When I took the cover off it was full of dust, my opinion is that the Amperex tubes are factory original and have never been replaced.
Tom Tutay, here in FL, who began modifying tube equipment since the mid sixties is sick and won't take any more work. Another possibility would be Scott Nixon. Joe Curcio, Dynaco and ARC modifier, charges $750 sans tubes for his mods, published many years ago in the pages of The Audio Amateur.
Tom Tutay, here in FL, who began modifying tube equipment since the mid sixties is sick and won't take any more work. Another possibility would be Scott Nixon. Joe Curcio, Dynaco and ARC modifier, charges $750 sans tubes for his mods, published many years ago in the pages of The Audio Amateur.
If Joe himself did the mods it would probably sound fairly good when complete. Much, much better than stock.
Ops, that's a preamp !!! Sorry, I didn't look closely at the pictures.
So ME would stretch my budget but go for something new, modern, with premium components. Why do you need so many tickets that you won't use? You can complement the PL Evo100 preamplifier with a phono pre, for example a Pro-Jet, there are models with MM / MC for only 100 Euros, or go for something more elaborate with selection of voltage and capacitance of the capsules, for a perfect match. ....
I don't like vintage equipment to repair (unless the price is a real bargain) and I don't think the sound is superior even if they leave it in perfect working condition.
But it's just an idea, my two cents ...
PrimaLuna Evo 100 Tube Preamplifier — PrimaLuna USA
Pro-Ject Phono Box
So ME would stretch my budget but go for something new, modern, with premium components. Why do you need so many tickets that you won't use? You can complement the PL Evo100 preamplifier with a phono pre, for example a Pro-Jet, there are models with MM / MC for only 100 Euros, or go for something more elaborate with selection of voltage and capacitance of the capsules, for a perfect match. ....
I don't like vintage equipment to repair (unless the price is a real bargain) and I don't think the sound is superior even if they leave it in perfect working condition.
But it's just an idea, my two cents ...
PrimaLuna Evo 100 Tube Preamplifier — PrimaLuna USA
Pro-Ject Phono Box
Yes, I had an ST-70 purchased at Stereo Exchange in lower Manhattan which I upgraded to the AR version - I didn't think it much of an improvement, but sold the amp for $1,200 in the early days of EBay.
I think that a Heath or Eico signal tracer would solve the OP issues in a snap.
for pretty vintage an EICO ST70 probably could be purchased cheap, throw out or bypass its tone controls and one would have an integrated amp about as good as one could be (assuming decent substitute for 7591) Output transformer quality was tops and at least as good as their HF87. The extruded aluminum face plate looks better than most of the inflated "value" geezer-prize toys.
I got my first one used in the late 1960's and carried it about a mile and half home in my arms. Good inverter circuit - probably better stock than a D90 which I owned.
Behold its beauty
https://img.canuckaudiomart.com/upl...co-st-70-with-7591-mullard-tube-amplifier.jpg
I got my first one used in the late 1960's and carried it about a mile and half home in my arms. Good inverter circuit - probably better stock than a D90 which I owned.
Behold its beauty
https://img.canuckaudiomart.com/upl...co-st-70-with-7591-mullard-tube-amplifier.jpg
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Joined 2009
Paid Member
EICO ST70 age = maybe late 1963 --I'll upload the test page if you wish in a bit
The steel chassis is much sturdier than say what Fisher did with KX200. I converted one ST70 to ppp 6BX7 triode years ago - choke input for power tubes 6DJ8 up front direct coupled to its stock 6SN7 inverter, no NFB - nice
https://i.imgur.com/EFL3v7C.jpg
Here's the tech part of that report
https://i.imgur.com/aBydg2c.jpg
The steel chassis is much sturdier than say what Fisher did with KX200. I converted one ST70 to ppp 6BX7 triode years ago - choke input for power tubes 6DJ8 up front direct coupled to its stock 6SN7 inverter, no NFB - nice
https://i.imgur.com/EFL3v7C.jpg
Here's the tech part of that report
https://i.imgur.com/aBydg2c.jpg
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I wish we could buy new empty chassis like this to build projects into, the current ePay boxes are really best for SS. I like the quality of the old style amps. I may have to custom order some locally. Maybe Leben comes closest.
Chaps,
After reading all the comments here I think I am out of my mind, why in the world go through all the time and trouble with a fifty years old preamplifier? Does anyone know an inexpensive shrink?
Someone pointed me to this MFA Magus, sold by Bruce Moore. All the info is in the ad. Looks like a simple, 4 tube design, please look at the photos. I do remember the Precision Fidelity C4.
MFA Magus C | Tube | Brentwood, California 94513 | Audiogon
After reading all the comments here I think I am out of my mind, why in the world go through all the time and trouble with a fifty years old preamplifier? Does anyone know an inexpensive shrink?
Someone pointed me to this MFA Magus, sold by Bruce Moore. All the info is in the ad. Looks like a simple, 4 tube design, please look at the photos. I do remember the Precision Fidelity C4.
MFA Magus C | Tube | Brentwood, California 94513 | Audiogon
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The whole point of DIY AUDIO is for technically minded or trained posters helping those with lesser technical skills repair older or old audio equipment .
All those posters were doing was trying to help you and its a bit disingenuous to trash their comments no matter how much you don't like the path they tell you to go down.
Head -fi for example is full of ---should I buy A/B/C or D because it/they sound "better " its like tube rolling ---"I think I will try this tube because of ---take your pick " .
All those posters were doing was trying to help you and its a bit disingenuous to trash their comments no matter how much you don't like the path they tell you to go down.
Head -fi for example is full of ---should I buy A/B/C or D because it/they sound "better " its like tube rolling ---"I think I will try this tube because of ---take your pick " .
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Joined 2009
Paid Member
I like the construction method - a big giant PCB. I don't think I have an easy way to make such large PCBs myself.
Frightfully sorry mate, but you are wrong. As I said it several times I do no have the knowledge to troubleshoot audio equipment. Several posters suggested I try something different, as you can see someone sent me a PM regarding the MFA.
Well, if we are at crossed purposes how unfortunate.
Cheers,
Well, if we are at crossed purposes how unfortunate.
Cheers,
here's an interesting note on "updating" SP3 - a new regulator board, correction of RIAA phono curve error, swapping out Mylar caps for polypropylene, change silver mica to polystyrene, a few redundant caps jumped with a wire. - in essence
more like the SP6 series.
When driving a tube amp, I'd imagine a Dyna PAS (4 tube sockets) with a number of variations would be "pretty good". Typically the phono stage could be pretty much stock, high level - gain stage direct coupled to a cathode follower with feedback to gain's grid. 6DJ8 are sometimes used in the phono stage - that would require a stronger power transformer than stock, IIRC, a Zener shunt regulator can sound nice. A simple cap multiplier too,
http://www.curcioaudio.com/SP-3 Mod Documentation.pdf
In the day, I heard a fair amount of tube stuff in my systems - CJ PV1, Precison Fidelity C7, several PAS mods including
"Last PAS", early Van Alstine, my own, RCA circuit, Bruce Moore "New Venusian", Moffat's earlier Theta, Tube God NB1, etc, A friend had SP3 so somewhat familiar with it too.
A couple hundred bucks and not much time should make a good tube preamp
more like the SP6 series.
When driving a tube amp, I'd imagine a Dyna PAS (4 tube sockets) with a number of variations would be "pretty good". Typically the phono stage could be pretty much stock, high level - gain stage direct coupled to a cathode follower with feedback to gain's grid. 6DJ8 are sometimes used in the phono stage - that would require a stronger power transformer than stock, IIRC, a Zener shunt regulator can sound nice. A simple cap multiplier too,
http://www.curcioaudio.com/SP-3 Mod Documentation.pdf
In the day, I heard a fair amount of tube stuff in my systems - CJ PV1, Precison Fidelity C7, several PAS mods including
"Last PAS", early Van Alstine, my own, RCA circuit, Bruce Moore "New Venusian", Moffat's earlier Theta, Tube God NB1, etc, A friend had SP3 so somewhat familiar with it too.
A couple hundred bucks and not much time should make a good tube preamp
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😀
That makes me feel calm, despite your warning, it seems that you will go for something new, although you do not want to delve into an expense greater than the one you have calculated.......🙂
That makes me feel calm, despite your warning, it seems that you will go for something new, although you do not want to delve into an expense greater than the one you have calculated.......🙂
Bruce and Scott could come up with some funky phono preampliers - "The New Venusian" was built on two large Bud chassis, all octal tubes, feedback RIAA, Its unregulated outboard supply was populated with many computer grade large electrolytic caps. It had a "pretty sound" imo.
A main concern when mating tube preamplifier to solid state power amplifier
is to avoid destruction upon turn-on and turn-off. I once forgot to turn a Citation 12 solid state amp off before turning off a Citation IV tube preamp. The amplified LF pulse pushed 4 SEAS woofers completely out of their gaps - like an inch and a half forwards, ruining 4 Dynaco A35 speakers.
Relays are used to prevent these problems. Frank Van Alstine in a Dynaco PAS mod had large value power supply caps which took a long time to charge and to discharge, so that preamp circuit could be switched on and off without any problems,. It was not remarkable sound quality wise IIRC.
I see there is a Dynaco Tube forum - that could be a wealth of ideas for what to do with 4 bottles. Three tube preamps are common too with two 12ax7 for phono and one tube sharing channels for the high level stage,
I have a double mu-follower preamp - in retrospect, simpler can be very good. My PAS nearly 50 years ago had Zener shunt regulation, polycarbonate coupling caps.
Dynaco PAS 3 Mods
A main concern when mating tube preamplifier to solid state power amplifier
is to avoid destruction upon turn-on and turn-off. I once forgot to turn a Citation 12 solid state amp off before turning off a Citation IV tube preamp. The amplified LF pulse pushed 4 SEAS woofers completely out of their gaps - like an inch and a half forwards, ruining 4 Dynaco A35 speakers.
Relays are used to prevent these problems. Frank Van Alstine in a Dynaco PAS mod had large value power supply caps which took a long time to charge and to discharge, so that preamp circuit could be switched on and off without any problems,. It was not remarkable sound quality wise IIRC.
I see there is a Dynaco Tube forum - that could be a wealth of ideas for what to do with 4 bottles. Three tube preamps are common too with two 12ax7 for phono and one tube sharing channels for the high level stage,
I have a double mu-follower preamp - in retrospect, simpler can be very good. My PAS nearly 50 years ago had Zener shunt regulation, polycarbonate coupling caps.
Dynaco PAS 3 Mods
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To compare a Marantz 7 with a modern, PCB based tube amp is to compare apples with pears. They sound completely different.
Before going in a choosen direction, one should know where this path leads to.
If you have no clue about the sonic differences of tube amps, no one can help you here.
You could even choose any cheap chinese, it wouldn't matter for you because there seem to be no knowledge about what it sounds like. The differences in sound signature are so big, its unbelievable. Every one picks his sound he (or she) prefers. Thats the reason why so many are continously rolling gear, because they are searching for their perfect match. In doing this, one is learning many things. The most important is, to have a congruent argument how circuits are sounding. The more advanced can furthermore tell how parts in circuits are sounding, too. And if you are on top of the hill, like a five star guide michelin cook, you know how a special circuit will sound with a special combination of very precious parts and tubes. Without knowing that all and have no clue of what and how to achieve, your right at the base of any mountain to climb upwards. This climbing is only possible by making your own eperiences with sound. Nobody can do it for you. And even this forum can't do it. Some things in life have to be done by yourself.
Before going in a choosen direction, one should know where this path leads to.
If you have no clue about the sonic differences of tube amps, no one can help you here.
You could even choose any cheap chinese, it wouldn't matter for you because there seem to be no knowledge about what it sounds like. The differences in sound signature are so big, its unbelievable. Every one picks his sound he (or she) prefers. Thats the reason why so many are continously rolling gear, because they are searching for their perfect match. In doing this, one is learning many things. The most important is, to have a congruent argument how circuits are sounding. The more advanced can furthermore tell how parts in circuits are sounding, too. And if you are on top of the hill, like a five star guide michelin cook, you know how a special circuit will sound with a special combination of very precious parts and tubes. Without knowing that all and have no clue of what and how to achieve, your right at the base of any mountain to climb upwards. This climbing is only possible by making your own eperiences with sound. Nobody can do it for you. And even this forum can't do it. Some things in life have to be done by yourself.
since we are dealing with single ended topology, power supply output impedance, RC decouplers employed , type of regulator used, will influence the subjective impressions of a given circuit.
I had a stock Precision Fidelity C7 . It had an IC B+ regulator - when that was replaced with a simple Zener referenced TIP50 cap multiplier and 10uF cap with R added to decouple its cascode 12AX7 first gain stage, sound quality improved immensely. It probably would change again if the power supply was cap input, nothing regulated and again still if LC supply and RC decouplers.
The type of resistor employed and also with capacitors influence the sound. Carbon composition resistors may
have their place.
Then there's the matter of synergism. What might sound great interfaced with one amplifier may not sound as great with another.
I had a stock Precision Fidelity C7 . It had an IC B+ regulator - when that was replaced with a simple Zener referenced TIP50 cap multiplier and 10uF cap with R added to decouple its cascode 12AX7 first gain stage, sound quality improved immensely. It probably would change again if the power supply was cap input, nothing regulated and again still if LC supply and RC decouplers.
The type of resistor employed and also with capacitors influence the sound. Carbon composition resistors may
have their place.
Then there's the matter of synergism. What might sound great interfaced with one amplifier may not sound as great with another.
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