The solid state diodes have a much lower on resistance, and a much lower voltage drop than a vacuum tube rectifier.
There would be a much larger transient charging current to a cap input filter, and it would also have a much faster rise time (lots of harmonics).
That could create nasty ground loops that were not heard before.
Even with a choke input filter, it could create problems too.
The higher transient current, and higher harmonic transients could also be impressed on other secondaries, such as the filament windings.
The B+ voltage would be increased by the low voltage drops of the solid state diodes, perhaps the electrolytic maximum voltage ratings might be reached or exceeded, increasing the leakage currents of the electrolytic and reducing its lifetime.
Without the complete schematic of the before and after, the observation of the increased hum is merely anecdotal, the true cause of more hum can not be known for sure.
There would be a much larger transient charging current to a cap input filter, and it would also have a much faster rise time (lots of harmonics).
That could create nasty ground loops that were not heard before.
Even with a choke input filter, it could create problems too.
The higher transient current, and higher harmonic transients could also be impressed on other secondaries, such as the filament windings.
The B+ voltage would be increased by the low voltage drops of the solid state diodes, perhaps the electrolytic maximum voltage ratings might be reached or exceeded, increasing the leakage currents of the electrolytic and reducing its lifetime.
Without the complete schematic of the before and after, the observation of the increased hum is merely anecdotal, the true cause of more hum can not be known for sure.
I used FR207 diodes in an octal plug with 100 Ohm 2W resistors to help with conduction angle.
With the 5U4 the B+ after the choke was 310V.
With the diodes, the voltage is 349V.
The topology is 5U4, 47uF cap, 5H choke, 220uF cap. This feeds the 300Bs through the output transformers.
I have a slight hum from a ground loop issue when sourced through my three way source selector (Sirius XM from a cell phone, Teak PD301 CD/Radio, Phono).
If I unplug the inputs, there is a barely perceptible hum when I put my ear up to the speaker with the SS diodes or with the 5U4. I will have to measure the hum voltage to be able to say if there is a difference.
There is no risk of exceeding the electrolytic ratings as my transformer does not put out enough voltage, hence the test with SS diodes.
The transformer input to the board is 278 - 0 - 278. Peak voltage should be 393, well under the cap 450V rating.
I am running a variac to supply power to the amp because with full line voltage the filament/heater voltages are way to high > 10% high.
Even at full line voltage the B+ with SS diodes will still be within the rating of the caps, but as you say would be stressing them as it would be close to rating.
With the 5U4 the B+ after the choke was 310V.
With the diodes, the voltage is 349V.
The topology is 5U4, 47uF cap, 5H choke, 220uF cap. This feeds the 300Bs through the output transformers.
I have a slight hum from a ground loop issue when sourced through my three way source selector (Sirius XM from a cell phone, Teak PD301 CD/Radio, Phono).
If I unplug the inputs, there is a barely perceptible hum when I put my ear up to the speaker with the SS diodes or with the 5U4. I will have to measure the hum voltage to be able to say if there is a difference.
There is no risk of exceeding the electrolytic ratings as my transformer does not put out enough voltage, hence the test with SS diodes.
The transformer input to the board is 278 - 0 - 278. Peak voltage should be 393, well under the cap 450V rating.
I am running a variac to supply power to the amp because with full line voltage the filament/heater voltages are way to high > 10% high.
Even at full line voltage the B+ with SS diodes will still be within the rating of the caps, but as you say would be stressing them as it would be close to rating.
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The tradeoff of raising B+ is liable to cause more hum.
You have to take into account all that you change to raise B+.
Then, you may have to change more than just the rectifier from tube to solid state.
As nickytheshaft said, his neighbor changed from a tube rectifier to solid state diodes gave him more hum.
Details that are forgotten may cause new problems (as apparently they did).
You have to take into account all that you change to raise B+.
Then, you may have to change more than just the rectifier from tube to solid state.
As nickytheshaft said, his neighbor changed from a tube rectifier to solid state diodes gave him more hum.
Details that are forgotten may cause new problems (as apparently they did).
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The 10H choke would be fine, the only issue would be it's resistance. If higher than the proposed choke, it would result in more voltage drop. that just requires the proper power transformer. Measure your dc resistance and do a voltage drop analysis.
I measured the rms noise on the 16 ohm taps of the transformers. My speakers are on the 8 ohm taps, but iI reasoned the 16 ohm taps would give larger values and make readings more accurate for comparison.
L R
5u4 3.1mV 2.6mV
SS 3.4mV 2.8mV
I consider the difference measurable, but insignificant.
I found another transformer on the shelf I can try, Edcor XPWR002 360-0-360. But I will have to switch all the caps to 500V rated capacitors to try it.
With B+ of 310V I have about 258Va-k, so according to WE I can get 4W per channel. With SS rectification I can get about 6.1W.
I actually can't hear a difference at the level I play the stereo, so I may just stick with the 5U4.
I may buy a second board and build a 2A3 amp with it by changing the output cathode bias resistors to 750 ohm and using 2.5V transformers for the filament. I have 4800R OPts, and more power transformers. Actually the 270FX would be about ideal for the 2A3s.
All this will have to wait for a while as I need to get back to work on my house remodeling.
I measured the rms noise on the 16 ohm taps of the transformers. My speakers are on the 8 ohm taps, but iI reasoned the 16 ohm taps would give larger values and make readings more accurate for comparison.
L R
5u4 3.1mV 2.6mV
SS 3.4mV 2.8mV
I consider the difference measurable, but insignificant.
I found another transformer on the shelf I can try, Edcor XPWR002 360-0-360. But I will have to switch all the caps to 500V rated capacitors to try it.
With B+ of 310V I have about 258Va-k, so according to WE I can get 4W per channel. With SS rectification I can get about 6.1W.
I actually can't hear a difference at the level I play the stereo, so I may just stick with the 5U4.
I may buy a second board and build a 2A3 amp with it by changing the output cathode bias resistors to 750 ohm and using 2.5V transformers for the filament. I have 4800R OPts, and more power transformers. Actually the 270FX would be about ideal for the 2A3s.
All this will have to wait for a while as I need to get back to work on my house remodeling.
If it's build by that schematic, it's not going to have enough drive out of the input stage before it goes into clipping and you won't see even 3W of output. Plus, my experience with that design is it has no grunt on the low end and tends to sound shrill. A standard EL34 amp will outperform it. The Boyuurange A50 using a very similar topology as did my first 300B amp before I rewired it as a cascode, which resolved these issues.
Tuning and modifying a JC Morrison style 300B DIY tube amp. - YouTube
So far one person has listened to it and was impressed.
I will take measurements in a few days to confirm how it performs.
The real question is what speakers do you drive with it.
I have Klipsch Heresy speakers which do quite well with it.
I was surprised with how sensitive it was compared to my calculations. It fared much better than I expected.
One thing to take in to consideration is that my speakers were from 1977 and were the original design for vacuum tube amplifiers. Paul hadn't made any major changes to the design from what the engineers told me when I was at the factory in 1979. So, if you use other speakers, your mileage will vary. Don't dis the amp because of your speakers.
I get 85dB Fast, C weighted listening to Ride Captain Ride By BS&T without evidence of clipping.
Low end is determinant by your transformers.
Get better transformers.
Again, YMMV.
I will take measurements in a few days to confirm how it performs.
The real question is what speakers do you drive with it.
I have Klipsch Heresy speakers which do quite well with it.
I was surprised with how sensitive it was compared to my calculations. It fared much better than I expected.
One thing to take in to consideration is that my speakers were from 1977 and were the original design for vacuum tube amplifiers. Paul hadn't made any major changes to the design from what the engineers told me when I was at the factory in 1979. So, if you use other speakers, your mileage will vary. Don't dis the amp because of your speakers.
I get 85dB Fast, C weighted listening to Ride Captain Ride By BS&T without evidence of clipping.
Low end is determinant by your transformers.
Get better transformers.
Again, YMMV.
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That design does have high input sensitivity, with the right speakers and without hearing another to A-B, it will probably sound fine. Enjoy.
Interesting that just changing the front end to a cascode on mine resolved the issue with the bass sounding thin, no need to spend $ on replacement transformers. It really cleaning up the midrange as well. The quality of the low end is not just determined by the transformers. Like I said, without hearing a "fixed" one, it probably sounds fine to you.
Watch the video and do that same 'scope test. My money is you will see heavy clipping starting at 12-15V P-P output into an 8ohm load. A THD test will show distortion numbers rocket past 3% at anything over 3W. Here is how the Boyuurange A50 fared, that uses basically the same topography as your's and another very similar 300B amp I build tested, starting at 12:55.
Boyuurange A50 Tube Amp Full Test Reisong - YouTube
Or feel free to ignore what I learned, I really don't care
Well I just ordered one got it for 41 euros on Aliexpress.
I have a power transformer, a choke and 2 output transformers that I can use with it as well as a el34 amp I have in progress.
I will make an external power box as I did with my previous 300b project as well as an external OPT box.
I will link the 2 amps by XLR connectors to switch them.
The older 300b will wait for my knowledg to evolve.
got it for 41 euros on Aliexpress.I have a power transformer, a choke and 2 output transformers that I can use with it as well as a el34 amp I have in progress.
I will make an external power box as I did with my previous 300b project as well as an external OPT box.
I will link the 2 amps by XLR connectors to switch them.
The older 300b will wait for my knowledg to evolve.