Hi Torben,
Thanks - If you can find the two papers - the one you draw and the paper you believe to come from the original service manual - we finally can determine the genuine TVA-1 circuit.
The schematic I found by checking several japanese pictures is slightly different compared to the circuit in Hiraga's book "Rörförstärkere". As mentioned erlier the bias resistors in the japanese amplifiers is 220K just like you suggested the highest value to be calculated from grid to cathode on KT88. The first picture in this thread is identical with the circuit in Hiraga's book.
It surprices me that you messured +B to heroic 570V. According to 2 times 190Vac times (approx.) 1,4 = leaves a little more than 532Vdc on the plates of KT88. Perhaps this is not a world of difference, but it makes me understand why the lower current drawn by KT88 keeps them steady.
The intension is to come as close to the original circuit as possible - but with stability. I think TVA-1 is a wonderful amplifier as well.
Regards
Kim
Thanks - If you can find the two papers - the one you draw and the paper you believe to come from the original service manual - we finally can determine the genuine TVA-1 circuit.
The schematic I found by checking several japanese pictures is slightly different compared to the circuit in Hiraga's book "Rörförstärkere". As mentioned erlier the bias resistors in the japanese amplifiers is 220K just like you suggested the highest value to be calculated from grid to cathode on KT88. The first picture in this thread is identical with the circuit in Hiraga's book.
It surprices me that you messured +B to heroic 570V. According to 2 times 190Vac times (approx.) 1,4 = leaves a little more than 532Vdc on the plates of KT88. Perhaps this is not a world of difference, but it makes me understand why the lower current drawn by KT88 keeps them steady.
The intension is to come as close to the original circuit as possible - but with stability. I think TVA-1 is a wonderful amplifier as well.
Regards
Kim
Hi again Torben,
You are a very qualified "painter" - I think you have a "future" there
I hobe your brother still got the amp. "I will be back" to you with details when my TVA-1 clone plays.
We have been looking for replacement OP's, and found some 70W transformers from "James Audio" in Taiwan. These OP's seems to be sufficiant for the "work" in this circuit. We have also looked at the expensive Hashimoto OP's - mostly because they have very high production standard. I already have a pair wounded by Bjarne Larsen in Vindinge,VRT transformer, reproduced according to the old TVA-1 standards.
Unfortunately Bjarne don't work any more , but all his knowledge followed to the new owner of VRT.
I am not sure whether the expensive Hashimoto or Tango OP's sounds better than the pair from VRT. We have messured the VRT's from 5Hz to 75kHz +- 1dB (the TVA-1 copies), but I think we will buy the pair from James Audio in order to compare the sound quality.
Nice to have some projects?
The best regards
Kim
You are a very qualified "painter" - I think you have a "future" there
I hobe your brother still got the amp. "I will be back" to you with details when my TVA-1 clone plays.
We have been looking for replacement OP's, and found some 70W transformers from "James Audio" in Taiwan. These OP's seems to be sufficiant for the "work" in this circuit. We have also looked at the expensive Hashimoto OP's - mostly because they have very high production standard. I already have a pair wounded by Bjarne Larsen in Vindinge,VRT transformer, reproduced according to the old TVA-1 standards.
Unfortunately Bjarne don't work any more , but all his knowledge followed to the new owner of VRT.
I am not sure whether the expensive Hashimoto or Tango OP's sounds better than the pair from VRT. We have messured the VRT's from 5Hz to 75kHz +- 1dB (the TVA-1 copies), but I think we will buy the pair from James Audio in order to compare the sound quality.
Nice to have some projects?
The best regards
Kim
Hi
I compared Torben's schematic of the power supply to mine this weekend and it is in fact exactly that. Would anyone be able to assist me in getting the appropriate specs for the NTC (thermistor) to replace the one in my amp? The body of mine was cracked and I took it out some time ago and subsequently misplaced (lost) it. Sadly I lack the knowledge to come up with the appropriate specs myself. I appreciate any help.
TIA
Paul
I compared Torben's schematic of the power supply to mine this weekend and it is in fact exactly that. Would anyone be able to assist me in getting the appropriate specs for the NTC (thermistor) to replace the one in my amp? The body of mine was cracked and I took it out some time ago and subsequently misplaced (lost) it. Sadly I lack the knowledge to come up with the appropriate specs myself. I appreciate any help.
TIA
Paul
Have just bought a TVA-1 on Ebay from 1978-79. Hobe to get it in one piece --- 40Kg by UPS ??
Your drawing and manual are most appreciated!
Regards Kim
Hi Kim
Congratulations with your TVA-1. How much did you pay and from which country did you get it. I might buy one myself some time – I suspect they are rather expensive though.
Paul
I do not know any details about the NTC resistor. As far as I remember it is physically rather large and in a metal case. In a few days I am going to see my brother, and I will have a look at the NTC resistor in his TVA-1. I do not think there is anything written on it – otherwise I would have included that information in my schematic. What I can do is measure the resistance when the amp is off and when it is on.
You might not want to use the thermistor at all – you could replace it by a couple of resistors like shown in the schematic in post 24 or you could simply replace it by one 4R7 5W resistor or a piece of wire (like in post 1). I think I would replace it by a single 4R7 5W resistor. Assuming a total current of approximately 200 mA a 4R7 resistor will drop a little less than 1 volt and dissipate 0.19 W.
Regards, Torben
Congratulations with your TVA-1. How much did you pay and from which country did you get it. I might buy one myself some time – I suspect they are rather expensive though.
Paul
I do not know any details about the NTC resistor. As far as I remember it is physically rather large and in a metal case. In a few days I am going to see my brother, and I will have a look at the NTC resistor in his TVA-1. I do not think there is anything written on it – otherwise I would have included that information in my schematic. What I can do is measure the resistance when the amp is off and when it is on.
You might not want to use the thermistor at all – you could replace it by a couple of resistors like shown in the schematic in post 24 or you could simply replace it by one 4R7 5W resistor or a piece of wire (like in post 1). I think I would replace it by a single 4R7 5W resistor. Assuming a total current of approximately 200 mA a 4R7 resistor will drop a little less than 1 volt and dissipate 0.19 W.
Regards, Torben
Hi Torben,
I found this from Belgium. The auction is closed but you could contact the seller anyway and ask!
Michaelson & Austin TVA1 vollständig restauriert bei eBay.de: Funk- Phonotechnik (endet 20.12.09 20:20:22 MEZ)
The auction here started at 800 Euro with a "sofort kaufen" of 1095 Euro. This is fair for a complete updated TVA-1 today!
A german friend of mine wanted 1500 Euro for a renewed TVA-1!
The price I payed was approx 580 Euro which included the TVA-1, post and carriage , plus 10 Euro extra in fee?? - What the fee was I never found out?
This Item I bought need new components and so on - we have to see how much. I might come close to 250-300 Euro for new components before it looks like new.
Best regards
Kim
I found this from Belgium. The auction is closed but you could contact the seller anyway and ask!
Michaelson & Austin TVA1 vollständig restauriert bei eBay.de: Funk- Phonotechnik (endet 20.12.09 20:20:22 MEZ)
The auction here started at 800 Euro with a "sofort kaufen" of 1095 Euro. This is fair for a complete updated TVA-1 today!
A german friend of mine wanted 1500 Euro for a renewed TVA-1!
The price I payed was approx 580 Euro which included the TVA-1, post and carriage , plus 10 Euro extra in fee?? - What the fee was I never found out?
This Item I bought need new components and so on - we have to see how much. I might come close to 250-300 Euro for new components before it looks like new.
Best regards
Kim
Hi,
The suggestion stated by Torben using one 5W resistor to replace the NCT thermistor could be one alternative.
A second possibility could be a 5-10 second delay 6 or 12vdc relay with a 25W aluminum resistor parallel or across the relay contacts.
The resistor size is, if we have 330Vdc across it, and allow the amp to draw 50mA at startup U/I = 6K6 - and the needed wattage is UxI 330x0,05= 16,5W
Because the resistor is only 530Vdc loaded in about 5-10 seconds 25W is sufficiant. The relay takes approx. 100mA from the heatersupply with a approx. 5 sek delay on the attached circuit.
One may have to ajust the resistors in the circuit as the design is made for 24V.
We will get some protection of the high volt capasitors at power on, and the heaters has some glow-up time before the full high voltage is applied.
Just one idea!
Regards
Attachments
Hi SP,
Yes I am very lucky to get the TVA-1 unmodified, from what can be seen on the pictures. I have not received the amplifier yet - the lady who sold it to me, can't lift it ! -)) - She needs help! I may get the M&A first in the new year.
I think Torben's drawing is very, very good and close to the real amplifier, and I will try to check the circuit of mine later and return to you with details.
I have my engineer-friend and I compete with him making the best tubeamps! - he is educated and I am some sort of a "parvenu" and autodidact inside elektronics. In spite of this, I reached 60kHz -2 dB with my TVA-1 clone 14 years ago. The jumping point is: Will the sonic sound be improved by the OP's on the real TVA-1? Is the TVA-1 OP's made by Partridge?
I really know nothing about the TVA-1 from Michaelson & Austin - I look foreward to hear this amplifier against my friends Mac MA2275. The MA2275 sounds like a very well designed solid state amp - but my god it sounds sterile compared to my LEAK Stereo 50 copy. I hobe and wish to get the tubesound from the Michaelson & Austin, TVA-1.
Best regards
Kim
Yes I am very lucky to get the TVA-1 unmodified, from what can be seen on the pictures. I have not received the amplifier yet - the lady who sold it to me, can't lift it ! -)) - She needs help! I may get the M&A first in the new year.
I think Torben's drawing is very, very good and close to the real amplifier, and I will try to check the circuit of mine later and return to you with details.
I have my engineer-friend and I compete with him making the best tubeamps! - he is educated and I am some sort of a "parvenu" and autodidact inside elektronics. In spite of this, I reached 60kHz -2 dB with my TVA-1 clone 14 years ago. The jumping point is: Will the sonic sound be improved by the OP's on the real TVA-1? Is the TVA-1 OP's made by Partridge?
I really know nothing about the TVA-1 from Michaelson & Austin - I look foreward to hear this amplifier against my friends Mac MA2275. The MA2275 sounds like a very well designed solid state amp - but my god it sounds sterile compared to my LEAK Stereo 50 copy. I hobe and wish to get the tubesound from the Michaelson & Austin, TVA-1.
Best regards
Kim
For the owners of Mac MA2275 I apologize!
The "sterile sound" from MA2275 may have something to do with older ears and hearing (my ears), and the fact that the OP's from this Mac amplifier is wounded - may be quadro-filar which brings the linearity more than four times up compared to "standard" OP's.
Sterile sound from one amplifier is a personal opinion and experience!
Regards
Kim
The TVA1 has stuck in my mind as a great sounding amp. Tube or transistor does not really enter into it and from what I have read of Tim de Paravicini his belief seems to be that he could design with tube or transistor and get the same result. I would love a set of his big monoblocks (509 I think they are).
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This point of difference between tube and transistor may have to be investigated further if we really want to messure characteristics and compare them.
Up untill this moment the last 15 transistor amplifiers made by me sounds more distinct in midrange as well as highrange - even with different mos-fet's and class A constructions.
I still remain to hear the sound of one transistoramp ( class A or any other circuit) that equals the sound from a single-end 845 or "only" a push-pull 7581A/KT66 amplifier.
If one looks at "the green grass of noise" messured on Brüel& Kjaer equipment from the tubes and compare this with noise coming from transistors (2.and3.harmonic) there is some difference - also in speed , raise time and the way tubes bends the square sinus at the corners.
My engineer friend as well as Tim de Paravicini , can't really understand or explain why the sound of tubes varies from one brand to another and from one circuit to another - the tubes seems to messure just like the same??? I can't either!
But I like the tubesound better!
Happy new year.
One statement from my egineer is: " If a transistor circuit is well designed , the type of transistors used has very little influence on messured frequence and performance overall".
He states the same contention in association with tubes -
In the latest two push-pull amplifiers( Leak stereo 20 and 50) made by me , we tried to change the input tube 12AX7 and brand, as well as the drivertube , 12AU7 / 12BH7a/E80CC among others.
We tried Telefunken,Philips,Brimar,Siemens,Golden Dragon and GE 5751 for input with only minor difference in messurement and soundstage- no significant adventure in sound perception.
We tried with the same brands in the driverstage and achieved some raise in power by use of 12BH7a and E80CC , but we could not messure or hear any improvement as far as the sonic sound was concerned.
The test system was Mac preamp and Mac CD together with JBL XPL160 and AR11/ AR3a .
Five people with "golden ears" listened.
Our conclusion was: If the sound system used has a reasonable good standard, the tubeamplifier affects and add very little to the sound overall (assumption that the tubeamplifier messures better than DIN. hi-fi standard ).
Personally I don't have "golden ears" - I just like to build tubeamps.
He states the same contention in association with tubes -
In the latest two push-pull amplifiers( Leak stereo 20 and 50) made by me , we tried to change the input tube 12AX7 and brand, as well as the drivertube , 12AU7 / 12BH7a/E80CC among others.
We tried Telefunken,Philips,Brimar,Siemens,Golden Dragon and GE 5751 for input with only minor difference in messurement and soundstage- no significant adventure in sound perception.
We tried with the same brands in the driverstage and achieved some raise in power by use of 12BH7a and E80CC , but we could not messure or hear any improvement as far as the sonic sound was concerned.
The test system was Mac preamp and Mac CD together with JBL XPL160 and AR11/ AR3a .
Five people with "golden ears" listened.
Our conclusion was: If the sound system used has a reasonable good standard, the tubeamplifier affects and add very little to the sound overall (assumption that the tubeamplifier messures better than DIN. hi-fi standard ).
Personally I don't have "golden ears" - I just like to build tubeamps.