Hello all
I have a question. Does anyone know what maximum idle current would be for Sansui 1000a opt? I have a pair and would like to know what output tubes could be considered as options.
Originally, the tubes would be biased around 30-33 mA, idle. Iirc, this is heavily into class ab1, could be ab2. Op conditions for the pair were on the order of: 470volts(anode), 30-33mA(idle), bias( varies from -19V to -26V[from threads I have read]). Also, I have seen specs for current peaks noted as 190mA, when operating as above.
I am ignorant regarding the rules of repurposing OPTs, and hence my query. I don't want to ruin some Fine hashimoto iron!!
I am considering an iteration of the Powers 6b4g amp but would like to know what other valves I could use with these OPTs.
Thanks for any facts or referrals to appropriate texts!
I have a question. Does anyone know what maximum idle current would be for Sansui 1000a opt? I have a pair and would like to know what output tubes could be considered as options.
Originally, the tubes would be biased around 30-33 mA, idle. Iirc, this is heavily into class ab1, could be ab2. Op conditions for the pair were on the order of: 470volts(anode), 30-33mA(idle), bias( varies from -19V to -26V[from threads I have read]). Also, I have seen specs for current peaks noted as 190mA, when operating as above.
I am ignorant regarding the rules of repurposing OPTs, and hence my query. I don't want to ruin some Fine hashimoto iron!!
I am considering an iteration of the Powers 6b4g amp but would like to know what other valves I could use with these OPTs.
Thanks for any facts or referrals to appropriate texts!
Let's start with the 1000A schematic. The "finals" are full pentode mode 7591s. 30+ WPC is expected from that PP pair.
Of course, you could use 7591s. In which case, this thread is (IMO) worth your time. While the focus is on UL mode, there is nothing to stop you from adding regulated g2 B+ and going with full pentode mode "finals".
6L6s work with the same O/P "iron" as 7591s. Therefore, consider triode wired 6L6GC "finals" and Class "AB2" operating conditions. Tubelab's PowerDrive neatly takes care of dragging the 6L6 control grids into a positive grid current regime.
Sovtek 6B4Gs are tougher than NOS. That toughness would allow for the "taller" B+ needed to compensate for the Hashimoto trafos' end to end impedance, which is "taller" than that usually associated with PP 6B4Gs. More voltage swing on the primary is needed to deal with the greater step down ratio. The fact that "Uncle" Ned Carlson has a way to set a Dyna ST-70 up so that (alternately) both the EL34/6CA7/KT77 group and Sovtek 6B4s can be used in the amp illustrates the toughness of the Russian variant.
Of course, you could use 7591s. In which case, this thread is (IMO) worth your time. While the focus is on UL mode, there is nothing to stop you from adding regulated g2 B+ and going with full pentode mode "finals".
6L6s work with the same O/P "iron" as 7591s. Therefore, consider triode wired 6L6GC "finals" and Class "AB2" operating conditions. Tubelab's PowerDrive neatly takes care of dragging the 6L6 control grids into a positive grid current regime.
Sovtek 6B4Gs are tougher than NOS. That toughness would allow for the "taller" B+ needed to compensate for the Hashimoto trafos' end to end impedance, which is "taller" than that usually associated with PP 6B4Gs. More voltage swing on the primary is needed to deal with the greater step down ratio. The fact that "Uncle" Ned Carlson has a way to set a Dyna ST-70 up so that (alternately) both the EL34/6CA7/KT77 group and Sovtek 6B4s can be used in the amp illustrates the toughness of the Russian variant.
So this is a scratch build with the Sansui iron? As you know, it was rated for 40WRMS output, but the idle current in the push-pull cancels, so it is the peak current that you should be worry about. IMO it should be a good mate with the 6B4G, and close to the current HW-40-5 model from Hashimoto.
Thank you all for your replies!
I had wondered about the ab2 option, Eli, and had tube labs power drive in mind too!! The powerDrive is an awesome tool. I'm sure George has it in fine, reliable form these days too.
I don't need a whole bunch of power as I'll be driving Altec 605b. I want 16Watts, max music with 6db headroom for peaks. This runs the 605b at half it's power rating and would still be plenty loud (around 110db!).
I have a question now, the crux of my perplexity. How are opt power ratings derived? These are rated 40watts. Is this just voltage times current? 40watts, divided by current swing above idle ( not cancelled) would be, in slightly rounded numbers, 145mA(max sig.)-80mA(idle)=65mA? If so , 40W/0.065=615Volts and...they are conservatively rated or,..I'm Wrong!
Any help or reference to texts will be much appreciated.
Once again, thanks to the three of you who responded above. Have a happy day, All. -Aubrey
I had wondered about the ab2 option, Eli, and had tube labs power drive in mind too!! The powerDrive is an awesome tool. I'm sure George has it in fine, reliable form these days too.
I don't need a whole bunch of power as I'll be driving Altec 605b. I want 16Watts, max music with 6db headroom for peaks. This runs the 605b at half it's power rating and would still be plenty loud (around 110db!).
I have a question now, the crux of my perplexity. How are opt power ratings derived? These are rated 40watts. Is this just voltage times current? 40watts, divided by current swing above idle ( not cancelled) would be, in slightly rounded numbers, 145mA(max sig.)-80mA(idle)=65mA? If so , 40W/0.065=615Volts and...they are conservatively rated or,..I'm Wrong!
Any help or reference to texts will be much appreciated.
Once again, thanks to the three of you who responded above. Have a happy day, All. -Aubrey
Hi,
The Sansui 1000A output transformers are great iron. They are heavily interleaved; much more so than the Dynaco ST70 iron. In fact, the Dynaco ST70 outputs are third rate at best compared to the Sansui iron you have.
The primary Plate to plate impedance of the Sansui iron is 6600 ohms. Secondary impedances are 8 & 16 ohms.
These will work great as is with 7591 or 6L6 type tubes. They are also good for about 40-45 watts of output power.
These will also work with 6B4G tubes if you half the impedances: IE. the 8 ohm tap becomes a 4 ohm tap and the 16 ohm secondary becomes an 8 ohm tap. This will cause the reflected primary impedance to be 3300 ohms plate to plate, which is exactly what a pair of 6B4G tubes in push pull want to see.
A pair of push pull 6B4G tubes will only give you around 8 watts if driven by a conventional RC coupled driver stage. In order to get 14-18 watts out of a pair, you will need to drive the output tubes with either a direct coupled cathode follower (6SN7) or MOSFet driver like Tubelab's "Powerdrive".
Hope this helps... Daniel
The Sansui 1000A output transformers are great iron. They are heavily interleaved; much more so than the Dynaco ST70 iron. In fact, the Dynaco ST70 outputs are third rate at best compared to the Sansui iron you have.
The primary Plate to plate impedance of the Sansui iron is 6600 ohms. Secondary impedances are 8 & 16 ohms.
These will work great as is with 7591 or 6L6 type tubes. They are also good for about 40-45 watts of output power.
These will also work with 6B4G tubes if you half the impedances: IE. the 8 ohm tap becomes a 4 ohm tap and the 16 ohm secondary becomes an 8 ohm tap. This will cause the reflected primary impedance to be 3300 ohms plate to plate, which is exactly what a pair of 6B4G tubes in push pull want to see.
A pair of push pull 6B4G tubes will only give you around 8 watts if driven by a conventional RC coupled driver stage. In order to get 14-18 watts out of a pair, you will need to drive the output tubes with either a direct coupled cathode follower (6SN7) or MOSFet driver like Tubelab's "Powerdrive".
Hope this helps... Daniel
They are conservatively rated if you only plan to use 16 Watts with 6dB headroom. You do not deduct the idle current from the calculation, in push-pull output stage, the output current swings +-145mA, that is 290mA peak-to-peak, or Io = 102.55mA rms. Then, Vo = 40 / 102.55 = 390V rms = 552V peak = 1103V peak-to-peak. The above calculation does not include the winding loss, so the actual voltage swing is likely higher, we also do not know your actual output stage design, so the calculation is just hypothetical...I have a question now, the crux of my perplexity. How are opt power ratings derived? These are rated 40watts. Is this just voltage times current? 40watts, divided by current swing above idle ( not cancelled) would be, in slightly rounded numbers, 145mA(max sig.)-80mA(idle)=65mA? If so , 40W/0.065=615Volts and...they are conservatively rated or,..I'm Wrong!
Hello again!
As basic as it is to many here, the way transformer power ratings are derived is what had me stuck. I'm still not authoritatively clear on how those ratings are derived. I have plenty of time to plan/design my system before building would begin and that's a good thing. I'm very confident that it is a fairly simple matter and will be glad to have clarity regarding this issue.
Thank you all for your responses. I look forward to much more such fun along the way.
Happiness to all - Aubrey
As basic as it is to many here, the way transformer power ratings are derived is what had me stuck. I'm still not authoritatively clear on how those ratings are derived. I have plenty of time to plan/design my system before building would begin and that's a good thing. I'm very confident that it is a fairly simple matter and will be glad to have clarity regarding this issue.
Thank you all for your responses. I look forward to much more such fun along the way.
Happiness to all - Aubrey
I'm a little late to the discussion; I use these transformers in 6B4G amps. Fixed bias, choke input supply, 5842/417A driver with autoformer splitter (similar to the MQ Seth).
They have been in my system nearly 15 years, nothing has managed to kick them out.
I have tried different output iron, but the Sansui/Hashimoto is killer good.
They have been in my system nearly 15 years, nothing has managed to kick them out.
I have tried different output iron, but the Sansui/Hashimoto is killer good.
I just re-read my early response to you, and it did not seem to address your question - in fact, I gave you the voltage swing while you were asking about the current it can handle.
Since you are designing the amp from scratch, you have a lot more flexibilty, perhaps you can post a preliminary schematic to kick off the discussion.AFAIK, the OPT's power rating is based on the primary winding characteritic, so either V2/R or I2R could be used to calculate it. The shortcut is just to go with an output stage that has proven to work, such as those suggested before.
Hello,
I have Sansui AU70 Tube amplifier, one of the channel output transformer gone bad. When I gave it for rewinding the technician made mistake with count and now the re-winded transformer doesn't sound good (very low on volume).
I need help of transformer winding data of output Transformer if any one has and don't want to risk on 2nd channel working transformer opening.
Please help me restore this old Sansui beauty.
Thanks,
Sach
I have Sansui AU70 Tube amplifier, one of the channel output transformer gone bad. When I gave it for rewinding the technician made mistake with count and now the re-winded transformer doesn't sound good (very low on volume).
I need help of transformer winding data of output Transformer if any one has and don't want to risk on 2nd channel working transformer opening.
Please help me restore this old Sansui beauty.
Thanks,
Sach
danFrank,
What ever the transformer insertion loss is: With 8 Ohm load on the 8 Ohm tap or 16 Ohm load on the 16 Ohm tap; you would get about 2X that insertion loss with 4 Ohm load on the 8 Ohm tap, and 8 Ohms load on the 16 Ohm tap.
Most of that insertion loss is from the primary DCR and the secondary DCR. This is a push pull transformer, so the ratio of primary DCR versus primary impedance is typically better than the DCR to primary impedance ratio for a single ended transformer. That is because push pull transformers do not need an air gap, so less turns is required to get enough inductance (and less turns can mean lower DCR). That means trying to use the Sansui OPT for 6B4G push pull application is quite valid.
Single ended transformers with typically 0.5 to 1 dB insertion loss, gives 1 to 2 dB insertion loss when loaded with 1/2 rated impedance.
Keep in mind that many loudspeakers have minimum impedances of 1/2 to 2/3 of their rated impedances, with some loudspeakers minimum impedance even lower than that.
What ever the transformer insertion loss is: With 8 Ohm load on the 8 Ohm tap or 16 Ohm load on the 16 Ohm tap; you would get about 2X that insertion loss with 4 Ohm load on the 8 Ohm tap, and 8 Ohms load on the 16 Ohm tap.
Most of that insertion loss is from the primary DCR and the secondary DCR. This is a push pull transformer, so the ratio of primary DCR versus primary impedance is typically better than the DCR to primary impedance ratio for a single ended transformer. That is because push pull transformers do not need an air gap, so less turns is required to get enough inductance (and less turns can mean lower DCR). That means trying to use the Sansui OPT for 6B4G push pull application is quite valid.
Single ended transformers with typically 0.5 to 1 dB insertion loss, gives 1 to 2 dB insertion loss when loaded with 1/2 rated impedance.
Keep in mind that many loudspeakers have minimum impedances of 1/2 to 2/3 of their rated impedances, with some loudspeakers minimum impedance even lower than that.
Last edited:
In my journey to find as many tube output transformer makers, I ran across Transcendar Transformers. They actually make Sansui AU70 and 1000A transformers.
Transcendar Transformers - Sansui
Transcendar Transformers - Sansui
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.