH type) 50W DALE resistors WITH -enough large- heatsink!
Most of heater biased tubes heater current is about 1-1.25 A and bias voltage 8-10V, so dissipation of heter bias resistor is over 8-10W.
IMHO conventional cooling is insufficinet in most cases (too high resistor temperature), therefore I use heatsinks.
It was actually me that back in the day discovered those surplus Dale flatwound resistors on ebay and ordered a large bunch of them, and Ale and others liked them too, but they've dried up recently. I've found a few other sources of nice porcelain and vitreous enamel resistors. Ohmite do some, for instance.
http://www.ebay.co.uk/itm/Ohmite-Re...797391?hash=item4ace10f3cf:g:~KIAAMXQVT9Svc-7
http://www.arcolresistors.com/resistors/ohmite-270-series-vitreous-enamelled-power/
http://www.alliedelec.com/ohmite-l25j25re/70022779/
https://www.tedss.com/2021000464
Stackable resistors make life easier:
http://www.newark.com/ohmite/f55j25r/resistor-power-25-ohm-55w-5/dp/99F6584
It's a question of hunting the good ones down. I did a big shootout a few years back, in which I liked the Dale ones, but any porcelain and vitreous enamel ones will be good sounding. Example:
http://www.mf-powerresistor.com/Vitreous_Enamel_Resistor.htm
I disliked metal film and metal clad (that was probably me saying that) but found the Welwyn ones pretty good - easiest option.
As said, must be rated between two and three times the actual current in the circuit. They do get hot. I mount them on top.
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Hi,
Welcome to the endless thread of 26 DHT. I can see you have already good alternative suggestions on the filament resistors. You can also check the 4P1L DHT Line Stage thread for more info. I remember other team members posted their impressions about various wire wound and non-inductive resistors. I also use Dale surplus like Andy and am very happy with the sound.
Regarding the AZ1 socket, I have to admit that in my experience (I have built like 5 different 26 DHT preamps with various designs) if you're using a SSHV2 shunt-regulator and/or a gyrator load (see 4P1L thread) then you won't easily notice a difference from using an expensive mesh type rectifier like AZ1. I use damper tubes and couldn't notice a difference from when I used the AZ1 before. The damper tubes also provides a smooth turn on time.
If you don't use shunt or CCS/Gyrator load, then yes.
Just my two pennies.
I also live in London btw!
cheers
Ale
Welcome to the endless thread of 26 DHT. I can see you have already good alternative suggestions on the filament resistors. You can also check the 4P1L DHT Line Stage thread for more info. I remember other team members posted their impressions about various wire wound and non-inductive resistors. I also use Dale surplus like Andy and am very happy with the sound.
Regarding the AZ1 socket, I have to admit that in my experience (I have built like 5 different 26 DHT preamps with various designs) if you're using a SSHV2 shunt-regulator and/or a gyrator load (see 4P1L thread) then you won't easily notice a difference from using an expensive mesh type rectifier like AZ1. I use damper tubes and couldn't notice a difference from when I used the AZ1 before. The damper tubes also provides a smooth turn on time.
If you don't use shunt or CCS/Gyrator load, then yes.
Just my two pennies.
I also live in London btw!
cheers
Ale
Hi Ale. It was reading your #26 pages that gave me the confidence to attempt this. So I will blame you if I fail!
I am using a choke supply instead of the Salas shunts, as that is what I heard, and enjoyed. We'll see how it goes.
And living in Plymouth, you might as well all be in another country!
I am using a choke supply instead of the Salas shunts, as that is what I heard, and enjoyed. We'll see how it goes.
And living in Plymouth, you might as well all be in another country!
I've emailed you - awkwardbydesign.
Since Ale has come in here, I'd reiterate what I said in my email - build his 01A preamp instead. It's the current state of the art in preamp design. Ale and I have had a few shootouts between that, 26 and 4P1L preamps and we're in agreement on the 01A design. It's pretty much as good as no preamp at all. Ale has PCBs and they're selling like hot cakes, so I should get in there. It supersedes all other preamp designs. It's more of a build, and you have to source some of the parts, but Ale can tell you more. It makes this thread rather redundant, if it's the best sound you are after.
In theory the 26 could be used in his circuit as well - I don't know who has tried this, and he'd have to give you the modifications. But simplest is just build the 01A as it is.
http://www.bartola.co.uk/valves/dht-pre-amplifier/01a-preamp-gen2/
Since Ale has come in here, I'd reiterate what I said in my email - build his 01A preamp instead. It's the current state of the art in preamp design. Ale and I have had a few shootouts between that, 26 and 4P1L preamps and we're in agreement on the 01A design. It's pretty much as good as no preamp at all. Ale has PCBs and they're selling like hot cakes, so I should get in there. It supersedes all other preamp designs. It's more of a build, and you have to source some of the parts, but Ale can tell you more. It makes this thread rather redundant, if it's the best sound you are after.
In theory the 26 could be used in his circuit as well - I don't know who has tried this, and he'd have to give you the modifications. But simplest is just build the 01A as it is.
http://www.bartola.co.uk/valves/dht-pre-amplifier/01a-preamp-gen2/
Andy, I have bought all the transformers and chokes for the 26. If it works then I might try for better, but one thing at a time! I am well out of my comfort zone already, so daren't get distracted by riper fruit higher up the tree!
I also liked the look of Rui's design, so that is where I am heading at the moment, with some input from my wife. I appreciate your advice on making the best, but I will be happy with something that works, for now. Learning a whole new discipline at my age is giving me a headache as it is!
I'll certainly have a look at Ale's 01A, but I'll stick with what I have actually heard, and have that to look forward to. If I survive this build!
Richard.
I also liked the look of Rui's design, so that is where I am heading at the moment, with some input from my wife. I appreciate your advice on making the best, but I will be happy with something that works, for now. Learning a whole new discipline at my age is giving me a headache as it is!
I'll certainly have a look at Ale's 01A, but I'll stick with what I have actually heard, and have that to look forward to. If I survive this build!
Richard.
This what I have already. So I need to make the thing as I understand it. Everyone is being really helpful, but too much information overloads my little brain! If I can successfully make this, then I will explore the multitude of options. BTW, I have put these photos into an album, but I don't know how to post them as thumbnails. So they are a bit big!
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Let's assume a HT of 150v for calculations. This is easily achieved with a 0A2 or 0D3 glow tube as regulator. This gives you roughly a 11 ohms cathode resistor and about 10v operating point at the top of it, and therefore 11.3v on the other side of the filament for a starved 1.3v filament, which is the output voltage of the regs. You will need to buy 2 of Rod Coleman's regulators, and I think the latest ones require a headroom of around 4-5 volts. So you want a 16v filament supply going into the regs. In my own supply I do this with a 25v 50VA transformer, Schottky diodes and a 280mH input choke, 2.7A. DCR is 3.5 ohms. I then use a dropper resistor to tune the final voltage. Another way to tune the filament supply is to use a small capacitor before the choke. I've attached a diagram for my 4P1L supply which gives you the idea. In this case the transformer is 20v. So you'll need to buy 2 of 20v to 25v transformers of good quality. Rod recommends JMS, and they do a 24v transformer at 50VA. When I order from them I ask them to use flying leads, not the plastic terminals shown. Easier to fit in a box, height-wise.
50VA Premier – JMS Online
I can supply a couple of my 2.7A 280mH chokes, or you can order Hammond 159ZC chokes from Bluebell Audio. Your 10,000uF caps look OK. A 15v filament transformer like the Weiss you have might be OK for cap input with a choke after it - maybe..... It's a bit close. But choke input makes an audible difference.
For the HT power supply I'd suggest a 80 rectifier - I have a few of those, though I actually use a AZ1 mesh. I see you have a third UX4 socket, which is good for a 80. And a glow tube as a simple reg. This can be fed with a dropper resistor for starters, or later a couple of DN2540 which is a better option. But for caps in the HT supply I would ONLY use motor run polypropylene caps. No electrolytics anywhere. 40uF motor run caps are cheap on ebay. or these:
Universal 25 UF Microfarad Motor Run Start Capacitor (400V 450V 500V) | eBay
You should be using an outboard HT supply and an outboard filament supply to keep the chokes away from the main chassis. I use 4 pole speakons for the HT supply and 4 pole XLRs for the filaments.
With these kind of filament bias designs, all the real quality is in the power supplies. The actual 26 circuit is very simple.
I've attached photos of my 26 preamp PSU and the filament supplies for my 4P1L amp. One has the transformers and chokes on top, the other inside.
50VA Premier – JMS Online
I can supply a couple of my 2.7A 280mH chokes, or you can order Hammond 159ZC chokes from Bluebell Audio. Your 10,000uF caps look OK. A 15v filament transformer like the Weiss you have might be OK for cap input with a choke after it - maybe..... It's a bit close. But choke input makes an audible difference.
For the HT power supply I'd suggest a 80 rectifier - I have a few of those, though I actually use a AZ1 mesh. I see you have a third UX4 socket, which is good for a 80. And a glow tube as a simple reg. This can be fed with a dropper resistor for starters, or later a couple of DN2540 which is a better option. But for caps in the HT supply I would ONLY use motor run polypropylene caps. No electrolytics anywhere. 40uF motor run caps are cheap on ebay. or these:
Universal 25 UF Microfarad Motor Run Start Capacitor (400V 450V 500V) | eBay
You should be using an outboard HT supply and an outboard filament supply to keep the chokes away from the main chassis. I use 4 pole speakons for the HT supply and 4 pole XLRs for the filaments.
With these kind of filament bias designs, all the real quality is in the power supplies. The actual 26 circuit is very simple.
I've attached photos of my 26 preamp PSU and the filament supplies for my 4P1L amp. One has the transformers and chokes on top, the other inside.
Attachments
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Once I take a mistake, and put 2k2 Welwyn W24 resistor instead of 220k as (400V) PSU discharging resistor.
After turn on I realized loud transformer buzzing, and after ten seconds I turn off it.
The W24 was extremely hot (about 200C, the enamell discolored), but after cooling the resistance remains the same.
After turn on I realized loud transformer buzzing, and after ten seconds I turn off it.
The W24 was extremely hot (about 200C, the enamell discolored), but after cooling the resistance remains the same.
For point to point building, I use these M3 nylon hexagonal spacers everywhere, 10, 15 or 20mm. You need to use a Nyloc nut so it doesn't rotate after soldering, and a solder tag. Offers a very flexible way of putting components where they go best. You can screw them together for more height, e.g. for mounting capacitors.
https://www.jprelec.co.uk/store.asp/c=715/PCB-Spacers-Hexagonal-Male-to-Female
TR Fastenings M3-N5ST-TC1 Nylon Insert Lock Nut M3 Pack Of 100 | Rapid Online
PJP C3 Solder Tags Plated M3 Pack Of 100 | Rapid Online
https://www.jprelec.co.uk/store.asp/c=715/PCB-Spacers-Hexagonal-Male-to-Female
TR Fastenings M3-N5ST-TC1 Nylon Insert Lock Nut M3 Pack Of 100 | Rapid Online
PJP C3 Solder Tags Plated M3 Pack Of 100 | Rapid Online
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