Clementine options

sweet & juicy SE amp for 1626 Darlings and the 6L6 family

Clementine options

Postby Olof » Thu Nov 20, 2014 7:20 am

Hi everyone! I finally have both time and resources to do some diy with tubes :))
I still have a few questions after lurking this fantastic forum for a while:

Is it a good idea to put a switch for UL/triode mode? I’ve seen a few other designs using a toggle switch to go from screen grid to plate through either the 100Ohm resistor or the center tap of the output transformer. From what i can tell from Shannons ULtra notes on this it’s not a good idea but I can’t really see why not? Should a switch for negative feedback also be included in that case perhaps? I don’t want to choose between a regular or UL clementine if I can have both.

Is it a good idea to use a switch between either 1.5k or 1.8k for R16 and R17, to be able to use both high and low power dissipation tubes?

Is it clever to use the unused filament tap for indication LEDs? This will not reflect the actual power in the circuit but on the other hand I assume it is better that it doesn’t interfere with the signal path?

I guess there is no need for a standby switch, but the lack of one makes me a bit… uneasy. Would the tubes suffer from hot starting through letting the filaments heat up first?

I get the impression that these would be minor additions that would make the design much more flexible. But maybe I’m just complicating things and should stick to the original design? (???)

Any input on this would be greatly appreciated!
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Re: Clementine options

Postby Shannon Parks » Fri Nov 21, 2014 9:46 am

By all means, DIY some mods to your heart's content - it's a big part of the fun factor. I would advise staying away from a standby switch, though. Too easy to make some large inductive voltage spikes without careful design.

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Re: Clementine options

Postby EWBrown » Fri Nov 21, 2014 5:11 pm

If you install a UL/Triode switch, I would suggest placing it on the rear of the chassis, just to avoid unintentional "hot" switching, while the amp is running.
It is best, and safest, to power off the amp, let it discharge for at least a minute or two, then flip the UL/Triode switch, then power up the amp on afterwards.
This avoids putting high voltage switching transients on the OPTs, and the resulting loud "pops" into your speakers, which could damage the tweeters.
Plus, hot-switching could damage the power tubes.

/ed B
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Re: Clementine options

Postby Olof » Fri Nov 28, 2014 4:05 am

Thanks a lot for the input! Staying away from standby switch and putting control switches on the back.

Just ordered iron from edcor, i guess now it's time to play the waiting game and redraw the schematic a million times before ordering the rest (lol)

/Olof
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Re: Clementine options

Postby Olof » Sat Dec 13, 2014 10:20 am

So after lurking around a bit I can't seem to find that many designs using an actual pentode mode for single ended output. There seems to be some consensus that the sound is too bad, do you have any opinions on this?

My idea was to have a switch from triode to UL to pentode, see attached image. Can you see any reason not to, I mean, why not? If it sounds bad I guess I'll just never use it (lol)
Can I go with a 100Ohm 0.5W resistor for the pentode path also or should I size it up since the current in the tube will be higher?

Olof
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Re: Clementine options

Postby Shannon Parks » Sun Dec 14, 2014 8:05 am

Olof wrote:So after lurking around a bit I can't seem to find that many designs using an actual pentode mode for single ended output. There seems to be some consensus that the sound is too bad, do you have any opinions on this?

My idea was to have a switch from triode to UL to pentode, see attached image. Can you see any reason not to, I mean, why not? If it sounds bad I guess I'll just never use it (lol)
Can I go with a 100Ohm 0.5W resistor for the pentode path also or should I size it up since the current in the tube will be higher?

Olof


Pentodes aren't my bag, but I think you'll need a decoupling cap on the pentode switch, too.

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Re: Clementine options

Postby Olof » Wed Dec 17, 2014 8:10 am

I'm not surprised, It doesn't seem to be anyone really who promotes it for single ended use. But since I haven't experienced it myself I'm gonna keep an open mind.

It seems there are plenty of ways to do it, I figure I'll just use spare components not used for the proper configuration (triode and UL). A 1k resistor to B+ and a 120u cap to ground perhaps? I have a few old 6L6s to try it on from my trusty mesa guitar amp, should it end in fireworks...

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Re: Clementine options

Postby Shannon Parks » Wed Dec 17, 2014 3:01 pm

Olof wrote:I'm not surprised, It doesn't seem to be anyone really who promotes it for single ended use. But since I haven't experienced it myself I'm gonna keep an open mind.

It seems there are plenty of ways to do it, I figure I'll just use spare components not used for the proper configuration (triode and UL). A 1k resistor to B+ and a 120u cap to ground perhaps? I have a few old 6L6s to try it on from my trusty mesa guitar amp, should it end in fireworks...

Olof


Seems A-OK to me. The real key here is that the triode mode doesn't really need negative feedback - its output impedance will be low enough with decent damping in the 5 to 8 range (solid state guys will laugh at that). But the UL and pentode versions will need around 9dB of negative feedback to get the damping factor in that same range. So you might want a feedback switch, too.

Good luck, Olof!

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Re: Clementine options

Postby Olof » Thu Dec 18, 2014 3:57 am

Gotcha! A three way switch for the modes of operation, a two way switch for feedback on/off, a two way switch for high/low bias, a small army of LEDs in the front to indicate what's up and something solid to hide behind when I fire it up!

I should have all the parts by the end of January, hopefully there can be some pics shortly after that.

Shannon Parks wrote:Good luck, Olof!

You have no idea how comforting that is, thank you!

Olof
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Re: Clementine options

Postby Olof » Mon Mar 09, 2015 7:11 am

And here we are, almost 4 months after I placed the order, with an email confirming that the edcors won't show up. Getting refund for the iron but not the 80 bucks of shipping. Sigh.

Other people have mentioned Don Audio selling edcors, but they don't sell the the correct ones for the clementine. They do however sell the GXSE10-8-5K (to little power handling?) and the CXSE25-8-5K (overkill?), would these work?

For the power transformer the closest i can find is the XPWR173, would that work with a beefier choke or dropping resistor?

Any other suggestions for vendors that sell fitting transformers to europe (and actually deliver) is greatly appreciated!
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Re: Clementine options

Postby Shannon Parks » Wed Mar 18, 2015 1:01 pm

Sorry to hear about the lost shipping charges and no trannies, Olof! Meanwhile those outputs will work great. But the power transformer looks a little too stout. You'd have voltages over 500V at turn on. Maybe a 600VCT toroid is available?

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Re: Clementine options

Postby Ludwig » Wed Mar 18, 2015 1:45 pm

Hi Olof,

That's bad news and really not acceptable - a similar thing happened to me with even worse customer service!

Luckily I found these guys, who make a similar range of power and output transformers.

Try their range on ebay, but if you can't find what you need just email and they might be able to make what you are after.
http://stores.ebay.com/musicalpowersupplies/

From memory I think if you google Musical Power Supplies they also have an online store outside of fleabay.

Cheers,
Tom.
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Re: Clementine options

Postby battradio » Wed Mar 18, 2015 1:56 pm

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Re: Clementine options

Postby Olof » Tue Apr 07, 2015 9:28 am

Thanks a lot for the input, I will look into your suggestions as soon as I have time for building things again. This was meant to be my Christmas project after all... (lol)
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