Hello guys,
I have Dynaco ST70 VTA board, bought by Bob Latino from USA.
I upgrade almost everything exclude output transformers. I think to use some Lundahl transformers whit amorphous core.
I see some people used LL1663/PP as well.
What is the differents in sound between transformers whit amorphous core and usual core LL1662PP?
Are LL1663PP have enough power for 35W in my Dynaco? Are is good for use different type of tubes KT88, KT66, EL34?
I think to use a lundahl covers for the transformers.
I don't use negative feedback in my amp. Without NFB sound is better and live.
Here have some pictures of my amp.
My Dynaco ST70 1st anniversary
Best regards
I have Dynaco ST70 VTA board, bought by Bob Latino from USA.
I upgrade almost everything exclude output transformers. I think to use some Lundahl transformers whit amorphous core.
I see some people used LL1663/PP as well.
What is the differents in sound between transformers whit amorphous core and usual core LL1662PP?
Are LL1663PP have enough power for 35W in my Dynaco? Are is good for use different type of tubes KT88, KT66, EL34?
I think to use a lundahl covers for the transformers.
I don't use negative feedback in my amp. Without NFB sound is better and live.
Here have some pictures of my amp.
My Dynaco ST70 1st anniversary
Best regards
Take a look at this for ideas as they recommend a different model as an upgrade, the 1682PP. Contact K&K or the company about what they think about the amorphous core in PP. K&K has a form also. Both 1663 & 1682 are limited to 40W so that would limit getting more power out of the big tubes, just like the stock transformers. Maybe the bigger LL1679 PP is more suited to you as it's rated to much higher power using the 4.5K primary taps. More $ though!
http://www.kandkaudio.com/poweramplifier.html
Another option in affordable bigger OPT's is the Hammond (should be available in your area). I'm thinking of the 1650R as it will give a great bandwidth at the lower power (50-60W) you will maybe use and is well regarded compared to other Hammond OPT's and many other transformers out there. It has a 5K primary and 100W rating.
http://www.kandkaudio.com/poweramplifier.html
Another option in affordable bigger OPT's is the Hammond (should be available in your area). I'm thinking of the 1650R as it will give a great bandwidth at the lower power (50-60W) you will maybe use and is well regarded compared to other Hammond OPT's and many other transformers out there. It has a 5K primary and 100W rating.
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Small story 
I bought a Dyna St 70 in early 70s as a kit. Dutifully assembled it. Happy as a clam for years.
Then decided to upgrade it using Full Curcio upgrades.
Wayyy more $$ than the original purchase price... it replaced most of the Dyna innards
Did sound a little better... not comensurate with the expense though.
A few years later, my Brother showed up with a new NAD amp.
Tried it in my system and my venerable ST70 sounded very poor (like s**t) ..in direct comparison... sad but ohh so true.
Dyna immediately went into storage.
IMO you are beating a Dead Horse.
I bought a Dyna St 70 in early 70s as a kit. Dutifully assembled it. Happy as a clam for years.Then decided to upgrade it using Full Curcio upgrades.
Wayyy more $$ than the original purchase price... it replaced most of the Dyna innards
Did sound a little better... not comensurate with the expense though.
A few years later, my Brother showed up with a new NAD amp.
Tried it in my system and my venerable ST70 sounded very poor (like s**t) ..in direct comparison... sad but ohh so true.
Dyna immediately went into storage.
IMO you are beating a Dead Horse.
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Otoh, a lot depends on the rest of your system.
I'd say a well done ST70 trounces any NAD except possibly on bass, and that depends on the speaker system.
But as far as spending a small fortune on Amorphous core outputs, my suggestion is to start from scratch and build an amp designed and intended for the performance level that one might get from amorphous cores. The main performance improvement for the amorphous core comes in HF response... so you might want to go with a biamp set up?
_-_-
I'd say a well done ST70 trounces any NAD except possibly on bass, and that depends on the speaker system.
But as far as spending a small fortune on Amorphous core outputs, my suggestion is to start from scratch and build an amp designed and intended for the performance level that one might get from amorphous cores. The main performance improvement for the amorphous core comes in HF response... so you might want to go with a biamp set up?
_-_-
+1
You can get to a point when you have to ask yourself WHY ARE YOU CHANGING PARTS? The answer is you are not happy with what you have now. So before you add even more changes to something you need to ask yourself do I just need a change.
Money is sometimes better spent on something new and exciting. Than does my modification sound better or just different.
Then after you have listened for a while to your new amp, put the old one back in if it sounds rubbish then you have answered your question.
Because the cost of the amp is in the transformers and if you are buying new output Tx's then you only need a mains and a chassis and your in a new situation.
Its a bit like people modifying a car they keep adding parts and yes its fast but it isn't a Ferrari and never will be. Sometimes when you look back, the cost of the parts might have bought you something much better ( as you then look at the souped up saloon with its rusty bodywork from age).
Act in haste and repent at leisure. (just for fun)
Regards
M. Gregg
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I'm in the group that says build something new, from the ground up.
The "classic" Mullard 5-20 topology yields good results in combination with so/so "iron". It definitely is less demanding, of O/P trafo quality, than Williamson style circuitry is. Those facts may cater to limited(?) availability of parts in Bulgaria.
A very nice implementation of the Mullard style setup is the Harman/Kardon Citation V. The Cit. 5 could be "cloned" using Russian 6П3С-E (6p3s-e) stock as "finals". The Cit. 5 setup can be improved by using an ECC99 as the LTP phase splitter and replacing the splitter's tail resistor with a constant current sink (CCS). Regulating O/P tube screen grid B+ is another performance improving modification.
The "classic" Mullard 5-20 topology yields good results in combination with so/so "iron". It definitely is less demanding, of O/P trafo quality, than Williamson style circuitry is. Those facts may cater to limited(?) availability of parts in Bulgaria.
A very nice implementation of the Mullard style setup is the Harman/Kardon Citation V. The Cit. 5 could be "cloned" using Russian 6П3С-E (6p3s-e) stock as "finals". The Cit. 5 setup can be improved by using an ECC99 as the LTP phase splitter and replacing the splitter's tail resistor with a constant current sink (CCS). Regulating O/P tube screen grid B+ is another performance improving modification.
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I'm currently hacking a Chinese Dynaclone ST70 and its OPTs suck. I want to spend EUR200 on a pair of Amplimo 100W UL toroids. Getting them to look nice will be a challenge though (unless I can get them nicely potted). I'm even thinking of tossing the pentode input and concertino phase splitter for a triode and long-tail pair, bit like the Mullard above. Which will involve a new PCB. But only if the Vanderveen toriods are as good as they claim to be.
They sound quite nice "triode strapped" if power requirements aren't an issue.
jeff
I have got the LL1620AM-PP lately for my simplified W5M EL34 PP amp. Here's what I have said in the other thread.
=============
First I use the Peerless output transformer came with the W5M kit. Unfortunately, it wasn't sound right to me. Then, I put the Lundahl LL1620-PP and it had much better performance. However, the vocal wasn't sweet at all unless I play with some latest CD music. I use Lundahl's amorphous core OPT for my single ended amps and I thought how would it make the difference with amorphous core OPT in PP amp. Then, I persuade my very best friend to buy a pair of the LL1620AM-PP for each of us. After I got the AM-PP OPT, I put that in, and wowhhhh, it sound so lovely with very finite details like SE amp and slamming punch bass.
=============
First I use the Peerless output transformer came with the W5M kit. Unfortunately, it wasn't sound right to me. Then, I put the Lundahl LL1620-PP and it had much better performance. However, the vocal wasn't sweet at all unless I play with some latest CD music. I use Lundahl's amorphous core OPT for my single ended amps and I thought how would it make the difference with amorphous core OPT in PP amp. Then, I persuade my very best friend to buy a pair of the LL1620AM-PP for each of us. After I got the AM-PP OPT, I put that in, and wowhhhh, it sound so lovely with very finite details like SE amp and slamming punch bass.
Of course it is always nice to hear of sonic successes, but a some more information helps to fill in the rest of the story. Like, what are the supporting pieces of equipment, speakers?
Another factor might be that in these older tube amp designs, there is loop feedback from the secondary of the OT. One of the weak points in these designs is that the feedback was often present so that the manufacturers could claim "20cycles to 20kc" frequency response. This response was at the expense of things like transient response and overshoot. So, if you put in a transformer with substantially better HF response, the job the feedback (keeping the HF "flat") is greatly reduced or eliminated.
So, if this is what is going on one might ask if this is a good thing or not? I'd say, it's probably a good thing, but a mighty expensive way to get an improvement - but who knows, maybe it is worth it?
_-_-
Another factor might be that in these older tube amp designs, there is loop feedback from the secondary of the OT. One of the weak points in these designs is that the feedback was often present so that the manufacturers could claim "20cycles to 20kc" frequency response. This response was at the expense of things like transient response and overshoot. So, if you put in a transformer with substantially better HF response, the job the feedback (keeping the HF "flat") is greatly reduced or eliminated.
So, if this is what is going on one might ask if this is a good thing or not? I'd say, it's probably a good thing, but a mighty expensive way to get an improvement - but who knows, maybe it is worth it?
_-_-
re
Thank You for all advice.
I read a lot on the internet and I got the impression that Dynaco ST70 is great. But it turns out that this is not so. This is just a "pipe."
When we compared it with a Denon PMA-2000IVR and one 300B amplifier with speakers TANNOY TYPE 2528, was dead sound - no soul - as mono.
Then I started doing upgrades to the elements. Already had a bass, high and medium, but no soul.
After removal of the negative feedback sound is more live, but i haven't heard my amplifiers whit these Tannoy speakers to judge the sound.
I listening whit DIY speakers with SEAS 27TFFC and Vifa MG22WO09-08 mid bass. They have better sound (not dead) vs Tannoy.
At this point I am too invested in this amp and I can't start a new project. The heart of a tube amp is the output transformer. Which makes me think that if I put a really nice transformer, the sound will be great. I think transformer with amorphous core give me the best results.
On the issue of AC balance I'm not aware of what is and is there any impact on sound quality. Please can someone explain.
I think to use KT88 in the future, may be Psvane KT88-T MkII.
After the time I'll replace my speaker whit something better. For now, not worth it.
Best regards
Evgeni
Thank You for all advice.
I read a lot on the internet and I got the impression that Dynaco ST70 is great. But it turns out that this is not so. This is just a "pipe."
When we compared it with a Denon PMA-2000IVR and one 300B amplifier with speakers TANNOY TYPE 2528, was dead sound - no soul - as mono.
Then I started doing upgrades to the elements. Already had a bass, high and medium, but no soul.
After removal of the negative feedback sound is more live, but i haven't heard my amplifiers whit these Tannoy speakers to judge the sound.
I listening whit DIY speakers with SEAS 27TFFC and Vifa MG22WO09-08 mid bass. They have better sound (not dead) vs Tannoy.
At this point I am too invested in this amp and I can't start a new project. The heart of a tube amp is the output transformer. Which makes me think that if I put a really nice transformer, the sound will be great. I think transformer with amorphous core give me the best results.
On the issue of AC balance I'm not aware of what is and is there any impact on sound quality. Please can someone explain.
I think to use KT88 in the future, may be Psvane KT88-T MkII.
After the time I'll replace my speaker whit something better. For now, not worth it.
Best regards
Evgeni
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Suggest that you reduce the cathode resistor by 10x. More if you can. You might prefer the effect upon the sound. Readjust the bias.
12AX7 might also sound better... but the gain will change.
You are *not* using the feedback loop from the 16ohm tap?
AC balance will set the gain or level for the *signal* so that both halves of the phase splitter/driver will send the same amplitude signal to the output tubes.
You would set that by using a signal generator and a scope to see the signal.
12AX7 might also sound better... but the gain will change.
You are *not* using the feedback loop from the 16ohm tap?
AC balance will set the gain or level for the *signal* so that both halves of the phase splitter/driver will send the same amplitude signal to the output tubes.
You would set that by using a signal generator and a scope to see the signal.
Thanks for information.
You mean, i to use 100 ohms or more for cathode res (now is 10 Ohms) Why, what is will better with 100 ohms res?
Yes i not use NFB from 16ohm tap. Now have little more bass, but sound is a "live"
For 12ax7 must change the scheme. She works on 1.2ma, but 12au7 works on 10ma bias.
I have to many 12at7
Mullard CV4024 and E180CC.Depends upon the "sound" you like. The "traditional" tube amp sound is subjectively strong sounding bass and warmth (2nd harmonic distortion) which occurs at lower frequencies as the impedance from the primary inductance approaches the effective output impedance of the tubes. If you like that sort of sound then you may not like the VdV Torroidal Output Trannies. The huge primary inductance that they offer means that the above mechanism happens off the bottom of the audible frequency range. Bass is extended but subjectively weaker. I built a prototype PPP KT88 Amp, tried it with VanderVenne PAT4006 and Hammond 1650T and preferred the Hammond as it did give that sound as described above, the PAT4006 did not.
Cheers,
Ian
REDUCE means make smaller.
They just need to be big enough to be able to measure the voltage drop and calculate the idle current through the tubes.
Regards
M. Gregg
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