Hello,
I'm thinking about making a stereo tube amplifier. I found Dynaco projects; mark 3 (60W) and stereo 70 mk2 (by Daniel Steele).
I would like to have about 50W output. MK3 is higher, but more expensive. And ST70 is only 35W, but cheaper. Maybe there is an option to increase ST70 power by eg. 10W? https://www.bonavolta.ch/hobby/en/audio/steele70.htm
And the second thing: the output transformer. I have a possibility to buy A470 transformer replicas (for ST70) or Hammond 1650NA (will be good for MK3?).
Btw, As you might see, I'm new in tubes. And sorry for my english 😀
I'm thinking about making a stereo tube amplifier. I found Dynaco projects; mark 3 (60W) and stereo 70 mk2 (by Daniel Steele).
I would like to have about 50W output. MK3 is higher, but more expensive. And ST70 is only 35W, but cheaper. Maybe there is an option to increase ST70 power by eg. 10W? https://www.bonavolta.ch/hobby/en/audio/steele70.htm
And the second thing: the output transformer. I have a possibility to buy A470 transformer replicas (for ST70) or Hammond 1650NA (will be good for MK3?).
Btw, As you might see, I'm new in tubes. And sorry for my english 😀
First, the power difference is less then one thinks. It's less then 3dB. It's more of a
convenience ( one heavy box or two a little lighter). It's also easier to install mkIII
behind each speaker , the ST70 needs to be in one place.
Second, have a peek at dynakitparts.com and tubes4hifi.com for kits. Both sell real transformers
which is essential if you want to build a real replica with all it's performance.
convenience ( one heavy box or two a little lighter). It's also easier to install mkIII
behind each speaker , the ST70 needs to be in one place.
Second, have a peek at dynakitparts.com and tubes4hifi.com for kits. Both sell real transformers
which is essential if you want to build a real replica with all it's performance.
Well, I prefer one box with two amps inside.
I visited dynakit webiste, but A470 and A431 transformers are out of stock. And they are little bit too expensive for me (+ shipping to UE and vat).
I asked about Hammond 1650NA bacause I can buy it locally.
I visited dynakit webiste, but A470 and A431 transformers are out of stock. And they are little bit too expensive for me (+ shipping to UE and vat).
I asked about Hammond 1650NA bacause I can buy it locally.
If you urge to build then make it as attractive as possible to get the best price when selling.
A dynaco clone ( a real build with original transformers chassies and schematics) will be the
best selling device.
If you urge for "just the build" then maybe som el84 type amp as first build will be reasonable.
A dynaco clone ( a real build with original transformers chassies and schematics) will be the
best selling device.
If you urge for "just the build" then maybe som el84 type amp as first build will be reasonable.
I have already built an Class-A amplifier on the EL84, but it has only 5W 😉
Generally, I don't want to sell it. It's just for me, for my home speakers. So I don't need to built 1:1 replica. I'm looking for something not very expensive and not very complicated. At the same time, I would like it to sound reasonably good, but I'm not an audiophile.
Generally, I don't want to sell it. It's just for me, for my home speakers. So I don't need to built 1:1 replica. I'm looking for something not very expensive and not very complicated. At the same time, I would like it to sound reasonably good, but I'm not an audiophile.
EDIT:
I just find out Dynaco MK2 is what I need. 50W from EL34 tubes 😀
Only output transformers question left. Btw, can I use A470 transformer for this? I can buy it too, but it's rated as 35W @ full bandwidth and 30Hz-15kHz @ 70W. Is narrower band only one problem?
I just find out Dynaco MK2 is what I need. 50W from EL34 tubes 😀
Only output transformers question left. Btw, can I use A470 transformer for this? I can buy it too, but it's rated as 35W @ full bandwidth and 30Hz-15kHz @ 70W. Is narrower band only one problem?
MkII uses A430 transformer ( same as MkIII )
The extra power comes from higher B+ and A430 transformer.
Ok, so again: can I replace A430/431 with 1650NA? This Hammond transformer is rated at 60W, the same Ra and UL taps.
It's about more than power specs and primary impedance. The output transformer has to be able to tolerate the feedback required by the circuit. Many of the Hammond transformers exhibit poor bandwidth, which could lead to instability if you just drop it into a Dynaco circuit. Unless you have an oscilloscope and other testing tools, you're taking a chance that the amp won't perform properly, or even oscillate.
Unfortunately the reproduction Dynaco transformers have gotten very, very expensive. There's a pair on eBay now for a fairly reasonable price. If you're determined to build the Mark II or III it would be worth the investment, IMO. Otherwise I would go with the A470s and build the ST-70.
What speakers are you planning to drive with this amp?
I see now that you're in the EU, which could be a problem for getting things shipped to you from the US. So that's definitely a problem.
Chances are that any output transformer is going to require adjustments to the feedback circuit(s). The Hammonds aren't bad, but the 1650N or P make better use of the windings than the NA or PA. (There's a thread somewhere on this site which mentions this)
Check your local and regional ads for used ST70 and MKIII amps. Surely there are some in the EU.
Not sure that I would recommend your building an unproven design for your first tube amp.
Refreshing an existing amp is much easier, and Dyna output transformers are much better.
And forget that ridiculous magic eye tube in the schematic.
My speakers are tannoy mercury m1.
I have oscilloscope and some electronic experience, so if you tell me what to look for, I think I could deal with it 🙂
I have oscilloscope and some electronic experience, so if you tell me what to look for, I think I could deal with it 🙂
Look for used amps in your area. Assuming that you have a receiver etc. now, you can take your time finding an amp.
Build a professionally designed tube amp kit, or restore a commercial tube amp to its proper operation. You should be
able to do that with few problems. Excellent output transformers are critical for good results, and Dynas are very good.
I doubt that a single ended tube amp would work very well for you, though. Stay with push-pull types.
However, unless you have substantial electronics experience, it's not likely to end well if you try to build an amp from scratch
with a circuit from the internet. I would not do that myself either. It's a lot of work and cost, and you don't have any assurance
of good results.
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I would think 35wpc would be plenty for those, in which case the A470s and an ST-70 circuit would be fine. If you stick to a proven circuit with the proper output transformers, you shouldn't have a problem. You could purchase a Tubes4HiFi or Dynakit driver board without too much trouble.
I would not fuss the the Steele modifications but follow the original ST-70 design.
You could try the Mark II circuit with the Hammonds, but even with a scope handy the results might be very disappointing.
Toroidy output transformers are hard to beat for the money, especially if you are in the EU. See this thread:
https://www.diyaudio.com/community/threads/kt88-amplifier.381883/page-4#post-6962119
Also, you could consider some rivals of the Dynaco designs; the Eico HF-87 circuit is relatively easy to get right and sounds great (and I have Dyna MkIIIs, ST70 and Eico HF-87). Especially with the Dave Gilispie EFB(tm) implemented. See a Eico HF-87 clone project here using Edcor output transformers:
https://www.diyaudio.com/community/...5-20-vs-ampex-6516.338682/page-3#post-7135654
(Schematic is in post #43)
And the Eico HF-87 EFB and GNF project here: https://audiokarma.org/forums/index...e-modifications-to-the-hf-87-nfb-loop.937912/
Please note that the GNF mod is specific to the original EICO transformers. If you use Toroidy, Hammond, Edcor etc you will have to adjust the GNF.
https://www.diyaudio.com/community/threads/kt88-amplifier.381883/page-4#post-6962119
Also, you could consider some rivals of the Dynaco designs; the Eico HF-87 circuit is relatively easy to get right and sounds great (and I have Dyna MkIIIs, ST70 and Eico HF-87). Especially with the Dave Gilispie EFB(tm) implemented. See a Eico HF-87 clone project here using Edcor output transformers:
https://www.diyaudio.com/community/...5-20-vs-ampex-6516.338682/page-3#post-7135654
(Schematic is in post #43)
And the Eico HF-87 EFB and GNF project here: https://audiokarma.org/forums/index...e-modifications-to-the-hf-87-nfb-loop.937912/
Please note that the GNF mod is specific to the original EICO transformers. If you use Toroidy, Hammond, Edcor etc you will have to adjust the GNF.
But you want an amplifier, not transformers. First decide on the amplifier that you want,
which then determines the output transformers needed.
For example, you cannot build a Dyna Stereo 70 without using the Dyna output transformers.
If you did, it would be some other amplifier instead, which was never properly designed.
which then determines the output transformers needed.
For example, you cannot build a Dyna Stereo 70 without using the Dyna output transformers.
If you did, it would be some other amplifier instead, which was never properly designed.
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Yes, but unless you have excellent building and testing skills, the output transformer may well determine what circuit you can build.
Those are good ideas, especially the toroid outputs, but in that case look at the amount of work it took to achieve decent bandwidth and stability! And there's no schematic offered yet for a beginner to follow.
Regarding the Eico circuits--again, without the Eico output transformers, a beginner is shooting in the dark in terms of stability and decent performance.