I emailed the seller and requested an updated schematic which I advised I would post here.
The seller sent the schematic which is as you linked to. Unfortunately it lacks values. I have attached it.
After reviewing it I find it is going to be problematic as the SRPP with 6SN7 has insufficient gain, unless a preamp is used from a CD player, etc. It looks like it will require 5V input to fully drive the output. One possibility is to change to the 6SL7 instead of the 6SN7.
I really wish the layout had been for the two cascaded triode stages as they had sufficient gain and is more of a standard topology for a 300B amp.
Actually, the components and values shown on the PWB in the ebay posting match the schematic with three gain stages and include the 22pf cap to ground on the input stage, which is not in the SRPP design.
At this point, the seller has given information for two totally different designs and I don't know what I am getting.
At this point, the seller has given information for two totally different designs and I don't know what I am getting.
Most of these sellers have no idea about the parts they sell. He probably just googled 300b 6sn7 and sent the first hit. You only get good support when the seller is the designer.
Sometimes I worry about Miller Effect Capacitance, sometimes I do not worry.
For a 300B, it is in the region of 60pf or so, and depends on the in-circuit gain, not on the mu (u).
And then I remember my high frequency hearing is limited to about 14kHz.
Miller Effect Capacitance can cause early high frequency roll off, and the lower impedance can cause the driver to have additional driver 2nd harmonic distortion at high frequencies.
Oh . . . never mind, the 2nd harmonic of 14kHz is 28kHz.
Well, my tweeters do not work at 28kHz, and my ears sure do not work there either.
Problem solved!
Another way to say all of the above is that a 6SL7 SRPP probably will work just fine to drive a 300B.
Your Ear's Mileage May Vary.
Just my 'practical' opinion.
For a 300B, it is in the region of 60pf or so, and depends on the in-circuit gain, not on the mu (u).
And then I remember my high frequency hearing is limited to about 14kHz.
Miller Effect Capacitance can cause early high frequency roll off, and the lower impedance can cause the driver to have additional driver 2nd harmonic distortion at high frequencies.
Oh . . . never mind, the 2nd harmonic of 14kHz is 28kHz.
Well, my tweeters do not work at 28kHz, and my ears sure do not work there either.
Problem solved!
Another way to say all of the above is that a 6SL7 SRPP probably will work just fine to drive a 300B.
Your Ear's Mileage May Vary.
Just my 'practical' opinion.
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I got 15,593 Ohms for Zout of a 6SL7 SRPP with 1.2K cathode resistors.
That puts the roll-off due to Miller up in the 17KHz range.
My ears are worse than yours so not an issue.
Whatever comes in I will build as specified before I start tinkering with it.
That puts the roll-off due to Miller up in the 17KHz range.
My ears are worse than yours so not an issue.
Whatever comes in I will build as specified before I start tinkering with it.
There are a few PCBs for J.C. Morrison 300B but not sure why you pick this one but I think it would work as long as you have enough voltage as they mention. I thought I have seen some sellers listing the complete build for around $500
I chose this board because the schematic provided showed a traditional three stage all triode amplifier, which is what I wanted to work with.
I thought the cathode output impedance of an SRPP was close to 1/Gm of the top tube.
For a 6SL7, that would be more like 1/1600uMhos = 625 Ohms.
But I guess I never really understood SRPP stages.
Help me understand the derivation of the output impedance of an SRPP stage.
For a 6SL7, that would be more like 1/1600uMhos = 625 Ohms.
But I guess I never really understood SRPP stages.
Help me understand the derivation of the output impedance of an SRPP stage.
I think you can mod as traditional three stage but probably has to change all the parts and use jumpers 😀
I used the formula here:
Determining Zout for SRPP
Yes I could rework it, but it would be a real hack job.
I will build it as is, then tinker with it.
I was trying to avoid drilling a chassis and doing a P-P layout to be able to use my pair of Psvane 300Bs and the One Electron Transformers I got as a retirement gift from work.
Determining Zout for SRPP
Yes I could rework it, but it would be a real hack job.
I will build it as is, then tinker with it.
I was trying to avoid drilling a chassis and doing a P-P layout to be able to use my pair of Psvane 300Bs and the One Electron Transformers I got as a retirement gift from work.
I also put together this pcb and used it for about 12 months. I thought it sounded great. It was my first diy project I didn’t really have any other tube amps to compare it to except a quad I had heard in the early 80s that sounded pretty good too. I had a guitar tech look over it. I later modified it according to a Renaud design from diyaudioprojects and converted it to point to point. Happy with that now, listen to it every day. There is another guy here who built the same eBay pcb in 2018 a little before me. He decided to use 6sl7 driver tubes to get more gain and seemed to be happy.
Hi,
did you have any problems with hum?
I tried the DOUK AUDIO pcb Stereo 300B Vacuum Tube Power Amplifier DIY KIT HiFi Audio Amp PCB Board Module | eBay and it hums a lot so i was in fact thinking of picking this kit.
Thanks,
did you have any problems with hum?
I tried the DOUK AUDIO pcb Stereo 300B Vacuum Tube Power Amplifier DIY KIT HiFi Audio Amp PCB Board Module | eBay and it hums a lot so i was in fact thinking of picking this kit.
Thanks,
This board has hum pot, look well design/clone that similar to others that I have seen. 5U4G is driving 300B while 1N5408 is for 6SN7. Wonder if you use choke. You may need to check the voltage again. It's similar to J.C. Morrison 300B
Yes I use a 10H 250mah choke
I will check the hum pots then, for the moment they are set to half of the resistance of the pot as described in the assembly guide DOUK sent me.
On my version there was a fairly low level of hum audible close to the speaker but could have been improved using one of the hum control methods discussed in threads on this site. With the re-make, the circuit included 5v regulation which works fine. Another who used the pcb. Though I didn’t have the volume issues cited. Cheap 300B project