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What are your thoughts on modifying or upgrading a vintage receiver versus restoring with original parts? My thinking is by modifying/upgrading, you are altering the intended sonic characteristics.
Follow Ups:
There are folks who spend tens of thousands of dollars restoring '57 Chevys to their original state. And any current Hyundai will outperform them in every possible category. Do you seek an historical reference or better sound quality?
rw
In context with the great responses below, keep in mind that:
1. Today's AC line voltages are higher than when the gear was built. The unit's power supply voltages change as a result.
2. The amount of RF energy around now is HUGE compared with the '60s and '70s. Now you've got a zillion cell phones, wireless web networks, remote controls, switching power supplies, etc., that the original designer had no knowledge of and are now bombarding the vintage gear.
3. The associated gear (speakers, signal sources, wire/interconnects, etc.) used now with vintage pieces often is quite different than what was used back at the time. That may have some impact as well.
4. The tubes themselves are somewhat different than years ago (in the case of tube gear).
5. The parts available today are often far superior (and often much cheaper) to what was available back then. They perform differently in a given circuit in many cases.
5. Finally, an individual owner doesn't have to live within the budget limits and other restrictions the original designer faced.
So I think some modification is often needed just for the piece to survive today's operating environment.
"2. The amount of RF energy around now is HUGE compared with the '60s and '70s. Now you've got a zillion cell phones, wireless web networks, remote controls, switching power supplies, etc., that the original designer had no knowledge of and are now bombarding the vintage gear."
I know, my basement workshop is a nightmare. I hear a strange frequency between stations on my 800c, and it makes it difficult to align. It also cuts the stereo reception. I cannot figure out exactly where it is coming from short of short of cutting every component off in the house. I live under a victor airway, and also the house elevation is fairly high compared to the surrounding area. It sounds like a motorized high frequency with a strange phase warp. Two computers, belkin wireless, external hard drives, cordless phone, two modems in the house - they are supposed to follow class restrictions, no?
That's why i posted here. Being the novice that i am, the responses to my question were of things i was not aware of. I have been educated.
Since the parts used in any particular older unit are not being manufactured today exactly as they were, and the original parts are surely out of spec by now, getting back to an "exact" stock sound is not exactly possible. However, you can make parts choices that can get you close if that's your specific obsession.
If you happen to be *that* interested in hearing what was intended by the designer here's an option: Purchase two units. Rebuild one as close to stock as you can and let it stand as your stock reference. The second unit can then be stuffed with boutique parts galore or circuit modded ad infinitum.
If nothing else, it takes the guess work out of whether or not you've made a definite improvement. More than that it keeps you in touch with what you have lost in the process of improving certain areas of the sound. You almost always lose something. I like going this route. It does require patience as you have to let parts burn in for quite a while. It's cool, and fun, to shootout both versions step by step. In the end it works for me. It's just one way to go.
I've found restoring solid state gear has offered me more improvement and appriciation of the original sound. "Maybe" more towards it's original intent - only assuming what it would have sounded like?
But on occasion I have found doing a total pull out and parts replacement with "some" tubed amps left me very dissapointed. What would start out as a vintage tube sound with great possibilities ended with a total loss of it's character and charm. Not the way I wanted to go. I know this could be a long thread on it's own.
As Jim pointed out, to my surprise, there are WAY more variables since it's production date. So bring it back to spec first and take it from there. Personally I wouldn't go parts "crazy" on it. Just the basics.
charles
I have mixed feelings about this. Restoration (replacement of out of spec or aged parts with the closest new equivalent) is fine for things like power amps. However, many older pieces, both SS and tube had out of spec. RIAA equalization curves, tone controls that weren't flat at the center position of the controls, volume controls with serious imbalance, and balance controls that aren't balanced at the center position. In most cases, I'd fix those defects; even though those errors may have been what gave that piece of gear its unique character. It was very rare to find a 60's tube (or SS) phono circuit that had an accurate RIAA equalization, some were off by more than 2 dB. After 1972 or 73, things were a lot better, but exceptions still exist - maybe even deliberately by the manufacturer to give their gear a little differentiation.
As far as upgrading or improving circuit designs, I tend to limit that to power supply upgrades in rectifiers and caps.
And a minor rant here. I do not believe in changing the circuit topology in Dynaco tube amps.
Jerry
Hi Jerry,
When you say this, "And a minor rant here. I do not believe in changing the circuit topology in Dynaco tube amps."
I'm curious as to why.
Just interested, as I have been doing a lot of reading online in preparation for an ST70 purchase.
Thanks!
Doug
The Dynaco amps are all designed with a single tube voltage amplifier and phase splitter. The ST70 uses the 7199 which was designed specifically to be an audio tube. This tube combines a pentode voltage amplifier and a triode section which is used as the driver and phase splitter. Something similar is done in all the other Dynas. The advantage of the single triode phase splitter is that the balance between the two outputs is determined by the value of the two resistors in series with the plate and cathode, so it does not need to be balanced externally, and does not depend on the tube properties for the balance. Distortion is also dependent on the matching of several pairs of resistors. The closer they are matched, the lower the distortion. It's quite easy through better matched resistors to drive the harmonic distortion at clipping down to 0.3% or less.
The second area I like is the single resistor used for cathode bias in the outputs. It makes the balance between the two outputs automatic, if they are a matched pair. It also facilitates the simple bias adjustment on Dyna amps.
In thise two areas, Hafler made a very good amp with a simple, low maintenance circuit. Why would you want to complicate that for no gain. I know the aftermarket folks tout advantages for their replacement boards, but if the distortion figures are low for the stock circuit it shows that the circuit is working well.
If the aftermarket circuit reduces the negative feedback, be aware that it also decreses the damping factor of the amp and that alone will change the sound because of speaker interactions that are different. I'm not at all convinced that the change in sound is because the amp is "better".
Trivia: Did you know that the 1.56 volt figure for correct bias was set at that voltage so that you could check your voltmeter against a fresh alkaline battery? That was important in the days of analog multimeters which were not all that accurate.
Since you're interested in the Stereo 70, and I have a little experience with that amp, let me make a few specific comments. First, the power supply is on the weak side. The monaural Mk IV, which uses the same circuit and output transformers puts out 40 watts compared to 35/ch for the ST70. Few ST70's in my experience actually clip at 35w/ch. Most I have measured are a few watts shy. I consider it to be a very good 30 watt/ch amp. Dyna's specs (and Eico's, too) always were is terms of 35 watts +/- 1 dB. Well, 1 dB is 26% in power. So they are saying 35 watts minus 26% or 25.9 watts. I never found one that bad, but you can see my point. McIntosh was the opposite. They were very conservative. The MC225 was rated at 25 W/ch., but they clip at around 34-35 w/ch. In fact, a Stereo 70 with carefully matched resistors measures very close to an MC225 through the midband. The MC 225 does have better output transformers and will do better at the frequency extremes (below 40 Hz and above 18 kHz)due to less core saturation and less leakage inductance.
The Stereo 70 (ST70 is commonly used, but that was an Eico integrated amp)is a very good sounding amp but a little weak on the low end. It has a fairly good damping factor of about 12-15. J Gordon Holt considered it the ideal match for the KLH Nine electrostatics.
If you parallel the channels, it becomes a good 60 watt amp with a DF of around 20-25, although I prefer the Mk II or Mk III for that.
Jerry
A bit of that was above my head, but interesting to consider and helpful as I want to learn as much as possible before making a decision.
In the end however, I think you've complicated my decision as I was leaning toward a new ST-70 copy kit (Bob Latino's) that touts a changed circuit board as a benefit.
I wonder if you have any recommendations for a similar / better performing amplifier within a comparable price range?
thank-you again..
Doug
Look for a pair of Dyna MK IV or better yet a pair of Mk II or Mk III. The MC225 is a great amp, but very pricey. The Marantz tube amps are excellent, but again, pricey; and any older amp will need restoration.
Do you have a link to Bob Latino's? I'm curious about his "improved" circuit. 7199's were not available until fairly recently, so that probably triggered some alternative circuits out of necessity.
The only new 7199 that I am aware of is the Sovtek. This is not everones favorite but the price is right. JAN Philips are going for $50. Do you know something I don't? Still, I agree with you about the orginal Dynaco circuit. It worked for me when I was running Mark IV's.
Dave
http://www.tubes4hifi.com/bob.htm
Thanks! That looks to be a very nice kit. The circuit is quite simple and has replaced the 7199 with 1 1/2 12AT7's (three triodes). There was no schematic available, but I'd guess he uses two of the 12AT7 triodes to replace the 7199's pentode voltage amplifier, and the third triode as the phase splitter and driver.
The power supply is beefed up, as needed.
That and the larger ST-120 look like very nice amps.
I'd go for it.
Jerry
...is an interesting concept to have to choose. I used to think just like bob24, that upgrading/modifying changes the intended sonics. Restoring tube gear over 30 years, now, I used to restore/rebuild with stock circuitry, first, always interested in hearing the original. If I liked the "original" enough, I left it that way. But, my upgrading often results in better than original sound. Now, I choose a bit more wisely. I know which phono stage I prefer, which line stage that satisfies, which amp circuitry I will prefer, etc. I might just redesign as I rebuild. Then again, I have tough love for certain stock items...decisions, decisions...
So, if you want to hear a vintage item the way it sounded back then, use carbon resistors and paper/mylar/polyester coupling caps, to mimic the sonics. If you hear the bass is too thick, after breaking in the parts, maybe an upgrade to PIO or polypropylene caps will add the texture and detail you want. Maybe, a simple swap of the RIAA EQ parts choices(polystyrene versus original mica or ceramic) will do the trick. If the newer version tubes need lower grid resistor values(like 7591s in Fisher 500/800 Rcvrs), then consider that mod a smart upgrade, which will still accommodate the rarer tubes. Upgrading of parts and design is meant to be just that, an upgrade. All in all, though, I still like to hear the original circuit, first...
I would start with a simple replacement of all the electrolytic caps. Providing the unit was in good working order and wasn't in need of some other repair work.
After that I would try simple upgrades. Like replacing mylar caps on the tone board with spraques, a better coupling cap if you have a film in that position.
After 30 years you really are NOT hearing the sound of that receiver. What you are hearing is aged caps that are out spec and maybe a drifted resistor or two.
NEVER feel bad about restoring a vintage piece. That is more a labor of love for the hobby and showing appreciation that the darn thing still rocks! Otherwise you would have chucked it in the trash! And as for upgrading a capacitor or two I'm sure the engineers of the time would have liked to use better parts. But remember they had to build these to a price point. But don't fall pry to the capacitor snake oil. Sometimes a ten cent capacitor IS the better one for that position. Especially on the preamp's amp board. Not the case for the tone board - upgrade away there.
charles
To use a phrase of the younger gen,you guys rock! Gals too if you replied. Thanks.
Good reply. I suppose if the consensus of a particular vintage piece of gear was that the original sound was "perfect", then it should probably be restored to its original sound. OTOH if it was weak in some area, then upgrades or modifications might be in order.
One thought.. When you restore an old piece, if you put in modern parts they are often of better quality than the originals. A simple example would be diodes. The modern ones you can buy for under a $1 are better than those old silicon ones. You can put really nice caps in the power supply and increase the capacitance. If you simply replace the rest of out of spec components - using carbon resistors and the cap types as suggested you will hear the circuit as the designer intended, just with a better power supply than was available at the time. Often the amp will have much more extended frequency response than even when new. Or you can put better signal caps and resistors in than the original as well. I don't know, you are still hearing the circuit as originally designed, just with better parts. And yes, you can tune the sound with cap and resistor choices as discussed earlier. Or, go for circuit mods. Often you need to mod the circuit to accept a different output tube because the old ones are unobatinium... but there is some other tube that is basically the same, but in a different pinout.
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