burnedfingers said:
I don't agree here.
Eliminating the resistors entirely will have a very nice effect on the
sound of the output stage. But since you usually need a way to check the bias current for the tube, something is required in the hole unless you come up with another means of measuring the bias current.
So, I do suggest reducing the resistance as low as possible. Imho 1 ohm would be a better bet.
A very inexpensive DVM, like ~20$ will read sufficiently accurately to do the job, and I do not think one needs "high accuracy" resistors in that hole to do the job either... and paralleling some rather normal resistors will get you a fairly accurate low value resistor too...
As far as the MkII & III iron, I never liked it no matter what i heard it with.
The true value of the ST70 is in the output iron, so keep that, or else just build a new amp from scratch... my 2 cents on that story.
and no, it wasn't a slam... but some people have great difficulty with installing new boards or modifying the electronics, so that is a caveat since people of all levels follow these threads.
_-_-bear
Here we go again!
Quote:
Eliminating the resistors entirely will have a very nice effect on the
sound of the output stage. But since you usually need a way to check the bias current for the tube, something is required in the hole unless you come up with another means of measuring the bias current.
So, I do suggest reducing the resistance as low as possible. Imho 1 ohm would be a better bet.
I'm sure the manufacturers of the aftermarket driver boards have given this due consideration and I haven't seen anyone else that shares your opinion. I'm still waiting for someone else to jump on the bandwagon and support your view. Personally I cannot measure any difference in distortion or hear any sonic difference so I am still unsold on the idea. Checking the bias by another means poses no problem so why wasn't this "idea" used origionally?
Value of Dynaco iron?
Well, to spend 250> for a used Dynaco in order to strip it of its iron to me doesn't make for good thinking. The transformers can be outdone by a pair of Hammond 1650K's for less money. The K's are rated for 50watts output vers the lower output of the Dynaco's.
Quote:
Eliminating the resistors entirely will have a very nice effect on the
sound of the output stage. But since you usually need a way to check the bias current for the tube, something is required in the hole unless you come up with another means of measuring the bias current.
So, I do suggest reducing the resistance as low as possible. Imho 1 ohm would be a better bet.
I'm sure the manufacturers of the aftermarket driver boards have given this due consideration and I haven't seen anyone else that shares your opinion. I'm still waiting for someone else to jump on the bandwagon and support your view. Personally I cannot measure any difference in distortion or hear any sonic difference so I am still unsold on the idea. Checking the bias by another means poses no problem so why wasn't this "idea" used origionally?
Value of Dynaco iron?
Well, to spend 250> for a used Dynaco in order to strip it of its iron to me doesn't make for good thinking. The transformers can be outdone by a pair of Hammond 1650K's for less money. The K's are rated for 50watts output vers the lower output of the Dynaco's.
HEy-Hey!!!,
Don't forget about the cloned Iron...triode Electronics sells A470's for ~$150 per pair. There is of course better stuff to clone than the simple Dynaco( don't think Haffler spared the OPT, that one was as cheap as it could be too, just that the perf spec was pretty good).
I salvaged a Peerless S-265-Q, a potted, 10k a-a, 40 watt output tx. I got it unwound and cloned for the remarkable sum of $100 each...and it can be done for anybody. Same thing with an Acro TO-330. As soon as I have need of that Iron, off it goes...anticipated price of less than $150 each for copies.
Anybody with a single of a rare and high performance bit of output Iron can do the same thing. Call Heyboer TX. They're in Michigan, and also do nice custom power Iron( and chokes too ), in DIY quantity.
regards,
Douglas
Don't forget about the cloned Iron...triode Electronics sells A470's for ~$150 per pair. There is of course better stuff to clone than the simple Dynaco( don't think Haffler spared the OPT, that one was as cheap as it could be too, just that the perf spec was pretty good).
I salvaged a Peerless S-265-Q, a potted, 10k a-a, 40 watt output tx. I got it unwound and cloned for the remarkable sum of $100 each...and it can be done for anybody. Same thing with an Acro TO-330. As soon as I have need of that Iron, off it goes...anticipated price of less than $150 each for copies.
Anybody with a single of a rare and high performance bit of output Iron can do the same thing. Call Heyboer TX. They're in Michigan, and also do nice custom power Iron( and chokes too ), in DIY quantity.
regards,
Douglas
Just curious to know if anyone else has used the SDS labs cap board in a ST-70.I bought one and like it alot(helped out the low end a fair bit.),but sometimes I wonder if there's too much capacitance there for the tube rectifier. (I prefer the sound,and slow start-up of a tube rect.)
I currently have a 5U4GB plugged in,since the Sovtek 5AR4's I had don't seem to hold up too well in this circuit. (running on the ragged edge of it's ratings,as previously mentioned.)
you can see the SDS labs board at: http://www.quadesl.com/schematics.shtml
Also,don't forget that the cathode resistors add a small amount of local feedback,and (can sometimes) help to eliminate crossover distortion.
I used this trick in a PP EL34 amp I'm (slowly...) working on,mostly fixed bias,with a bit of cathode bias,to give a little local feedback,and try to knock distortion down a bit.
A slightly outdated (I've since tweaked the circuit a bit.) schematic can be seen at: http://www.users.qwest.net/~ptaylor/Audio/EL34Protoamp/EL34PushPull.jpg
I currently have a 5U4GB plugged in,since the Sovtek 5AR4's I had don't seem to hold up too well in this circuit. (running on the ragged edge of it's ratings,as previously mentioned.)
you can see the SDS labs board at: http://www.quadesl.com/schematics.shtml
Also,don't forget that the cathode resistors add a small amount of local feedback,and (can sometimes) help to eliminate crossover distortion.
I used this trick in a PP EL34 amp I'm (slowly...) working on,mostly fixed bias,with a bit of cathode bias,to give a little local feedback,and try to knock distortion down a bit.
A slightly outdated (I've since tweaked the circuit a bit.) schematic can be seen at: http://www.users.qwest.net/~ptaylor/Audio/EL34Protoamp/EL34PushPull.jpg
burnedfingers said:
because in 1957 no one had a $20 DVM that could reliably measure millivolts!
People had regular old VOMs and the really cool people had VTVMs, both of which were none to accurate in the 1.5v range...
So there wasn't much choice to be had in this respect.
You are free to do what you like with the cathode resistor. Few people have apparently thought to see what happens to the sound without the cathode resistor. And, if you are either satisfied with your sound now, or don't want to try that, you are under no obligation to follow my suggestion(s).
Didn't say it was a good idea to strip the amp down for the iron.
I said that the main *value* to the amp is in good iron, so it makes sense to *either* work with the configuration (which can be made to sound quite nice) or to go out and build an entirely new amplifier from scratch - once you get to the point where you are questioning the output iron or considering changing it...
Hope that makes sense?
_-_-bear
I myself have owned the Quicksilver monoblocks (KT88 versions) and a few Dynaco 70's (some modded some stock) and agree that with a better power supply, upgraded board the Dyna 70 sonically sounds nicer than the Quickies. I tried a few tube types in the Quicksilvers (Tung 6550's, GE 6550's and GEC KT88's as well as quite a few Chinese/Russian versions, and have abandoned the KT88 family as an output, at least for now). I really like the midrange of an EL34, although the bass seemed weaker to me than the KT88. With an upgraded power supply on the Dyna 70 you will fix that problem. If looks are important, then the Quickies win hands down as I find the Dyna 70 somewhat of an ugly duckling. I recently played with a Michaelson Audio Integrated (4 EL34's per channel) and the bass was outstanding. I am selling this amp for another project, and have returned to my trusty ol' Threshold amp (one of the only ss amps I would allow in my system 
)
)I guess that I cannot agree that the Dynaco sounds better than the "Quickeys". Having had (3) sets of them, one of which was a modified KT88 version, one a modified 8417, and one a stock 8417. There is no comparison in my opinion. The Dynaco was a cheap $100 amp in its day and today its a cheap $300 amp.
In stock form the Dynaco has no low end and no real definition. I own several Dynaco's with power supply mods and one with everything including the kitchen sink and they in my opinion are nothing to write home about. To each his own I guess.
In stock form the Dynaco has no low end and no real definition. I own several Dynaco's with power supply mods and one with everything including the kitchen sink and they in my opinion are nothing to write home about. To each his own I guess.
Well I'm not raving about the amp, I'm actually indicating that I don't like the KT88 family of tube. To me its mush, with no lush. There are many EL34 amps that are much better quality than the Dyna but I dropped my Quickies soon after I heard my Michaelson Audio Integrated. Of course I've returned to ss amplification for now, but will probably go with a hotrodded Bogen amp I picked up on E-Bay not long ago. Uses 7355 outputs. I'm converting ot an EL34, and usual upgrades.
Perhaps, but I'm using what I have as a judgement for the amps. My favorite amp is my Threshold S/300. I know its not tube, but the bass is absolutely fantastic, hands down surpassed the tube gear. I have three preamps and am about to build Franks 6SN7 linestage. I own a Counterpoint SA-3000, hotrodded Pas (which I still don't like after oodles of work), and a Classe DR-5. Speakers, JBL L-250's and Tannoy HPD-315's in custom bass reflex cabs.
I recently had a pair of JBL 4333's but sold em', too much beam for me, even on tubes.
I recently had a pair of JBL 4333's but sold em', too much beam for me, even on tubes.
That was me...
The input stage was a constant current sourced dual 6DJ8 (per channel) cascode with cross coupling. Lots of detail, gain, and good balance too. We sold lots of the boards as kits, as well as doing ton's of mods with them. I estimated over 1000 ST-70 and MK-2,3,4, and 6's with our driver cards.
Just stumbled onto this forum, so I figured why not join...
The input stage was a constant current sourced dual 6DJ8 (per channel) cascode with cross coupling. Lots of detail, gain, and good balance too. We sold lots of the boards as kits, as well as doing ton's of mods with them. I estimated over 1000 ST-70 and MK-2,3,4, and 6's with our driver cards.
Just stumbled onto this forum, so I figured why not join...
Hey Andy!
Long time no see!
I still have a copy of the schematic you sent me of that input stage!
What was that, like 25 years ago??
Nice.
And, Burnedfingers... I think you made a comment about the lack of "low end and no definition"?
Try getting rid of those cathode resistors?
And for definition, you need to at minimum change the stock coupling caps, upgrade the power supply AND use a suitable load, since they are TUBE AMPS and only 35 watts on a good day going down hill!
Oh, I'd run 'em in triode too...
Look, it's not a SOTA tube amp, it's a Dyna ST 70, and it can be made to sound pretty darn good if you do a good set of mods on it.
Choose wisely, Luke...
_-_-bear
Long time no see!
I still have a copy of the schematic you sent me of that input stage!
What was that, like 25 years ago??
Nice.
And, Burnedfingers... I think you made a comment about the lack of "low end and no definition"?
Try getting rid of those cathode resistors?
And for definition, you need to at minimum change the stock coupling caps, upgrade the power supply AND use a suitable load, since they are TUBE AMPS and only 35 watts on a good day going down hill!
Oh, I'd run 'em in triode too...
Look, it's not a SOTA tube amp, it's a Dyna ST 70, and it can be made to sound pretty darn good if you do a good set of mods on it.
Choose wisely, Luke...
_-_-bear
Burnedfingers: proof?
Easy!
Take a ST-70 or other suitable amp, remove the cathode resistors (or reduce substantially to a small fraction of original value), compare with ur ears, or test gear as you wish.
CJ stuff is not my cup-of-tea to be polite about it.
But feel free to try it on any amp you like.
If you don't agree about the audible effects then feel free to disregard this idea!
What's the problem?
Ivegotmono: dunno.
Never did that. I'd simply reduce the resistor by a factor of 10 or more... or eliminate if you prefer... of course you lose the "fuses" on the tubes if you eliminate.
They come into play when the tubes short and try to destroy the power transformer...
imho that is why they are there: fuses and ease of bias set w/old analog meters.
_-_-bear
Easy!
Take a ST-70 or other suitable amp, remove the cathode resistors (or reduce substantially to a small fraction of original value), compare with ur ears, or test gear as you wish.
CJ stuff is not my cup-of-tea to be polite about it.
But feel free to try it on any amp you like.
If you don't agree about the audible effects then feel free to disregard this idea!
What's the problem?
Ivegotmono: dunno.
Never did that. I'd simply reduce the resistor by a factor of 10 or more... or eliminate if you prefer... of course you lose the "fuses" on the tubes if you eliminate.
They come into play when the tubes short and try to destroy the power transformer...
imho that is why they are there: fuses and ease of bias set w/old analog meters.
_-_-bear
Hey
With the availability of reasonably high quality digital meters, make the cathode resistors 1-ohm, rather than a cap bypass on a higher value. You're then looking for .036 mv for 36 ma and so on.
Clearly would sound better imho.
Also: Make sure you have 1-K 5-W screen resistors (especially with current EL-34's from JJ or EH), and bias to taste. The original amp ran 50 ma per tube (1.5 V on 15 ohms for both tubes), I think 40 per is okay. Check here for an excellent online bias calculator: http://www.webervst.com/tubes/calcbias.htm .
HAVE FUN
With the availability of reasonably high quality digital meters, make the cathode resistors 1-ohm, rather than a cap bypass on a higher value. You're then looking for .036 mv for 36 ma and so on.
Clearly would sound better imho.
Also: Make sure you have 1-K 5-W screen resistors (especially with current EL-34's from JJ or EH), and bias to taste. The original amp ran 50 ma per tube (1.5 V on 15 ohms for both tubes), I think 40 per is okay. Check here for an excellent online bias calculator: http://www.webervst.com/tubes/calcbias.htm .
HAVE FUN
Hey
With the availability of reasonably high quality digital meters, make the cathode resistors 1-ohm, rather than a cap bypass on a higher value.
Clearly would sound better imho. You're then looking for .036 = 36 ma etc.
Make sure you have 1-K 5-W screen resistors (especially with current EL-34's from JJ or EH), and bias to taste. The original amp ran 50 ma per tube (1.5 V on 15 ohms for both tubes), I think 40 per is okay. Check here for an excellent online bias calculator: http://www.webervst.com/tubes/calcbias.htm .
HAVE FUN
With the availability of reasonably high quality digital meters, make the cathode resistors 1-ohm, rather than a cap bypass on a higher value.
Clearly would sound better imho. You're then looking for .036 = 36 ma etc.
Make sure you have 1-K 5-W screen resistors (especially with current EL-34's from JJ or EH), and bias to taste. The original amp ran 50 ma per tube (1.5 V on 15 ohms for both tubes), I think 40 per is okay. Check here for an excellent online bias calculator: http://www.webervst.com/tubes/calcbias.htm .
HAVE FUN
Now that this thread has been revived, would any of the ST-70 experts be so kind as to post an opinion of this kit:
http://cgi.ebay.ca/ws/eBayISAPI.dll...ndexURL=4&photoDisplayType=2#ebayphotohosting
http://cgi.ebay.ca/ws/eBayISAPI.dll...ndexURL=4&photoDisplayType=2#ebayphotohosting
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