10W SET

Mike H · Post by **Mike H** » Wed Oct 05, 2011 4:42 pm

Nah unit #1 seems to check out, just increase cathode resistor for unit #2 so it's under 10W, sorted.

A clue is in the fact that on schematic it sez "5 watt" for the "1k ohm", yes 'cause it's dissipating 2.5W.

I suggest the 1k could be increased to something like 3.3k, that would reduce Ia to about 20 - 30mA, the cathode will then be around 75V.

Dave the bass · Post by **Dave the bass** » Wed Oct 05, 2011 4:53 pm

pre65 wrote:Perhaps I should do something completely different ?

yes!

pre65 wrote:Like hibernation.

no!

Gwaaarrn, build it as is but knowing it could be a bit manky (tech word that) but put it right using your newly honed fault finding and fettling skills.

That way you'll know how it works and can then adjust values to get safe OP's and the like. Think of the knowledge and skills you'll gain.

Valves are more forgiving than Transistors so a brief over running of anode dissipation wint kill 'em.

I'll sponsor you with even more 6EM7's, gwwwwaaaarrrrn!

DTB

Post by **Nick** » Wed Oct 05, 2011 5:05 pm

Mike H wrote:Nah unit #1 seems to check out, just increase cathode resistor for unit #2 so it's under 10W, sorted.

A clue is in the fact that on schematic it sez "5 watt" for the "1k ohm", yes 'cause it's dissipating 2.5W.

I suggest the 1k could be increased to something like 3.3k, that would reduce Ia to about 20 - 30mA, the cathode will then be around 75V.

Yes, and then check what a crap op point that will put the valve into.

Post by **Nick** » Wed Oct 05, 2011 5:06 pm

You may as well just use the BK circuit, direct couple and stand the cathode at 150v or so. Still too much anode voltage IMHO.

pre65 · Post by **pre65** » Wed Oct 05, 2011 5:08 pm

I don't know if this gives the circuit any credulity, but it was on a Svetlana technical bulletin.

http://www.tube-town.net/info/sed-techn ... eNo46.html

Mike H · Post by **Mike H** » Wed Oct 05, 2011 5:12 pm

Nick wrote:Yes, and then check what a crap op point that will put the valve into.

Well spotted bwana

I'd go with your method

pre65 · Post by **pre65** » Wed Oct 05, 2011 5:17 pm

Well, Mike may be able to answer this one.

I was thinking of using an old amp and modding as necessary. Paul was saying a choke loaded cathode follower was ideal.

This is the circuit in question.

Dave the bass · Post by **Dave the bass** » Wed Oct 05, 2011 5:19 pm

Nick wrote:You may as well just use the BK circuit, direct couple and stand the cathode at 150v or so. Still too much anode voltage IMHO.

HT was 325V DC if using the BK cct. Worth remembering the heater will need elevating otherwise the heater cathode insulation can be breached.

DTB

Mike H · Post by **Mike H** » Thu Oct 06, 2011 4:01 pm

Always something isn't there?

(That's one reason I like 6SN7's, 200V incl. signal)

Phil you're deviating from going-with-as-is into DIY (design it yerself)

Personally I still prefer my DC-coupled grid, common-cathode idea (IT in anode) which Nick seems to agree with ~ in basic principle at any rate

Post by **Nick** » Thu Oct 06, 2011 4:39 pm

Personally I still prefer my DC-coupled grid, common-cathode idea (IT in anode) which Nick seems to agree with ~ in basic principle at any rate

Hey, don't bring me into this

pre65 · Post by **pre65** » Thu Oct 06, 2011 5:19 pm

I've been without electric since 11.00 and it came back on about 4.50 PM.

I had a reply to my wanted ad for Eric Barbour's amp article and I'm now studying the 4 pages. It's still 6EM7 driven but cathode follower. 1st impression is favourable.

Mike H · Post by **Mike H** » Thu Oct 06, 2011 6:15 pm

pre65 wrote:I've been without electric since 1100

It was tough in the middle ages

pre65 · Post by **pre65** » Wed Oct 19, 2011 11:09 am

pre65 wrote:I found this circuit earlier.

Seems quite simple.

Any thoughts ?

I posted this circuit a while ago, and no one made any comments.

Does the panel think it would work as drawn ?

andrew Ivimey · Post by **andrew Ivimey** » Wed Oct 19, 2011 11:34 am

'MQ parafeed output' - what's/how's that?

I've very happily built a 10watt SE class A amplifier. Twas very easy indeed and it sounds very good indeed and it was very cheap indeed and it gets very very hot indeed; it is a Nelson Pass Aleph M - the schematic is freely available on the web and circuit boards are for sale from Hongkers.

Much Respect to NP, indeed!

Mike H · Post by **Mike H** » Wed Oct 19, 2011 2:06 pm

Oh the MQ parafeed is MagneQuest ~ examples here:

http://www.magnequest.com/new.htm

audio-talk

10W SET

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