Nice photos here:
http://www.jogis-roehrenbude.de/Roe...Radio-Restauration/Knipschild_TVA-1/TVA-1.htm
My friend has one like this. I was going to copy it for a mono sub amp but when I pulled off the bottom cover there were a few differences between the actual component values and the schematic values.
I gave up but would still be keen to make a copy because it is a great sounding amp.
If someone knows about this circuit or can check values I might be able to borrow my friends again.
sp
http://www.jogis-roehrenbude.de/Roe...Radio-Restauration/Knipschild_TVA-1/TVA-1.htm
My friend has one like this. I was going to copy it for a mono sub amp but when I pulled off the bottom cover there were a few differences between the actual component values and the schematic values.
I gave up but would still be keen to make a copy because it is a great sounding amp.
If someone knows about this circuit or can check values I might be able to borrow my friends again.
sp
stoolpigeon said:
Hi
I am about to make a TVA-1 "clone" . Please take a look at: leakstereo20
The intension is to make an upgrade version of the famous amplifier, with regulated fet-psu for the drivertubes. The drivers may be changed along with the messurement of the output power. I need the approx. 60-70 watt power for my AR3a speakers. For the time being the tubepreamp to drive the TVA-1 copy takes all the time available. The first attempt to make the TVA-1 was made 14 years ago. Look at: AR3a
It would be a great help if you could borrow your friends TVA-1 and check out the component values - whether the component values is similar to the original circuit.
One detail: the 330K resistor in the negative bias circuit may have to be changed to 100K ( maybe also the 0,47uF to 1,5uF) because old KT88 draws a higher amount of mA as when the internal resistance changes with age of the outputtubes.
Some nice pictures from a japanese hi-fi freak:
Michaelson Austin TVA-1
Michaelson Austin TVA-1
Michaelson Austin TVA-1
Michaelson Austin TVA-1
Michaelson Austin TVA-1
regards
Kim
Yes - I talked to a German Hi-fi entusiast, who checked out a very erly TVA-1 to be exactly identical to the shown circuit. Find the amplifier here: Restauration TVA 1 .
Mr. Knipschild did not have any experience with his TVA-1 and burning components or tubes. On the other hand some hi-fi people had called for help with heat and fire from TVA-1 amplifiers.
Another guy in Belgium stated that some strange unexplained changes has been made to later versiones of the TVA-1.
I have heard the original without checking the values of the components. I am very sorry I did'nt. This amplifier sounded as one of the best I have ever listen to when talking about push-pull with power beyond 30 watt.
If anyone has the answer whether the stated circuit can be verified as identical to the real TVA-1 amplifier, I would like to know?
regards
Kim
After I have checked out several japanese renoval TVA-1 amplifiers from the close-up pictures taken ( as mentioned above erlier) , the following circuit comes up:
If one looks close to the mentioned pictures, some older versions uses 47R as cathode resistor for the KT88, while later amplifiers has 33R hooked up to GND. In the feed-back circuit the original circuit says 3K9 parallel with 470P - where as the seen print on the pictures shows 3K3 /330P. Otherwise the rest of the attached circuit should be identical with the real TVA-1 amplifier from Michaelson & Austin.
As for the feed-back resistor - and capsize it all depends on the chosen OP's if one don't have the original types in stock.
For JDev:
Look at the pictures and you will get an idea of the resistor wattage if you unable to calculate the optimal size.
Regards
Kim
Attachments
Original TVA-1 circuit
Hi SP,
Thanks - this could be a great help. The TVA-1 clone need to be as close as possible to the original amplifier from Michaelson & Austin ( in my opinion), when we talk about the driver - and outputstage. The psu is quite another story - this is here the improvement comes in. If we can't reach top-spec's with the mentioned circuit, it shall be modified.
Today I just received mail from hi-fi friend in Germany, who may offer me to buy a late TVA-1 amp. If we can find a reasonable price I may buy this amplifier.
In spite the possible offer of a original TVA-1, I still want to continue the project from: leakstereo20 , and your info concerning the component values is important to me as well as for other DIY people.
On this stage I can't stop making the TVA-1 clone - all the components including OP's and powertransformer has been bought, and the psu-print is ready for soldering.
All the fact's with Raa, B+, distortion and voltage messurement concerning the TVA-1 circuit shall be accessible for everybody on the amateursite mentioned above.
Thanks for your help in advance
Kim
Hi SP,
Thanks - this could be a great help. The TVA-1 clone need to be as close as possible to the original amplifier from Michaelson & Austin ( in my opinion), when we talk about the driver - and outputstage. The psu is quite another story - this is here the improvement comes in. If we can't reach top-spec's with the mentioned circuit, it shall be modified.
Today I just received mail from hi-fi friend in Germany, who may offer me to buy a late TVA-1 amp. If we can find a reasonable price I may buy this amplifier.
In spite the possible offer of a original TVA-1, I still want to continue the project from: leakstereo20 , and your info concerning the component values is important to me as well as for other DIY people.
On this stage I can't stop making the TVA-1 clone - all the components including OP's and powertransformer has been bought, and the psu-print is ready for soldering.
All the fact's with Raa, B+, distortion and voltage messurement concerning the TVA-1 circuit shall be accessible for everybody on the amateursite mentioned above.
Thanks for your help in advance
Kim
Hi SP,
Super - this is what we all need to be sure of real TVA-1 circuit. Please find following changes on the attached circuit which is :
1. Plate resistors for ECC83 is 200K ( instead of 330K)
2. Plate resistors for ECC81 is 33K ( instead of 47K) /
cathode resistor is 2K2 (instead of 33K??- this 33K MUST BE WRONG!)
3. + B resistor ( between the two 33K for ECC81) is 6K8(instead of 12K)
4. The negative bias resistors is 200K ( instead of 330K)
5. Cathode resistor for KT88 may have the value of 33R (instead of 47R)
6. Feedback resistor is 3K3 parallel with 330P
7. The negative bias resistor for ECC83 cathode has been changed to a single 33K ( instead of 47K parallel with 100K) - Not so important.
8. Please check whether M&A really had a 10K in series with 2K2 to the signal screen on KT88.
When my tubepreamp is ready , the TVA-1 project will start. If you can help me on this one, I shall return to you with all possible information according to voltage, messurement and linearity to the Michaelson and Austin circuit. I have already a pair of OP's , but I have been thinking of a pair of Hashimoto outputtransformers. ( may take some time but you will get the info)
You can find the former Sansui supplier "Hashimoto" KT88 OP's at :
leakstereo20
- on this page find the direct link to Hashimoto and Tango as well.
- Or buy from the Netherlands:
Transformers Tango Hashimoto Tamura Partridge main page
I think the quality of the TVA-1 OP's can be reached with a pair from "Hashimoto".
Best regards
Kim
Super - this is what we all need to be sure of real TVA-1 circuit. Please find following changes on the attached circuit which is :
1. Plate resistors for ECC83 is 200K ( instead of 330K)
2. Plate resistors for ECC81 is 33K ( instead of 47K) /
cathode resistor is 2K2 (instead of 33K??- this 33K MUST BE WRONG!)
3. + B resistor ( between the two 33K for ECC81) is 6K8(instead of 12K)
4. The negative bias resistors is 200K ( instead of 330K)
5. Cathode resistor for KT88 may have the value of 33R (instead of 47R)
6. Feedback resistor is 3K3 parallel with 330P
7. The negative bias resistor for ECC83 cathode has been changed to a single 33K ( instead of 47K parallel with 100K) - Not so important.
8. Please check whether M&A really had a 10K in series with 2K2 to the signal screen on KT88.
When my tubepreamp is ready , the TVA-1 project will start. If you can help me on this one, I shall return to you with all possible information according to voltage, messurement and linearity to the Michaelson and Austin circuit. I have already a pair of OP's , but I have been thinking of a pair of Hashimoto outputtransformers. ( may take some time but you will get the info)
You can find the former Sansui supplier "Hashimoto" KT88 OP's at :
leakstereo20
- on this page find the direct link to Hashimoto and Tango as well.
- Or buy from the Netherlands:
Transformers Tango Hashimoto Tamura Partridge main page
I think the quality of the TVA-1 OP's can be reached with a pair from "Hashimoto".
Best regards
Kim
Attachments
Many years ago, I went to listen to a Decca cartridge and insisted on a valve amplifier. Sadly, the LP only got part-way through one side before there was a nasty crackling sound, one channel went dead, and an output valve glowed red. Yes, it was a TVA-1. I would guess the reason was that the TVA-1 was designed and tested with real GEC KT88, but production versions received dubious "equivalents". I'd be very careful about output valve choice today...
Hi EC8010,
Yes - this issue about glowing output valves may be connected to the two 330K negative bias resistors. On the japanese pictures the 330K resistors was changed to 200K in the TVA-1 ! - this is important because old KT88's changes resistanse as they gets older, and "runs" with the bias. The old GEC KT88 was probably better made/produced than the newer reissues of the same type. I think that the old "real" KT88/6550A could last longer - with high bias - but we can't get them any more.
The TVA-1 sounds really great - and it is possible to make the TVA-1 work better and with stability by adding a few changes to the circuit - even with the reissue KT88 output valves.
The TVA-1 OP's is the key to the great sound. We need the info from SP.
Regards
Kim
Yes - this issue about glowing output valves may be connected to the two 330K negative bias resistors. On the japanese pictures the 330K resistors was changed to 200K in the TVA-1 ! - this is important because old KT88's changes resistanse as they gets older, and "runs" with the bias. The old GEC KT88 was probably better made/produced than the newer reissues of the same type. I think that the old "real" KT88/6550A could last longer - with high bias - but we can't get them any more.
The TVA-1 sounds really great - and it is possible to make the TVA-1 work better and with stability by adding a few changes to the circuit - even with the reissue KT88 output valves.
The TVA-1 OP's is the key to the great sound. We need the info from SP.
Regards
Kim
Can anyone give me 100 NOS GEC KT88 to test? Oh, and 100 modern production as well.
Your suggestion that reducing the grid-leak resistor fixed the problem because non-GEC KT88 pass more grid current (causing runaway) sounds highly likely. It would be nice to get some measurements on a representative sample to prove it one way or the other...
Your suggestion that reducing the grid-leak resistor fixed the problem because non-GEC KT88 pass more grid current (causing runaway) sounds highly likely. It would be nice to get some measurements on a representative sample to prove it one way or the other...
In order to make some test and messurement of the "Clone" TVA-1 , two 6550 quad's has been bought. From Tube Amp Doctor a 6550C-SVT , Russian quad and another Russian reissue Tungsol 6550A quad. The TVA-1 project is a clone because of the OP's as they are not the original types from M&A. The third test quad is KT88 , Gold Lion reissue.
The idea of the test involves two pair of OP's . One pair wounded by VRT transformer in DK with Raa approx. 5K6 and 5K - 40% tap UL - 15Hz = 56kHz. +- 1 dB . Second pair may have to be the Hashimoto Raa 5K OP's as mentioned erlier. All the values and test result comes later - much later.
- Have never seen any documentation related to the well known "original" TVA-1 circuit - just heard the TVA-1 play like a dream over AR3a. ( a thunder bottom!)
Regards
The idea of the test involves two pair of OP's . One pair wounded by VRT transformer in DK with Raa approx. 5K6 and 5K - 40% tap UL - 15Hz = 56kHz. +- 1 dB . Second pair may have to be the Hashimoto Raa 5K OP's as mentioned erlier. All the values and test result comes later - much later.
- Have never seen any documentation related to the well known "original" TVA-1 circuit - just heard the TVA-1 play like a dream over AR3a. ( a thunder bottom!)
Regards
My TVA1 sort of
I have been following this thread with interest as I have a TVA1 myself. Actually, along with my partner at the time, we were the original US importers of this amp. Some 25 years ago my amp was extensively modified by Mike Moffat of Theta renown. At the time, he nicknamed the amp Chernobyl apparently with good reason. It has in fact lunched a few tubes. I did note that the cathode resistor is in 33 ohms and apparently Mike changed the negative bias resistor to 220K. It still eats tubes. Oh, if you are wondering, yes the modifications greatly improved the amp. The input circuitry was extensively modified. No more 12AX7's or 12AT7's. Now just a single 12BZ7 for each channel. Power is down a bit but the improvement in sound was well worth it.
Paul
I have been following this thread with interest as I have a TVA1 myself. Actually, along with my partner at the time, we were the original US importers of this amp. Some 25 years ago my amp was extensively modified by Mike Moffat of Theta renown. At the time, he nicknamed the amp Chernobyl apparently with good reason. It has in fact lunched a few tubes. I did note that the cathode resistor is in 33 ohms and apparently Mike changed the negative bias resistor to 220K. It still eats tubes. Oh, if you are wondering, yes the modifications greatly improved the amp. The input circuitry was extensively modified. No more 12AX7's or 12AT7's. Now just a single 12BZ7 for each channel. Power is down a bit but the improvement in sound was well worth it.
Paul
Hi,
Sorry did not notice your reply untill now.
We have been wondering why the TVA-1 circuit "eats" up the op-tubes, if one changes the bias circuit and takes care of the current from the KT88's. The circuit seems to be straight foreward.
My engineer says that one explanation could be the oversized outputtransformers combined with the phase out of control. A simple lead-lack on the inputtube would turn the phase enough to avoid oscillation.
I don't know the 12BZ7 tube , but would like to see the circuit if possible. Later on I will try to return with details from the "clone" TVA-1 as well as some messurements from the STA100, which uses quite different drivertubes - but interesting circuit.
Regards
Sorry did not notice your reply untill now.
We have been wondering why the TVA-1 circuit "eats" up the op-tubes, if one changes the bias circuit and takes care of the current from the KT88's. The circuit seems to be straight foreward.
My engineer says that one explanation could be the oversized outputtransformers combined with the phase out of control. A simple lead-lack on the inputtube would turn the phase enough to avoid oscillation.
I don't know the 12BZ7 tube , but would like to see the circuit if possible. Later on I will try to return with details from the "clone" TVA-1 as well as some messurements from the STA100, which uses quite different drivertubes - but interesting circuit.
Regards
Hi
My brother bought a second hand TVA-1 some 25 years ago. It was an early unit, serial number 17, dated 1979. The first couple of years, it caused him a lot of trouble. Several output valves were destroyed. Sending the unit to service a couple of times did not solve the problem.
I was getting interested in valve equipment at the time and I had learnt a bit from reading a few chapters from a couple of textbooks. I offered to have a look at the amplifier. I had no schematic at the time so I started to draw one from scratch. Nothing seemed really wrong. I decided to replace all resistors in the bias circuit, including the bias pots. I did not change the values. Furthermore I decided to lower the bias current. It was supposed to be 60 mA. The B+ was 570 V so each output valve dissipated well above 30 W. I set the current at 50 mA. That was all. And the amp has not failed a single time for more than 20 years now.
The schematic I drew differs from the one posted above. I will see if I can find it and post it. A few years later I got a schematic from what I believe to be an original service manual. I will post that as well, IF I can find it. It may take a couple of days. The schematic posted above is identical to a schematic of the TVA-1 shown in a book written by Jean Hiraga.
One last thing: If the resistance between the grid and cathode is too high the output valve will be prone to bias drift. According to the data sheet of the KT88 this resistance should be no more than 220 kOhms. At this point the TVA-1 seems not to be designed properly.
By the way, I think the TVA-1 is a wonderful amplifier.
Regards, Torben
My brother bought a second hand TVA-1 some 25 years ago. It was an early unit, serial number 17, dated 1979. The first couple of years, it caused him a lot of trouble. Several output valves were destroyed. Sending the unit to service a couple of times did not solve the problem.
I was getting interested in valve equipment at the time and I had learnt a bit from reading a few chapters from a couple of textbooks. I offered to have a look at the amplifier. I had no schematic at the time so I started to draw one from scratch. Nothing seemed really wrong. I decided to replace all resistors in the bias circuit, including the bias pots. I did not change the values. Furthermore I decided to lower the bias current. It was supposed to be 60 mA. The B+ was 570 V so each output valve dissipated well above 30 W. I set the current at 50 mA. That was all. And the amp has not failed a single time for more than 20 years now.
The schematic I drew differs from the one posted above. I will see if I can find it and post it. A few years later I got a schematic from what I believe to be an original service manual. I will post that as well, IF I can find it. It may take a couple of days. The schematic posted above is identical to a schematic of the TVA-1 shown in a book written by Jean Hiraga.
One last thing: If the resistance between the grid and cathode is too high the output valve will be prone to bias drift. According to the data sheet of the KT88 this resistance should be no more than 220 kOhms. At this point the TVA-1 seems not to be designed properly.
By the way, I think the TVA-1 is a wonderful amplifier.
Regards, Torben