Sunil: I forgot to answer your question about best measurable indicator of tube life.
AFAIK, there isn't a better measurement than the power tube bias.
At very least. it will tell you how "hot" you're running the power tube, plus it will show whether there's any DRIFT (often UPWARDS) in the bias.
I had one EH 300B that wouldn't hold bias; I thought it was something I had done.
After trying everyhting I could think-of to stabilize it, I contacted the seller who admitted that some of the EH tubes are prone to drift, and he sent me a replacement...
AFAIK, there isn't a better measurement than the power tube bias.
At very least. it will tell you how "hot" you're running the power tube, plus it will show whether there's any DRIFT (often UPWARDS) in the bias.
I had one EH 300B that wouldn't hold bias; I thought it was something I had done.
After trying everyhting I could think-of to stabilize it, I contacted the seller who admitted that some of the EH tubes are prone to drift, and he sent me a replacement...
Thanks hareynolds. I had the same problem when the B+ was closer to 350v. It would keep moving about +/-5 ~ 70mA setting.
Tried a different secondary with 375v and both tubes are now ~ 66mA with ~ 400hrs.
Have to admit, I didn't have a power conditioner earlier and our mains voltage is notorious. I used to get spikes of 15v on the supposedly 230v line and have seen 247v often enough.
I put in a 3KV servo stabilizer and its been 230v +/- 2v since. That seemed to make a big difference in keeping things sane.
Tried a different secondary with 375v and both tubes are now ~ 66mA with ~ 400hrs.
Have to admit, I didn't have a power conditioner earlier and our mains voltage is notorious. I used to get spikes of 15v on the supposedly 230v line and have seen 247v often enough.
I put in a 3KV servo stabilizer and its been 230v +/- 2v since. That seemed to make a big difference in keeping things sane.
I am planning to make a MI200 clone with GM70s. I have the Output transformers and tubes. I will substitute powerdrive Mosfets for the 6BX7s and use a Hedge cascode circuit for input/predriver with further circuit bootstrapped 6AV5s and mosfet. There are a lot of changes to perform to the circuit resistor values and local feedback circuitry. Are there any experiences done or can I ask for advice?
I have a quick question. I am running a TSE2, 300b tubes, using a Hammond 373CZ power transformer. It is 650v CT @ 173mA, has a 3A rectifier and 5A driver tube winding.
I am running about 65mA on the 300b tubes, all holds perfectly stable.
Running at 72 degrees F room temp, the PT runs at about 60 degrees C (140 degrees F) and is quite warm to the touch. Other components stay only slightly warm, other than the expected power resistor and regulator heat. All parts are well ventilated, and the chassis temp is about 95 degrees F.
Am I OK within temp specs, or should I look to try a larger VA transformer to cool things down?
Matt
I am running about 65mA on the 300b tubes, all holds perfectly stable.
Running at 72 degrees F room temp, the PT runs at about 60 degrees C (140 degrees F) and is quite warm to the touch. Other components stay only slightly warm, other than the expected power resistor and regulator heat. All parts are well ventilated, and the chassis temp is about 95 degrees F.
Am I OK within temp specs, or should I look to try a larger VA transformer to cool things down?
Matt
My rule of thumb (literally) is that if you can hold your hand on the transformer for 10 seconds it's OK.
Hammonds are known to run hot, and they generally don't die from heat. There were two instances in the last couple of years where a Hammond developed an internal short, but both occurred in the first few months of operation or were there at manufacture and it took some time for the amp to fail. The 5 volt winding shorted to the 6.3 volt winding putting B+ on the heaters causing the bypass cap to blow.
I have an Allied 6K7VG (made by Hammond) in my SSE. I often ran that thing at 100 mA per output tube for about 230 mA total. It's specced for 150 mA. It got too hot to touch quickly, and started smelling funny after several hours of continuous operation. It has a 2004 date on it and it's still working fine.
Hammonds are known to run hot, and they generally don't die from heat. There were two instances in the last couple of years where a Hammond developed an internal short, but both occurred in the first few months of operation or were there at manufacture and it took some time for the amp to fail. The 5 volt winding shorted to the 6.3 volt winding putting B+ on the heaters causing the bypass cap to blow.
I have an Allied 6K7VG (made by Hammond) in my SSE. I often ran that thing at 100 mA per output tube for about 230 mA total. It's specced for 150 mA. It got too hot to touch quickly, and started smelling funny after several hours of continuous operation. It has a 2004 date on it and it's still working fine.
Fired up the TSE-II - 2A3 today. The tubes biased right up to 35ma with 323 B+. I had the 300b up till now and have a chassis to build.
Before the TSEs I completed an Aikido Octal (6SN7) which was also bare board. They are a fabulous combination.
The preamp is posted on another Aikido thread here. I don't want to post in both posts.
Need help with the 5842s, they are at 199 & 201v. Should that be reduced ? The B- is 165v.
Before the TSEs I completed an Aikido Octal (6SN7) which was also bare board. They are a fabulous combination.
The preamp is posted on another Aikido thread here. I don't want to post in both posts.
Need help with the 5842s, they are at 199 & 201v. Should that be reduced ? The B- is 165v.
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I've run the 2A3 for about 20hrs. The voltages are all stable. There's not much info on biasing the TSE-2A3. The rectifier and B+ are fixed, so should I raise the current. The 5842s are at 199 & 201v, thought I'd leave them as is for now.
B+ 323
B- 165
2A3 61v
2A3 35mA
Can somebody help ?
Hi,
did you check this page:
Setting the Bias | Tubelab
The anode voltage of the driver tubes should be set to ~ 175 V
did you check this page:
Setting the Bias | Tubelab
The anode voltage of the driver tubes should be set to ~ 175 V
The 5842 has a wide variety of characteristics. The parts listed on the BOM may not cover the spread of all tubes. If the adjustment pot is at one end and you still can't get do 175 volts, you could change the value of R10 and R21. I needed to go to 470 ohms for some tubes.
In reality there shouldn't be much difference between 175 and 185 volts, and some Raytheon tubes had lower distortion on 185 volts. Genuine WE 471A's tended to do best on 175 volts.
In reality there shouldn't be much difference between 175 and 185 volts, and some Raytheon tubes had lower distortion on 185 volts. Genuine WE 471A's tended to do best on 175 volts.
George, thanks for chiming in. There is some play left on both sets of trimmers. The B+ has dropped below 310 on a secondary of 300-0-300 which surprised me, thought I'd get ~ 320v.
Trying a different rectifier - 5U4GB (N.E.C). Had a Brimar GZ34 (current stock /model) earlier. They were bright Orange, the 'juiciest' glow among all the tubes
The N.E.Cs look ok.
One thing I have to say about the RCA 2A3s I'm using, they hold bias changes really well, real quick. A reaaally slow turning of the pots, alternating channels, works really well.
The EH300Bs were crappy in this area, would continue drifting.
Trying a different rectifier - 5U4GB (N.E.C). Had a Brimar GZ34 (current stock /model) earlier. They were bright Orange, the 'juiciest' glow among all the tubes
The N.E.Cs look ok. One thing I have to say about the RCA 2A3s I'm using, they hold bias changes really well, real quick. A reaaally slow turning of the pots, alternating channels, works really well.
The EH300Bs were crappy in this area, would continue drifting.
Just finished my TSE-II 300B. Sounds great! I did have to do a few simple things to manage heat from R36 and IC3. Moved R36 off-board to side of the chassis. I mounted C3 horizontal to give the IC3 heat sink some breathing room, and installed a small 12V fan inside the chassis. Chassis has a perforated bottom and top vents. Used a Landfall Systems 17x13 chassis. Edcor 5K:8 OPT and Hammond PT. B+ is 360, 5842s at 175V, 300Bs bias at 70ma. Everything is working great. If could offer any constructive criticism, it would be to widen the pcb slightly, giving a little more room between the IC3 / D1 heat sinks and the adjacent row of capacitors. Widening that side of the pcb would also give more breathing room to R36. Things get hot along that side - manageable, but hot. Anyway, I'm really enjoying it, and appreciate Georges smart design and his support on this forum. BTW, the SSE I built ten years is still running strong.
