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Valve amp modification/design on a budget. Advice requested... - Page 2

post #16 of 19

Do you have a schematic of the final design? I'm curious and interested. I'm currently rebuilding my MSSH to make the most out of what I've got and wondering how it'll compare to what you came up with.

 

Currently my HV+ is 170 V and I'm regulating it using a TL783. I'm curious how that'll work out...

 

Oh and I'm using 250 V caps on the HV+. I use 100 V caps as AC filtering caps on the LV+ (25 V), then 63 V caps after the reg. I like to go for double the voltage rating for safety, longevity and performance. A 63 V running at 59 V won't last very long. It also wont perform as well as a 100 V cap.

post #17 of 19
Thread Starter 
I'd certainly agree that the capacitor voltage rating is on the edge, but a good brand capacitor should be able to handle its rated voltage, however the caps don't get warm at all and are from good 105°C lines. All in all I'll probably change them and get some nice big snap-ins next time I order stuff. This current build was only a proof of concept that I'm fairly pleased with. Anyway here's the schematic for what I'm using now: https://www.dropbox.com/s/tiw5fknsitc52m2/12AU.JPG (dropbox link as the outdated version of firefox on the school computers won't let me upload photos to Head-Fi). Yeah, I know it's not exactly tidy with the coupling cap before the valve input but I'm really stuck with transformer issues, and can't find one that I can get a decent B+ from for under 30€, which is fairly irritating as I need about 10-15mA for this design (if any european has anything that they don't particularily want/need and don't mind selling, drop me a PM)... Maybe I'll have to try a 555 or MAX1777 based switcher... I'd still like to look at using a valve based output stage, but it does look a fairly costly endeavour to get something useful (other than possibly parafeed with mains transformers). I'm sure more improvements will be coming to this design, but I dont have the materials to do so at the moment as I've used almost everything up. (including my last 4 BC560s, so an order is definately forthcoming once I get into the summer holidays). Exam week starts in a week and a half, so even if I'm around I won't achieve a great deal on this project until after I've finished on the 21st. Thanks for your replies and good luck with your projects, Chris Edit: sorry about the spacing, this version of firefox doesn't seem to let me add empty lines to seperate into paragraphs...
Edited by Goobley - 6/4/13 at 7:45am
post #18 of 19
Quote:
Originally Posted by Goobley View Post

I'd certainly agree that the capacitor voltage rating is on the edge, but a good brand capacitor should be able to handle its rated voltage, however the caps don't get warm at all and are from good 105°C lines. All in all I'll probably change them and get some nice big snap-ins next time I order stuff. This current build was only a proof of concept that I'm fairly pleased with. 

Anyway here's the schematic for what I'm using now:


Yeah, I know it's not exactly tidy with the coupling cap before the valve input but I'm really stuck with transformer issues, and can't find one that I can get a decent B+ from for under 30€, which is fairly irritating as I need about 10-15mA for this design (if any european has anything that they don't particularily want/need and don't mind selling, drop me a PM)... Maybe I'll have to try a 555 or MAX1777 based switcher... I'd still like to look at using a valve based output stage, but it does look a fairly costly endeavour to get something useful (other than possibly parafeed with mains transformers). I'm sure more improvements will be coming to this design, but I dont have the materials to do so at the moment as I've used almost everything up. (including my last 4 BC560s, so an order is definately forthcoming once I get into the summer holidays).

Exam week starts in a week and a half, so even if I'm around I won't achieve a great deal on this project until after I've finished on the 21st. 


Thanks for your replies and good luck with your projects, 
Chris 

Edit: sorry about the spacing, this version of firefox doesn't seem to let me add empty lines to seperate into paragraphs...

 

I think I'm too tired right now. Is this a voltage doubler in the PSU? It's confusing since the caps aren't polarized in the schematic. If it works the way I think it works, then you'd get better performances without R11 and R12. These seems to lower the voltage before it even gets to the first AC filtering cap.

 

I built a voltage multiplier like the one in the SOHA II with a 30-0-30 transformer and got a regulated 170 V B+. With those 22 V transformers, you could build yourself a 130 V B+. Not sure about current, though.

 

You built a mirror like in the SOHA II, but not a CCS. That's interesting, as I am going for the opposite. I'm building a tail CCS like the SOHA's, but will use a single plate resistor and parallel the triodes instead of using the mirror. What was your rational for going with this setup?

post #19 of 19
Thread Starter 

It's a pair of half wave voltage doublers, one positive one negative. R11 and R12 are stop-gap measures that I put in place to make sure that the caps that I'm using that are too low voltage don't see more than their rating -yes I'll have to change them really, but I'm certainly now considering investing in another transformer and a 6080 and making a poor mans Crack.

 

I had forgotten until you reminded me that the SOHA II uses an active current mirror load, I had been browsing TubeCAD and decided that the Common Cathode amplifier was a nice front-end if I wanted to keep two complete dual triodes in use in my amp, because as has been noted in this thread, there's no real point in paralleling tubes to drive a high impedance load as you just get increased Miller Capacitance. On my first proof of concept however, I had just used a plate resistor (I have a trimpot on the cathode even though I only put a resistor in the schematic), but to get the I and V that I wanted I was oblidged to use a load that was far too low for an ECC82/12AU7, so I looked for another alternative and remebered how much mirrors like this increases that impedance (this must have remained in my subconscious from when I last looked at the SOHA design pages :D. After applying these changes the amp sounds much more full.

 

Personally I woudn't be inclined to use only a tail CCS and would instead look to what I see as one of the best CCSs in existence, the one that is used in the torpedo with an LED biased shunt on the cathode, I think that the PSRR that an anode CCS affords is really not something to be missed if you're going for a CCS... I'm currently trying to get a more tubey sound, which is why mine is biased with a resistor.

 

Cheers,

Chris

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