SIC Diodes.
I am using 10 Diodes with my 2P29L project, loaded with Ale's gyrator, I found that using just 6 meant that I had to run at 22mA to get 150 Volt on the anode, which didn't sound that good, I might increase this to even more, (ran out of diodes), just to decrease the current that I'm running at, however the sound does seem very integrated with better Timbre. Now You have brought up another Valve to play with, You've yet again got me champing at the bit, I take it that there is no need for a source follower with the 26 as opposed to the 01a?
Yes it’s fixed, but it does appear to be better audibly as with a resistor, there is also less heat & theoretically should not drift as much depending on the amount of diodes & type used, listening tests proved very promising on this, also thershould be less feedback, I don’t profess to know why it works, but it does appear to. I just had to try it! It,s not the first time I’ve used this method, although the last time was an IDHT (2C22).which was successful
Found this on the web:
"In general we would try to minimise the ground impedance, but there is a useful exception to this rule. In stand-alone preamps and low power (usually single ended) amps there may be one or more additional stages of smoothing after the reservoir capacitor, before supplying the audio circuit. In such cases it is beneficial to split the usual dropping resistance into two parts (usually but not necessarily equal) and so deliberately create a real balanced filter, as illustrated in fig. 15.7. The added resistance in the negative side of the circuit helps isolate the noisy rectifier/reservoir circuit from the amplifier proper, and will keep ripple current out of the audio ground. One or both of the dropping resistors could be replaced by a smoothing choke...."
The Valve Wizard
Maybe the benefits are isolation of noisy currents in the ground wiring. I'm on thin ice here, but does this make sense?
Diode Bias
Frank, I have done more tests with the diode bias on both 2P29L & 01a, while the verdict is out on the 01a. I wouldn’t both with the 2P29L, I used a 12W 100R Mills (might change this to 110R to increase neg bias)instead, it’s night & Day better, you need too many diodes & it just masks the sound & makes vocals sound very sibilant & congested, so with that Amp it’s filament bias for me! Andy mentioned using a 120R resistor for His 26 project to give some feedback, I haven’t tried this, but will on the 01a when I get round to it. I must say my 29L sounds amazing with Ale’s Gyrator, I run mine at 14mA & 187V.
Try the 26 with 10 diodes and a 120R resistor. I don't find it masks the sound - on the contrary, it's super detailed. You can decrease the number of diodes as shown. This is normal bias - not filament bias - and I'm sure that also comes into it. The resistors have tiny current through them, so you can use any kind of boutique ones you fancy. I've only used 120R so far, but intend to try different combinations of resistor/diode. This is now my daily preamp.
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Thanks for that Andy, I will play around with it a little, I've tried everything with the 2P29L, 6 diodes, 8 diodes, 8 & so on up to 12, it wasn't as good, but a combination of resistor/diode could be the way to go, I tried also Russian Resistors & others, but Mills was better. I have quite a few 26's to play with too!
All other things being equal, I like the thoriated 01A and 10Y the best. But since I just have a 2 stage amp, things are not equal since I want some current through the first stage. 3mA is too little, but 7mA with a 26 starts to come into range. For me it just seems to shine with these diodes in a way it didn't do in filament bias - I was quite surprised at the improvement. It brings the 26 back into my top tier. I haven't tried 10Y yet, but since my system is on 24/7 I don't want to wear out my limited stock. As to the 4P1L I haven't tried that with diodes, but I'm not so keen on 4P1L into 4P1L. There's something in the high treble of the 2P29L that doesn't quite convince me, otherwise it's good, handles 15mA, and filament bias suits it. So for now it's back to where I started in 2009 - the 26.
Thanks a lot dor the feedback...I know the Mills quiet well...if you like them, try
ER58100RJT TE Connectivity / CGS | Mouser Deutschland
...the ER series...and tell us what you think...
Hello Bjarne. You are referring to my preamps using two 126C in series. While this is a very good sound and I recommend it, it's huge and there are alternatives. Ale's gyrator is fine, and both cheaper and more compact. My own preamp uses NP Acoustics plate chokes from Vietnam. These are amorphous core and very good value - I love the sound. PM me if you are interested and I'll talk to Phương Nguyễn who made them for me. He's also on npacoustic@gmail.com though mostly he uses Facebook and Messenger.
Hi Bjarne - No, use the 126C, much better because more inductance. You just use the primary, and it's a much better sound with 2 in series. Maximum current is 15mA. I use it with a 26 at 7mA. But the NP acoustics amorphous chokes should not be expensive. I will talk to Phuong and ask him for a price.