• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Universal tube preamp PCB, ECC99/6N6P/ECC88/ECC85/6922/6DJ8 etc. MU follower or SRPP

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#81
psmith001 said:
I did a version of this that I'm happy to share the KiCad project with you if it would be of any help to you. The PCB design is done, but I never had it made to test to ensure everything will work. I guess I was holding back to try and see if I could fit everything into the magical 100mm x 100mm. 🙂
Click to expand...

Sure, that wouldn't hurt. Currently I have the schematic drawn up, footprints assigned, I'm moving a bit slower than I had hoped but now I just need to lay it out. Hopefully today or tomorrow, then I can get a separate thread started so as to not hijack this one from Koifarm's great project.
 
#91
Vunce said:
Koifarm,
Your pcb design is sounding very good as my AD1862 dac output stage configured for SRPP with 6n6p tubes and a linear psu.
I had high hopes for the imported little SMPS but it didn’t work out. I was getting an audible low frequency warbly tone plus higher frequency noise heard from the tweeters. I swapped out the SMPS and replaced with a regulated linear HV/LV supply and voilà!! Dead silent background and sounds very good to my ears :spin:.
Thanks again Koifarm!
Click to expand...
Try ECC88 (6N23P, PCC88) instead of 6N6P.
6N6P is a good tube, but more for buffer or line stage , but for DAC, especially after the passive I/V stage, you need a finer tube with higher amplification.
With passive I/V, you should go with the smallest possible resistor, because increasing the value of that resistor increases distortions. You can install 100R trimmers and find the sweet spot and then replace them with resistors.
I think the AD1862 could work with the 50R as well.
 
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#96
Hi Gary,
Thanks for your reply.
No stock of Omron in Element 14 malaysia .

Please look at the datasheet for TE range.
Is the model RT424005 suitable alternative?

Otherwise, any serious problem if l bypass the relay?
Tube are not too expensive anyway
Regards

kp93300
 
#97
No it isn't, still wrong pin dimensions. You need a relay with pin out dimensions as shown in the original relay or in the ones linked by myself and Vunce.

The relay mutes the output for a time delay while the tubes warm up - tubes wont be damaged, more of a problem for the following power amp and speakers, or turn on the linestage first, wait 30 seconds or so and then turn on the power amp - reverse order when turning off the system.
 
#100
Vunce said:
I believe its very similar, if not the same, as the SMPS you were working with.
Click to expand...
IMG_20220820_115557_resized_20220820_115649305.jpg


Same board setup different parts.
 
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